acterization of battery materials and has been extensively reviewed$^{666}$.

The increased penetration depth of higher energy X-rays is transformative for operando battery PXRD. By utilizing high-energy X-rays, commercial cells can be measured operando with no concessions in cell performance.$^{667}$ The thick steel casing of cylindrical cells requires photon energies of at least 60keV, preferably 90keV.$^{668}$ PXRD in pouch cells can be measured at lower energies and has been demonstrated on laboratory instruments with Mo radiation (18 keV). The ability to perform measurements inside conventional cells is important for two key reasons. First, it enables measurements on highly aged cells, which is essential to understand degradation and cycling stability in active materials.$^{669}$ Secondly, battery performance and aging phenomena are well known to be intrinsically linked to the form factor of cells.$^{670}$ Failure mode analysis including the growth of irreversible phases, Li inventory loss, and consequently the cell's state of health can be directly inferred from PXRD measurements.

Operando SAXS is an emerging technique for batteries. Most active materials are crystalline, and therefore more easily probed with traditional PXRD. However, several promising next-generation chemistries involve amorphous materials, and more suitable for SAXS.$^{671}$ When used as an anode, Si becomes amorphous, and determining the lithiation state of the electrode is challenging, but important for optimizing these electrodes.$^{672}$ Lithiation of Si drives expansion and changes in electron density, altering the SAXS pattern. Solid-state electrolytes are currently being studied intensely for high-energy density batteries. The microstructure of polymer and glassy electrolytes can be analyzed with SAXS, towards optimizing their microstructure and understanding their complicated solid state chemistry.$^{673}$

Under the right conditions, the pair distribution function of battery materials can be calculated from the PXRD pattern. This technique has proven useful for understanding disorder inside amorphous or poorly crystalline materials, and how short-range and long-range ordering inside active materials can differ. The ability

to probe the structure of amorphous and disordered materials overlaps with SAXS. Pair distribution function measurements are preferably performed at very high photon energies to obtain a large angular range. The added value of real-space analysis using PDF has been demonstrated in battery applications, most commonly exploiting differences between the short range and long range ordering in cathode materials, where doping, vacancies, and nonstoichiometric compounds are ubiquitous. Wiaderek et al. showed how PDF can determine the phase transition mechanism of O-doped $FeF_3$, which undergoes a partial, irreversible amorphization, invisible in the conventional powder pattern.$^{674}$ The extreme data quality requirements for useful PDF have until recently limited broad adoption of operando measurements. Advances in cell design now allow structure dynamics of very complex materials to be probed in situ, such as defect-rich, mechanochemically synthesized $Li_4Mn_2O_5$$^{642}$ or Cu/CuF$_2$ nanocomposites with extremely small crystallites (0.5-1.0 nm).$^{675}$ A combined real space and reciprocal space analysis revealed the formation of a weak superlattice induced by local ordering. Anode materials are frequently amorphous alloys, with poorly understood intercalation mechanisms. These systems are particularly amenable to PDF structure analysis, ranging from the Si anode,$^{676}$ which is well-known for irreversible first-cycle disordering, to the more exotic Na$^3$P system,$^{677}$ where the sodiation/desodiation reactions follow different pathways.

PXRD can be used complementary in neutron powder diffraction, which is much more sensitive to Li atoms, and therefore very useful in operando battery measurements.$^{678}$ In comparison to PXRD, neutrons have exceptional angular resolution, good penetration depth, and moderate speed, but have several specific drawbacks, such as the need for deuterated electrolytes, and the challenge of instrument access.$^{679}$

## 8.3 Single Particle Diffraction

While *in situ*/operando powder X-ray diffraction is an extremely powerful technique to study
crystalline structure dynamics in intercalation materials, it is limited to only probing many electrode particles at once. To observe structural details like lattice tilting and strain gradients in individual particles, single particle diffraction is needed. The focusing optics of a synchrotron X-ray source allows for a small beam diameter which reduces the scattering volume in an *in situ/operando* cell. A smaller scattering volume results in a spotted rather than complete Debye-Scherrer ring on a 2D detector. Each spot along the ring is the diffraction peak associated with a single particle of electrode material, and peak width and movement along the ring ($\chi$ rotation) is now resolvable. This unlocked resolution allows for the observation of phenomena like crystal mosaicity, particle rotation, and phase transition mechanisms in intercalation materials$^{651,652,680,681}$.

Single particle *in situ/operando* X-ray diffraction has been used to study multiple different battery intercalation materials. In Singer et al.$^{652}$, disordered $LiNi_{1/2}Mn_{3/2}O_4$, a spinel intercalation Li-ion cathode material, was studied using *operando* single particle XRD. They are able to resolve single particle peaks and report about particle rotation and lattice expansion and contraction. In addition, single particle diffraction revealed nonequilibrium dynamics of a structural phase transition in $LiNi_{1/2}Mn_{3/2}O_4$ where upon charge, the phase transition is facilitated by a solid solution of the two phases, but during discharge, the two phases are distinct and coexist in nanoparticles$^{652}$.

Single particle diffraction was also used to study a layered sodium-ion battery cathode material in Huang et al.$^{651}$. Nanoparticle peaks of $Na_{2/3}[Ni_{1/3}Mn_{2/3}]O_2$ were resolved along the Debye-Scherrer ring using *operando* single particle XRD. From the dynamic peak width behavior of the single particles, increasing layer distortions were observed during charge. They also reported an aligning of crystalline layers just prior to the P2-O2 phase transition which revealed that the P2-O2 phase transition proceeds through an intermediate phase$^{651}$.

Work by Zhang and van Hulzen$^{680,681}$ also utilized small X-ray beam size to study single particle behavior in lithium iron phosphate

(LFP) and lithium nickel manganese cobalt oxide (NMC) lithium-ion battery intercalation materials. By following single particle diffraction peaks, they were able to observe a variety of phase transition mechanisms. Specifically, they observed a rate dependent phase transition within single nanoparticles of LFP$^{680}$, first-order and solid solution phase transitions in LFP, and a solid solution phase transition in NMC$^{681}$.

## 8.4 Operando Bragg Coherent Diffractive Imaging

Bragg coherent diffraction imaging is excellently suited for studying electrochemical systems *operando*. The high penetration depth of hard X-rays (typically around 10 keV) allows collecting data from fully operational, multi-component devices, for example rechargeable battery coin cells in transmission geometry. Moreover, the high angular sensitivity of Bragg diffraction enables one to isolate signal from a specific crystal structure by tuning the scattering angle $2\theta$ to the Bragg angle of that structure. Finally, the nanoparticulate systems often comprise of randomly oriented nanoparticles: most of the illuminated particles of the same crystal structure will generate no signal generating sparse diffraction profile on the Ewald sphere and allowing to isolate signal from a single nanocrystal buried in the electrode.

Operando BCDI has been extensively used to characterize the changes inside positive electrodes of rechargeable lithium-ion batteries$^{76,77,682-684}$. The initial developments were led by Shpyrko, Meng and coauthors$^{682}$. Typically, an *operando* coin-cell consists of a Lithium anode, separator, and cathode. As in commercial rechargeable lithium-ion batteries, the cathode is made of mostly active material (nanocrystals), mixed with carbon black for improved electrical conductivity, and a polymer matrix. The polymer binder creates space between the crystalline particles, which otherwise would degrade mechanically due to their swelling and shrinking during charge and discharge. After the electrode slurry is cast on the current collector, baking introduces pores,
which will later be filled with electrolyte providing access to the active nanocrystals. The electrode thickness is typically 50-100 µm, similar to conventionally created electrodes for electrochemical characterization. Prior to coin-cell assembly, openings in the stainless-steel coin-cell casting are made and covered with X-ray transparent kapton⁶⁸⁵. The transmission of the whole device at 10 keV is on the order of 50 %, with the cathode absorbing the most. In one operando BCDI study, the authors study 3D strain evolution of a single LiNi₀.₅Mn₁.₅O₄ (500nm)³ nanocrystal in a fully operational coin cell battery under operando conditions during charge/discharge cycles⁶⁸². operando strain imaging revealed a stripe morphology due to phase coexistence and coherency strain at the interface between the two phases. The authors were able to determine the stripe size and estimate the interface energy based on Cahn-Hilliard formalism⁶⁸⁶. Because BCDI maps the strain field inside a single nanocrystal, one can directly calculate the strain energy of the crystal by numerically integrating the strain field. The authors in⁶⁸² found a strain energy on the order of few femtojoules.

Point defects, such as Lithium vacancies, naturally occur during intercalation due to a change of the lithium-ion concentration and can be well characterized using average measurements and equilibrium modelling⁶⁸⁷. The importance of linear and planar defects in the properties of crystalline electrochemical systems is indisputable. Yet because extended defects are metastable, studying materials properties in their proximity remains challenging because it requires operando measurements. Therefore, recent BCDI studies focused on defect dynamics in individual nanoparticles operando. Shpyrho, Meng and co-authors reported operando 3D imaging of dislocation dynamics in individual battery cathode nanoparticles using BCDI⁷⁶ (see Figure 42, top). The defects were only mobile during charge or discharge, suggesting ionic diffusion as the driving force behind dislocation migration. Furthermore, the local displacement field around dislocations allowed the authors to map the local elastic constants around the defect. In

<figure><img src="image_66.png" /></figure>

Figure 42: (a) Schematic of an *operando* Bragg Coherent Diffractive Imaging experiment. Coherent X-rays (red) are incident on a cathode nanoparticle (green) embedded in a fully operational coin-cell. A schematic of an edge dislocation for a cubic unit cell structure is shown with the extra half-plane colored purple. The diffracted X-rays carry information about the 3D density of Bragg planes and their atomic displacement along the reciprocal lattice vector. The latter allows identifying the type of dislocation. (Reprinted from Ref. ⁷⁶. Copyright 2015 American Association for the Advancement of Science). (b) The changes in the displacement field of a Li-rich layered oxide nanocrystal during charge (shown on a 2D slice through 3D particle). The voltage versus Li⁺ is indicated. Two edge dislocations emerge at 4.3 V. (c) Strain calculated from the displacement field in (b). White arrows indicate the position of the edge dislocations at 4.3 V. (Reprinted from Ref. ⁷⁷. Copyright 2018 Springer Nature.)
a subsequent study, the same groups reported nucleation of dislocations inside a previously dislocation-free nanocrystal of a lithium-rich layered oxide material<sup>77</sup> (see Figure 42, bottom). The dislocations were also mobile and were associated with the notorious voltage fade in the high energy-density material. The authors used the results from *operando* BCDI to design and execute an annealing experiment, which led to the voltage recovery. Subsequent *operando* BCDI work showed the presence of 2D domain boundaries during a phase transformation<sup>683</sup> and a metastable antiphase-domain boundary during dislocation pair formation<sup>688</sup>.

The BCDI method is a unique, powerful tool for studying lattice distortions inside individual nanocrystals. Yet due to the limited spatial resolution, the retrieved density of Bragg planes, i.e., the Ewald function, is generally not atomically sharp at the boundary. Therefore, a user-defined threshold (typically around 0.2 when the maximum of the Ewald function is 1) is used to somewhat arbitrarily define the particle boundary. To overcome the arbitrariness, some authors, when calculating properties such as strain energy, average over multiple threshold values<sup>77</sup>. Because of the slight ambiguity of where the particle boundary is, BCDI has lower surface sensitivity than other approaches, and *operando* BCDI was initially thought to be inapplicable for studying electrocatalytic reactions at the surface. Initial *operando* studies at open circuit conditions have revealed that structural rearrangements in bulk can occur<sup>689</sup>, especially during dealloying<sup>690</sup> and thermal annealing<sup>691</sup>.

Very recently, *operando* BCDI studies on electrocatalysts under potential control have been reported in different configurations. Sheyfer and coauthors imaged a nanograin of Pt inside of a polycrystalline Pt foil, which mechanically stabilizes the particle under intense irradiation.<sup>692</sup> A carefully positioned nanopipette supplied liquid electrolyte and reference/counter electrodes for high quality, low background diffraction, at the cost of complexity and poor quality electrochemistry. Atlan et al. imaged a more traditional Pt/C catalyst using a flow cell.<sup>477</sup> In both cases, substantial strain

evolution on the exposed facets, corners, and edges is observed as a function of potential, attributed to electrolyte adsorption and surface oxidation. Comparison of the experimentally reconstructed nanoparticles with DFT or molecular dynamics simulations allows surface and bulk strain to be more confidently assessed. Furthermore, BCDI of nanoparticle electrocatalysts allow strain effects on dozens of facets with different surface crystallography to be analyzed simultaneously<sup>477,691</sup>, along with edges and corner features which cannot be probed using single crystal approaches. The advent of fourth-generation X-ray synchrotron sources with highly spatially coherent beams and much-increased brightness will improve the spatial resolution and enhance the capability of *operando* BCDI to bulk and surface structural rearrangements inside smaller nanocrystals, which are relevant for electrocatalysis, and investigate phenomena next to their surface.

## 8.5 Operando Surface Scattering in Intercalation Batteries

Interface reactions critical for intercalation compounds. Therefore, X-ray surface scattering and diffraction have been used extensively for investigating the formation of solid-electrolyte-interphases and interfaces in both anode and cathode materials. In early work, Hirayama and others have developed an *in situ* cell for conducting *operando* surface studies in solid oxide cathodes<sup>693-695</sup>. They developed a cell with two modes alternating during the measurements: mode 1 with liquid electrolyte inside the cell for electrochemical reactions and mode 2 with liquid electrolyte out of the cell for X-ray measurements. Specifically, the work investigated the formation of the solid electrolyte interface on the layered oxides LiCoO<sub>2</sub> and LiNi<sub>0.8</sub>Co<sub>0.2</sub>O<sub>2</sub> and spinel oxide LiMn<sub>2</sub>O<sub>4</sub>. A critical development for these studies was synthesizing epitaxial thin films with surface roughness below 1 nm on electrically conducting substrates (for example, Nb-doped SrTiO<sub>3</sub>), required for high-quality reflectivity data and quantitative fits for the present layers and their densities. Subsequent work on lithium-ion in-
tercalation hosts also included surface diffraction and bulk diffraction from thin films$^{696,697}$.

*In situ* X-ray surface scattering was also used for studying interfaces at the anode. For example, small and wide-angle scattering in epitaxial graphene on SiC showed LiF crystal growth with (002) planes parallel to graphene layers and the presence of other amorphous species in the solid-electrolyte interphase$^{698}$. *In situ* X-ray reflectivity in CrSi multilayers revealed a predominant lithiation at interfaces$^{699}$. Subsequent work used *operando* X-ray reflectivity to study interface roughness and propagation in conversion reactions and alloying in multilayers$^{700-704}$. *Operando* GISAXS on patterned electrodes were used to elucidate dynamics during conversion reactions$^{705}$.

Toney and colleagues have used *in situ* X-ray reflectivity to investigate the electrochemical lithiation of silicon anodes, elucidating the formation process, structure, and behavior of the SEI layer in lithium-ion batteries$^{706-711}$. They presented a mechanistic model of the first two (de)lithiation processes of a silicon wafer, highlighting the differences in reactions of Li ions with crystalline and amorphous structure and providing insights into the formation and evolution of the SEI layer on native oxide-terminated silicon anode$^{706}$. They proposed a three-stage lithiation mechanism, with mechanistic insights into the SEI growth process revealing two well-defined inorganic SEI layers next to the Si anode$^{707-709}$. Additionally, they used a model system combining electrochemical experiments with X-ray reflectivity measurements to quantitatively link capacity-fading mechanisms to electrochemical and chemical processes in lithium-ion batteries, identifying SEI growth as the major contribution to capacity fading and providing insights into the factors affecting SEI growth$^{710}$. Overall, *operando* X-ray surface scattering contributed to a better understanding of the formation, structure, behavior, and growth mechanisms of the SEI layer.

# 9 Conclusions

In the past decades, *in situ* and *operando* X-ray scattering techniques have been developed into highly flexible tools for experimental research in electrochemistry and energy science. As shown above, these techniques can be applied to a large variety of sample materials and sample types, allowing to bridge the material gap between well-defined model systems and the complex systems employed in technological applications. Furthermore, they can provide structural information on length scales from the atomic to the micrometer scale, enabling characterization of complex, hierarchically structured materials, and on time scales from milliseconds to days. This allows to study a wide range of phenomena. The scope of these studies reaches from work aiming at a deep fundamental understanding of the atomic arrangement at electrochemical phase boundaries to the determination of structural changes of materials in actual devices.

X-ray scattering methods can be readily combined with other methods, allowing multimodal analysis. Obtaining simultaneously X-ray scattering and electrochemical data is routine in current *in situ* and *operando* studies. Furthermore, parallel probing the sample in other regions of the electromagnetic spectrum, e.g., by optical reflectivity$^{53,712,713}$, has already been demonstrated. On the horizon are experiments where X-ray scattering is performed together with spectroscopic characterization of the sample. Currently, such studies are performed via independent measurements by different techniques, but parallel data acquisition is in principle straightforward. An obvious extension would be combined studies by X-ray scattering and spectroscopic methods, such as X-ray fluorescence and X-ray absorption spectroscopy, as these signals are anyway generated by the incident beam. These would provide simultaneous structural data and information about the chemical composition and the oxidation states of relevant species, respectively. Also feasible is a combination with vibrational spectroscopy, specifically infrared absorption or Raman spectroscopy. These could provide parallel data
on molecular species, e.g., adsorbed intermediates. Such experiments would allow an unambiguous correlation of the electrode structure with data that pertain the electrode's reactivity, which would justify the higher experimental efforts required with such studies. As such multimodal characterization is also of interest in many fields outside of electrochemistry, the permanent installation of suitable setups is an emerging trend at high-end synchrotron sources.

Other future developments in this field are linked to the emergence of XFELs and fourth-generation synchrotron sources, which offer X-ray beams of unprecedented brilliance. With the first of these machines in the hard X-ray regime up and running and more of them on the horizon, X-ray scattering methods are developing into even more powerful tools. This development is still ongoing and will advance the more widespread use of these techniques as well as the development of even more sophisticated X-ray scattering methods and their applications to electrochemical systems. In particular, these new sources deliver beams that can be highly focused, have a high coherent fraction, and provide short X-ray pulses for ultrafast time-resolved measurements. These properties are advantageous for imaging material systems with high local resolution. One route here is mapping of the structure and other properties with nanobeam, the other is based on coherent imaging, which may now be applied to much smaller objects, such as nanoparticles with diameters of a few 10 nm or lower. The short pulses may be employed to address fundamental questions on the structural dynamics of electrochemical systems on femto- to nanosecond time scales. Such ultrafast X-ray scattering studies have already been demonstrated for molecular systems and thin films.⁷¹⁴⁻⁷¹⁸ They necessarily employ pump-probe approaches and thus will require systems that allow highly repeatable measurements.

The new experimental capabilities pose on the other hand new challenges for *in situ* and *operando* studies. To avoid severe radiation effects when using intense, highly focused X-ray beams, novel approaches with regards to sample

and cell geometry will be required. These may involve new methods of radiation product removal via fast electrolyte exchange, e.g., turbulent flow cells, scavenger molecules, or schemes for minimizing local exposure, such as rapid translation of the beam across the sample. For studies of individual nanoparticles, methods for strong anchoring on suitable substrates have to be developed. In addition, the application of *in situ* and *operando* X-ray scattering methods has to be extended to a wider range of systems, including highly reactive or uncommon electrode materials. For a fundamental understanding of the interfaces in such systems, studies of suitable model systems will be necessary. The latter will require setups that allow electrode preparation and characterization under UHV conditions and controlled transfer into electrochemical environment.

The high brilliance at high energies of 4th generation synchrotron sources also opens up possibilities to study in detail larger electrochemical devices, and materials within, typically used in industrial applications. Beside the fact that such experiments generate large amount of data due to the large probed volume, they also suffer from complicated diffraction patterns as many different materials are probed at the same time. Therefore significant effort still needs to be put forward to develop fast algorithms for data analysis, dealing with effects such as the parallax, and employing machine learning to overcome the problem of large datasets. We also foresee that the upcoming instrumentation upgrades will allow X-ray scattering techniques to be part of the artificial intelligence assisted materials discovery workflows by enabling high throughput *operando* and *in-situ* studies.

Overall, *in situ* and *operando* X-ray-based methods employing synchrotron radiation have tremendous capabilities for in-depth characterization of electrochemical systems. Together with computational methods, the results obtained by these methods can lead to crucial insights into the structure and properties of the involved complex materials and phase boundaries under reaction conditions. These provide a knowledge base for further developments in
energy science and many other areas of high technological relevance. However, the potential of synchrotron-based methods is still not fully tapped by the community, mainly because these approaches are considered technically challenging and time-consuming in terms of beam time acquisition and data analysis. The management of many synchrotron sources has realized this and is starting to initiate remedies. These range from support in data analysis by high-level software and experienced personnel to quick-access schemes for pressing research matters. *In situ* and *operando* studies are by nature more complex experiments than routine sample characterization and thus have been performed in the past predominantly by specialist groups that design dedicated setups for electrochemical research on their own. Such setups are now starting to be offered directly at the beamlines, making *in situ* and *operando* more accessible. We hope that the introduction to these techniques given in the present review helps to encourage the electrochemistry and energy science community to make larger use of these powerful tools and employ them for their research.

<table><caption>Table 2: Acronyms used in the text.</caption><thead><tr><td>Acronym</td><td>Full name</td></tr></thead><tbody><tr><td>1D</td><td>one-dimensional</td></tr><tr><td>2D</td><td>two-dimensional</td></tr><tr><td>3D</td><td>three-dimensional</td></tr><tr><td>AFM</td><td>atomic force microscopy</td></tr><tr><td>AIMD</td><td>ab initio molecular dynamics</td></tr><tr><td>AMPIX</td><td>Argonne multi-purpose in situ X-ray</td></tr><tr><td>ASAXS</td><td>anomalous small angle X-ray scattering</td></tr><tr><td>BCDI</td><td>Bragg coherent diffractive imaging</td></tr><tr><td>BD</td><td>bidentate</td></tr><tr><td>BN</td><td>binuclear</td></tr><tr><td>CMOS</td><td>complementary metal-oxide semiconductor</td></tr><tr><td>CO<sub>2</sub>RR</td><td>carbon dioxide reduction reaction</td></tr><tr><td>COF</td><td>covalent organic framework</td></tr><tr><td>CORR</td><td>carbon monoxide reduction reaction</td></tr><tr><td>CS</td><td>corner-sharing</td></tr><tr><td>CTR</td><td>crystal truncation rod</td></tr><tr><td>CV</td><td>cyclic voltammetry</td></tr><tr><td>DCM</td><td>distorted crystal model</td></tr><tr><td>DFT</td><td>density functional theory</td></tr><tr><td>ECSA</td><td>electrochemically active surface area</td></tr><tr><td>ES</td><td>edge-sharing</td></tr><tr><td>ETEM</td><td>environmental transmission electron microscope</td></tr><tr><td>FA</td><td>fulvic acid</td></tr><tr><td>FS</td><td>face-sharing</td></tr><tr><td>FWHM</td><td>full width at half maximum</td></tr><tr><td>GDL</td><td>gas diffusion layer</td></tr><tr><td>GISAXS</td><td>grazing incidence small angle X-ray scattering</td></tr><tr><td>GIXRD</td><td>grazing incidence X-ray diffraction</td></tr><tr><td>GIXS</td><td>grazing incidence X-ray scattering</td></tr><tr><td>GTSAXS</td><td>grazing incidence transmission small-angle X-ray Scattering</td></tr><tr><td>HER</td><td>hydrogen evolution reaction</td></tr><tr><td>HESXRD</td><td>high energy surface X-ray diffraction</td></tr><tr><td>HOR</td><td>hydrogen oxidation reaction</td></tr><tr><td>ICP-MS</td><td>inductively coupled plasma mass spectrometry</td></tr><tr><td>IL</td><td>ionic liquid</td></tr><tr><td>IRF</td><td>instrumental resolution function</td></tr><tr><td>IS</td><td>inner sphere</td></tr><tr><td>LFP</td><td>lithium iron phospbate</td></tr><tr><td>LPTEM</td><td>liquid phase transmission electron microscope</td></tr></tbody></table>
<table><caption>Table 2: Acronyms used in the text. (cont.)</caption><thead><tr><td>Acronym</td><td>Full name</td></tr></thead><tbody><tr><td>MD</td><td>molecular dynamics</td></tr><tr><td>MEA</td><td>membrane electrode assembly</td></tr><tr><td>ML</td><td>monolayer</td></tr><tr><td>MN</td><td>mononuclear</td></tr><tr><td>MoD</td><td>monodentate</td></tr><tr><td>NMC</td><td>lithium nickel manganese cobalt oxide</td></tr><tr><td>NRR</td><td>N<sub>2</sub> reduction reaction</td></tr><tr><td>OER</td><td>oxygen evolution reaction</td></tr><tr><td>ORR</td><td>oxygen reduction reaction</td></tr><tr><td>OS</td><td>outer sphere</td></tr><tr><td>PDF</td><td>pair distribution function</td></tr><tr><td>PEEK</td><td>polyether ether ketone</td></tr><tr><td>PEG</td><td>polyethylene glycol</td></tr><tr><td>PEM(FC)</td><td>proton exchange membrane (fuel cell)</td></tr><tr><td>PGM</td><td>platinum group metal</td></tr><tr><td>PV</td><td>pseudo-Voigt</td></tr><tr><td>PXRD</td><td>powder X-ray diffraction</td></tr><tr><td>QXAFS</td><td>quick scan X-ray absorption fine structure</td></tr><tr><td>RASXS</td><td>resonant anomalous surface X-ray scattering</td></tr><tr><td>RAXS</td><td>resonance anomalous X-ray scattering</td></tr><tr><td>RHE</td><td>reversible hydrogen electrode</td></tr><tr><td>SAXS</td><td>small angle X-ray scattering</td></tr><tr><td>SOFC</td><td>solid oxide fuel cell</td></tr><tr><td>STM</td><td>scanning tunneling microscopy</td></tr><tr><td>SXRD</td><td>surface X-ray diffraction</td></tr><tr><td>TD</td><td>tridentate</td></tr><tr><td>TeD</td><td>tetradentate</td></tr><tr><td>TEM</td><td>transmission electron microscope</td></tr><tr><td>TMSAXS</td><td>transmission small angle X-ray scattering</td></tr><tr><td>TN</td><td>trinuclear</td></tr><tr><td>UHV</td><td>ultrahigh vacuum</td></tr><tr><td>UPD</td><td>under potential deposition</td></tr><tr><td>WAXS</td><td>wide angle X-ray scattering</td></tr><tr><td>XANES</td><td>X-ray absorption near edge spectroscopy</td></tr><tr><td>XAS</td><td>X-ray absorption spectroscopy</td></tr><tr><td>XFEL</td><td>X-ray free electron laser</td></tr><tr><td>XPCS</td><td>X-ray photon correlation spectroscopy</td></tr><tr><td>XRD</td><td>X-ray diffraction</td></tr><tr><td>XRD-CT</td><td>X-ray diffraction computed tomography</td></tr><tr><td>XRR</td><td>X-ray reflectivity</td></tr><tr><td>XRV</td><td>X-ray voltammogram</td></tr><tr><td>XSW</td><td>X-ray standing wave</td></tr></tbody></table>

<table><caption>Table 3: Symbols used in the text.</caption><tr><td>α<sub>c</sub></td><td>critical angle</td></tr><tr><td>α<sub>f</sub></td><td>exit angle</td></tr><tr><td>α<sub>i</sub></td><td>incident angle</td></tr><tr><td>α</td><td>phase factor</td></tr><tr><td>n̄</td><td>density functional operator</td></tr><tr><td>δ<sub>ij</sub></td><td>Kroneker delta</td></tr><tr><td>ε<sub>ph</sub></td><td>photon energy</td></tr><tr><td>ε</td><td>wave field vector</td></tr><tr><td>η</td><td>mixing parameter</td></tr><tr><td>ħ</td><td>reduced Planck constant</td></tr><tr><td>λ</td><td>X-ray wavelength</td></tr><tr><td>Λ</td><td>penetration depth</td></tr><tr><td>μ</td><td>attenuation coefficient</td></tr><tr><td>Ω</td><td>profile function</td></tr><tr><td>φ</td><td>phase</td></tr><tr><td>ρ<sub>e</sub></td><td>electron density</td></tr><tr><td>ρ(r)</td><td>pair density function</td></tr><tr><td>σ<sub>0</sub></td><td>layer width</td></tr><tr><td>θ</td><td>Bragg angle</td></tr><tr><td>2θ</td><td>scattering angle</td></tr><tr><td>θ<sub>j</sub></td><td>occupancy of site j</td></tr><tr><td>a<sub>1</sub>, a<sub>2</sub>, a<sub>3</sub></td><td>lattice vector</td></tr><tr><td>b<sub>1</sub>, b<sub>2</sub>, b<sub>3</sub></td><td>reciprocal space vector</td></tr><tr><td>f<sub>0,j</sub></td><td>atomic form factor of atom j</td></tr><tr><td>f', f''</td><td>dispersion corrections</td></tr><tr><td>F</td><td>structure factor</td></tr><tr><td>F<sub>N</sub>R</td><td>non-resonant structure factor</td></tr><tr><td>F<sub>N</sub>R</td><td>resonant structure factor</td></tr><tr><td>G<sub>hkl</sub></td><td>reciprocal lattice point</td></tr><tr><td>g(R)</td><td>pair distribution function</td></tr><tr><td>G(r)</td><td>reduced pair distribution function</td></tr><tr><td>h, k, l</td><td>Miller indices</td></tr><tr><td>H</td><td>peak width</td></tr><tr><td>I</td><td>scattering intensity</td></tr><tr><td>k<sub>f</sub></td><td>scattered wave vector</td></tr><tr><td>k<sub>i</sub></td><td>incident wave vector</td></tr><tr><td>k</td><td>wave vector</td></tr><tr><td>M</td><td>Debye Waller factor</td></tr><tr><td>N<sub>n</sub></td><td>number of unit cells</td></tr><tr><td>n</td><td>index of refraction</td></tr><tr><td>P</td><td>particle form factor</td></tr><tr><td>q</td><td>scattering vector</td></tr><tr><td>Q</td><td>momentum transfer</td></tr><tr><td>R<sub>G</sub></td><td>radius of gyration</td></tr><tr><td>r</td><td>distance vector</td></tr><tr><td>R</td><td>difference vector</td></tr><tr><td>R</td><td>distance vector</td></tr><tr><td>s<sub>hkl</sub></td><td>density of hkl Bragg planes</td></tr><tr><td>S(Q)</td><td>scattering amplitude</td></tr><tr><td>S<sub>l</sub>(Q)</td><td>total scattering structure function</td></tr><tr><td>S<sub>L</sub>(Q)</td><td>liquid structure factor</td></tr><tr><td>T</td><td>domain size</td></tr><tr><td>u</td><td>displacement vector</td></tr><tr><td>V<sub>c</sub></td><td>unit cell volume</td></tr></table>
# 10 Biographies

Olaf Magnussen is a full professor of solid state physics at Kiel University, Germany, since 2001. He obtained his PhD from Ulm University, Germany, in the group of Prof. Jürgen Behm in 1993. After a Postdoc with Dr. Ben Ocko at Brookhaven National Laboratory he returned to Ulm, where he obtained his habilitation in 2001. Focus of his research are studies of the atomic-scale structure and dynamics of electrochemical interfaces. He has been employing synchrotron-based *in situ* and *operando* X-ray scattering techniques for the past 30 years to studies of electrode surface structure, adsorbate layers, liquid-liquid interfaces, electrodeposition, corrosion, and electrocatalytic processes. His current research focuses on *operando* studies of electrocatalysts for energy conversion, in particular, by employing high-energy surface scattering methods.

Jakub Drnec obtained his PhD degree at University of Victoria, Canada, in the field of surface electrochemistry. Currently he is a beamline scientist at European Synchrotron (ESRF) in Grenoble (France), developing new high energy X-rays experimental techniques to study materials for energy conversion and storage. His main goal is to probe materials in their working environment in order to better understand their functioning. His current projects involve *operando* investigations of fuel cells and batteries, fundamental studies of electrocatalyst's degradation and structure-activity relationships, and development of *operando* electrochemical cells and data analysis routines.

Canrong Qiu received his Ph.D. degree in 2016 from University of Alaska Fairbanks, USA in the field of environmental chemistry under the supervision of Prof. Thomas P. Trainor. After his Ph.D., he moved to Germany and worked as a postdoc with Dr. Moritz Schmidt at Helmholtz Zentrum Dresden Rossendorf and Olaf Magnussen at Kiel University. Since November 2022, he has been working as a staff scientist at the P25 beamline of PETRA III at Deutsches Elektronen-Synchrotron (DESY) in Hamburg. His research interest includes resolving and characterizing molecular-scale in-

terfacial processes of different adsorbates on environment or energy relevant substrates using modern synchrotron X-ray techniques. In addition, he is also developing Python-based high performance data analysis software, in particular, the open-source DaFy software package (https://github.com/jackey-qiu/DaFy) for processing and modeling surface X-ray diffraction data.

Isaac Martens received his B.Sc. in Biochemistry from the University of Calgary, before completing his Ph.D. studies at the University of British Columbia on in situ electrochemistry under supervision of D. Bizzotto and D.P. Wilkinson. He recently completed a postdoctoral appointment at the European Synchrotron Radiation Facility developing operando techniques for battery studies.

Jason Huang is a Ph.D. candidate at Cornell University in the lab of Prof. Andrej Singer where he studies the dynamics and defect mechanisms of electrochemically active crystalline materials using advanced in situ and operando X-ray scattering techniques. Previously, he received his B.S. (2019) in Nanoengineering from the University of California, San Diego. There, he worked in the lab of Prof. Ping Liu and studied materials for Li-ion and Li-metal batteries. Jason is interested in understanding how active materials change under electrochemical environments and applying those findings to develop the next generation of energy materials.

Raphaël Chattot obtained his Ph.D. in Electrocatalysis from the University of Grenoble-Alpes in 2017 under the direction of Dr. Frédéric Maillard and Dr. Laetitia Dubau. After an 18-month period as a postdoctoral researcher between the Laboratory of Electrochemistry and Physicochemistry of Materials and Interfaces (LEPMI, Grenoble, France) and the European Synchrotron Radiation Facility (ESRF, Grenoble, France) he joined the ESRF as a Junior Scientist at the ID31 beamline (Jakub Drnec and Veijo Honkimäki's group). Since 2021 he is a permanent researcher of the French National Center for Scientific Research (CNRS) at the Institute Charles Gerhardt (ICGM, Montpellier France). His research focuses notably on exploring the funda-
mental role of nanoscale structural disorder in electrocatalysis for energy conversion systems such as fuel cells and water electrolyzers by means of advanced *in situ* and *operando* X-ray scattering techniques.

Andrej Singer received his Ph.D. (2012) in Physics from the University of Hamburg, Germany in the lab of Prof. Edgar Weckert and Prof. Ivan Vartanyants, following a Physics diploma from the University of Muenster, Germany. He studied the properties of new X-ray sources, particularly their ability to generate interference patterns, similar to lasers in optics. He then worked as a Postdoc in the lab of Prof. Oleg Shpyrko at the University of California, San Diego. Dr Singer's group uses coherent X-ray scattering techniques at synchrotrons and free-electron lasers to study a wide range of materials, spanning from quantum materials to applied energy materials in operando dbtained his PhD degree at University of Victoria, Canada, in the field of surface electrochemistry. He is a beamline scientist at European Synchrotron (ESRF) in Grenoble (France), developing new high energy X-rays experimental techniques to study materials for energy conversion and storage. His main goal is to probe materials in their working environment in order to better understand their functioning. His current projects involve operando investigations of fuel cells and batteries, fundamental studies of electrocatalyst's degradation and structure-activity relationships, and development of operando electrochemical cells and data analysis routines. Dr. Singer is interested in understanding the fundamental properties of energy materials and quantum materials out-of-equilibrium.

**Acknowledgement** O. M. M. and C. Q. acknowledge financial support by the German Federal Ministry of Education and Research (BMBF) via Project 05K19FK3. R.C. acknowledge financial support from the French National Research Agency through the HOLYCAT project (grant number no ANR-22-CE05-0007). Work at Cornell University was supported by the Center for Alkaline-based Energy Solutions, an Energy Frontier Research Center funded by DOE, Office of Science, BES under Award #

## References

(1) Kolb, D.; Rath, D.; Wille, R.; Hansen, W. An ESCA study on the electrochemical double layer of emersed electrodes. *Ber. Bunsenges. Phys. Chem* **1983**, *87*, 1108–1113.

(2) Kolb, D. Surface science aspects of interfacial electrochemistry. *J. Vac. Sci. Technol. A* **1986**, *4*, 1294–1391.

(3) Als-Nielsen, J.; McMorrow, D. *Elements of modern X-ray physics*; Wiley, NY, 2001.

(4) Feidenhans'l, R. Surface structure determination by X-ray diffraction. *Surf. Sci. Rep.* **1989**, *10*, 105.

(5) Robinson, I. K.; Tweet, D. J. *Surface X-ray diffraction*; IOP Publishing, 1992; Vol. 55; p 599.

(6) Vlieg, E. In *Surface and interface science*; K. Wandelt, Ed.; Wiley-VCH, NY, 2013; Vol. 1; pp 375–425.

(7) Ewald, P. P. X-ray diffraction by finite and imperfect crystal lattices. *Proc. Phys. Soc.* **1940**, *52*, 167–174.

(8) Vartanyants, I. A.; Robinson, I. K. Partial coherence effects on the imaging of small crystals using coherent x-ray diffraction. *J. Phys.: Condens. Matter* **2001**, *13*, 10593.

(9) Vlieg, E. Characterization of solid-liquid interfaces using X-ray diffraction. 2004; p 31.

(10) Chaikin, P. M.; Lubensky, T. C. *Principles of condensed matter physics*; Cambridge University Press, Cambridge, 1995.

(11) Keen, D. A comparison of various commonly used correlation functions for describing total scattering. *Journal of Applied Crystallography* **2001**, *34*, 172–177.
(12) Pershan, P.; Schlossman, M. *Liquid surfaces and interfaces*; Cambridge University Press, Cambridge, 2012.

(13) Magnussen, O.; Ocko, B.; Regan, M.; Penanen, K.; Pershan, P.; Deutsch, M. X-ray reflectivity measurements of surface layering in liquid mercury. *Phys. Rev. Lett* **1995**, *74*, 4444–4447.

(14) Guinier, A.; Fournet, G. *Small-angle scattering of X-rays*; Structure of matter series; Wiley, 1955.

(15) Gommes, C. J.; Jaksch, S.; Frielingshaus, H. Small-angle scattering for beginners. *J. Appl. Crystallogr.* **2021**, *54*, 1832–1843.

(16) Sun, Y. Anomalous small-angle X-ray scattering for materials chemistry. *Trends Chem. Sci.* **2021**, *3*, 1045–1060.

(17) Bazin, D. Anomalous wide angle X-ray scattering (AWAXS) and heterogeneous catalysts. *Appl. Catal., A* **2002**, *226*, 87–113.

(18) Bazin, D.; Lynch, J.; Ramos-Fernandez, M. X-ray absorption spectroscopy and anomalous wide angle X-ray scattering: Two basic tools in the analysis of heterogeneous catalysts. *Oil Gas Sci. Technol.* **2003**, *58*, 667–683.

(19) Yu, C.; Koh, S.; Leisch, J. E.; Toney, M. F.; Strasser, P. Size and composition distribution dynamics of alloy nanoparticle electrocatalysts probed by anomalous small angle X-ray scattering (ASAXS). *Faraday Discuss.* **2009**, *140*, 283–296.

(20) Gilbert, J. A.; Kariuki, N. N.; Subbaraman, R.; Kropf, A. J.; Smith, M. C.; Holby, E. F.; Morgan, D.; Myers, D. J. In Situ anomalous small-angle X-ray scattering studies of platinum nanoparticle fuel cell electrocatalyst degradation. *J. Am. Chem. Soc.* **2012**, *134*, 14823–14833.

(21) Gilbert, J. A.; Kariuki, N. N.; Wang, X.; Kropf, A. J.; Yu, K.; Groom, D. J.; Ferreira, P. J.; Morgan, D.; Myers, D. J. Pt catalyst degradation in aqueous and fuel cell environments studied via inoperando anomalous small-angle X-ray scattering. *Electrochim. Acta* **2015**, *173*, 223–234.

(22) Hemberg, O.; Otendal, M.; Hertz, H. M. Liquid-metal-jet anode electron-impact x-ray source. *Appl. Phys. Lett.* **2003**, *83*, 1483–1485.

(23) Bartzsch, S.; Oelfke, U. Line focus x-ray tubes—a new concept to produce high brilliance x-rays. *Phys. Med. Biol.* **2017**, *62*, 8600.

(24) Baruchel, J., Hodeau, J.-L., Lehmann, M. S., Regnard, J.-R., Schlenker, C., Eds. *Neutron and synchrotron radiation for condensed matter studies*; Springer, Heidelberg, 1994.

(25) Willmott, P. *An introduction to synchrotron radiation: Techniques and applications*; Wiley, 2019.

(26) Kaduk, J. A.; Billinge, S. J.; Dinnebier, R. E.; Henderson, N.; Madsen, I.; Černý, R.; Leoni, M.; Lutterotti, L.; Thakral, S.; Chateigner, D. Powder diffraction. *Nat. Rev. Methods Primers* **2021**, *1*, 77.

(27) Phillips, J. C.; Cerino, J. A.; Hodgson, K. O. A four-circle diffractometer on a focused, tuneable synchrotron radiation source: mechanical design, computer control and evaluation of system performance. *J. Appl. Crystallogr.* **1979**, *12*, 592–600.

(28) Lohmeier, M.; Vlieg, E. Angle calculations for a six-circle surface X-ray diffractometer. *J. Appl. Crystallogr.* **1993**, *26*, 706–716.

(29) Murphy, B.; Greve, M.; Runge, B.; Koops, C.; Elsen, A.; Stettner, J.; Seeck, O.; Magnussen, O. A novel X-ray
diffractometer for studies of liquid-liquid interfaces. *J. Synchrotron Radiat.* **2014**, *21*, 45–56.

(30) Schlepütz, C. M.; Mariager, S. O.; Pauli, S. A.; Feidenhans'l, R.; Willmott, P. R. Angle calculations for a (2+3)-type diffractometer: focus on area detectors. *J. Appl. Crystallogr.* **2010**, *44*, 73–83.

(31) Kieffer, J.; Karkoulis, D. PyFAI, a versatile library for azimuthal regrouping. *J. Phys. Conf. Ser.* **2013**, *425*, 202012.

(32) Drnec, J.; Zhou, T.; Pintea, S.; Onderwaater, W.; Vlieg, E.; Renaud, G.; Felici, R. Integration techniques for surface X-ray diffraction data obtained with a two-dimensional detector. *J. Appl. Crystallogr.* **2014**, *47*, 365–377.

(33) Roobol, S.; Onderwaater, W.; Drnec, J.; Felici, R.; Frenken, J. BINoculars: data reduction and analysis software for two-dimensional detectors in surface X-ray diffraction. *J. Appl. Crystallogr.* **2015**, *48*, 1324–1329.

(34) Harlow, G. S.; Pfaff, S.; Abbondanza, G.; Hegedüs, Z.; Lienert, U.; Lundgren, E. HAT: a high-energy surface X-ray diffraction analysis toolkit. *J. Appl. Crystallogr.* **2023**, *56*, 312–321.

(35) Favre-Nicolin, V.; Girard, G.; Leake, S.; Carnis, J.; Chushkin, Y.; Kieffer, J.; Paleo, P.; Richard, M.-I. PyNX: high-performance computing toolkit for coherent X-ray imaging based on operators. *J. Appl. Crystallogr.* **2020**, *53*, 1404–1413.

(36) GSAS-II. https://subversion.xray.aps.anl.gov/trac/pyGSAS, Accessed: 2023-04-11.

(37) TOPAS. https://www.bruker.com/f
r/products-and-solutions/diffrac
tometers-and-x-ray-microscopes/x
-ray-diffractometers/diffrac-sui
te-software/diffrac-topas.html,
Accessed: 2023-04-11.

(38) FullProf. https://www.ill.eu/sites/fullprof/, Accessed: 2023-04-11.

(39) PDFGUI. https://www.diffpy.org/products/pdfgui.html, Accessed: 2023-04-11.

(40) DISCUS. https://tproffen.github.io/DiffuseCode/, Accessed: 2023-04-11.

(41) SASView. https://www.sasview.org/, Accessed: 2023-04-11.

(42) BornAgain. https://www.bornagainproject.org/, Accessed: 2023-04-11.

(43) GenX. https://aglavic.github.io/genx/, Accessed: 2023-04-11.

(44) ANA-ROD. https://www.esrf.fr/computing/scientific/joint_project_s/ANA-ROD/index.htm, Accessed: 2023-04-11.

(45) BINoculars. https://github.com/id03/binoculars, Accessed: 2023-04-11.

(46) pyNX. https://www.esrf.fr/computing/scientific/PyNX/README.html, Accessed: 2023-04-11.

(47) IUCr software. https://www.iucr.org/resources/other-directories/software, Accessed: 2023-04-11.

(48) Stoecker, W. C.; Starbuck, J. W. Ef-
fect of soller slits on X-ray intensity in
a modern diffractometer. *Rev. Sci. In-
strum.* **1965**, *36*, 1593–1598.

(49) Kowarik, S.; Bogula, L.; Boitano, S.; Carlà, F.; Pithan, H.; Schäfer, P.; Wilming, H.; Zykov, A.; Pithan, L. A novel 3D printed radial collimator for x-ray diffraction. *Rev. Sci. Instrum.* **2019**, *90*, 035102.

(50) Olsson, A.; Hellsing, M. S.; Rennie, A. R. New possibilities using additive manufacturing with materials that are difficult to process and with complex structures. *Phys. Scripta* **2017**, *92*, 053002.
(51) Chen, Y.; Han, D.; Wang, J.; Yang, Y.; Hu, W. Stacking of micro-aperture arrays: A new strategy to construct Söller collimator for x rays. *Rev. Sci. Instrum.* **2020**, *91*.

(52) Magnussen, O.; Krug, K.; Ayyad, A.; Stettner, J. In situ diffraction studies of electrode surface structure during gold electrodeposition. *Electrochim. Acta* **2008**, *53*, 3449–3458.

(53) Reikowski, F.; Maroun, F.; Pacheco, I.; Wiegmann, T.; Allongue, P.; Stettner, J.; Magnussen, O. M. Operando surface X-ray diffraction studies of structurally defined Co3O4 and CoOOH thin films during oxygen evolution. *ACS Catal.* **2019**, *9*, 3811–3821.

(54) Asset, T.; Gommes, C. J.; Drnec, J.; Bordet, P.; Chattot, R.; Martens, I.; Nelayah, J.; Job, N.; Maillard, F.; Dubau, L. Disentangling the degradation pathways of highly defective PtNi / C nanostructures – an operando wide and small angle X-ray scattering study. *ACS Catal.* **2019**, *9*, 160–167.

(55) Redoxme AB, Magnetic mount gas diffusion electrode X-ray diffraction electrochemical cell. 2023; https://redox.me/collections/spectro-electrochemical-cells/products/gde-xrd-ec-1-75-ml-gas-diffusion-electrode-x-ray-diffraction-electrochemical-cell.

(56) Petkov, V. et al. Nanoalloy catalysts inside fuel cells: An atomic-level perspective on the functionality by combined in operando x-ray spectroscopy and total scattering. *Nano Energy* **2018**, *49*, 209–220.

(57) Martens, I. et al. X-ray transparent proton-exchange membrane fuel cell design for in situ wide and small angle scattering tomography. *J. Power Sources* **2019**, *437*, 226906.

(58) Moss, A. B.; Hätinen, J.; Kúš, P.; Garg, S.; Mirolo, M.; Chorkendorff, I.; Seger, B.; Drnec, J. Versatile high energy X-ray transparent electrolysis cell for operando measurements. *J. Power Sources* **2023**, *562*, 232754.

(59) Benck, J. D.; Rettenwander, D.; Jackson, A.; Young, D.; Chiang, Y.-M. Aparatus for operando x-ray diffraction of fuel electrodes in high temperature solid oxide electrochemical cells. *Rev. Sci. Instrum.* **2019**, *90*, 023910.

(60) Chattot, R. et al. Electrochemical strain dynamics in noble metal nanocatalysts. *J. Am. Chem. Soc.* **2021**, *143*, 17068–17078.

(61) Henderson, R. The potential and limitations of neutrons, electrons and X-rays for atomic resolution microscopy of unstained biological molecules. *Q. Rev. Biophys.* **1995**, *28*, 171–193.

(62) Bras, W.; Myles, D. A. A.; Felici, R. When x-rays alter the course of your experiments. *J. Phys.: Condens. Matter* **2021**, *33*, 423002.

(63) Caër, S. L. Water radiolysis: Influence of oxide surfaces on H2 production under ionizing radiation. *Water* **2011**, *3*, 235–253.

(64) Hill, M.; Smith, F. Calculation of initial and primary yields in the radiolysis of water. *Radiat. Phys. Chem.* **1994**, *43*, 265–280.

(65) Uehara, S.; Nikjoo, H. Monte Carlo simulation of water radiolysis for low-energy charged particles. *J. Radiat. Res.* **2006**, *47*, 69–81.

(66) Terrissol, M.; Beaudre, A. Simulation of space and time evolution of radiolytic species induced by electrons in water. *Radiat. Prot. Dosim.* **1990**, *31*, 175–177.

(67) Swallow, A. J. In *Radiation chemistry of organic compounds: International series*
of monographs on radiation effects in materials; Charlesby, A., Ed.; Pergamon: Amsterdam, 2016; OCLC: 1100973316.

(68) Roots, R.; Okada, S. Estimation of life times and diffusion distances of radicals involved in X-ray-induced DNA strand breaks or killing of mammalian cells. *Radiat. Res.* **1975**, *64*, 306.

(69) Spotheim-Maurizot, M.; Mostafavi, M.; Douki, T.; Belloni, J. *Radiation chemistry: From basics to applications in material and life sciences*; EDP Sciences, Les Ulis, France, 2008.

(70) Fritsch, B.; Körner, A.; Couasnon, T.; Blukis, R.; Taherkhani, M.; Benning, L. G.; Jank, M. P. M.; Spieker, E.; Hutzler, A. Tailoring the acidity of liquid media with ionizing radiation – rethink- ing the acid-base correlation beyond pH. *J. Phys. Chem. Lett.* **2023**, *14*, 4644–4651.

(71) Thomä, S. L. J.; Zobel, M. Beam-induced redox chemistry in iron oxide nanoparticle dispersions at ESRF–EBS. *J. Synchrotron Radiat.* **2023**, *30*, 440–444.

(72) Fritsch, B. et al. Radiolysis-driven evolution of gold nanostructures – model verification by scale bridging in situ liquid-phase transmission electron microscopy and X-ray diffraction. *Adv. Sci.* **2022**, *9*, 2202803.

(73) Fourme, R.; Honkimäki, V.; Girard, E.; Medjoubi, K.; Dhaussy, A.-C.; Kahn, R. Reduction of radiation damage and other benefits of short wavelengths for macro-molecular crystallography data collection. *J. Appl. Crystallogr.* **2012**, *45*, 652–661.

(74) Pfeifer, M. A.; Williams, G. J.; Vartanyants, I. A.; Harder, R.; Robinson, I. K. Three-dimensional mapping of a deformation field inside a nanocrystal. *Nature* **2006**, *442*, 63–66.

(75) Robinson, I.; Harder, R. Coherent X-ray diffraction imaging of strain at the nanoscale. *Nat. Mater.* **2009**, *8*, 291–8.

(76) Ulvestad, A.; Singer, A.; Clark, J. N.; Cho, H. M.; Kim, J. W.; Harder, R.; Maser, J.; Meng, Y. S.; Shpyrko, O. G. Topological defect dynamics in operando battery nanoparticles. *Science* **2015**, *348*, 1344–1347.

(77) Singer, A. et al. Nucleation of dislocations and their dynamics in layered oxide cathode materials during battery charging. *Nat. Energy* **2018**, *3*, 641–647.

(78) Renaud, G.; Lazzari, R.; Leroy, F. Probing surface and interface morphology with Grazing Incidence Small Angle X-Ray Scattering. *Surf. Sci. Rep.* **2009**, *64*, 255–380.

(79) Hejral, U. et al. High-energy X-ray diffraction from surfaces and nanoparticles. *Phys. Rev. B* **2017**, *96*, 195433/1.

(80) Egami, T.; Billinge, S. J. In *Pergamon Materials Series*, 2nd ed.; Takeshi Egami, S. J. B., Ed.; Elsevier Inc., 2012; Vol. 16; p 55–111.

(81) Clearfield, A.; Reibenspies, J. H.; Bhuvanesh, N. E. *Principles and applications of powder diffraction*; Wiley, 2009.

(82) Pfeiffer, F. X-ray ptychography. *Nat. Photonics* **2017**, *12*, 9–17.

(83) Park, C.; Fenter, P. A.; Sturchio, N. C.; Regalbuto, J. R. Probing outer-sphere adsorption of aqueous metal complexes at the oxide-water interface with resonant anomalous X-ray reflectivity. *Phys. Rev. Lett.* **2005**, *94*, 076104.

(84) Park, C.; Fenter, P. A. Phasing of resonant anomalous X-ray reflectivity spectra and direct Fourier synthesis of element-specific partial structures at buried interfaces. *J. Appl. Crystallogr.* **2007**, *40*, 290–301.
(85) Li, T.; Senesi, A. J.; Lee, B. Small angle X-ray scattering for nanoparticle research. *Chem. Rev.* **2016**, *116*, 11128–11180.

(86) Pauw, B. R. Everything SAXS: small-angle scattering pattern collection and correction. *J. Phys.: Condens. Matter* **2013**, *25*, 383201.

(87) Dinnebier, R. E.; Billinge, S. J. L. Powder diffraction: theory and practice; Royal Society of Chemistry, 2008.

(88) Percharsky, K., Vitalij, Zavalij, P. Y. *Fundamentals of powder diffraction and structural characterization of materials*; Springer US: Boston, MA, 2009.

(89) Bunge, H. J. Influence of texture on powder diffraction. *Texture. Microstruct.* **1997**, *29*, 1–26.

(90) Rietveld, H. M. A profile refinement method for nuclear and magnetic structures. *J. Appl. Crystallogr.* **1969**, *2*, 65–71.

(91) Thompson, P.; Cox, D. E.; Hastings, J. B. Rietveld refinement of Debye–Scherrer synchrotron X-ray data from Al2O3. *J. Appl. Crystallogr.* **1987**, *20*, 79–83.

(92) Balzar, D. et al. Size-strain linebroadening analysis of the ceria roundrobin sample. *J. Appl. Crystallogr.* **2004**, *37*, 911–924.

(93) Scherrer, P. Bestimmung dergröße und der inneren struktur von kolloidteilchen mittels röntgenstrahlen. *Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse* **1918**, *1918*, 98–100.

(94) Takeshi, E.; Billinge, S. J. *Pergamon Materials Series*; 2012; Vol. 16; p 55–111.

(95) Festersen, S.; Runge, B.; Koops, C.; Bertram, F.; Ocko, B.; Deutsch, M.;

Murphy, B. M.; Magnussen, O. M. Nucleation and growth of PbBrF crystals at the liquid mercury-electrolyte interface studied by operando X-ray scattering. *Langmuir* **2020**, *36*, 10905–10915.

(96) Magnussen, O. M.; Ocko, B. M.; Wang, J. X.; Adzic, R. R. In-situ X-ray diffraction and STM studies of bromide adsorption on Au(111) electrodes. *J. Phys. Chem.* **1996**, *100*, 5500–5508.

(97) Gustafson, J.; Shipilin, M.; Zhang, C.; Stierle, A.; Hejral, U.; Ruett, U.; Gutowski, O.; Carlsson, P. A.; Skoglundh, M.; Lundgren, E. High-energy surface X-ray diffraction for fast surface structure determination. *Science* **2014**, *343*, 758–761.

(98) Fuchs, T.; Drnec, J.; Calle-Vallejo, F.; Stubb, N.; Sandbeck, D. J. S.; Ruge, M.; Cherevko, S.; Harrington, D. A.; Magnussen, O. M. Structure dependency of the atomic-scale mechanisms of platinum electro-oxidation and dissolution. *Nat. Catal.* **2020**, *3*, 754–761.

(99) Fuchs, T.; Briega-Martos, V.; Drnec, J.; Stubb, N.; Martens, I.; Calle-Vallejo, F.; Harrington, D. A.; Cherevko, S.; Magnussen, O. M. Anodic and cathodic platinum dissolution processes involve different oxide species. *Angew. Chem. Int. Ed.* **2023**, *34*, e202304293.

(100) Fuchs, T.; Briega-Martos, V.; Fehrs, J. O.; Qiu, C. R.; Mirolo, M.; Yuan, C. T.; Cherevko, S.; Drnec, J.; Magnussen, O. M.; Harrington, D. A. Driving force of the initial step in electrochemical Pt(111) oxidation. *J. Phys. Chem. Lett.* **2023**, *14*, 3589–3593.

(101) Jacobse, L.; Vonk, V.; McCrum, I. T.; Seitz, C.; Koper, M. T.; Rost, M. J.; Stierle, A. Electrochemical oxidation of Pt(111) beyond the place-exchange model. *Electrochim. Acta* **2022**, *407*, 139881.
(102) Reikowski, F.; Wiegmann, T.; Stettner, J.; Drnec, J.; Honkimaeki, V.; Maroun, F.; Allongue, P.; Magnussen, O. M. Transmission surface diffraction for operating studies of heterogeneous interfaces. *J. Phys. Chem. Lett.* **2017**, *8*, 1067–1071.

(103) Wiegmann, T.; Drnec, J.; Reikowski, F.; Stettner, J.; Maroun, F.; Magnussen, O. M. In situ transmission X-ray micro-diffraction from thin metal films electrodeposited in microfluidic channels. *J. Electrochem. Soc.* **2020**, *167*, 112505.

(104) Zhang, Y.; Chen, S.; Cai, Y.; Lu, L.; Fan, D.; Shi, J.; Huang, J.; Luo, S.-N. Novel X-ray and optical diagnostics for studying energetic materials: A review. *Engineering* **2020**, *6*, 992–1005.

(105) Dekker, F.; Kuipers, B.; Petukhov, A.; Tuinier, R.; Philipse, A. Scattering from colloidal cubic silica shells: Part I, particle form factors and optical contrast variation. *J. Colloid Interface Sci.* **2020**, *571*, 419–428.

(106) Gommes, C. J.; Chattot, R.; Drnec, J. Stochastic models of dense or hollow nanoparticles and their scattering properties. *J. Appl. Crystallogr.* **2020**, *53*, 811–823.

(107) Ruge, M.; Drnec, J.; Rahn, B.; Reikowski, F.; Harrington, D. A.; Carla, F.; Felici, R.; Stettner, J.; Magnussen, O. M. Structural reorganization of Pt(111) electrodes by electrochemical oxidation and reduction. *J. Am. Chem. Soc.* **2017**, *139*, 4532–4539.

(108) Lu, X.; Yager, K. G.; Johnston, D.; Black, C. T.; Ocko, B. M. Grazing-incidence transmission X-ray scattering: surface scattering in the Born approximation. *J. Appl. Crystallogr.* **2013**, *46*, 165–172.

(109) Snigirev, A.; Kohn, V.; Snigireva, I.; Lengeler, B. A compound refractive lens

for focusing high-energy X-rays. *Nature* **1996**, *384*, 49–51.

(110) Mimura, H. et al. Breaking the 10-nm barrier in hard-X-ray focusing. *Nat. Phys.* **2010**, *6*, 122–125.

(111) Singer, A.; Vartanyants, I. A. Coherence properties of focused X-ray beams at high-brilliance synchrotron sources. *J. Synchrotron Radiat.* **2014**, *21*, 5–15.

(112) Qazilbash, M. M. et al. Nanoscale imaging of the electronic and structural transitions in vanadium dioxide. *Phys. Rev. B* **2011**, *83*, 165108.

(113) Singer, A. et al. Nonequilibrium Phase Precursors during a Photoexcited Insulator-to-Metal Transition in V2O3. *Phys. Rev. Lett.* **2018**, *120*, 207601.

(114) Hruszkewycz, S. O.; Folkman, C. M.; Highland, M. J.; Holt, M. V.; Baek, S. H.; Streiffer, S. K.; Baldo, P.; Eom, C. B.; Fuoss, P. H. X-ray nanodiffraction of tilted domains in a poled epitaxial BiFeO3 thin film. *Appl. Phys. Lett.* **2011**, *99*, 232903.

(115) Luo, A. et al. X-ray nano-imaging of defects in thin film catalysts via cluster analysis. *Appl. Phys. Lett.* **2022**, *121*, 153904.

(116) Christiansen-Salameh, J. et al. Understanding nanoscale structural distortions in Pb(Zr(0.2)Ti(0.8))O(3) by utilizing X-ray nanodiffraction and clustering algorithm analysis. *J. Synchrotron Radiat.* **2021**, *28*, 207–213.

(117) Williams, G. J.; Pfeifer, M. A.; Vartanyants, I. A.; Robinson, I. K. Three-dimensional imaging of microstructure in Au nanocrystals. *Phys. Rev. Lett.* **2003**, *90*, 175501.

(118) Ulvestad, A. et al. Avalanching strain dynamics during the hydriding phase transformation in individual palladium nanoparticles. *Nat. Commun.* **2015**, *6*, 10092.
(119) Bjorling, A.; Marcal, L. A. B.; Solla-Gullon, J.; Wallentin, J.; Carbone, D.; Maia, F. Three-dimensional coherent Bragg imaging of rotating nanoparticles. *Phys. Rev. Lett.* **2020**, *125*, 246101.

(120) Wu, L.; Yoo, S.; Suzana, A. F.; Assefa, T. A.; Diao, J.; Harder, R. J.; Cha, W.; Robinson, I. K. Three-dimensional coherent X-ray diffraction imaging via deep convolutional neural networks. *Npj Comput. Mater.* **2021**, *7*, 175.

(121) Fienup, J. R. Phase retrieval algorithms: a comparison. *Appl. Opt.* **1982**, *21*, 2758–2769.

(122) Gorobtsov, O.; Singer, A. Shear displacement gradient in X-ray Bragg coherent diffractive imaging. *J. Synchrotron Radiation.* **2022**, *29*, 866–870.

(123) Newton, M. C.; Leake, S. J.; Harder, R.; Robinson, I. K. Three-dimensional imaging of strain in a single ZnO nanorod. *Nat. Mater.* **2010**, *9*, 120–4.

(124) Hofmann, F.; Phillips, N. W.; Das, S.; Karamched, P.; Hughes, G. M.; Douglas, J. O.; Cha, W.; Liu, W. Nanoscale imaging of the full strain tensor of specific dislocations extracted from a bulk sample. *Phys. Rev. Materials* **2020**, *4*, 013801.

(125) Whitehead, L. W.; Williams, G. J.; Quiney, H. M.; Vine, D. J.; Dilanian, R. A.; Flewett, S.; Nugent, K. A.; Peele, A. G.; Balaur, E.; McNulty, I. Diffractive imaging using partially coherent X-rays. *Phys. Rev. Lett.* **2009**, *103*, 243902.

(126) Clark, J. N.; Huang, X.; Harder, R.; Robinson, I. K. High-resolution three-dimensional partially coherent diffraction imaging. *Nat. Commun.* **2012**, *3*, 993.

(127) Shabalin, A. G.; Yefanov, O. M.; Nosik, V. L.; Bushuev, V. A.; Vartanyants, I. A. Dynamical effects in

Bragg coherent x-ray diffraction imaging of finite crystals. *Phys. Rev. B* **2017**, *96*, 064111.

(128) Gorobtsov, O. Y.; Vartanyants, I. A. Phase of transmitted wave in dynamical theory and quasi-kinematical approximation. *Phys. Rev. B* **2016**, *93*, 184107.

(129) Rodenburg, J. M.; Hurst, A. C.; Cullis, A. G.; Dobson, B. R.; Pfeiffer, F.; Bunk, O.; David, C.; Jefimovs, K.; Johnson, I. Hard-X-ray lensless imaging of extended objects. *Phys. Rev. Lett.* **2007**, *98*, 34801.

(130) Dierolf, M.; Menzel, A.; Thibault, P.; Schneider, P.; Kewish, C. M.; Wepf, R.; Bunk, O.; Pfeiffer, F. Ptychographic X-ray computed tomography at the nanoscale. *Nature* **2010**, *467*, 436–439.

(131) Singer, A.; Boucheron, L.; Dietze, S. H.; Jensen, K. E.; Vine, D.; McNulty, I.; Dufresne, E. R.; Prum, R. O.; Mochrie, S. G. J.; Shpyrko, O. G. Domain morphology, boundaries, and topological defects in biophotonic gyroid nanostructures of butterfly wing scales. *Sci. Adv.* **2016**, *2*, e1600149–e1600149.

(132) Thibault, P.; Dierolf, M.; Menzel, A.; Bunk, O.; David, C.; Pfeiffer, F. High-resolution scanning X-ray diffraction microscopy. *Science* **2008**, *321*, 379–382.

(133) Schropp, A. et al. Full spatial characterization of a nanofocused x-ray free-electron laser beam by Ptychographic imaging. *Sci. Rep.* **2013**, *3*, 1633.

(134) Donnelly, C.; Guizar-Sicairos, M.; Scagnoli, V.; Gliga, S.; Holler, M.; Raabe, J.; Heyderman, L. J. Three-dimensional magnetization structures revealed with X-ray vector nanotomography. *Nature* **2017**, *547*, 328–331.

(135) Holler, M.; Guizar-Sicairos, M.; Tsai, E. H.; Dinapoli, R.; Muller, E.; Bunk, O.; Raabe, J.; Aeppli, G.
High-resolution non-destructive three-
dimensional imaging of integrated
circuits. *Nature* **2017**, *543*, 402–406.

(136) Walker, F.; Specht, E. E. Resonant anomalous X-ray scattering: Theory and applications. 1994.

(137) Flagg, L. Q. et al. Resonant X-ray diffraction reveals the location of counterions in doped organic mixed ionic conductors. *Chem. Mater.* **2023**, *35*, 3960–3967.

(138) Qiu, C.; Eng, P. J.; Hennig, C.; Schmidt, M. Formation and aggregation of ZrO2 nanoparticles on muscovite (001). *J. Phys. Chem. C* **2018**, *122*, 3865–3874.

(139) Joly, Y. X-ray absorption near-edge structure calculations beyond the muffin-tin approximation. *Phys. Rev. B* **2001**, *63*, 125120.

(140) Soldo-Olivier, Y.; Sibert, E.; De Santis, M.; Joly, Y.; Grunder, Y. Unraveling the charge distribution at the metal-electrolyte interface coupling in situ surface resonant X-ray diffraction with Ab initio calculations. *ACS Catal.* **2022**, *12*, 2375–2380.

(141) Grunder, Y.; Lucas, C. A.; Thompson, P. B. J.; Joly, Y.; Soldo-Olivier, Y. Charge reorganization at the adsorbate covered electrode surface probed through in situ resonant X-ray diffraction combined with ab initio modeling. *J. Phys. Chem. C* **2022**, *126*, 4612–4619.

(142) Toney, M. In *Studies of electrodes by in situ x-ray scattering*; Melendres, C., Ed.; Synchrotron techniques in interfacial electrochemistry. NATO ASI Series; 1993; pp 109–125.

(143) Toney, M.; McBreen, J. In situ synchrotron x-ray techniques for determining atomic structures at electrode/electrolyte interfaces. *Interface* **1993**, *2*, 22–31.

(144) Toney, M.; Ocko, B. Atomic structure at electrode interfaces. *Synchrotron Raydiat.News* **1993**, *6*, 28–33.

(145) Ocko, B. M.; Magnussen, O. M.; Wang, J. X.; Adzic, R. R.; Wandlowski, T. The structure and phase behavior of electrodeposited halides on single-crystal metal surfaces. *Physica B Condens. Matter.* **1996**, *221*, 238–244.

(146) Ocko, B.; Wandlowski, T. Halide electroadsorption on single crystal surfaces. *Mat. Res. Soc. Symp. Proc* **1997**, *451*, 55–67.

(147) Nagy, Z.; You, H. Applications of surface X-ray scattering to electrochemistry problems. *Electrochim. Acta* **2002**, *47*, 3037–3055.

(148) Magnussen, O. Ordered anion adlayers on metal electrode surfaces. *Chem. Rev* **2002**, *102*, 679–725.

(149) Lucas, C. A.; Markovic, N. M. In-situ X-ray diffraction studies of the electrode/solution interface. *Adv. Electrochem. Sci. Eng.* **2006**, *9*, 1–45.

(150) Grunder, Y.; Lucas, C. A. Surface X-ray diffraction studies of single crystal electrocatalysts. *Nano Energy* **2016**, *29*, 378–393.

(151) You, H. X-ray scattering and imaging studies of electrode structure and dynamics. *Chem. Rec.* **2019**, *19*, 1220–1232.

(152) Fenter, P. A. X-ray reflectivity as a probe of mineral-fluid interfaces: a user guide. *Rev. Mineral. Geochem.* **2002**, *49*, 149–220.

(153) Fenter, P.; Sturchio, N. C. Mineral-water interfacial structures revealed by synchrotron x-ray scattering. *Prog. Surf. Sci.* **2005**, *77*, 171–258.

(154) Huang, K. G.; Gibbs, D.; Zehner, D. M.; Sandy, A. R.; Mochrie, S. G. J. Phase-behavior of the Au(111) surface - discom-
mensurations and kinks. *Phys. Rev. Lett.* **1990**, *65*, 3313-3316.

(155) Sandy, A. R.; Mochrie, S. G. J.; Zehner, D. M.; Huang, K. G.; Gibbs, D. Structure and phases of the Au(111) surface - X-ray-scattering measurements. *Phys. Rev. B* **1991**, *43*, 4667-4687.

(156) Sandy, A. R.; Mochrie, S. G. J.; Zehner, D. M.; Grubel, G.; Huang, K. G.; Gibbs, D. Reconstruction of the Pt(111) surface. *Phys. Rev. Lett.* **1992**, *68*, 2192-2195.

(157) Sandy, A. R.; Mochrie, S. G. J.; Zehner, D. M.; Grubel, G.; Huang, K. G.; Gibbs, D. Au(111) and Pt(111) surface phase-behavior. *Surf. Sci.* **1993**, *287*, 321-324.

(158) Grubel, G.; Gibbs, D.; Zehner, D. M.; Abernathy, D. L.; Sandy, A. R.; Mochrie, S. G. J. Phase-behavior of Au and Pt surfaces. *Surf. Sci.* **1993**, *287*, 842-846.

(159) Kolb, D. Reconstruction phenomena at metal-electrolyte interfaces. *Prog. Surf. Sci* **1996**, *51*, 109-173.

(160) Ocko, B. M.; Wang, J.; Davenport, A.; Isaacs, H. In situ X-ray reflectivity and diffraction studies of the Au(001) reconstruction in an electrochemical-cell. *Phys. Rev. Lett.* **1990**, *65*, 1466-1469.

(161) Wang, J.; Davenport, A. J.; Isaacs, H. S.; Ocko, B. M. Surface-charge induced ordering of the Au(111) surface. *Science* **1992**, *255*, 1416-1418.

(162) Wang, J.; Ocko, B. M.; Davenport, A. J.; Isaacs, H. S. In situ X-ray-diffraction and X-ray-reflectivity studies of the Au(111) electrolyte interface - reconstruction and anion adsorption. *Phys. Rev. B* **1992**, *46*, 10321-10338.

(163) Ocko, B. M.; Helgesen, G.; Schardt, B.; Wang, J.; Hamelin, A. Charge induced

(1x3) reconstruction of the Au(110) surface - an X-ray-scattering study. *Phys. Rev. Lett.* **1992**, *69*, 3350-3353.

(164) Feng, Y. J.; Bohnen, K. P.; Chan, C. T. First-principles studies of Au(100)-hex reconstruction in an electrochemical environment. *Phys. Rev. B: Condens. Matter* **2005**, *72*, 125401/1.

(165) Jacob, T. Potential-induced lifting of the Au(100)-surface reconstruction studied with DFT. *Electrochim. Acta* **2007**, *52*, 2229-2235.

(166) Kondo, T.; Zegenhagen, J.; Takakusagi, S.; Uosaki, K. In situ real-time study on potential induced structure change at Au(111) and Au(100) single crystal electrode/sulfuric acid solution interfaces by surface x-ray scattering. *Surf. Sci.* **2015**, *631*, 96-104.

(167) Tidswell, I. M.; Markovic, N. M.; Lucas, C. A.; Ross, P. N. In-situ X-ray-scattering study of the Au(001) reconstruction in alkaline and acidic electrolytes. *Phys. Rev. B* **1993**, *47*, 16542-16553.

(168) Tidswell, I.; Markovic, N.; Ross, P. Potential dependent structure of single crystal gold interfaces in alkaline electrolyte: an in situ x-ray scattering study. *Surf. Sci* **1994**, *317*, 241-252.

(169) Grunder, Y.; Harlow, G. S.; Cocklin, E.; Fogg, J.; Beane, J. W.; Lucas, C. A. Potential-dependent surface compression of gold and its link to electrocatalytic reactivity. *Surf. Sci.* **2019**, *680*, 113-118.

(170) Gao, X.; Hamelin, A.; Weaver, M. Atomic relaxation at ordered electrochemical surfaces probed by scanning tunneling microscopy: Au(111) in aqueous solution compared with ultrahigh-vacuum environments. *J. Chem. Phys* **1991**, *95*, 6993-6996.

(171) Gao, X.; Hamelin, A.; Weaver, M. Potential-dependent reconstruction at
ordered Au(100)-aqueous interfaces as probed by atomic-resolution scanning tunneling microscopy. *Phys. Rev. Lett* **1991**, *67*, 618-621.

(172) Gao, X.; Hamelin, A.; Weaver, M. Reconstruction at ordered Au(110)-aqueous interfaces as probed by atomic resolution scanning tunneling microscopy. *Phys. Rev. B* **1991**, *44*, 10983-10986.

(173) Gao, X.; Weaver, M. Electrode potential-induced reconstruction of Au(100): Effect of chemisorption on nanoscale dynamics as probed by in-situ scanning tunneling microscopy. *J. Phys. Chem* **1993**, *97*, 8685-8689.

(174) Magnussen, O.; Hotlos, J.; Behm, R.; Batina, N.; Kolb, D. An in-situ scanning tunneling microscopy study of electrochemically induced 'hex' <-> transitions on Au(100) electrodes. *Surf. Sci* **1993**, *296*, 310-332.

(175) Magnussen, O.; Wiechers, J.; Behm, R. In situ scanning tunneling microscopy observations of the potential-dependent (1x2) reconstruction on Au(110) in acidic electrolytes. *Surf. Sci* **1993**, *289*, 139-151.

(176) Lucas, C.; Markovic, N.; Ross, P. Surface structure and relaxation at the Pt(110)/electrolyte interface. *Phys. Rev. Lett* **1996**, *77*, 4922-4925.

(177) Markovic, N. M.; Grgur, B. N.; Lucas, C. A.; Ross, P. N. Surface electrochemistry of CO on Pt(110)-(1x2) and Pt(110)-(1x1) surfaces. *Surf. Sci.* **1997**, *384*, L805-L814.

(178) Kibler, L.; Cuesta, A.; Kleinert, M.; Kolb, D. In-situ STM characterization of the surface morphology of platinum single crystal electrodes as a function of their preparation. *J. Electroanal. Chem* **2000**, *484*, 73-82.

(179) LaGraff, J.; Gewirth, A. In-situ observation of oxygen adlayer formation

on Cu(110) electrode surfaces. *Surf. Sci* **1995**, *326*, L461-L466.

(180) Broekmann, P.; Wilms, M.; Spänig, A.; Hommrich, J.; Stuhlmann, C.; Wandelt, K. In-situ STM study of the sulfate induced Cu(111) reconstruction. *ECS Meeting Abstract* **1999**, *99-1*, 1111-1111.

(181) Broekmann, P.; Wilms, M.; Wandelt, K. Atomic structures of a Cu(111) surface under electrochemical conditions: an in-situ STM study. *Surf. Rev. Lett* **1999**, *6*, 907-916.

(182) Broekmann, P.; Wilms, M.; Spaenig, A.; Wandelt, K. Formation of adsorbate structures on Cu(111) during hydrogen evolution. *Proc. Electrochem. Soc.* **2002**, *2000-30*, 124-129.

(183) Wan, L.-J.; Itaya, K. In situ scanning tunneling microscopy of Cu(110): atomic structures of halide adlayers and anodic dissolution. *J. Electroanal. Chem* **1999**, *473*, 10-18.

(184) Maurice, V.; Strehblow, H.-H.; Marcus, P. In situ STM study of the initial stages of oxidation of Cu(111) in aqueous solution. *Surf. Sci* **2000**, *458*, 185-194.

(185) Matsushima, H.; Taranovskyy, A.; Haak, C.; Gründer, Y.; Magnussen, O. Reconstruction of Cu(100) electrode surfaces during hydrogen evolution. *J. Am. Chem. Soc* **2009**, *131*, 10362-10363.

(186) Lucas, C. A. et al. Temperature-induced ordering of metal/adsorbate structures at electrochemical interfaces. *J. Am. Chem. Soc.* **2009**, *131*, 7654-7661.

(187) Gründer, Y.; Markovic, N. M.; Thompson, P.; Lucas, C. A. Temperature effects on the atomic structure and kinetics in single crystal electrochemistry. *Surf. Sci.* **2015**, *631*, 123-129.

(188) Pierce, M. S.; Komanicky, V.; Barbour, A.; Hennessy, D. C.; Zhu, C.; Sandy, A.; You, H. Dynamics of the Au
(001) surface in electrolytes: in situ coherent X-ray scattering. *Phys. Rev. B: Condens. Matter Mater. Phys.* **2012**, *86*, 085410/1–085410/7.

(189) You, H.; Pierce, M.; Komanicky, V.; Barbour, A.; Zhu, C. Study of electrode surface dynamics using coherent surface X-ray scattering. *Electrochim. Acta* **2012**, *82*, 570–575.

(190) Lucas, C. A. Surface relaxation at the metal/electrolyte interface. *Electrochim. Acta* **2002**, *47*, 3065–3074.

(191) Tidswell, I.; Markovic, N.; Ross, P. Potential dependent surface relaxation of the Pt(001)/ electrolyte interface. *Phys. Rev. Lett* **1993**, *71*, 1601–1604.

(192) Lucas, C. A. Atomic structure at the electrochemical interface. *J. Phys. D: Appl. Phys.* **1999**, *32*, A198–A201.

(193) Lucas, C.; Markovic, N.; Ross, P. Adsorption of halide anions at the Pt(111)-solution interface studied by in situ surface x-ray scattering. *Phys. Rev. B* **1997**, *55*, 7964–7971.

(194) Wang, J. X.; Robinson, I. K.; Ocko, B. M.; Adzic, R. R. Adsorbate-geometry specific subsurface relaxation in the CO/Pt(111) system. *J. Phys. Chem. B* **2005**, *109*, 24–26.

(195) Saracino, M.; Broekmann, P.; Gentz, K.; Becker, M.; Keller, H.; Janetzko, F.; Bridow, T.; Wandelt, K.; Dosch, H. Surface relaxation phenomena at electrified interfaces. Revealing adsorbate, potential, and solvent effects by combined x-ray diffraction, STM and DFT studies. *Phys. Rev. B: Condens. Matter Mater. Phys.* **2009**, *79*, 115448/1–115448/11.

(196) Gründer, Y.; Kaminski, D.; Golks, F.; Krug, K.; Stettner, J.; Magnussen, O.; Franke, A.; Stremme, J.; Pehlke, E. reversal of chloride-induced Cu(001) subsurface buckling in electrochemical environment: An in situ surface x-ray diffrac-

tion and density functional theory study. *Phys. Rev. B* **2010**, *81*, 174114.

(197) Lucas, C. A.; Markovic, N. M.; Grüber, B. N.; Ross, P. N. Structural effects during CO adsorption on Pt-bimetallic surfaces I. The Pt(100) electrode. *Surf. Sci.* **2000**, *448*, 65–76.

(198) Ball, M. J.; Lucas, C. A.; Markovic, N. M.; Stamenkovic, V.; Ross, P. N. Surface X-ray scattering studies of the growth of Pd thin films on the Pt(001) electrode surface and the effects of the adsorption of CO. *Surf. Sci.* **2003**, *540*, 295–302.

(199) Gallagher, M. E.; Lucas, C. A.; Stamenkovic, V.; Markovic, N. M.; Ross, P. N. Surface structure and relaxation at the Pt3Sn(111)/electrolyte interface. *Surf. Sci.* **2003**, *544*, L729–L734.

(200) Stamenkovic, V. R.; Arenz, M.; Lucas, C. A.; Gallagher, M. E.; Ross, P. N.; Markovic, N. M. Surface chemistry on bimetallic alloy surfaces: Adsorption of anions and oxidation of CO on Pt3Sn(111). *J. Am. Chem. Soc.* **2003**, *125*, 2736–2745.

(201) Harlow, G. S.; Aldous, I. M.; Thompson, P.; Gründer, Y.; Hardwick, L. J.; Lucas, C. A. Adsorption, surface relaxation and electrolyte structure at Pt(111) electrodes in non-aqueous and aqueous acetonitrile electrolytes. *Phys. Chem. Chem. Phys.* **2019**, *21*, 8654–8662.

(202) Nichols, R. J.; Nouar, T.; Lucas, C. A.; Haiss, W.; Hofer, W. A. Surface relaxation and surface stress of Au(111). *Surf. Sci.* **2002**, *513*, 263–271.

(203) Gründer, Y.; Lucas, C. A. Potential-induced structural deformation at electrode surfaces. *Curr. Opin. Electrochem.* **2020**, *19*, 168–174.
(204) Fleischmann, M.; Olivier, A.; Robinson, J. In situ x-ray diffraction studies of electrode solution interfaces. *Electrochim. Acta* **1986**, *31*, 899-906.

(205) Fleischmann, M.; Mao, B. In situ X-ray diffraction measurements of the surface structure of Pt in the presence of "weakly" adsorbed H. *J. Electroanal. Chem* **1988**, *247*, 311-313.

(206) Fleischmann, M.; Mao, B. In-situ X-ray diffraction investigations of the UPD of the Tl and Pb on Ag and Au electrodes. *J. Electroanal. Chem* **1988**, *247*, 297-309.

(207) Melroy, O.; Toney, M.; Borges, G.; Samant, M.; Kortright, J.; Ross, P.; Blum, L. Two-dimensional compressibility of electrochemically adsorbed lead on silver (111). *Phys. Rev. B* **1988**, *38*, 10962-10965.

(208) Samant, M.; Toney, M.; Borges, G.; Blum, L.; Melroy, O. Grazing incidence X-ray diffraction of lead monolayers at a silver (111) and gold (111) electrode/ electrolyte interface. *J. Chem. Phys* **1988**, *92*, 220-225.

(209) Melroy, O.; Toney, M.; Borges, G.; Samant, M.; Kortright, J.; Ross, P.; Blum, L. An in-situ grazing incidence X-ray scattering study of the initial stages of electrochemical growth of lead on silver (111). *J. Electroanal. Chem* **1989**, *258*, 403-414.

(210) Toney, M.; Melroy, O. In situ X-ray scattering of monolayers adsorbed at electrochemical interfaces. *Mat. Res. Soc. Symp. Proc* **1989**, *143*, 37-42.

(211) Wandlowski, T. In *Thermodynamics and electrified interfaces, Encyclopedia of Electrochemistry Vol. 1*; Bard, A., Stratmann, M., Eds.; WILEY-VCH: Weinheim, 2003; Chapter 3.3, pp 383-467.

(212) Ocko, B. M.; Watson, G. M.; Wang, J. Structure and electrocompression of

electrodeposited iodine monolayers on Au(111). *J. Phys. Chem.* **1994**, *98*, 897-906.

(213) Magnussen, O. M.; Ocko, B. M.; Adzic, R. R.; Wang, J. X. X-ray-diffraction studies of ordered chloride and bromide monolayers at the Au(111)-solution interface. *Phys. Rev. B* **1995**, *51*, 5510-5513.

(214) Inukai, J.; Osawa, Y.; Itaya, K. Adlayer structures of chlorine, bromine, and iodine on Cu(111) electrode in solution: in-situ STM and ex-situ studies. *J. Phys. Chem. B* **1998**, *102*, 10034-10040.

(215) Gründer, Y.; Drünkler, A.; Golks, F.; Wijts, G.; Stettner, J.; Zegenhagen, J.; Magnussen, O. Structure and electro-compression of chloride adlayers on Cu(111). *Surf. Sci* **2011**, *605*, 1732-1737.

(216) Gründer, Y.; Stettner, J.; Magnussen, O. M. Review-in-situ surface X-ray diffraction studies of copper electrodes: atomic-scale interface structure and growth behavior. *J. Electrochem. Soc.* **2019**, *166*, D3049-D3057.

(217) Wandlowski, T.; Wang, J.; Magnussen, O.; Ocko, B. Structural and kinetic aspects of bromide adsorption on Au(100). *J. Phys. Chem* **1996**, *100*, 10277-10287.

(218) Wang, J. X.; Watson, G. M.; Ocko, B. M. Ordered binary ionic adlayers on a Au(110) electrode: Coadsorption of alkali metal cations with iodide anions. *J. Phys. Chem.* **1996**, *100*, 6672-6677.

(219) Ocko, B.; Wang, J.; Wandlowski, T. Bromide adsorption on Ag(001): a potential induced two-dimensional ising order-disorder transition. *Phys. Rev. Lett* **1997**, *79*, 1511-1514.

(220) Wandlowski, T.; Wang, J.; Ocko, B. Adsorption of bromide at the Ag(100)
electrode surface. *J. Electroanal. Chem* **2001**, *500*, 418-434.

(221) Huemann, S.; Hai, N. T. M.; Broekmann, P.; Wandelt, K.; Zajonz, H.; Dosch, H.; Renner, F. X-ray diffraction and STM study of reactive surfaces under electrochemical control: Cl and I on Cu(100). *J. Phys. Chem. B* **2006**, *110*, 24955-24963.

(222) Keller, H.; Saracino, M.; Nguyen, H. M. T.; Broekmann, P. Templating the near-surface liquid electrolyte: In situ surface x-ray diffraction study on anion/cation interactions at electrified interfaces. *Phys. Rev. B: Condens. Matter Mater. Phys.* **2010**, *82*, 245425/1-245425/7.

(223) Keller, H.; Saracino, M.; Nguyen, H. M. T.; Huynh, T. M. T.; Broekmann, P. Competitive anion/water and cation/water interactions at electrified copper/electrolyte interfaces probed by in situ X-ray diffraction. *J. Phys. Chem. C* **2012**, *116*, 11068-11076.

(224) Pham, D. T.; Keller, H.; Breuer, S.; Huemann, S.; Hai, N. T. N.; Zoerlein, C.; Wandelt, K.; Broekmann, P. Anion/cation layers at electrified interfaces: a comprehensive STM, XRD and XPS case study. *Chimia* **2009**, *63*, 115-121.

(225) Mitchell, S. J.; Brown, G.; Rikvold, P. A. Dynamics of Br electrosorption on single-crystal Ag(100): a computational study. *J. Electroanal. Chem.* **2000**, *493*, 68-74.

(226) Abou Hamad, I.; Wandlowski, T.; Brown, G.; Rikvold, P. A. Electrosorption of Br and Cl on Ag(100): experiments and computer simulations. *J. Electroanal. Chem.* **2003**, *554-555*, 211-219.

(227) Tolentino, H.; De Santis, M.; Gauthier, Y.; Langlais, V. Chlorine chemisorption on Cu(001) by surface X-ray diffraction: Geometry and substrate relaxation. *Surf. Sci.* **2007**, *601*, 2962-2966.

(228) Nakamura, M.; Nakajima, Y.; Sato, N.; Hoshi, N.; Sakata, O. Structure of the electrical double layer on Ag(100): Promotive effect of cationic species on Br adlayer formation. *Phys. Rev. B* **2011**, *84*, 165433/1-165433/5.

(229) Nakamura, M.; Kaminaga, H.; Endo, O.; Tajiri, H.; Sakata, O.; Hoshi, N. Structural dynamics of the electrical double layer during capacitive charging/discharging processes. *J. Phys. Chem. C* **2014**, *118*, 22136-22140.

(230) Nakamura, M.; Sato, N.; Hoshi, N.; Sakata, O. Outer Helmholtz plane of the electrical double layer formed at the solid electrode-liquid interface. *ChemPhysChem* **2011**, *12*, 1430-1434.

(231) Tanaka, S.; Tajiri, H.; Sakata, O.; Hoshi, N.; Nakamura, M. Interfacial structure of Pt(110) electrode during hydrogen evolution reaction in alkaline solutions. *J. Phys. Chem. Lett.* **2022**, *13*, 8403-8408.

(232) Grunder, Y.; Lucas, C. A. Probing the charge distribution at the electrochemical interface. *Phys. Chem. Chem. Phys.* **2017**, *19*, 8416-8422.

(233) Kolb, D. In *Advances in electrochemistry and electrochemical engineering*; Gerischer, H., Tobias, C., Eds.; Wiley-Interscience: New York, 1978; Vol. 11; pp 125-271.

(234) Staikov, G.; Budevski, E.; Lorenz, W. *Electrochemical phase formation and growth*; VCH: Weinheim, 1997.

(235) Adzic, R.; Wang, J.; Vitus, C.; Ocko, B. The electrodeposition of Pb monolayer on low index Pt surfaces: and x-ray scattering and scanning tunneling microscopy study. *Surf. Sci.* **1993**, *293*, L876-L883.

(236) Toney, M.; Gordon, J.; Samant, M.; Borges, G.; Melroy, O. In-situ atomic structure of underpotentially deposited
monolayers of Pb and Tl on Au(111) and Ag(111): a surface X-ray scattering study. *J. Phys. Chem* **1995**, *99*, 4733-4744.

(237) Toney, M.; Gordon, J.; Samant, M.; Borges, G.; Melroy, O.; Yee, D.; Sorensen, L. Unterpotentially deposited thallium on silver(111) by in situ surface x-ray scattering. *Phys. Rev. B* **1992**, *45*, 9362-9374.

(238) Polewska, W.; Wang, J.; Ocko, B.; Adzic, R. Scanning tunnelling microscopy of electrodeposited Thallium monolayers on Au(111) in alkaline solution and a comparison with surface x-ray scattering data. *J. Electroanal. Chem* **1994**, *376*, 41-47.

(239) Wang, J. X.; Adzic, R. R.; Ocko, B. M. X-Ray-Scattering Study of Tl-Adlayers on the Au(111) Electrode in Alkaline-Solutions - Metal Monolayer, Oh- Coadsorption, and Oxide Formation. *J. Phys. Chem. 1994*, *98*, 7182-7190.

(240) Wang, J. X.; Adzic, R. R.; Magnussen, O. M.; Ocko, B. M. Structural evolution during electrocrystallization: Deposition of Tl on Ag(100) from monolayer to bilayer and to bulk crystals. *Surf. Sci.* **1995**, *344*, 111-121.

(241) Wang, J.; Adzic, R.; Magnussen, O.; Ocko, B. Structure of electrodeposited Tl overlayers on Au(100) studies via surface x-ray scattering. *Surf. Sci* **1995**, *335*, 120-128.

(242) Adzic, R.; Wang, J. Bromide adsorption induced formation of thallium bromide adlayers with varying composition and structure on the Au(111) electrode surface. *J. Phys. Chem. B* **1998**, *102*, 6305-6308.

(243) Wang, J.; Robinson, I.; Adzic, R. Formation of well-ordered surface compounds by coadsorption of thallium and bromide on the Au(111) electrode surface. *Surf. Sci* **1998**, *412/413*, 374-383.

(244) Toney, M.; Gordon, J.; Samant, M.; Borges, G.; Wiesler, D. In-situ surface X-ray scattering measurements of electrochemically deposited Bi on Ag(111): Structure, compressibility, and comparison with ex situ low-energy electron diffraction measurements. *Langmuir* **1991**, *7*, 796-802.

(245) Chen, C. H.; Kepler, K. D.; Gewirth, A. A.; Ocko, B. M.; Wang, J. Electrodeposited bismuth monolayers on Au(111) electrodes - comparison of surface X-ray-scattering, scanning-tunneling-microscopy, and atomic-force microscopy lattice structures. *J. Phys. Chem.* **1993**, *97*, 7290-7294.

(246) Tamura, K.; Ocko, B. M.; Wang, J. X.; Adzic, R. R. Structure of active adlayers on bimetallic surfaces: Oxygen reduction on Au(111) with Bi adlayers. *J. Phys. Chem. B* **2002**, *106*, 3896-3901.

(247) Zheng, S.; Krug, K.; Golks, F.; Kaminski, D.; Morin, S.; Magnussen, O. Study of Bi UPD structures on Au(100) using in situ surface x-ray scattering. *J. Electroanal. Chem* **2010**, *649*, 189-197.

(248) Lucas, C.; Markovic, N.; Ross, P. Underpotential deposition of lead onto Pt(001): Interface structure and the influence of adsorbed bromide. *Langmuir* **1997**, *13*, 5517-5520.

(249) Lucas, C. A.; Markovic, N. M.; Ross, P. N. Underpotential deposition of Cu on Pt(001): Interface structure and the influence of adsorbed bromide. *Phys. Rev. B* **1998**, *57*, 13184-13191.

(250) Markovic, N.; Grgur, B.; Lucas, C.; Ross, R. Underpotential deposition of lead on Pt(111) in the presence of bromide: RRDPt(111)E and X-ray scattering studies. *J. Electroanal. Chem* **1998**, *448*, 183-188.

(251) Ball, M.; Lucas, C. A.; Markovic, N. M.; Murphy, B. M.; Steadman, P.;
Schmidt, T. J.; Stamenkovic, V.; Ross, P. N. X-ray scattering studies of irreversibly adsorbed bismuth on the Pt(111) electrode surface. *Langmuir* **2001**, *17*, 5943–5946.

(252) Schmidt, T. J.; Stamenkovic, V. R.; Lucas, C. A.; Markovic, N. M.; Ross, P. N. Surface processes and electrocatalysis on the Pt(hkl)/Bi-solution interface. *Phys. Chem. Chem. Phys.* **2001**, *3*, 3879–3890.

(253) Toney, M.; Howard, J.; Richer, J.; Borges, G.; Gordon, J.; Melroy, O. Electrochemical deposition of copper on a gold electrode in sulfuric acid: resolution of the interfacial structure. *Phys. Rev. Lett* **1995**, *75*, 4472–4475.

(254) Nakamura, M.; Endo, O.; Ohta, T.; Ito, M.; Yoda, Y. Surface X-ray diffraction study of Cu UPD on Au(1 1 1) electrode in 0.5 M H2SO4 solution: the coadsorption structure of UPD copper, hydration water molecule and bisulfate anion on Au(1 1 1). *Surf. Sci.* **2002**, *514*, 227–233.

(255) Lucas, C. A.; Markovic, N. M.; Ross, P. N. Electrochemical deposition of copper onto Pt(111) in the presence of (bi)sulfate anions. *Phys. Rev. B* **1997**, *56*, 3651–3654.

(256) Markovic, N.; Gasteiger, H.; Lucas, C.; Tidswell, I.; Ross, P. The effect of chloride on the underpotential deposition of copper on Pt(111): AES, LEED, RRDE and x-ray scattering studies. *Surf. Sci* **1995**, *335*, 91–100.

(257) Tidswell, I.; Lucas, C.; Markovic, N.; Ross, P. Surface structure determination using anomalous x-ray scattering: underpotential deposition of copper on Pt(111). *Phys. Rev. B* **1995**, *51*, 10205–10208.

(258) Lucas, C. A.; Markovic, N. M.; Tidswell, I. M.; Ross, P. N. In situ

X-ray scattering study of the Pt(111)-solution interface: Ordered anion structures and their influence on copper underpotential deposition. *Physica B* **1996**, *221*, 245–250.

(259) Markovic, N.; Grgur, B.; Lucas, C.; Ross, P. UPD of Cu on Pt(100): effects of anions on adsorption isotherms and interface structures. *Electrochim. Acta* **1998**, *44*, 1009–1017.

(260) Markovic, N. M.; Grgur, B. N.; Lucas, C. A.; Ross, P. N. Underpotential deposition of lead onto Pt(100) in acid solutions: Adsorption isotherms and interface structures. *J. Chem. Soc., Faraday trans.* **1998**, *94*, 3373–3379.

(261) Wang, J.; Robinson, I.; DeVilbiss, J.; Adzic, R. Structural trends among ionic metal-halide adlayers on electrode surfaces. *J. Phys. Chem. B* **2000**, *104*, 7951–7959.

(262) Wang, J. X.; Marinkovic, N. S.; Adzic, R. R.; Ocko, B. M. Anomalous lattice expansion of the electrodeposited Ag bilayer on Pt(111). *Surf. Sci.* **1998**, *398*, L291–L296.

(263) Marinkovic, N.; Wang, J.; Marinkovic, J.; Adzic, R. Unusual adsorption properties of silver adlayers on the Pt(111) electrode surface. *J. Phys. Chem* **1999**, *103*, 139–144.

(264) Markovic, N. M.; Lucas, C. A.; Climent, V.; Stamenkovic, V.; Ross, P. N. Surface electrochemistry on an epitaxial palladium film on Pt(111): surface microstructure and hydrogen electrode kinetics. *Surf. Sci.* **2000**, *465*, 103–114.

(265) Ball, M. J.; Lucas, C. A.; Markovic, N. M.; Stamenkovic, V.; Ross, P. N. From sub-monolayer to multilayer - an in situ X-ray diffraction study of the growth of Pd films on Pt(111). *Surf. Sci.* **2002**, *518*, 201–209.
(266) Lucas, C. A.; Markovic, N. M.; Ross, P. N. The adsorption and oxidation of carbon monoxide at the Pt(111)/electrolyte interface: atomic structure and surface relaxation. *Surf. Sci.* **1999**, *425*, L381–L386.

(267) Markovic, N.; Grgur, B.; Lucas, C.; Ross, R. Electrooxidation of CO and H2/CO mixtures on Pt(111) in acid solutions. *J. Phys. Chem. B* **1999**, *103*, 487–495.

(268) Markovic, N. M.; Lucas, C. A.; Rodes, A.; Stamenkovi, V.; Ross, P. N. Surface electrochemistry of CO on Pt(111): anion effects. *Surf. Sci.* **2002**, *499*, L149–L158.

(269) Tolmachev, Y. V.; Menzel, A.; Tkachuk, A. V.; Chu, Y. S.; You, H. In situ surface X-ray scattering observation of long-range ordered ($\sqrt{19}$)R23.4$^{circirc}$-13CO structure on Pt(111) in aqueous electrolytes. *Electrochem. Solid-State Lett.* **2003**, *7*, E23.

(270) Chang, K. C.; Menzel, A.; Komanicky, V.; You, H. Electrosorbed carbon monoxide monolayers on Pt(111). *Electrochim. Acta* **2007**, *52*, 5749–5758.

(271) Villegas, I.; Weaver, M. J. Carbon-monoxide adlayer structures on platinum(111) electrodes - a synergy between in-situ scanning-tunneling-microscopy and infrared-spectroscopy. *J. Chem. Phys.* **1994**, *101*, 1648–1660.

(272) Villegas, I.; Gao, X. P.; Weaver, M. J. Local-structure and phase-transitions within ordered electrochemical, adlayers - some new insights from in-situ scanning-tunneling-microscopy. *Electrochim. Acta* **1995**, *40*, 1267–1275.

(273) Lucas, C. A.; Markovic, N. M.; Ross, P. N. Structural effects induced by CO adsorption on Pt-bimetallic surfaces. *Surf. Rev. Lett.* **1999**, *6*, 917–922.

(274) Menzel, A.; Tolmachev, Y. V.; Chang, K. C.; Komanicky, V.; Chu, Y. S.; Rehr, J. J.; You, H. Polarization-dependent resonant anomalous surface x-ray scattering of CO/Pt(111). *Europhys. Lett.* **2006**, *74*, 1032–1038.

(275) Markovic, N. M.; Lucas, C. A.; Grgur, B. N.; Ross, P. N. Surface electro-chemistry of CO and H2/CO mixtures at Pt(100) interface. Electrode kinetics and interfacial structures. *J. Phys. Chem. B* **1999**, *103*, 9616–9623.

(276) Wakisaka, M.; Ohkanda, T.; Yoneyama, T.; Uchida, H.; Watanabe, M. Structures of a CO adlayer on a Pt(100) electrode in HClO4 solution studied by in situ STM. *Chem. Commun.* **2005**, 2710–2712.

(277) Wakisaka, M.; Yoneyama, T.; Ashizawa, S.; Hyuga, Y.; Ohkanda, T.; Uchida, H.; Watanabe, M. Structural variations of CO adlayers on a Pt(100) electrode in 0.1 M HClO4 solution: an in situ STM study. *Phys. Chem. Chem. Phys.* **2013**, *15*, 11038–11047.

(278) Gallagher, M. E.; Blizanac, B. B.; Lucas, C. A.; Ross, P. N.; Markovic, N. M. Structure sensitivity of CO oxidation on gold single crystal surfaces in alkaline solution: Surface X-ray scattering and rotating disk measurements. *Surf. Sci.* **2005**, *582*, 215–226.

(279) Lucas, C. A.; Markovic, N. M.; Ross, P. N. Structural effects during CO adsorption on Pt-bimetallic surfaces II. The Pt(111) electrode. *Surf. Sci.* **2000**, *448*, 77–86.

(280) Lucas, C. A.; Markovic, N. M.; Ball, M.; Stamenkovic, V.; Climent, V.; Ross, P. N. Surface structure and relaxation during the oxidation of carbon monoxide on Pt-Pd bimetallic surfaces. *Surf. Sci.* **2001**, *479*, 241–246.
(281) Kondo, T.; Masuda, T.; Aoki, N.; Uosaki, K. Potential-dependent structures and potential-induced structure changes at Pt(111) single-crystal electrode/sulfuric and perchloric acid interfaces in the potential region between hydrogen underpotential deposition and surface oxide formation by in situ surface X-ray scattering. *J. Phys. Chem. C* **2016**, null.

(282) Liu, Y.; Barbour, A.; Komanicky, V.; You, H. X-ray crystal truncation rod studies of surface oxidation and reduction on Pt(111). *J. Phys. Chem. C* **2016**, *0*, acs.jpcc.6b00492.

(283) Holby, E. F.; Greeley, J.; Morgan, D. Thermodynamics and hysteresis of oxide formation and removal on platinum (111) surfaces. *J. Phys. Chem. C* **2012**, *116*, 9942-9946.

(284) Nakamura, M.; Nakajima, Y.; Hoshi, N.; Tajiri, H.; Sakata, O. Effect of non-specifically adsorbed ions on the surface oxidation of Pt(111). *ChemPhysChem* **2013**, *14*, 2426-2431.

(285) Lucas, C. A.; Thompson, P.; Gruender, Y.; Markovic, N. M. The structure of the electrochemical double layer: Ag(111) in alkaline electrolyte. *Electrochem. Commun.* **2011**, *13*, 1205-1208.

(286) Toney, M.; Howard, J.; Richter, J.; Borges, G.; Gordon, J.; Melroy, O.; Wiesler, D.; Yee, D.; Sorensen, L. Voltage-dependent ordering of water molecules at an electrolyte-electrolyte interface. *Nature* **1994**, *368*, 444-446.

(287) Toney, M.; Howard, J.; Richer, J.; Borges, G.; Gordon, J.; Melroy, O.; Wiesler, D.; Yee, D.; Sorensen, L. Distribution of water molecules at (Ag(111)/electrolyte interface as studied with surface X-ray scattering. *Surf. Sci* **1995**, *335*, 326-332.

(288) Karl, J., Robert M.; Barbour, A.; Komanicky, V.; Zhu, C.; Sandy, A.;

Pierce, M. S.; You, H. Charge-induced equilibrium dynamics and structure at the Ag(001)-electrolyte interface. *Phys. Chem. Chem. Phys.* **2015**, *17*, 16682-16687.

(289) Spohr, E. In *Computer simulation of electrochemical interfaces*; Alkire, R., Kolb, D., Eds.; Advances in electrochemical science and engineering; VCH: Weinheim, 1999; Vol. 6; pp 1-76.

(290) Spohr, E. Molecular simulation of the electrochemical double layer. *Electrochim. Acta* **1999**, *44*, 1697-1705.

(291) Magnussen, O.; Groß, A. Toward an atomic-scale understanding of electrochemical interface structure and dynamics. *J. Am. Chem. Soc* **2019**, *141*, 4777-4790.

(292) Gross, A.; Sakong, S. Ab initio simulations of water/metal interfaces. *Chem. Rev.* **2022**, *122*, 10746-10776.

(293) Zhou, H. et al. Understanding controls on interfacial wetting at epitaxial graphene: experiment and theory. *Phys. Rev. B: Condens. Matter Mater. Phys.* **2012**, *85*, 035406/1.

(294) Hayashi, R.; Hoshi, N.; Sakata, O.; Nakamura, M. Potential dependence of the buckling structure of the interfacial water bilayer on a graphene electrode. *J. Phys. Chem. C* **2018**, *122*, 7795-7800.

(295) Mezger, M. et al. Molecular layering of fluorinated ionic liquids at a charged sapphire (0001) surface. *Science* **2008**, *322*, 424-428.

(296) Yamamoto, R.; Morisaki, H.; Sakata, O.; Shimotani, H.; Yuan, H. T.; Iwasa, Y.; Kimura, T.; Wakabayashi, Y. External electric field dependence of the structure of the electric double layer at an ionic liquid/Au interface. *Appl. Phys. Lett.* **2012**, *101*.
(297) Voegeli, W.; Arakawa, E.; Matsushita, T.; Sakata, O.; Wakabayashi, Y. Dynamical response of the electric double layer structure of the DEME-TFSI ionic liquid to potential changes observed by time-resolved X-ray reflectivity. *Z. fur Phys. Chem. 2016*, **230**, 577–585.

(298) Uysal, A. et al. Structural origins of potential dependent hysteresis at the electrified graphene/ionic liquid interface. *J. Phys. Chem. C 2014*, **118**, 569–574.

(299) Uysal, A. et al. Interfacial ionic ‘liquids’: connecting static and dynamic structures. *J. Phys.: Condens. Matter* **2014**, *27*, 032101.

(300) Petach, T. A.; Mehta, A.; Marks, R.; Johnson, B.; Toney, M. F.; Goldhaber-Gordon, D. Voltage-controlled interfacial layering in an ionic liquid on SrTiO3. *ACS Nano* **2016**, *10*, 4565–4569.

(301) Reichert, P.; Kjaer, K. S.; van Driel, T. B.; Mars, J.; Ochsmann, J. W.; Pontoni, D.; Deutsch, M.; Nielsen, M. M.; Mezger, M. Molecular scale structure and dynamics at an ionic liquid/electrode interface. *Faraday Discuss.* **2018**, *206*, 141–157.

(302) Douglas, T.; Yoo, S.; Dutta, P. Ionic liquid solutions show anomalous crowding behavior at an electrode surface. *Langmuir* **2022**, *38*, 6322–6329.

(303) Chu, M. Q.; Miller, M.; Dutta, P. Crowding and anomalous capacitance at an electrode-ionic liquid interface observed using operando X-ray scattering. *ACS Cent. Sci.* **2016**, *2*, 175–180.

(304) Chu, M.; Miller, M.; Douglas, T.; Dutta, P. Ultraslow dynamics at a charged silicon–ionic liquid interface revealed by X-ray reflectivity. *J. Phys. Chem. C* **2017**, *121*, 3841–3845.

(305) Henrich, V. E.; Cox, P. A. *The surface science of metal oxides*; Cambridge Univ. Press, Cambridge, UK, 1994.

(306) Diebold, U.; Li, S. C.; Schmid, M. Oxide surface science. *Annu. Rev. Phys. Chem.* **2010**, *61*, 129–148.

(307) Tanwar, K. S.; Catalano, J. G.; Petitto, S. C.; Ghose, S. K.; Eng, P. J.; Trainor, T. P. Hydrated α-Fe2O3 (11⁻ 02) surface structure: Role of surface preparation. *Surf. Sci.* **2007**, *601*, L59–L64.

(308) Tanwar, K. S.; Lo, C. S.; Eng, P. J.; Catalano, J. G.; Walko, D. A.; Brown Jr, G. E.; Waychunas, G. A.; Chaka, A. M.; Trainor, T. P. Surface diffraction study of the hydrated hematite (1102) surface. *Surf. Sci.* **2007**, *601*, 460–474.

(309) Grumelli, D. et al. Electrochemical stability of the reconstructed Fe3O4(001) surface. *Angew. Chem., Int. Ed.* **2020**, *59*, 21904–21908.

(310) Bliem, R. et al. Subsurface cation vacancy stabilization of the magnetite (001) surface. *Science* **2014**, *346*, 1215–1218.

(311) Arndt, B.; Bliem, R.; Gamba, O.; van der Hoeven, J. E. S.; Noei, H.; Diebold, U.; Parkinson, G. S.; Stierle, A. Atomic structure and stability of magnetite Fe3O4(001): An X-ray view. *Surf. Sci.* **2016**, *653*, 76–81.

(312) Schlegel, M. L.; Nagy, K. L.; Fenter, P.; Sturchio, N. C. Structures of quartz (100)-and (101)-water interfaces determined by x-ray reflectivity and atomic force microscopy of natural growth surfaces. *Geochim. Cosmochim. Acta* **2002**, *66*, 3037–3054.

(313) Fenter, P.; McBride, M. T.; Srajer, G.; Sturchio, N. C.; Bosbach, D. Structure of barite (001)- and (210)-water interfaces. *J. Phys. Chem. B* **2001**, *105*, 8112–8119.

(314) Zhang, Z.; Fenter, P.; Sturchio, N. C.; Bedzyk, M. J.; Machesky, M. L.; Wesolowski, D. J. Structure of rutile
TiO2 (110) in water and 1 molal Rb⁺ at pH 12: Inter-relationship among surface charge, interfacial hydration structure, and substrate structural displacements. *Surf. Sci.* **2007**, *601*, 1129–1143.

(315) Lee, S. S.; Fenter, P.; Nagy, K. L.; Sturchio, N. C. Monovalent ion adsorption at the muscovite (001)-solution interface: Relationships among ion coverage and speciation, interfacial water structure, and substrate relaxation. *Langmuir* **2012**, *28*, 8637–8650.

(316) Lee, S. S.; Fenter, P.; Park, C.; Sturchio, N. C.; Nagy, K. L. Hydrated cation speciation at the muscovite (001)-water interface. *Langmuir* **2010**, *26*, 16647–16651.

(317) Cheng, L.; Fenter, P.; Sturchio, N. C.; Zhong, Z.; Bedzyk, M. J. X-ray standing wave study of arsenite incorporation at the calcite surface. *Geochim. Cosmochim. Acta* **1999**, *63*, 3153–3157.

(318) Callagon, E.; Fenter, P.; Nagy, K. L.; Sturchio, N. C. Incorporation of Pb at the calcite (104)-water interface. *Environ. Sci. Technol.* **2014**, *48*, 9263–9269.

(319) Rihs, S.; Sturchio, N. C.; Orlan-dini, K.; Cheng, L.; Teng, H.; Fenter, P.; Bedzyk, M. J. Interaction of uranyl with calcite in the presence of EDTA. *Environ. Sci. Technol.* **2004**, *38*, 5078–5086.

(320) Bracco, J. N.; Lee, S. S.; Braha, I.; Dorfman, A.; Fenter, P.; Stack, A. G. Pb sorption at the barite (001)-water interface. *J. Phys. Chem. C* **2020**, *124*, 22035–22045.

(321) Bracco, J. N.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Jindra, S.; Warren, D. M.; Kommu, A.; Fenter, P.; Kubicki, J. D.; Stack, A. G. Simultaneous adsorption and incorporation of Sr2⁺ at the barite (001)-water interface. *J. Phys. Chem. C* **2018**, *123*, 1194–1207.

(322) Catalano, J. G.; Park, C.; Fenter, P.; Zhang, Z. Simultaneous inner-and outer-sphere arsenate adsorption on corundum and hematite. *Geochim. Cosmochim. Acta* **2008**, *72*, 1986–2004.

(323) Qiu, C.; Majs, F.; Eng, P. J.; Stubbs, J. E.; Douglas, T. A.; Schmidt, M.; Trainor, T. P. In situ structural study of the surface complexation of lead (II) on the chemically mechanically polished hematite (1102) surface. *J. Colloid Interface Sci.* **2018**, *524*, 65–75.

(324) Qiu, C.; Majs, F.; Douglas, T. A.; Schmidt, M.; Trainor, T. P. In situ structural study of Sb (V) adsorption on hematite (1102) using X-ray surface scattering. *Environ. Sci. Technol.* **2018**, *52*, 11161–11168.

(325) Snir, N.; Yatom, N.; Toroker, M. C. Progress in understanding hematite electrochemistry through computational modeling. *Comput. Mater. Sci.* **2019**, *160*, 411–419.

(326) Catalano, J. G.; Zhang, Z.; Fenter, P.; Bedzyk, M. J. Inner-sphere adsorption geometry of Se (IV) at the hematite (100)-water interface. *J. Colloid Interface Sci.* **2006**, *297*, 665–671.

(327) Catalano, J. G.; Zhang, Z.; Park, C.; Fenter, P.; Bedzyk, M. J. Bridging arsenate surface complexes on the hematite (012) surface. *Geochim. Cosmochim. Acta* **2007**, *71*, 1883–1897.

(328) Qiu, C.; Chen, W.; Schmidt, M.; Majs, F.; Douglas, T. A.; Trainor, T. P. Selective adsorption of Pb (II) on an annealed hematite (1102) surface: Evidence from crystal truncation rod X-ray diffraction and density functional theory. *Environ. Sci. Technol.* **2020**, *54*, 6651–6660.

(329) Diebold, U. The surface science of titanium dioxide. *Surf. Sci. Rep.* **2003**, *48*, 53–229.
(330) Zhang, Z. et al. Ion adsorption at the rutile-water interface: Linking molecular and macroscopic properties. *Langmuir* **2004**, *20*, 4954–4969.

(331) Předota, M.; Zhang, Z.; Fenter, P.; Wesolowski, D.; Cummings, P. Electric double layer at the rutile (110) surface. 2. Adsorption of ions from molecular dynamics and X-ray experiments. *J. Phys. Chem. B* **2004**, *108*, 12061–12072.

(332) Zhang, Z. et al. Structure of hydrated Zn2+ at the rutile TiO2 (110)-aqueous solution interface: Comparison of X-ray standing wave, X-ray absorption spectroscopy, and density functional theory results. *Geochim. Cosmochim. Acta* **2006**, *70*, 4039–4056.

(333) Kohli, V.; Zhang, Z.; Park, C.; Fenter, P. Rb+ and Sr2+ adsorption at the TiO2 (110)- electrolyte interface observed with resonant anomalous X-ray reflectivity. *Langmuir* **2010**, *26*, 950–958.

(334) Park, C.; Fenter, P. A.; Nagy, K. L.; Sturchio, N. C. Hydration and distribution of ions at the mica-water interface. *Phys. Rev. Lett.* **2006**, *97*, 016101.

(335) Park, C.; Fenter, P. A.; Sturchio, N. C.; Nagy, K. L. Thermodynamics, interfacial structure, and pH hysteresis of Rb+ and Sr2+ adsorption at the muscovite (001)-solution interface. *Langmuir* **2008**, *24*, 13993–14004.

(336) Schlegel, M. L.; Nagy, K. L.; Fenter, P.; Cheng, L.; Sturchio, N. C.; Jacobsen, S. D. Cation sorption on the muscovite (0 0 1) surface in chloride solutions using high-resolution X-ray reflectivity. *Geochim. Cosmochim. Acta* **2006**, *70*, 3549–3565.

(337) Lee, S. S.; Schmidt, M.; Laanait, N.; Sturchio, N. C.; Fenter, P. Investigation of structure, adsorption free energy,

and overcharging behavior of trivalent yttrium adsorbed at the muscovite (001)-water interface. *J. Phys. Chem. C* **2013**, *117*, 23738–23749.

(338) Lee, S. S.; Nagy, K. L.; Fenter, P. Distribution of barium and fulvic acid at the mica-solution interface using in-situ X-ray reflectivity. *Geochim. Cosmochim. Acta* **2007**, *71*, 5763–5781.

(339) Lee, S. S.; Nagy, K. L.; Park, C.; Fenter, P. Enhanced uptake and modified distribution of mercury (II) by fulvic acid on the muscovite (001) surface. *Environ. Sci. Technol.* **2009**, *43*, 5295–5300.

(340) Lee, S. S.; Park, C.; Fenter, P.; Sturchio, N. C.; Nagy, K. L. Competitive adsorption of strontium and fulvic acid at the muscovite-solution interface observed with resonant anomalous X-ray reflectivity. *Geochim. Cosmochim. Acta* **2010**, *74*, 1762–1776.

(341) Qiu, C.; Eng, P. J.; Hennig, C.; Schmidt, M. Competitive adsorption of ZrO2 nanoparticle and alkali cations (Li+-Cs+) on muscovite (001). *Langmuir* **2018**, *34*, 12270–12278.

(342) Schmidt, M.; Wilson, R. E.; Lee, S. S.; Soderholm, L.; Fenter, P. Adsorption of plutonium oxide nanoparticles. *Langmuir* **2012**, *28*, 2620–2627.

(343) Schmidt, M.; Lee, S.; Wilson, R.; Soderholm, L.; Fenter, P. Sorption of tetravalent thorium on muscovite. *Geochim. Cosmochim. Acta* **2012**, *88*, 66–76.

(344) Schmidt, M.; Lee, S. S.; Wilson, R. E.; Knope, K. E.; Bellucci, F.; Eng, P. J.; Stubbs, J. E.; Soderholm, L.; Fenter, P. Surface-mediated formation of Pu (IV) nanoparticles at the muscovite-electrolyte interface. *Environ. Sci. Technol.* **2013**, *47*, 14178–14184.

(345) Trotochaud, L.; Young, S. L.; Raney, J. K.; Boettcher, S. W. Nickel-iron
oxyhydroxide oxygen-evolution electro-catalysts: The role of intentional and incidental iron incorporation. *J. Am. Chem. Soc.* **2014**, *136*, 6744–6753.

(346) Cheng, L.; Fenter, P.; Nagy, K. L.; Schlegel, M. L.; Sturchio, N. C. Molecular-scale density oscillations in water adjacent to a mica surface. *Phys. Rev. Lett.* **2001**, *87*, 156103/1.

(347) Bracco, J. N.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Heberling, F.; Fenter, P.; Stack, A. G. Hydration structure of the barite (001)-water interface: Comparison of x-ray reflectivity with molecular dynamics simulations. *J. Phys. Chem. C* **2017**, *121*, 12236–12248.

(348) Arsic, J.; Kaminski, D.; Poodt, P.; Vlieg, E. Liquid ordering at the brushite-{010}-water interface. *Phys. Rev. B* **2004**, *69*, 245406.

(349) Geissbühler, P.; Fenter, P.; DiMasi, E.; Srajer, G.; Sorensen, L.; Sturchio, N. Three-dimensional structure of the calcite-water interface by surface X-ray scattering. *Surf. Sci.* **2004**, *573*, 191–203.

(350) Fenter, P.; Sturchio, N. C. Calcite (104)-water interface structure, revisited. *Geochim. Cosmochim. Acta* **2012**, *97*, 58–69.

(351) Catalano, J. G.; Fenter, P.; Park, C. Water ordering and surface relaxations at the hematite (110)-water interface. *Geochim. Cosmochim. Acta* **2009**, *73*, 2242–2251.

(352) Catalano, J. G.; Fenter, P.; Park, C. Interfacial water structure on the (012) surface of hematite: ordering and reactivity in comparison with corundum. *Geochim. Cosmochim. Acta* **2007**, *71*, 5313–5324.

(353) Rao, R. R. et al. Towards identifying the active sites on RuO₂(110) in catalyzing oxygen evolution. *Energy Environ. Sci.* **2017**, *10*, 2626–2637.

(354) Rao, R. R. et al. Surface orientation dependent water dissociation on rutile ruthenium dioxide. *J. Phys. Chem. C* **2018**, *122*, 17802–17811.

(355) Rao, R. R. et al. Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces. *Nat. Catal.* **2020**, *3*, 516–525.

(356) Rao, R. R. et al. pH- and cation-dependent water oxidation on rutile RuO₂(110). *J. Phys. Chem. C* **2021**, *125*, 8195–8207.

(357) Fahrenkrug, E.; Maldonado, S. Electrochemical liquid-liquid-solid (ec-LLS) crystal growth: A low-temperature strategy for covalent semiconductor crystal growth. *Acc. Chem. Res.* **2015**, *48*, 1881–1890.

(358) He, J.; Liang, S.; Li, F.; Yang, Q.; Huang, M.; He, Y.; Fan, X.; Wu, M. Recent development in liquid metal materials. *ChemistryOpen* **2021**, *10*, 360–372.

(359) Zuraiqi, K. et al. Liquid metals in catalysis for energy applications. *Joule* **2020**, *4*, 2290–2321.

(360) Elsen, A.; Murphy, B.; Ocko, B.; Taman, L.; Deutsch, M.; Kuzmenko, I.; Magnussen, O. Surface layering at the mercury-electrolyte interface. *Phys. Rev. Lett* **2010**, *104*, 105501–1–105501–4.

(361) Runge, B.; Festersen, S.; Koops, C. T.; Elsen, A.; Deutsch, M.; Ocko, B. M.; Seeck, O. H.; Murphy, B. M.; Magnussen, O. M. Temperature- and potential-dependent structure of the mercury-electrolyte interface. *Phys. Rev. B* **2016**, *93*, 165408–1–165408–9.

(362) Regan, M.; Kawamoto, E.; Lee, S.; Pershan, P.; Maskil, N.; Deutsch, M.; Magnussen, O.; Ocko, B.; Berman, L. Surface layering in liquid gallium: an X-ray reflectivity study. *Phys. Rev. Lett* **1995**, *75*, 2498–2501.
(363) DiMasi, E.; Tostmann, H.; Shpyrko, O. G.; Deutsch, M.; Pershan, P. S.; Ocko, B. M. Surface-induced order in liquid metals and binary alloys. *J. Condens. Matter Phys.* **2000**, *12*, A209–A214.

(364) Duval, J. F. L.; Bera, S.; Michot, L. J.; Daillant, J.; Belloni, L.; Konovalov, O.; Pontoni, D. X-Ray reflectivity at polarized liquid-Hg-aqueous-electrolyte interface: Challenging macroscopic approaches for ion-specificity issues. *Phys. Rev. Lett.* **2012**, *108*.

(365) Elsen, A.; Festersen, S.; Runge, B.; Koops, C.; Ocko, B.; Deutsch, M.; Seeck, O.; Murphy, B.; Magnussen, O. In situ x-ray studies of adlayer-induced crystal nucleation at the liquid-liquid interface. *Proc. Natl. Acad. Sci* **2013**, *110*, 6663–6668.

(366) Murphy, B. M.; Festersen, S.; Magnussen, O. M. The atomic scale structure of liquid metal-electrolyte interfaces. *Nanoscale* **2016**, *8*, 13859–13866.

(367) Hazelnis, J. P.; Sartori, A.; Cheek, Q. B.; Giri, R. P.; MacInnes, M. M.; Murphy, B. M.; Magnussen, O. M.; Maldonado, S. Detection of Ge-containing adlayers at the liquid Hg/water interface by in situ X-ray reflectivity in aqueous borate electrolytes containing dissolved GeO2. *J. Phys. Chem. C* **2022**, *126*, 8177–8189.

(368) Sartori, A.; Giri, R. P.; Fujii, H.; Hovelmann, S. C.; Warias, J. E.; Jordt, P.; Shen, C.; Murphy, B. M.; Magnussen, O. M. Role of chemisorbing species in growth at liquid metal-electrolyte interfaces revealed by in situ X-ray scattering. *Nat. Commun.* **2022**, *13*.

(369) Luo, G.; Malkova, S.; Yoon, J.; Schultz, D.; Lin, B.; Meron, M.; Benjamin, I.; Vanysek, P.; Schlossman, M. Ion distributions near a liquid-liquid interface. *Science* **2006**, *311*, 216–218.

(370) Luo, G.; Malkova, S.; Yoon, J.; Schultz, D. G.; Lin, B.; Meron, M.; Benjamin, I.; Vanysek, P.; Schlossman, M. L. Ion distributions at the nitrobenzene-water interface electrified by a common ion. *J. Electroanal. Chem.* **2006**, *593*, 142–158.

(371) Laanait, N.; Yoon, J.-S.; Hou, B.-Y.; Vanysek, P.; Meron, M.; Lin, B.-H.; Luo, G.-M.; Benjamin, I.; Schlossman, M. L. Communications: Monovalent ion condensation at the electrified liquid/liquid interface. *J. Chem. Phys.* **2010**, *132*, 171101/1.

(372) Laanait, N.; Mihaylov, M.; Hou, B.; Yu, H.; Vanysek, P.; Meron, M.; Lin, B.; Benjamin, I.; Schlossman, M. L. Tuning ion correlations at an electrified soft interface. *Proc. Natl. Acad. Sci. U. S. A.*, *Early Ed.* **2012**, 1–6.

(373) Hou, B.; Laanait, N.; Yu, H.; Bu, W.; Yoon, J.; Lin, B.; Meron, M.; Luo, G.; Vanysek, P.; Schlossman, M. L. Ion distributions at the water/1,2-dichloroethane interface: Potential of mean force approach to analyzing X-ray reflectivity and interfacial tension measurements. *J. Phys. Chem. B* **2013**, *117*, 5365–5378.

(374) Nishi, N.; Uruga, T.; Tanida, H. Potential dependent structure of an ionic liquid at ionic liquid/water interface probed by X-ray reflectivity measurements. *J. Electroanal. Chem.* **2015**, *759*, 129–136.

(375) Katakura, S.; Amano, K.-i.; Sakka, T.; Bu, W.; Lin, B.; Schlossman, M. L.; Nishi, N. Evolution and reversible polarity of multilayering at the ionic liquid/water interface. *J. Phys. Chem. B* **2020**, *124*, 6412–6419.

(376) Yu, H.; Yzeiri, I.; Hou, B.; Chen, C.-H.; Bu, W.; Vanysek, P.; Chen, Y.-S.; Lin, B.; Kral, P.; Schlossman, M. L. Electric field effect on phospholipid monolayers at an aqueous-organic liquid-liquid interface. *J. Phys. Chem. B* **2020**, *114*, 11012–11016.
interface. *J. Phys. Chem. B* **2015**, *119*, 9319–9334.

(377) Sabatier, P. *La catalyse en chimie organique*; C. Béranger, 1920; Vol. 3.

(378) Zhao, Z.-j.; Liu, S.; Zha, S.; Cheng, D.; Studt, F.; Henkelman, G.; Gong, J. Theory-guided design of catalytic materials using scaling relationships and reactivity descriptors. *Nat. Rev. Mater.* **2019**, *4*, 792–804.

(379) Hammes-Schiffer, S. Catalysts by design: The power of theory. *Acc. Chem. Res.* **2017**, *50*, 561–566.

(380) Zhai, L.; Lo, T. W. B.; Xu, Z.-L.; Potter, J.; Mo, J.; Guo, X.; Tang, C. C.; Tsang, S. C. E.; Lau, S. P. In situ phase transformation on nickel-based selenides for enhanced hydrogen evolution reaction in alkaline medium. *ACS Energy Lett.* **2020**, *5*, 2483–2491.

(381) Hung, S. F.; Zhu, Y. P.; Tzeng, G. Q.; Chen, H. C.; Hsu, C. S.; Liao, Y. F.; Ishii, H.; Hiraoka, N.; Chen, H. M. In situ spatially coherent identification of phosphide-based catalysts: Crystallographic latching for highly efficient overall water electrolysis. *ACS Energy Lett.* **2019**, *4*, 2813–2820.

(382) Chabanier, C.; Irissou, E.; Guay, D.; Pelletier, J. F.; Sutton, M.; Lurio, L. B. Hydrogen absorption in thermally prepared RuO[sub 2] electrode. *Electrochem. Solid-State Lett.* **2002**, *5*, E40.

(383) Chabanier, C.; Guay, D. Activation and hydrogen absorption in thermally prepared RuO2 and IrO2. *J. Electroanal. Chem.* **2004**, *570*, 13–27.

(384) Weber, T.; Abb, M. J. S.; Khalid, O.; Pfrommer, J.; Carla, F.; Znaiguia, R.; Vonk, V.; Stierle, A.; Over, H. In situ studies of the electrochemical reduction of a supported ultrathin single-crystalline

RuO₂(110) layer in an Acidic environment. *J. Phys. Chem. C* **2019**, *123*, 3979–3987.

(385) Weber, T.; Abb, M. J. S.; Evertsson, J.; Sandroni, M.; Drnec, J.; Vonk, V.; Stierle, A.; Lundgren, E.; Over, H. In situ studies of the cathodic stability of single-crystalline IrO₂(110) ultrathin films supported on RuO₂(110)/Ru(0001) in an acidic environment. *Phys. Chem. Chem. Phys.* **2020**, *22*, 22956–22962.

(386) Weber, T.; Vonk, V.; Abb, M. J. S.; Evertsson, J.; Sandroni, M.; Drnec, J.; Stierle, A.; Lundgren, E.; Over, H. Extraordinary stability of IrO₂(110) ultrathin films supported on TiO₂(110) under cathodic polarization. *Phys. Chem. Lett.* **2020**, *11*, 9057–9062.

(387) Over, H. Fundamental studies of planar single-crystalline oxide model electrodes (RuO₂, IrO₂) for acidic water splitting. *ACS Catal.* **2021**, *11*, 8848–8871.

(388) Chu, Y. S.; Lister, T. E.; Cullen, W. G.; You, H.; Nagy, Z. Commensurate water monolayer at the RuO2(110)/water interface. *Phys. Rev. Lett.* **2001**, *86*, 3364–3367.

(389) Chen, A.; Ostrom, C. Palladium-based nanomaterials: Synthesis and electrochemical applications. *Chem. Rev.* **2015**, *115*, 11999–12044.

(390) Adams, B. D.; Chen, A. The role of palladium in a hydrogen economy. *Mater. Today* **2011**, *14*, 282–289.

(391) Lewis, F. A. The hydrides of palladium and palladium alloys. *Platin. Met. Rev.* **1960**, *4*, 132–137.

(392) Lewis, F. A. The palladium-hydrogen system: Structures near phase transition and critical points. *Int. J. Hydrogen Energ.* **1995**, *20*, 587–592.

(393) Scholtus, N. A.; Hall, W. K. Hysteresis in the Palladium—Hydrogen System. *J. Chem. Phys.* **1963**, *39*, 868–870.
(394) Schwarz, R. B.; Khachaturyan, A. G. Thermodynamics of open two-phase systems with coherent interfaces: Application to metal-hydrogen systems. *Acta Mater.* **2006**, *54*, 313–323.

(395) Eastman, J. A.; Thompson, L. J.; Kestel, B. J. Narrowing of the palladium-hydrogen miscibility gap in nanocrystalline palladium. *Phys. Rev. B* **1993**, *48*, 84–92.

(396) Bugaev, A. L. et al. Core-shell structure of palladium hydride nanoparticles revealed by combined X-ray absorption spectroscopy and X-ray diffraction. *J. Phys. Chem. C* **2017**, *121*, 18202–18213.

(397) Johnson, N. J.; Lam, B.; MacLeod, B. P.; Sherbo, R. S.; Moreno-Gonzalez, M.; Fork, D. K.; Berlinguette, C. P. Facets and vertices regulate hydrogen uptake and release in palladium nanocrystals. *Nat. Mater.* **2019**, *18*, 454–458.

(398) Yamauchi, M.; Kobayashi, H.; Kitagawa, H. Hydrogen storage mediated by Pd and Pt nanoparticles. *ChemPhysChem* **2009**, *10*, 2566–2576.

(399) Fukai, Y.; Akuma, N. Formation of superabundant vacancies in Pd hydride under high hydrogen pressures. *Phys. Rev. Lett.* **1994**, *73*, 1640–1643.

(400) Benck, J. D.; Jackson, A.; Young, D.; Rettenwander, D.; Chiang, Y. M. Producing high concentrations of hydrogen in palladium via electrochemical insertion from aqueous and solid electrolytes. *Chem. Mater.* **2019**, *31*, 4234–4245.

(401) Berlinguette, C. P.; Chiang, Y. M.; Munday, J. N.; Schenkel, T.; Fork, D. K.; Koningstein, R.; Trevithick, M. D. Revisiting the cold case of cold fusion. *Nature* **2019**, *570*, 45–51.

(402) Felici, R.; Bertalot, L.; DeNinno, A.; LaBarbera, A.; Violante, V. In situ measurement of the deuterium (hydrogen)

charging of a palladium electrode during electrolysis by energy dispersive x-ray diffraction. *Rev. Sci. Instrum.* **1995**, *66*, 3344–3348.

(403) Knies, D. L.; Violante, V.; Grabowski, K. S.; Hu, J. Z.; Dominguez, D. D.; He, J. H.; Qadri, S. B.; Hubler, G. K. In-situ synchrotron energy-dispersive x-ray diffraction study of thin Pd foils with Pd:D and Pd:H concentrations up to 1:1. *J. Appl. Phys.* **2012**, *112*, 083510.

(404) Schirber, J. E.; Morosin, B. Lattice constants of β-PdHₓ and PdDₓ with x near 1.0. *Phys. Rev. B* **1975**, *12*, 117–118.

(405) Tripodi, P.; Di Gioacchino, D.; Vinko, J. D. AC electrical resistance measurements of PdHₓ samples versus composition x. *J. Alloy. Compd.* **2009**, *486*, 55–59.

(406) Zhang, W. S.; Zhang, Z. F.; Zhang, Z. L. Some problems on the resistance method in the in situ measurement of hydrogen content in palladium electrode. *J. Electroanal. Chem.* **2002**, *528*, 1–17.

(407) Jisrawi, N. M.; Wiesmann, H.; Ruckman, M. W.; Thurston, T. R.; Reisfeld, G.; Ocko, B. M.; Strongin, M. In situ x-ray investigation of hydrogen charging in thin film bimetallic electrodes. *J. Mater. Res.* **1997**, *12*, 2091–2098.

(408) Lebouin, C.; Soldo-Olivier, Y.; Sibert, E.; De Santis, M.; Maillard, F.; Faure, R. Evidence of the substrate effect in hydrogen electroinsertion into palladium atomic layers by means of in situ surface X-ray diffraction. *Langmuir* **2009**, *25*, 4251–4255.

(409) Soldo-Olivier, Y.; Sibert, E.; Previdello, B.; Lafouresse, M. C.; Maillard, F.; De Santis, M. H. electro-insertion into Pd/Pt(1 1 1) nanofilms: an original method for isotherm measurement
coupled to in situ surface X-ray diffraction structural study. *Electrochim. Acta* **2013**, *112*, 905-912.

(410) Langhammer, C.; Zhdanov, V. P.; Zorić, I.; Kasemo, B. Size-dependent kinetics of hydriding and dehydriding of Pd nanoparticles. *Phys. Rev. Lett.* **2010**, *104*, 2-5.

(411) Syrenova, S. et al. Hydride formation thermodynamics and hysteresis in individual Pd nanocrystals with different size and shape. *Nat. Mater.* **2015**, *14*, 1236-1244.

(412) Lee, J. H.; Kattel, S.; Jiang, Z.; Xie, Z.; Yao, S.; Tackett, B. M.; Xu, W.; Marinkovic, N. S.; Chen, J. G. Tuning the activity and selectivity of electroreduction of CO2 to synthesis gas using bimetallic catalysts. *Nat. Commun.* **2019**, *10*, 1-8.

(413) Drnec, J.; Harrington, D.; Magnussen, O. Electrooxidation of Pt(111) in acid solution. *Curr. Opin. Electrochem.* **2017**, *4*, 69-75.

(414) You, H.; Zurawski, D. J.; Nagy, Z.; Yonco, R. M. *In-situ* x-ray reflectivity study of incipient oxidation of Pt(111) surface in electrolyte solutions. *J. Chem. Phys.* **1994**, *100*, 4699-4702.

(415) Chu, Y. S.; You, H.; Tanzer, J. A.; Lister, T. E.; Nagy, Z. Surface resonance X-ray scattering observation of core-electron binding-energy shifts of Pt(111)-surface atoms during electrochemical oxidation. *Phys. Rev. Lett.* **1999**, *83*, 552-555.

(416) You, H.; Chu, Y. S.; Lister, T. E.; Nagy, Z.; Ankudinov, A. L.; Rehr, J. J. Resonance X-ray scattering from Pt(111) surfaces under water. *Physica B Conders. Matter.* **2000**, *283*, 212-216.

(417) Drnec, J.; Ruge, M.; Reikowski, F.; Rahn, B.; Carla, F.; Felici, R.; Stettner, J.; Magnussen, O. M.; Harring-

ton, D. A. Initial stages of Pt(111) electrooxidation: dynamic and structural studies by surface X-ray diffraction. *Electrochim. Acta* **2017**, *224*, 220-227.

(418) Drnec, J.; Ruge, M.; Reikowski, F.; Rahn, B.; Carla, F.; Felici, R.; Stettner, J.; Magnussen, O. M.; Harrington, D. A. Pt oxide and oxygen reduction at Pt(111) studied by surface X-ray diffraction. *Electrochem. Commun.* **2017**, *84*, 50-52.

(419) Ruge, M.; Drnec, J.; Rahn, B.; Reikowski, F.; Harrington, D.; Carlà, F.; Felici, R.; Stettner, J.; Magnussen, O. Electrochemical oxidation of smooth and nanoscale rough Pt(111): An in situ surface X-ray scattering study. *J. Electrochem. Soc* **2017**, *164*, H608-H614.

(420) Fowler, B.; Lucas, C. A.; Omer, A.; Wang, G.; Stamenković, V. R.; Marković, N. M. Segregation and stability at Pt3Ni(111) surfaces and Pt75Ni25 nanoparticles. *Electrochim. Acta* **2008**, *53*, 6076-6080.

(421) Kumeda, T.; Otsuka, N.; Tajiri, H.; Sakata, O.; Hoshi, N.; Nakamura, M. Interfacial structure of PtNi surface alloy on Pt(111) electrode for oxygen reduction reaction. *ACS Omega* **2017**, *2*, 1858-1863.

(422) Kobayashi, S.; Aoki, M.; Wakisaka, M.; Kawamoto, T.; Shirasaka, R.; Suda, K.; Tryk, D. A.; Inukai, J.; Kondo, T.; Uchida, H. Atomically flat Pt skin and striking enrichment of Co in underlying alloy at Pt₃Co(111) single crystal with unprecedented activity for the oxygen reduction reaction. *ACS Omega* **2018**, *3*, 154-158.

(423) Yang, R.; Strasser, P.; Toney, M. F. Dealloying of Cu₃Pt(111) studied by surface X-ray scattering. *J. Phys. Chem. C* **2011**, *115*, 9074-9080.

(424) Drnec, J.; Bizzotto, D.; Carlà, F.; Fiala, R.; Sode, A.; Balmes, O.; Detlefs, B.;
Dufrane, T.; Felici, R. An in-situ X-ray diffraction study on the electrochemical formation of PtZn alloys on Pt(1 1 1) single crystal electrode. *Appl. Surf. Sci.* **2015**, *354*, 443-449.

(425) Escudero-Escribano, M.; Pedersen, A. F.; Ulrikkeholm, E. T.; Jensen, K. D.; Hansen, M. H.; Rossmeisl, J.; Stephens, I. E. L.; Chorkendorff, I. Active-phase formation and stability of Gd/Pt(111) electrocatalysts for oxygen reduction: An in situ grazing incidence X-Ray diffraction study. *Chem. - Eur. J.* **2018**, *24*, 12280-12290.

(426) Abbou, S.; Chattot, R.; Martin, V.; Claudel, F.; Solà-Hernandez, L.; Beauger, C.; Dubau, L.; Maillard, F. Manipulating the Corrosion Resistance of SnO2Aerogels through Doping for Efficient and Durable Oxygen Evolution Reaction Electrocatalysis in Acidic Media. *ACS Catal.* **2020**, *10*, 7283-7294.

(427) Daiane Ferreira da Silva, C.; Claudel, F.; et al. Oxygen evolution reaction activity and stability benchmarks for supported and unsupported IrO. *ACS Catal.* **2021**, *11*, 4107-4116.

(428) Ehelebe, K.; Seeberger, D.; Paul, M. T. Y.; Thiele, S.; Mayrhofer, K. J. J.; Cherevko, S. Evaluating electrocatalysts at relevant currents in a half-cell: The impact of Pt loading on oxygen reduction reaction. *J. Electrochem. Soc.* **2019**, *166*, F1259-F1268.

(429) Geiger, S. et al. The stability number as a metric for electrocatalyst stability benchmarking. *Nat. Catal.* **2018**, *1*, 508-515.

(430) Kasian, O.; Geiger, S.; Mayrhofer, K. J.; Cherevko, S. Electrochemical on-line ICP-MS in electrocatalysis research. *Chem. Rec.* **2019**, *19*, 2130-2142.

(431) Lopes, P. P. et al. Eliminating dissolution of platinum-based electrocatalysts at the atomic scale. *Nat. Mater.* **2020**, *19*, 1207-1214.

(432) Sandbeck, D. J.; Sandbeck, D. J.; Inaba, M.; Quinson, J.; Bucher, J.; Zana, A.; Arenz, M.; Arenz, M.; Cherevko, S. Particle size effect on platinum dissolution: Practical considerations for fuel cells. *ACS Appl. Mater. Interfaces* **2020**, *12*, 25718-25727.

(433) Stariha, S.; Macauley, N.; Sneed, B. T.; Langlois, D.; More, K. L.; Mukundan, R.; Borup, R. L. Recent advances in catalyst accelerated stress tests for polymer electrolyte membrane fuel cells. *J. Electrochem. Soc.* **2018**, *165*, F492-F501.

(434) Topalov, A. A.; Cherevko, S.; Zeradjanin, A. R.; Meier, J. C.; Katsounaros, I.; Mayrhofer, K. J. Towards a comprehensive understanding of platinum dissolution in acidic media. *Chem. Sci.* **2014**, *5*, 631-638.

(435) Uchimura, M.; Sugawara, S.; Suzuki, Y.; Zhang, J.; Kocha, S. S. Electrocatalyst durability under simulated automotive drive cycles. *ECS Trans.* **2008**, *16*, 225-234.

(436) Borup, R.; Meyers, J.; et al. Scientific aspects of polymer electrolyte fuel cell durability and degradation. *Chem. Rev.* **2007**, *107*, 3904-3951.

(437) De Bruijn, F. A.; Dam, V. A.; Janssen, G. J. Review: Durability and degradation issues of PEM fuel cell components. *Fuel Cells* **2008**, *8*, 3-22.

(438) Dubau, L. et al. A review of PEM fuel cell durability: Materials degradation, local heterogeneities of aging and possible mitigation strategies. *Wiley Interdiscip. Rev.: Energy Environ.* **2014**, *3*, 540-560.

(439) Weiß, A.; Siebel, A.; Bernt, M.; Shen, T.-H.; Tileli, V.; Gasteiger, H. A. Impact of intermittent operation on lifetime and performance of a PEM water electrolyzer. *J. Electrochem. Soc.* **2019**, *166*, F487-F497.
(440) Meier, J. C.; Galeano, C.; Katsounaros, I.; Witte, J.; Bongard, H. J.; Topalov, A. A.; Baldizzone, C.; Mezzavilla, S.; Schüth, F.; Mayrhofer, K. J. Design criteria for stable Pt/C fuel cell catalysts. *Beilstein J. Nanotechnol.* **2014**, *5*, 44–67.

(441) Goerigk, G.; Haubold, H.-G.; Lyon, O.; Simon, J.-P. Anomalous small-angle X-ray scattering in materials science. *J. Appl. Crystallogr.* **2003**, *36*, 425–429.

(442) Haubold, H.-G.; Wang, X.; Jungbluth, H.; Goerigk, G.; Schilling, W. In situ anomalous small-angle X-ray scattering and X-ray absorption near-edge structure investigation of catalyst structures and reactions. *J. Mol. Struct.* **1996**, *383*, 283–289.

(443) Haubold, H. G.; Wang, X. H.; Goerigk, G.; Schilling, W. In situ anomalous small-angle X-ray scattering investigation of carbon-supported electrocatalysts. *J. Appl. Crystallogr.* **1997**, *30*, 653–658.

(444) Smith, M. C.; Gilbert, J. A.; Mawdsley, J. R.; Seifert, S.; Myers, D. J. In situ small-angle X-ray scattering observation of Pt catalyst particle growth during potential cycling. *J. Am. Chem. Soc.* **2008**, *130*, 8112–8113.

(445) Povia, M.; Herranz, J.; Binninger, T.; Nachtegaal, M.; Diaz, A.; Kohlbrecher, J.; Abbott, D. F.; Kim, B. J.; Schmidt, T. J. Combining SAXS and XAS to study the operando degradation of carbon-supported Pt-nanoparticle fuel cell catalysts. *ACS Catal.* **2018**, *8*, 7000–7015.

(446) Yu, C.; Holby, E. F.; Yang, R.; Toney, M. F.; Morgan, D.; Strasser, P. Growth trajectories and coarsening mechanisms of metal nanoparticle electrocatalysts. *ChemCatChem* **2012**, *4*, 766–770.

(447) Tuaev, X.; Rudi, S.; Petkov, V.; Hoell, A.; Strasser, P. In situ study of atomic structure transformations of Pt-Ni nanoparticle catalysts during electrochemical potential cycling. *ACS Nano* **2013**, *7*, 5666–5674.

(448) Schröder, J.; Pittkowski, R. K.; Du, J.; Kirkensgaard, J. J. K.; Arenz, M. Investigating the particle growth in bimodal Pt/C catalysts by in-situ small-angle X-ray scattering: Challenges in the evaluation of stress test protocol-dependent degradation mechanisms. *J. Electrochem. Soc.* **2022**, *169*, 104504.

(449) Schröder, J.; Pittkowski, R. K.; Martens, I.; Chattot, R.; Drnec, J.; Quinson, J.; Kirkensgaard, J. J.; Arenz, M. Tracking the catalyst layer depth-dependent electrochemical degradation of a bimodal Pt/C fuel cell catalyst: A combined operando small- and wide-angle X-ray scattering study. *ACS Catal.* **2022**, *12*, 2077–2085.

(450) Sasaki, K.; Marinkovic, N.; Isaacs, H. S.; Adzic, R. R. Synchrotron-based in situ characterization of carbon-supported platinum and platinum monolayer electrocatalysts. *ACS Catal.* **2016**, *6*, 69–76.

(451) Martens, I.; Chattot, R.; Drnec, J. Decoupling catalyst aggregation, ripening, and coalescence processes inside operating fuel cells. *J. Power Sources* **2022**, *521*, 230851.

(452) Sekizawa, O. et al. Key structural transformations and kinetics of Pt nanoparticles in PEFC Pt/C electrocatalysts by a simultaneous operando time-resolved QXAFS-XRD technique. *Top. Catal.* **2018**, *61*, 889–901.

(453) Uruga, T.; Tada, M.; Sekizawa, O.; Takagi, Y.; Yokoyama, T.; Iwasawa, Y. SPring-8 BL36XU: Synchrotron radiation X-ray-based multi-analytical beamline for polymer electrolyte fuel cells
under operating conditions. *Chem. Rec.* **2019**, *19*, 1444–1456.

(454) Martens, I.; Chattot, R.; Rasola, M.; Blanco, M. V.; Honkimäki, V.; Bizzotto, D.; Wilkinson, D. P.; Drnec, J. Probing the dynamics of platinum surface oxides in fuel cell catalyst layers Using in situ X-ray diffraction. *ACS Appl. Energy Mater.* **2019**, *2*, 7772–7780.

(455) Hornberger, E. et al. In situ stability studies of platinum nanoparticles supported on ruthenium-titanium mixed oxide (RTO) for fuel cell cathodes. *ACS Catal.* **2018**, *8*, 9675–9683.

(456) Schmies, H. et al. Unravelling degradation pathways of oxide-supported Pt fuel cell nanocatalysts under in situ operating conditions. *Adv. Energy Mater.* **2018**, *8*, 1–13.

(457) Schmies, H. et al. Anisotropy of Pt nanoparticles on carbon- And oxide-support and their structural response to electrochemical oxidation probed by- And situ techniques. *Phys. Chem. Chem. Phys.* **2020**, *22*, 22260–22270.

(458) Hornberger, E. et al. Impact of carbon N-doping and pyridinic-N content on the fuel cell performance and durability of carbon-supported Pt nanoparticle catalysts. *ACS Appl. Mater. Interfaces* **2022**, *14*, 18420–18430.

(459) Schmies, H. et al. Impact of carbon support functionalization on the electrochemical stability of Pt fuel cell catalysts. *Chem. Mater.* **2018**, *30*, 7287–7295.

(460) Martens, I.; Vamvakeros, A.; et al. Imaging heterogeneous electrocatalyst stability and decoupling degradation mechanisms in operating hydrogen fuel cells. *ACS Energy Lett.* **2021**, *6*, 2742–2749.

(461) Chattot, R.; Mirolo, M.; Martens, I.; Kumar, K.; Martin, V.; Gasmi, A.; Dubau, L.; Maillard, F.; Castanheira, L.;

Drnec, J. Beware of cyclic voltammetry! Measurement artefact in accelerated stress test of fuel cell cathode revealed by operando X-ray diffraction. *J. Power Sources* **2023**, *555*, 232345.

(462) Redmond, E. L.; Setzler, B. P.; Juhas, P.; Billinge, S. J.; Fuller, T. F. In-situ monitoring of particle growth at PEMFC cathode under accelerated cycling conditions. *Electrochem. Solid-State Lett.* **2012**, *15*, 72–74.

(463) Mistry, H.; Varela, A. S.; Kühl, S.; Strasser, P.; Cuenya, B. R. Nanostructured electrocatalysts with tunable activity and selectivity. *Nat. Rev. Mater.* **2016**, *1*.

(464) Beermann, V.; Holtz, M. E.; Paddgett, E.; De Araujo, J. F.; Muller, D. A.; Strasser, P. Real-time imaging of activation and degradation of carbon supported octahedral Pt-Ni alloy fuel cell catalysts at the nanoscale using: In situ electrochemical liquid cell STEM. *Energy Environ. Sci.* **2019**, *12*, 2476–2485.

(465) Beker, A. F.; Sun, H.; Lemang, M.; Van Omme, J. T.; Spruit, R. G.; Bremmer, M.; Basak, S.; Pérez Garza, H. H. In situ electrochemistry inside a TEM with controlled mass transport. *Nanoscale* **2020**, *12*, 22192–22201.

(466) Jinschek, J. R. Advances in the environmental transmission electron microscope (ETEM) for nanoscale in situ studies of gas-solid interactions. *Chem. Commun.* **2014**, *50*, 2696–2706.

(467) Lončar, A.; Escalera-López, D.; Cherevko, S.; Hodnik, N. Inter-relationships between Oxygen Evolution and Iridium Dissolution Mechanisms. *Angew. Chem. Int. Ed.* **2022**, *61*, e202114437.

(468) Wagner, J. B.; Cavalca, F.; Damsgaard, C. D.; Duchstein, L. D.;
Hansen, T. W. Exploring the environmental transmission electron microscope. *Micron* **2012**, *43*, 1169–1175.

(469) Zhu, G. Z.; Prabhudev, S.; Yang, J.; Gabardo, C. M.; Botton, G. A.; Soleymani, L. In situ liquid cell TEM study of morphological evolution and degradation of Pt-Fe nanocatalysts during potential cycling. *J. Phys. Chem. C* **2014**, *118*, 22111–22119.

(470) Mavrikakis, M.; Hammer, B.; Nørskov, J. K. Effect of strain on the reactivity of metal surfaces. *Phys. Rev. Lett.* **1998**, *81*, 2819–2822.

(471) Strasser, P. et al. Lattice-strain control of the activity in dealloyed core-shell fuel cell catalysts. *Nat. Chem.* **2010**, *2*, 454–460.

(472) Chattot, R. et al. Break-in bad: On the conditioning of fuel cell nanoalloy catalysts. *ACS Catal.* **2022**, 15675–15685.

(473) Petkov, V.; Maswadeh, Y.; Vargas, J. A.; Shan, S.; Kareem, H.; Wu, Z.-P.; Luo, J.; Zhong, C.-J.; Shastri, S.; Kenesei, P. Deviations from Vegard's law and evolution of the electrocatalytic activity and stability of Pt-based nanoalloys inside fuel cells by in operando X-ray spectroscopy and total scattering. *Nanoscale* **2019**, *11*, 5512–5525.

(474) Hornberger, E. et al. On the electrocatalytic oxygen reduction reaction activity and stability of quaternary RhMopdoped PtNi/C octahedral nanocrystals. *Chem. Sci.* **2022**, *13*, 9295–9304.

(475) Kong, Z. et al. Origin of high activity and durability of twisty nanowire alloy catalysts under oxygen reduction and fuel cell operating conditions. *J. Am. Chem. Soc.* **2020**, *142*, 1287–1299.

(476) Wu, Z. P. et al. Alloying–realloying enabled high durability for Pt–Pd-3d-transition metal nanoparticle fuel cell catalysts. *Nat. Commun.* **2021**, *12*, 1–14.

(477) Atlan, C. et al. Imaging the strain evolution of a platinum nanoparticle under electrochemical control. *Nat. Mater.* **2023**,

(478) Reier, T.; Oezaslan, M.; Strasser, P. Electrocatalytic oxygen evolution reaction (OER) on Ru, Ir, and Pt catalysts: A comparative study of nanoparticles and bulk materials. *ACS Catal.* **2012**, *2*, 1765–1772.

(479) Danilovic, N. et al. Activity-stability trends for the oxygen evolution reaction on monometallic oxides in acidic environments. *Phys. Chem. Lett.* **2014**, *5*, 2474–2478.

(480) Cherevko, S. et al. Oxygen and hydrogen evolution reactions on Ru, RuO₂, Ir, and IrO₂ thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability. *Catal. Today* **2016**, *262*, 170–180.

(481) Weber, T. et al. Potential-induced pitting corrosion of an IrO₂(110)-RuO₂(110)/Ru(0001) model electrode under oxygen evolution reaction conditions. *ACS Catal.* **2019**, *9*, 6530–6539.

(482) Weber, T. et al. Operando stability studies of ultrathin single-crystalline IrO₂(110) films under acidic oxygen evolution reaction conditions. *ACS Catal.* **2021**, *11*, 12651–12660.

(483) Weber, T.; Vonk, V.; Abb, M. J. S.; Evertsson, J.; Stierle, A.; Lundgren, E.; Over, H. In situ synchrotron-based studies of IrO₂(110)-TiO₂(110) under harsh acidic water splitting conditions: Anodic stability and radiation damages. *J. Phys. Chem. C* **2022**, *126*, 20243–20250.

(484) Povia, M. et al. Operando X-ray characterization of high surface area iridium oxides to decouple their activity losses for the oxygen evolution reaction. *Energy Environ. Sci.* **2019**, *12*, 3038–3052.
(485) McCrory, C. C. L.; Jung, S.; Fer-
rer, I. M.; Chatman, S. M.; Peters, J. C.;
Jaramillo, T. F. Benchmarking hydro-
gen evolving reaction and oxygen evolv-
ing reaction electrocatalysts for solar wa-
ter splitting devices. *J. Am. Chem. Soc.* **2015**, *137*, 4347–4357.

(486) Burke, M. S.; Enman, L. J.; Batchel-
lor, A. S.; Zou, S.; Boettcher, S. W.
Oxygen evolution reaction electrocatal-
ysis on transition metal oxides and
(oxy)hydroxides: Activity trends and de-
sign principles. *Chem. Mater.* **2015**, *27*,
7549–7558.

(487) Han, L.; Dong, S.; Wang, E. Transition-metal (Co, Ni, and Fe)-based electrocatalysts for the water oxidation reaction. *Adv. Mater.* (Weinheim, Ger.) **2016**, *28*, 9266–9291.

(488) Zhao, Q.; Yan, Z.; Chen, C.; Chen, J.
Spinels: Controlled preparation, oxy-
gen reduction/evolution reaction appli-
cation, and beyond. *Chem. Rev.* **2017**,
*117*, 10121–10211.

(489) Song, F.; Bai, L.; Moysiadou, A.; Lee, S.; Hu, C.; Liardet, L.; Hu, X. Transition metal oxides as electrocatalysts for the oxygen evolution reaction in alkaline solutions: An application-inspired renaissance. *J. Am. Chem. Soc.* **2018**, *140*, 7748–7759.

(490) Pourbaix, M. *Atlas of electrochemical equilibria in aqueous solutions*; Pergamon Press, London, 1966.

(491) Bergmann, A.; Martinez-Moreno, E.; Teschner, D.; Chernev, P.; Gliech, M.; Ferreira de Araujo, J.; Reier, T.; Dau, H.; Strasser, P. Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution. *Nat. Commun.* **2015**, *6*, 8625.

(492) Gao, L.; Cui, X.; Sewell, C. D.; Li, J.; Lin, Z. Recent advances in activating surface reconstruction for the high-efficiency

oxygen evolution reaction. *Chem. Soc. Rev.* **2021**, *50*, 8428–8469.

(493) Tung, C.-W.; Hsu, Y.-Y.; Shen, Y.-P.; Zheng, Y.; Chan, T.-S.; Sheu, H.-S.; Cheng, Y.-C.; Chen, H. M. Reversible adapting layer produces robust single-crystal electrocatalyst for oxygen evolution. *Nat. Commun.* **2015**, *6*, 8106.

(494) Wang, H. Y.; Hung, S. F.; Hsu, Y. Y.; Zhang, L. L.; Miao, J. W.; Chan, T. S.; Xiong, Q. H.; Liu, B. In situ spectroscopic identification of mu-OO bridging on spinel Co3O4 water oxidation electrocatalyst. *J. Phys. Chem. Lett.* **2016**, *7*, 4847–4853.

(495) Wiegmann, T. et al. Operando identification of the reversible skin layer on Co3O4 as a three-dimensional reaction zone for oxygen evolution. *ACS Catal.* **2022**, *12*, 3256–3268.

(496) Hsu, C.-S.; Suen, N.-T.; Hsu, Y.-Y.; Lin, H.-Y.; Tung, C.-W.; Liao, Y.-F.; Chan, T.-S.; Sheu, H.-S.; Chen, S.-Y.; Chen, H. M. Valence- and element-dependent water oxidation behaviors: in situ X-ray diffraction, absorption and electrochemical impedance spectroscopies. *Phys. Chem. Chem. Phys.* **2017**, *19*, 8681–8693.

(497) May, K. J.; Carlton, C. E.; Sto-
erzinger, K. a.; Risch, M.; Suntivich, J.;
Lee, Y.-L.; Grimaud, A.; Shao-Horn, Y.
Influence of oxygen evolution during wa-
ter oxidation on the surface of perovskite
oxide catalysts. *Phys. Chem. Lett.* **2012**,
*3*, 3264–3270.

(498) Risch, M.; Grimaud, A.; May, K. J.; Stoerzinger, K. A.; Chen, T. J.; Mansour, A. N.; Shao-Horn, Y. Structural changes of cobalt-based perovskites upon water oxidation investigated by EXAFS. *J. Phys. Chem. C* **2013**, *117*, 8628–8635.

(499) Fabbri, E. et al. Dynamic surface self-reconstruction is the key of highly active
perovskite nano-electrocatalysts for wa-
ter splitting. *Nat. Mater.* **2017**, *16*, 925–931.

(500) Baeumer, C. et al. Tuning electrochemi-
ally driven surface transformation in
atomically flat LaNiO₃ thin films for en-
hanced water electrolysis. *Nat. Mater.*
**2021**, *20*, 674.

(501) Samira, S.; Hong, J.; Camayang, J. C. A.; Sun, K.; Hoffman, A. S.; Bare, S. R.; Nikolla, E. Dynamic surface reconstruction unifies the electrocatalytic oxygen evolution performance of nonstoichio-metric mixed metal Oxides. *JACS Au* **2021**, *1*, 2224–2241.

(502) Wan, G. et al. Amorphization mechanism of SrIrO₃ electrocatalyst: How oxygen redox initiates ionic diffusion and structural reorganization. *Sci. Adv.* **2021**, *7*, eabc7323.

(503) Hori, Y. Electrochemical CO2 reduction on metal electrodes. *Mod. Aspects Electrochem.* **2008**, *42*, 89–189.

(504) Nitopi, S. et al. Progress and perspectives of electrochemical CO2 reduction on copper in aqueous electrolyte. *Chem. Rev.* **2019**, *119*, 7610–7672.

(505) Birdja, Y. Y.; Perez-Gallent, E.; Figueiredo, M. C.; Gottle, A. J.; Calle-Vallejo, F.; Koper, M. T. M. Advances and challenges in understanding the electrocatalytic conversion of carbon dioxide to fuels. *Nat. Energy* **2019**, *4*, 732–745.

(506) Scott, S. B. et al. Absence of oxidized phases in Cu under CO reduction conditions. *ACS Energy Lett.* **2019**, *4*, 803–804.

(507) Lee, S. H. et al. Oxidation state and surface reconstruction of Cu under CO2 reduction conditions from in situ X-ray characterization. *J. Am. Chem. Soc.* **2021**, *143*, 588–592.

(508) Lei, Q. et al. Structural evolution and strain generation of derived-Cu catalysts during CO2 electroreduction. *Nat. Commun.* **2022**, *13*, 4857.

(509) Timoshenko, J. et al. Steering the structure and selectivity of CO2 electroreduction catalysts by potential pulses. *Nat. Catal.* **2022**, *5*, 259–267.

(510) Amirbeigiarab, R.; Tian, J.; Herzog, A.; Qiu, C. R.; Bergmann, A.; Cuenya, B. R.; Magnussen, O. M. Atomic-scale surface restructuring of copper electrodes under CO2 electroreduction conditions. *Nat. Catal.* **2023**, https://doi.org/10.1038/s41929-023-01009-z.

(511) Chang, C.-J.; Lin, S.-C.; Chen, H.-C.; Wang, J.; Zheng, K. J.; Zhu, Y.; Chen, H. M. Dynamic reoxidation/reduction-driven atomic interdiffusion for highly selective CO2 reduction toward methane. *J. Am. Chem. Soc.* **2020**, *142*, 12119–12132.

(512) Dutta, A.; Montiel, I. Z.; Erni, R.; Kiran, K.; Rahaman, M.; Drnec, J.; Broekmann, P. Activation of bimetallic AgCu foam electrocatalysts for ethanol formation from CO2 by selective Cu oxidation/reduction. *Nano Energy* **2020**, *68*, 104331.

(513) Medina-Ramos, J. et al. Structural dynamics and evolution of bismuth electrodes during electrochemical reduction of CO2 in imidazolium-based ionic liquid solutions. *ACS Catal.* **2017**, *7*, 7285–7295.

(514) Medina-Ramos, J. et al. Cathodic corrosion at the bismuth-ionic liquid electrolyte interface under conditions for CO2 reduction. *Chem. Mater.* **2018**, *30*, 2362–2373.

(515) Gao, L.-F. et al. Domino effect: Gold electrocatalyzing lithium reduction to accelerate nitrogen fixation. *Angew. Chem. Int. Ed.* **2021**, *60*, 5257–5261.
(516) Blair, S. J. et al. Lithium-mediated electrochemical nitrogen reduction: Tracking electrode-electrolyte enterfaces via time-resolved neutron reflectometry. *ACS Energy Lett.* **2022**, *7*, 1939–1946.

(517) Patil, S. B. et al. Enhanced $N_2$ affinity of 1T–$MoS_2$ with a unique pseudosix-membered ring consisting of N-LiS-Mo-S-Mo for high ambient ammonia electrosynthesis performance. *J. Mater. Chem.A* **2021**, *9*, 1230–1239.

(518) Liu, S.; Wang, M.; Qian, T.; Ji, H.; Liu, J.; Yan, C. Facilitating nitrogen accessibility to boron-rich covalent organic frameworks via electrochemical excitation for efficient nitrogen fixation. *Nat. Commun.* **2019**, *10*, 3898.

(519) Principi, E.; Di Cicco, A.; Witkowska, A.; Marassi, R. Performance of a fuel cell optimized for *in situ* X-ray absorption experiments. *J. Synchrotron Radiat.* **2007**, *14*, 276–281.

(520) Petrova, O.; Kulp, C.; van den Berg, M. W. E.; Klementiev, K. V.; Otto, B.; Otto, H.; Lopez, M.; Bron, M.; Grünert, W. A spectroscopic proton-exchange membrane fuel cell test setup allowing fluorescence x-ray absorption spectroscopy measurements during state-of-the-art cell tests. *Rev. Sci. Instrum.* **2011**, *82*, 044101.

(521) Vamvakeros, A. et al. DLSR: a solution to the parallax artefact in X-ray diffraction computed tomography data. *J. Appl. Crystallogr.* **2020**, *53*, 1531–1541.

(522) Petkov, V.; Prasai, B.; Shan, S.; Ren, Y.; Wu, J.; Cronk, H.; Luo, J.; Zhong, C.-J. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies. *Nanoscale* **2016**, *8*, 10749–10767.

(523) Hardy, J. S.; Coyle, C. A.; Bonnett, J. F.; Templeton, J. W.; Canfield, N. L.;

Edwards, D. J.; Mahserejian, S. M.; Ge, L.; Ingram, B. J.; Stevenson, J. W. Evaluation of cation migration in lanthanum strontium cobalt ferrite solid oxide fuel cell cathodes via *in-operando* X-ray diffraction. *J. Mater. Chem.A* **2018**, *6*, 1787–1801.

(524) Yang, X.; Hardy, J. S.; Coyle, C. A.; Bonnett, J. F.; Mahserejian, S. M.; Stevenson, J. W. In-operando XRD study of the effects of water vapor on phase formation in LSM/YSZ SOFC cathodes. *J. Electrochem. Soc.* **2022**, *169*, 024512.

(525) Khan, M. Z.; Song, R.-H.; Mehran, M. T.; Lee, S.-B.; Lim, T.-H. Controlling cation migration and inter-diffusion across cathode/interlayer/electrolyte interfaces of solid oxide fuel cells: A review. *Ceram. Int.* **2021**, *47*, 5839–5869.

(526) Liu, D.-J.; Almer, J.; Cruse, T. Characterization of Cr poisoning in a solid oxide fuel cell cathode using a high energy X-ray microbeam. *J. Electrochem. Soc.* **2010**, *157*, B744.

(527) Korjus, O.; Aruväli, J.; Kivi, I.; Kodu, M.; Lust, E.; Nurk, G. Simultaneous operando characterization of crystallographic and electrochemical properties of Ni–$Ce_{0.1}O_{2-s}$ solid oxide fuel cell anode. *J. Electrochem. Soc.* **2018**, *165*, F1043–F1050.

(528) Li, T. et al. Design of next-generation ceramic fuel cells and real-time characterization with synchrotron X-ray diffraction computed tomography. *Nat. Commun.* **2019**, *10*, 1497.

(529) Moss, A. B.; Garg, S.; Mirolo, M.; Rodriguez, C. A. G.; Ilvonen, R.; Chorkendorff, I.; Drnec, J.; Seger, B. In operando investigations of oscillatory water and carbonate effects in MEA-based CO2 electrolysis devices. *Joule* **2023**, *7*, 350–365.
(530) Garg, S.; Xu, Q.; Moss, A. B.; Mirolo, M.; Deng, W.; Chorkendorff, I.; Drnec, J.; Seger, B. How alkali cations affect salt precipitation and CO₂ electrolysis performance in membrane electrode assembly electrolyzers. *Energy Environ. Sci.* **2023**, *16*, 1631–1643.

(531) Rosenfeld, G.; Poelsema, B.; Comsa, G. In *Growth and properties of ultrathin epitaxial layers*; King, D., Woodruff, D., Eds.; The chemical physics of solid surface; Elsevier Science B.V.: Amsterdam, 1999; Vol. 8; Chapter 3, pp 66–101.

(532) Evans, J. W.; Thiel, P. A.; Bartelt, M. C. Morphological evolution during epitaxial thin film growth: Formation of 2D islands and 3D mounds. *Surf. Sci. Rep.* **2006**, *61*, 1–128.

(533) Krug, K.; Stettner, J.; Magnussen, O. In-situ surface x-ray diffraction studies of homoepitaxial electrochemical growth on Au(100). *Phys. Rev. Lett* **2006**, *96*, 246101/1–246101/4.

(534) Ruge, M.; Golks, F.; Zegenhagen, J.; Magnussen, O.; Stettner, J. In operando GISAXS studies of mound coarsening in electrochemical homoepitaxy. *Phys. Rev. Lett* **2014**, *112*, 055503/1–055503/5.

(535) Giesen, M.; Beltramo, G.; Dieluweit, S.; Müller, J.; Ibach, H.; Schmickler, W. The thermodynamics of electrochemical annealing. *Surf. Sci* **2005**, *595*, 127–137.

(536) Giesen, M. Step and island dynamics at solid vacuum and solid/liquid interfaces. *Prog. Surf. Sci* **2001**, *68*, 1–153.

(537) Labayen, M.; Ramirez, C.; Schattke, W.; Magnussen, O. Quasi-collective motion of nanoscale metal strings in metal surfaces. *Nat. Mater.* **2003**, *2*, 783–787.

(538) Kaminski, D.; Radenovic, N.; Deij, M. A.; van Enckevort, W. J. P.; Vlieg, E. Liquid ordering at the KDP 100-solution interface. *Cryst. Growth Des.* **2006**, *6*, 588–591.

(539) Ayyad, A.; Stettner, J.; Magnussen, O. Electrocompression of the Au(111) surface layer during Au electrodeposition. *Phys. Rev. Lett* **2005**, *94*, 066106.

(540) Golks, F.; Stettner, J.; Gründer, Y.; Krug, K.; Zegenhagen, J.; Magnussen, O. Anomalous potential dependence in homoepitaxial Cu(001) electrodeposition: an in situ surface x-ray diffraction study. *Phys. Rev. Lett* **2012**, *108*, 256101/1–256101/5.

(541) Golks, F.; Gründer, Y.; Stettner, J.; Krug, K.; Zegenhagen, J.; Magnussen, O. In situ surface x-ray diffraction studies of homoepitaxial growth on Cu(001) from aqueous acidic electrolyte. *Surf. Sci* **2014**, *631*, 112–122.

(542) Golks, F.; Gründer, Y.; Drünkler, A.; Roy, J.; Stettner, J.; Zegenhagen, J.; Magnussen, O. In-situ surface X-ray diffraction studies of the influence of the PEG-Cl-complex on homoepitaxial electrodeposition on Cu(001). *J. Electrochem. Soc* **2014**, *160*, D3165–D3170.

(543) Krug, K.; Kaminski, D.; Golks, F.; Stettner, J.; Magnussen, O. Real-time surface X-ray scattering study of Au(111) electrochemical dissolution. *J. Phys. Chem. C* **2010**, *114*, 18634–18644.

(544) Golks, F.; Krug, K.; Gründer, Y.; Zegenhagen, J.; Stettner, J.; Magnussen, O. High-speed in situ surface x-ray diffraction studies of the electrochemical dissolution of Au(001). *J. Am. Chem. Soc* **2011**, *133*, 3772–3775.

(545) Renner, F. U.; Stierle, A.; Dosch, H.; Kolb, D. M.; Lee, T. L.; Zegenhagen, J. Initial corrosion observed on the atomic scale. *Nature* **2006**, *439*, 707–710.

(546) Renner, F. U.; Stierle, A.; Dosch, H.; Kolb, D. M.; Zegenhagen, J. The influence of chloride on the initial anodic dissolution of Cu3Au(111). *Electrochem. Commun.* **2007**, *9*, 1639–1642.
(547) Renner, F. U.; Grunder, Y.; Lyman, P. F.; Zegenhagen, J. In-situ X-ray diffraction study of the initial dealloying of Cu₃Au(001) and Cu₀·83Pd₀·17 (001). *Thin Solid Films* **2007**, *515*, 5574–5580.

(548) Renner, F. U.; Stierle, A.; Dosch, H.; Kolb, D. M.; Lee, T. L.; Zegenhagen, J. In situ x-ray diffraction study of the initial dealloying and passivation of Cu3Au(111) during anodic dissolution. *Phys. Rev. B* **2008**, *77*, 235433.

(549) Renner, F. U.; Ankah, G. N.; Pareek, A. In-situ surface-sensitive X-ray diffraction study on the influence of iodide over the selective electrochemical etching of Cu3Au (111). *Surf. Sci.* **2012**, *606*, L37–L40.

(550) Ankah, G. N.; Pareek, A.; Cherevko, S.; Topalov, A. A.; Rohwerder, M.; Renner, F. U. The influence of halides on the initial selective dissolution of Cu3Au (111). *Electrochim. Acta* **2012**, *85*, 384–392.

(551) Ankah, G. N.; Meimandi, S.; Renner, F. U. Dealloying of Cu₃Pd single crystal surfaces. *J. Electrochem. Soc.* **2013**, *160*, C390–C395.

(552) Ankah, G. N.; Pareek, A.; Cherevko, S.; Zegenhagen, J.; Renner, F. U. Hierarchical nanoporous films obtained by surface cracking on Cu-Au and ethanethiol on Au(001). *Electrochim. Acta* **2014**, *140*, 352–358.

(553) Pareek, A.; Ankah, G. N.; Cherevko, S.; Ebbinghaus, P.; Mayrhofer, K. J. J.; Erbe, A.; Renner, F. U. Effect of thiol self-assembled monolayers and plasma polymer films on dealloying of Cu-Au alloys. *RSC Adv.* **2013**, *3*, 6586–6595.

(554) Erlebacher, J. An atomistic description of dealloying - Porosity evolution, the critical potential, and rate-limiting behavior. *J. Electrochem. Soc.* **2004**, *151*, C614–C626.

(555) Van Petegem, S.; Brandstetter, S.; Maass, R.; Hodge, A. M.; ElDasher, B. S.; Biener, J.; Schmitt, B.; Borca, C.; Van Swygenhoven, H. On the microstructure of nanoporous gold: An x-ray diffraction study. *Nano Lett.* **2009**, *9*, 1158–1163.

(556) Dotzler, C. J.; Ingham, B.; Illy, B. N.; Wallwork, K.; Ryan, M. P.; Toney, M. F. In-situ observation of strain development and porosity evolution in nanoporous gold foils. *Adv. Funct. Mater.* **2011**, *21*, 3938–3946.

(557) Lin, B.; Kong, L.; Hodgson, P. D.; Mudie, S.; Hawley, A.; Dumee, L. F. Controlled porosity and pore size of nano-porous gold by thermally assisted chemical dealloying - a SAXS study. *RSC Adv.* **2017**, *7*, 10821–10830.

(558) Goessler, M.; Hengge, E.; Bogar, M.; Albu, M.; Knez, D.; Amenitsch, H.; Wuerschum, R. In situ study of nanoporosity evolution during dealloying AgAu and CoPd by grazing-incidence small-angle X-ray scattering. *J. Phys. Chem. C* **2022**, *126*, 4037–4047.

(559) Chen-Wiegart, Y.-c. K.; Harder, R.; Dunand, D. C.; McNulty, I. Evolution of dealloying induced strain in nanoporous gold crystals. *Nanoscale* **2017**, *9*, 5686–5693.

(560) Schofield, E. J.; Ingham, B.; Turnbull, A.; Toney, M. F.; Ryan, M. P. Strain development in nanoporous metallic foils formed by dealloying. *Appl. Phys. Lett.* **2008**, *92*, 043118/1.

(561) Teng, H. H.; Fenter, P.; Cheng, L.; Sturchio, N. C. Resolving orthoclase dissolution processes with atomic force microscopy and X-ray reflectivity. *Geochim. Cosmochim. Acta* **2001**, *65*, 3459–3474.

(562) Fenter, P.; Lee, S. S. Hydration layer structure at solid-water interfaces. *MRS Bull.* **2014**, *39*, 1056–1061.
(563) Fenter, P.; Park, C.; Cheng, L.; Zhang, Z.; Krekeler, M.; Sturchio, N. Orthoclase dissolution kinetics probed by in situ X-ray reflectivity: Effects of temperature, pH, and crystal orientation. *Geochim. Cosmochim. Acta* **2003**, *67*, 197–211.

(564) Fenter, P.; Lee, S.; Park, C.; Catalano, J.; Zhang, Z.; Sturchio, N. Probing interfacial reactions with X-ray reflectivity and X-ray reflection interface microscopy: Influence of NaCl on the dissolution of orthoclase at pOH 2 and 85° C. *Geochim. Cosmochim. Acta* **2010**, *74*, 3396–3411.

(565) Budevski, E.; Staikov, G.; Lorenz, W. *Electrochemical phase formation and growth*; Advances in Electrochemical Science and Engineering; VCH, Weinheim, 1996.

(566) Soldo-Olivier, Y.; De Santis, M.; Liang, W.; Sibert, E. Growth mechanisms of Pd nanofilms electrodeposited onto Au(111): an in situ grazing incidence X-ray diffraction study. *Phys. Chem. Chem. Phys.* **2016**, *18*, 2830–2839.

(567) Ocko, B. M.; Robinson, I. K.; Weinert, M.; Randler, R. J.; Kolb, D. M. Thickness induced buckling of bcc copper films. *Phys. Rev. Lett.* **1999**, *83*, 780–783.

(568) Randler, R. J.; Kolb, D. M.; Ocko, B. M.; Robinson, I. K. Electrochemical copper deposition on Au(100): a combined in situ STM and in situ surface X-ray diffraction study. *Surf. Sci.* **2000**, *447*, 187–200.

(569) Pfeifer, M. A.; Robach, O.; Ocko, B. M.; Robinson, I. K. Thickness-related instability of Cu thin films on Ag(100). *Physica B Condens. Matter.* **2005**, *357*, 152–158.

(570) Schindler, W.; Koop, T.; Kazimirov, A.; Scherb, G.; Zegenhagen, J.; Schultz, T.;

Feidenhans'l, R.; Kirschner, J. Noncoherent growth patches in pseudomorphic films: Unusual strain relief in electrodeposited Co on Cu(001). *Surf. Sci. Lett.* **2000**, *465*, L783–L788.

(571) Schindler, W. Electrodeposited magnetic monolayers: In-situ studies of magnetism and structure. *Top. Appl. Phys.* **2003**, *85*, 243–258.

(572) Lucas, C. A.; Maroun, F.; Sisson, N.; Thompson, P.; Grunder, Y.; Cortes, R.; Allongue, P. Film and interface atomic structures of electrodeposited Co/Au(111) layers: An in situ X-ray scattering study as a function of the surface chemistry and the electrochemical potential. *J. Phys. Chem. C* **2016**, *120*, 3360–3370.

(573) Maroun, F.; Reikowski, F.; Di, N.; Wiegmann, T.; Stettner, J.; Magnussen, O. M.; Allongue, P. Potential dependence of the structure and magnetism of electrodeposited Pd/Co/Au(111) layers. *J. Electroanal. Chem.* **2018**, *819*, 322–330.

(574) Zegenhagen, J.; Renner, F. U.; Reitzle, A.; Lee, T. L.; Warren, S.; Stierle, A.; Dosch, H.; Scherb, G.; Fimland, B. O.; Kolb, D. M. In situ X-ray analysis of solid/electrolyte interfaces: electrodeposition of Cu and Co on Si(111): H and GaAs(001) and corrosion of Cu3Au(111). *Surf. Sci.* **2004**, *573*, 67–79.

(575) Reitzle, A.; Renner, F. U.; Lee, T. L.; Zegenhagen, J.; Kolb, D. M. Electrochemical growth of copper on well-defined n-Si(111): H surfaces. *Surf. Sci.* **2005**, *576*, 19–28.

(576) Ziegler, J. C.; Scherb, G.; Bunk, O.; Kazimirov, A.; Cao, L. X.; Kolb, D. M.; Johnson, R. L.; Zegenhagen, J. Pb deposition on n-Si(111): H electrodes: an in situ X-ray study. *Surf. Sci.* **2000**, *452*, 150–160.
(577) Warren, S.; Reitzle, A.; Kazimirov, A.; Ziegler, J. C.; Bunk, O.; Cao, L. X.; Renner, F. U.; Kolb, D. M.; Bedzyk, M. J.; Zegenhagen, J. A structure study of the electroless deposition of Au on Si(111): H. *Surf. Sci.* **2002**, *496*, 287–298.

(578) Zegenhagen, J.; Lee, T. L.; Gruender, Y.; Renner, F. U.; Fimland, B. O. The adsorption and growth of copper on as-terminated GaAs(001): Physical vapour versus electrochemical deposition. *Z. fur Phys. Chem.* **2007**, *221*, 1273–1286.

(579) Grunder, Y.; Renner, F. U.; Lee, T. L.; Dheeraj, D. L.; Fimland, B. O.; Zegenhagen, J. The electrodeposition of copper onto UHV-prepared GaAs(001) surfaces. *Surf. Sci.* **2009**, *603*, L105–L108.

(580) Munford, M.; Maroun, F.; Cortès, R.; Allongue, P.; Pasa, A. Electrochemical growth of gold on well-defined vicinal H-Si(111) surfaces studied by AFM and XRD. *Surf. Sci.* **2003**, *537*, 95–112.

(581) Borissov, D.; Pareek, A.; Renner, F. U.; Rohwerder, M. Electrodeposition of Zn and Au-Zn alloys at low temperature in an ionic liquid. *Phys. Chem. Chem. Phys.* **2010**, *12*, 2059–2062.

(582) Tsuyuki, Y.; Fujimura, T.; Kumoto, M.; Fukunaka, Y.; Pianetta, P.; Homma, T. Analysis of cathodic reaction process of SiCl4 during Si electrodeposition in ionic liquids. *J. Electrochem. Soc.* **2017**, *164*, D994–D998.

(583) Renner, F. U.; Kageyama, H.; Siroma, Z.; Shikano, M.; Schoder, S.; Grunder, Y.; Sakata, O. Gold model anodes for Li-ion batteries: Single crystalline systems studied by in situ X-ray diffraction. *Electrochim. Acta* **2008**, *53*, 6064–6069.

(584) Esbenshade, J. L.; Barile, C. J.; Fister, T. T.; Bassett, K. L.; Fenter, P.; Nuzzo, R. G.; Gewirth, A. A. Improving electrodeposition of Mg through an open circuit potential hold. *J. Phys. Chem. C* **2015**, *119*, 23366–23372.

(585) Ingham, B. et al. Particle size effect of hydrogen-induced lattice expansion of palladium nanoclusters. *Phys. Rev. B* **2008**, *78*, 245408.

(586) Ustarroz, J.; Hammons, J. A.; Van Ingelgem, Y.; Tzedaki, M.; Hubin, A.; Teryn, H. Multipulse electrodeposition of Ag nanoparticles on HOPG monitored by in-situ by Small-Angle X-ray Scattering. *Electrochem. Commun.* **2011**, *13*, 1320–1323.

(587) Ustarroz, J.; Altantzis, T.; Hammons, J. A.; Hubin, A.; Bals, S.; Teryn, H. The role of nanocluster aggregation, coalescence, and recrystallization in the electrochemical deposition of platinum nanostructures. *Chem. Mater.* **2014**, *26*, 2396–2406.

(588) Richardson, S. J.; Burton, M. R.; Luo, X.; Staniec, P. A.; Nandhakumar, I. S.; Terrill, N. J.; Elliott, J. M.; Squires, A. M. Watching mesoporous metal films grow during templated electrodeposition with in situ SAXS. *Nanoscale* **2017**, *9*, 10227–10232.

(589) Hammons, J. A.; Ilavsky, J. Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous sample-rotated small angle X-ray scattering and electrochemical methods approach. *Electrochim. Acta* **2017**, *228*, 462–473.

(590) Hammons, J. A.; Besford, Q. A.; Ilavsky, J.; Christofferson, A. J. Manipulating meso-scale solvent structure from Pd nanoparticle deposits in deep eutectic solvents. *J. Chem. Phys.* **2021**, *155*, 074505.

(591) Keist, J. S.; Hammons, J. A.; Wright, P. K.; Evans, J. W.; Orme, C. A. Coupling in situ atomic force microscopy (AFM) and ultra-small-angle X-ray scattering (USAXS) to study the evolution
of zinc morphology during electrodeposition within an imidazolium based ionic liquid electrolyte. *Electrochim. Acta* **2020**, *342*, 136073.

(592) Liang, Y.-C. et al. Formation process of mesostructured PtRu nanoparticles electrodeposited on a microemulsion lyotropic liquid crystalline template as revealed by in situ XRD, SAXS, and XANES. *J. Phys. Chem. C* **2012**, *116*, 26649–26655.

(593) Dupont, M. F.; Dose, W. M.; Donne, S. W. In-situ investigation of the electrodeposition of manganese dioxide using small angle X-ray scattering. *J. Electrochem. Soc.* **2015**, *162*, A1809.

(594) Dupont, M. F.; Gibson, A. J.; Elbourne, A.; Forghani, M.; Cross, A. D.; Donne, S. W. In situ investigation of the electrodeposition mechanism of manganese dioxide from a citrate electrolyte: the effect of intermediate stabilization on material morphology. *J. Electrochem. Soc.* **2020**, *167*, 040520.

(595) Moehl, G. E.; Bartlett, P. N.; Hector, A. L. Using GISAXS to detect correlations between the locations of gold particles electrodeposited from an aqueous solution. *Langmuir* **2020**, *36*, 4432–4438.

(596) Pattadar, D.; Cheek, Q.; Sartori, A.; Zhao, Y.; Giri, R. P.; Murphy, B.; Magnussen, O.; Maldonado, S. Evidence for facilitated surface transport during Ge crystal growth by indium in liquid HgIn alloys at room temperature. *Cryst. Growth Des.* **2021**, *21*, 1645–1656.

(597) Sanyal, M. K.; Agrawal, V. V.; Bera, M. K.; Kalyanikutty, K. P.; Daillant, J.; Blot, C.; Kubowicz, S.; Konovalov, O.; Rao, C. N. R. Formation and ordering of gold nanoparticles at the toluene-water interface. *J. Phys. Chem. C* **2008**, *112*, 1739–1743.

(598) Sanyal, M. K. The use of grazing incidence X-ray scattering techniques to probe chemical reactions at the liquid-liquid interface: the formation and ordering of gold nanoparticles. *J. Mater. Chem.* **2009**, *19*, 4300–4306.

(599) Bera, M. K.; Sanyal, M. K.; Yang, L.; Biswas, K.; Gibaud, A.; Rao, C. N. R. Small-angle x-ray scattering study of the aggregation of gold nanoparticles during formation at the toluene-water interface. *Phys. Rev. B* **2010**, *81*, 115415.

(600) Maiti, S.; Sanyal, M. K.; Varghese, N.; Satpati, B.; Dasgupta, D.; Daillant, J.; Carriere, D.; Konovolov, O.; Rao, C. N. R. Formation of single-crystalline CuS at the organic-aqueous interface. *J. Phys.: Condens. Matter* **2013**, *25*, 395401.

(601) Maiti, S.; Sanyal, M. K.; Jana, M. K.; Runge, B.; Murphy, B. M.; Biswas, K.; Rao, C. N. R. Evidence of contact epitaxy in the self-assembly of HgSe nanocrystals formed at a liquid-liquid interface. *J. Phys.: Condens. Matter* **2017**, *29*, 095101.

(602) Toney, M.; Davenport, A.; Oblongsky, L.; Ryan, M.; Vitus, C. Atomic structure of the passive oxide film formed on iron. *Phys. Rev. Lett* **1997**, *79*, 4282–4285.

(603) Davenport, A. J.; Oblonsky, L. J.; Ryan, M. P.; Toney, M. F. The structure of the passive film that forms on iron in aqueous environments. *J. Electrochem. Soc.* **2000**, *147*, 2162–2173.

(604) Magnussen, O. M.; Scherer, J.; Ocko, B. M.; Behm, R. J. In situ X-ray scattering study of the passive film on Ni(111) in sulfuric acid solution. *J. Phys. Chem. B* **2000**, *104*, 1222–1226.

(605) Scherer, J.; Ocko, B. M.; Magnussen, O. M. Structure, dissolution, and passivation of Ni(111) electrodes in sulfuric acid solution: an in situ STM, X-ray
scattering, and electrochemical study.
*Electrochim. Acta* **2003**, *48*, 1169–1191.

(606) Medway, S. L.; Lucas, C. A.; Kowal, A.; Nichols, R. J.; Johnson, D. In situ studies of the oxidation of nickel electrodes in alkaline solution. *J. Electroanal. Chem.* **2006**, *587*, 172–181.

(607) Reikowski, F.; Maroun, F.; Allongue, P.; Ruge, M.; Stettner, J.; Magnussen, O. In situ surface X-ray diffraction study of ultrathin epitaxial Co films on Au(111) in alkaline solution. *Electrochim. Acta* **2016**, *197*, 273–281.

(608) Chu, Y. S.; Robinson, I. K.; Gewirth, A. A. Comparison of aqueous and native oxide formation on Cu(111). *J. Chem. Phys.* **1999**, *110*, 5952–5959.

(609) Maurice, V.; Marcus, P. Progress in corrosion science at atomic and nanometric scales. *Prog. Mater. Sci.* **2018**, *95*, 132–171.

(610) Melendres, C. A.; You, H.; Maroni, V. A.; Nagy, Z.; Yun, W. Specular x-ray reflection for the "in situ" study of electrode surfaces. *J. Electroanal. Chem. Interfacial Electrochem.* **1991**, *297*, 549.

(611) You, H.; Nagy, Z.; Melendres, C. A.; Zurawski, D. J.; Chiarello, R. P.; Yonco, R. M.; Kim, H. K.; Maroni, V. A. X-ray reflectivity studies of the metal/solution interphase. *Proc. Electrochem. Soc.* **1992**, *92-1*, 73–88.

(612) Melendres, C. A.; Feng, Y. P.; Lee, D. D.; Sinha, S. K. X-ray diffuse scattering for the in situ study of electrochemically induced pitting on metal surfaces. *J. Electrochem. Soc.* **1995**, *142*, L19.

(613) Angerer, P.; Mann, R.; Gavrilovic, A.; Nauer, G. E. In situ X-ray diffraction study of the electrochemical reaction on lead electrodes in sulphate electrolytes. *Mater. Chem. Phys.* **2009**, *114*, 983–989.

(614) Kim, D. H.; Lee, H. H.; Kim, S. S.; Kang, H. C.; Noh, D. Y.; Kim, H.; Sinha, S. K. Chemical depth profile of passive oxide on stainless steel. *Appl. Phys. Lett.* **2004**, *85*, 6427–6429.

(615) Ingham, B.; Ko, M.; Kear, G.; Kappen, P.; Laycock, N.; Kimpton, J. A.; Williams, D. E. In situ synchrotron X-ray diffraction study of surface scale formation during CO2 corrosion of carbon steel at temperatures up to 90 degrees C. *Corros. Sci.* **2010**, *52*, 3052–3061.

(616) Ingham, B.; Ko, M.; Laycock, N.; Burnell, J.; Kappen, P.; Kimpton, J. A.; Williams, D. E. In situ synchrotron X-ray diffraction study of scale formation during CO2 corrosion of carbon steel in sodium and magnesium chloride solutions. *Corros. Sci.* **2012**, *56*, 96–104.

(617) Ko, M.; Laycock, N. J.; Ingham, B.; Williams, D. E. In situ synchrotron X-ray diffraction studies of CO2 corrosion of carbon steel with scale inhibitors ATMPA and PEI at 80 degrees C. *Corrosion* **2012**, *68*, 1085–1093.

(618) Ko, M.; Ingham, B.; Laycock, N.; Williams, D. E. In situ synchrotron X-ray diffraction study of the effect of chromium additions to the steel and solution on CO2 corrosion of pipeline steels. *Corros. Sci.* **2014**, *80*, 237–246.

(619) Ingham, B.; Ko, M.; Laycock, N.; Kirby, N. M.; Williams, D. E. First stages of siderite crystallisation during CO2 corrosion of steel evaluated using in situ synchrotron small- and wide-angle X-ray scattering. *Faraday Discuss.* **2015**, *180*, 171–190.

(620) Ko, M.; Ingham, B.; Laycock, N.; Williams, D. E. In situ synchrotron X-ray diffraction study of the effect of microstructure and boundary layer conditions on CO2 corrosion of pipeline steels. *Corros. Sci.* **2015**, *90*, 192–201.
(621) Sk, M. H.; Abdullah, A. M.; Ko, M.; Ingham, B.; Laycock, N.; Arul, R.; Williams, D. E. Local supersaturation and the growth of protective scales during CO2 corrosion of steel: Effect of pH and solution flow. *Corros. Sci.* **2017**, *126*, 26–36.

(622) Ingham, B.; Holmes-Hewett, W.; Ko, M.; Kirby, N. M.; Sk, M. H.; Abdullah, A. M.; Laycock, N. J.; Williams, D. E. Surface layer formation in the earliest stages of corrosion of steel in CO2-Saturated Brine at 80 °C: studied by in situ synchrotron X-ray methods. *J. Electrochem. Soc.* **2018**, *165*, C842.

(623) Ingham, B.; Ko, M.; Shaw, P.; Sk, M. H.; Abdullah, A. M.; Laycock, N.; Williams, D. E. Effects of oxygen on scale formation in CO2 corrosion of steel in hot brine: In situ synchrotron X-ray diffraction study of anodic products. *J. Electrochem. Soc.* **2018**, *165*, C756–C761.

(624) Bertram, F.; Zhang, F.; Evertsson, J.; Carla, F.; Pan, J.; Messing, M. E.; Mikkelsen, A.; Nilsson, J. O.; Lundgren, E. In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy. *J. Appl. Phys.* **2014**, *116*, 034902/1.

(625) Lee, W.; Park, S.-J. Porous anodic aluminum oxide: Anodization and templated synthesis of functional nanostructures. *Chem. Rev.* **2014**, *114*, 7487–7556.

(626) Napolskii, K. S.; Roslyakov, I. V.; Eliseev, A. A.; Byelov, D. V.; Petukhov, A. V.; Grigoryeva, N. A.; Bouwman, W. G.; Lukashin, A. V.; Chumakov, A. P.; Grigoriev, S. V. The kinetics and mechanism of long-range pore ordering in anodic films on aluminum. *J. Phys. Chem. C* **2011**, *115*, 23726–23731.

(627) Roslyakov, I. V.; Chumakov, A. P.; Eliseev, A. A.; Leontiev, A. P.; Konovalov, O. V.; Napolskii, K. S. Evolution of pore ordering during anodizing of aluminum single crystals: In situ small-angle X-ray scattering study. *J. Phys. Chem. C* **2021**, *125*, 9287–9295.

(628) Gorisse, T.; Dupre, L.; Zelsmann, M.; Vlad, A.; Coati, A.; Garreau, Y.; Buttard, D. In situ investigation of the early-stage growth of nanoporous alumina. *J. Nanomater.* **2018**, *2018*, 6428271.

(629) Vinogradov, N. A.; Harlow, G. S.; Carla, F.; Evertsson, J.; Rullik, L.; Linpe, W.; Felici, R.; Lundgren, E. Observation of pore growth and self-organization in anodic alumina by time-resolved X-ray scattering. *ACS Appl. Nano Mater.* **2018**, *1*, 1265–1271.

(630) Evertsson, J.; Vinogradov, N. A.; Harlow, G. S.; Carla, F.; McKibbin, S. R.; Rullik, L.; Linpe, W.; Felici, R.; Lundgren, E. Self-organization of porous anodic alumina films studied in situ by grazing-incidence transmission small-angle X-ray scattering. *RSC Adv.* **2018**, *8*, 18980–18991.

(631) Harlow, G. S.; Drnec, J.; Wiegmann, T.; Lipe, W.; Evertsson, J.; Persson, A. R.; Wallenberg, R.; Lundgren, E.; Vinogradov, N. A. Observing growth under confinement: Sn nanopillars in porous alumina templates. *Nanoscale Adv.* **2019**, *1*, 4764–4771.

(632) Linpe, W.; Harlow, G. S.; Evertsson, J.; Hejral, U.; Abbondanza, G.; Lenrick, F.; Seifert, S.; Felici, R.; Vinogradov, N. A.; Lundgren, E. The state of electrodeposited Sn nanopillars within porous anodic alumina from in situ X-ray observations. *ACS Appl. Nano Mater.* **2019**, *2*, 3031–3038.

(633) Richter, K.; Bornmann, P. X-ray heating chamber investigations of reforming
Pt–Al₂O₃ catalysts. *Cryst. Res. Technol.* **1981**, *16*, 367–375.

(634) Ushakov, V.; Moroz, E. X-ray diffraction studies of reforming platinum-alumina catalysts in a high-temperature chamber. *React. Kinet. Catal. L.* **1985**, *27*, 351–355.

(635) Srinivasan, R.; De Angelis, R.; Davis, B. Alloy formation in Pt-Sn-Alumina Catalysts: In situ X-ray Diffraction Study. *J. Catal.* **1987**, *106*, 449–457.

(636) Xiong, Y. et al. Revealing the atomic ordering of binary intermetallics using in situ heating techniques at multilength scales. *Proc. Natl. Acad. Sci. U. S. A.* **2019**, *116*, 1974–1983.

(637) Zeng, W. J.; Wang, C.; Yan, Q. Q.; Yin, P.; Tong, L.; Liang, H. W. Phase diagrams guide synthesis of highly ordered intermetallic electrocatalysts: separating alloying and ordering stages. *Nat. Commun.* **2022**, *13*, 1–8.

(638) Schnepp, Z.; Danks, A. E.; Hollamby, M. J.; Pauw, B. R.; Murray, C. A.; Tang, C. C. In situ synchrotron X-ray diffraction study of the sol-gel synthesis of Fe3N and Fe3C. *Chem. Mater.* **2015**, *27*, 5094–5099.

(639) Chambers, M. S.; Hunter, R. D.; Hollamby, M. J.; Pauw, B. R.; Smith, A. J.; Snow, T.; Danks, A. E.; Schnepp, Z. In situ and ex situ X-ray diffraction and small-angle X-ray scattering investigations of the sol–gel synthesis of Fe₃N and Fe₃C. *Inorg. Chem.* **2022**, *61*, 6742–6749.

(640) Chattot, R.; Asset, T.; Drnec, J.; Bordet, P.; Nelayah, J.; Dubau, L.; Maillard, F. Atomic-scale snapshots of the formation and growth of hollow PtNi/C nanocatalysts. *Nano Lett.* **2017**, *17*, 2447–2453.

(641) Brant, W. R.; Li, D.; Gu, Q.; Schmid, S. Comparative analysis of ex-situ and operando X-ray diffraction experiments

for lithium insertion materials. *J. Power Sources* **2016**, *302*, 126–134.

(642) Diaz-Lopez, M.; Cutts, G. L.; Allan, P. K.; Keeble, D. S.; Ross, A.; Pralong, V.; Spiekermann, G.; Chater, P. A. Fast operando X-ray pair distribution function using the DRIX electrochemical cell. *J. Synchrotron Radiat.* **2020**, *27*, 1190–1199.

(643) Villevieille, C.; Sasaki, T.; Novák, P. Novel electrochemical cell designed for operando techniques and impedance studies. *RSC Adv.* **2014**, *4*, 6782–6789.

(644) Suzuki, K. et al. High-energy X-ray compton scattering imaging of 18650-type lithium-ion battery cell. *Condens. Matter* **2019**, *4*, 66.

(645) Reimers, J. N.; Dahn, J. R. Electrochemical and in situ X-ray diffraction studies of lithium intercalation in LiₓCoO₂. *J. Electrochem. Soc.* **1992**, *139*, 2091–2097.

(646) Amatucci, G. G.; Tarascon, J. M.; Klein, L. C. CoO₂, The end member of the Lix CoO₂ solid solution. *J. Electrochem. Soc.* **1996**, *143*, 1114.

(647) Sottmann, J.; Pralong, V.; Barrier, N.; Martin, C. An electrochemical cell for operando bench-top X-ray diffraction. *J. Appl. Crystallogr.* **2019**, *52*, 485–490.

(648) Borkiewicz, O. J.; Shyam, B.; Wiaderek, K. M.; Kurtz, C.; Chupas, P. J.; Chapman, K. W. The AMPIX electrochemical cell: a versatile apparatus for in situ X-ray scattering and spectroscopic measurements. *J. Appl. Crystallogr.* **2012**, *45*, 1261–1269.

(649) Tripathi, A. M.; Su, W.-N.; Hwang, B. J. In situ analytical techniques for battery interface analysis. *Chem. Soc. Rev.* **2018**, *47*, 736–851.

(650) Jung, R.; Linsenmann, F.; Thomas, R.; Wandt, J.; Solchenbach, S.; Maglia, F.; Stinner, C.; Tromp, M.; Gasteiger, H. A.
Nickel, manganese, and cobalt dissolution from Ni-rich NMC and their effects on NMC622-graphite cells. *J. Electrochem. Soc.* **2019**, *166*, A378.

(651) Huang, J. J. et al. Disorder dynamics in battery nanoparticles during phase transitions revealed by operando single-particle diffraction. *Adv. Energy Mater.* **2022**, *12*, 2103521.

(652) Singer, A.; Ulvestad, A.; Cho, H.-M.; Kim, J. W.; Maser, J.; Harder, R.; Meng, Y. S.; Shpyrko, O. G. Nonequilibrium structural dynamics of nanoparticles in LiNi1/2Mn3/2O4 cathode under operando conditions. *Nano Lett.* **2014**, *14*, 5295–5300.

(653) Liang, G.; Hao, J.; D'Angelo, A. M.; Peterson, V. K.; Guo, Z.; Pang, W. K. A robust coin-cell design for in situ synchrotron-based X-ray powder diffraction analysis of battery materials. *Batter. Supercaps* **2021**, *4*, 380–384.

(654) Ghanty, C. et al. Li⁺-ion extraction/insertion of Ni-rich Li₁+x(Ni_yCo_zMn_z)wO₂ (0.005<x<0.03; y:z=8:1, w≈1) electrodes: In situ XRD and raman spectroscopy study. *ChemElectroChem* **2015**, *2*, 1479–1486.

(655) Lu, X. et al. 3D microstructure design of lithium-ion battery electrodes assisted by X-ray nano-computed tomography and modelling. *Nat. Commun.* **2020**, *11*, 2079.

(656) Ziesche, R. F. et al. 4D imaging of lithium-batteries using correlative neutron and X-ray tomography with a virtual unrolling technique. *Nat. Commun.* **2020**, *11*, 777.

(657) Chianelli, R. R.; Scanlon, J. C.; Rao, B. M. L. Dynamic X-ray diffraction. *J. Electrochem. Soc.* **1978**, *125*, 1563–1566.

(658) Dahn, J. Structure and electrochemistry of Li1±yNiO2 and a new Li2NiO2 phase

with the Ni (OH)2 structure. *Solid State Ion.* **1990**, *44*, 87–97.

(659) Borkiewicz, O. J.; Wiaderek, K. M.; Chupas, P. J.; Chapman, K. W. Best practices for operando battery experiments: Influences of X-ray experiment design on observed electrochemical reactivity. *Phys. Chem. Lett.* **2015**, *6*, 2081–2085.

(660) Thurston, T. R.; Jisrawi, N. M.; Mukerjee, S.; Yang, X. Q.; McBreen, J.; Daroux, M. L.; Xing, X. K. Synchrotron x-ray diffraction studies of the structural properties of electrode materials in operating battery cells. *Appl. Phys. Lett.* **1996**, *69*, 194–196.

(661) Martens, I.; Vostrov, N.; Mirolo, M.; Colalongo, M.; Kúš, P.; Richard, M.-I.; Wang, L.; Zhu, X.; Schülli, T. U.; Drnec, J. Revisiting phase transformation mechanisms in LiNi₀.₅Mn₁.₅O₄ high voltage cathodes with operando microdiffraction. *ACS Mater. Lett.* **2022**, *4*, 2528–2536.

(662) Whitehead, A. H.; Edström, K.; Rao, N.; Owen, J. R. In situ X-ray diffraction studies of a graphite-based Li-ion battery negative electrode. *J. Power Sources* **1996**, *63*, 41–45.

(663) Hatchard, T. D.; Dahn, J. R. In Situ XRD and electrochemical study of the reaction of lithium with amorphous silicon. *J. Electrochem. Soc.* **2004**, *151*, A838.

(664) Misra, S.; Liu, N.; Nelson, J.; Hong, S. S.; Cui, Y.; Toney, M. F. In situ X-ray diffraction studies of (de)lithiation mechanism in silicon nanowire anodes. *ACS Nano* **2012**, *6*, 5465–5473.

(665) Nelson, J.; Misra, S.; Yang, Y.; Jackson, A.; Liu, Y. J.; Wang, H. L.; Dai, H. J.; Andrews, J. C.; Cui, Y.; Toney, M. F. In operando X-ray diffraction and transmission X-ray microscopy of lithium sulfur batteries. *J. Am. Chem. Soc.* **2012**, *134*, 6337–6343.
(666) Lin, F. et al. Synchrotron X-ray ana-
lytical techniques for studying materials
electrochemistry in rechargeable batter-
ies. *Chem. Rev.* **2017**, *117*, 13123–13186.

(667) Matras, D. et al. Emerging chemical het-
erogeneities in a commercial 18650 NCA
Li-ion battery during early cycling re-
vealed by synchrotron X-ray diffraction
tomography. *J. Power Sources* **2022**,
*539*, 231589.

(668) Shearing, P. et al. Mapping internal tem-
peratures during high-rate battery appli-
cations. *Nature* **2023**, *617*, 507–512.

(669) Harlow, J. E. et al. A wide range of test-
ing results on an excellent lithium-ion
cell chemistry to be used as benchmarks
for new battery technologies. *J. Elec-
trochem. Soc.* **2019**, *166*, A3031–A3044.

(670) Daubinger, P.; Schelter, M.; Peter-
sohn, R.; Nagler, F.; Hartmann, S.; Her-
rmann, M.; Giffin, G. A. Impact of brac-
ing on large format prismatic lithium-ion
battery cells during aging. *Adv. Energy
Mater.* **2021**, *12*, 2102448.

(671) Berhaut, C. L.; Dominguez, D. Z.; Ku-
mar, P.; Jouneau, P.-H.; Porcher, W.;
Aradilla, D.; Tardif, S.; Pouget, S.; Lyon-
nard, S. Multiscale multiphase lithiation
and delithiation mechanisms in a com-
posite electrode unraveled by simultane-
ous *operando* small-angle and wide-angle
X-ray scattering. *ACS Nano* **2019**, *13*,
11538–11551.

(672) Berhaut, C. L. et al. Prelithiation of sili-
con/graphite composite anodes: Benefits
and mechanisms for long-lasting Li-Ion
batteries. *Energy Stor. Mater.* **2020**, *29*,
190–197.

(673) Möhl, G. E.; Metwalli, E.; Müller-
Buschbaum, P. In operando small-
angle X-ray scattering investigation of
nanostructured polymer electrolyte for
lithium-ion batteries. *ACS Energy Lett.*
**2018**, *3*, 1525–1530.

(674) Wiaderek, K. M.; Borkiewicz, O. J.; Castillo-Martínez, E.; Robert, R.; Pereira, N.; Amatucci, G. G.; Grey, C. P.; Chupas, P. J.; Chapman, K. W. Comprehensive insights into the structural and chemical changes in mixed-anion FeOF electrodes by using operando PDF and NMR Spectroscopy. *J. Am. Chem. Soc.* **2013**, *135*, 4070–4078.

(675) Hua, X.; Robert, R.; Du, L.-S.; Wiaderek, K. M.; Leskes, M.; Chapman, K. W.; Chupas, P. J.; Grey, C. P. Comprehensive study of the CuF₂ conversion reaction mechanism in a lithium ion battery. *J. Phys. Chem. C* **2014**, *118*, 15169–15184.

(676) Key, B.; Morcrette, M.; Tarascon, J.-M.; Grey, C. P. Pair distribution function analysis and solid state NMR studies of silicon electrodes for lithium ion batteries: Understanding the (de)lithiation mechanisms. *J. Am. Chem. Soc.* **2010**, *133*, 503–512.

(677) Sottmann, J.; Di Michiel, M.; Fjel-
lvåg, H.; Malavasi, L.; Margadonna, S.;
Vajeeston, P.; Vaughan, G. B. M.;
Wragg, D. S. Chemical structures of
specific sodium ion battery components
determined by operando pair distribu-
tion function and X-ray diffraction com-
puted tomography. *Angew. Chem. Int.
Ed.* **2017**, *56*, 11385–11389.

(678) Vitoux, L.; Reichardt, M.; Sallard, S.; Novák, P.; Sheptyakov, D.; Villevieille, C. A cylindrical cell for operando neutron diffraction of Li-ion battery electrode materials. *Front. Energy Res. 2018*, *6*, Article 76.

(679) Taminato, S. et al. Real-time ob-
servations of lithium battery reac-
tions—operando neutron diffraction
analysis during practical operation. *Sci.
Rep.* **2016**, *6*, 28843.

(680) Zhang, X.; van Hulzen, M.; Singh, D. P.;
Brownrigg, A.; Wright, J. P.; van
Dijk, N. H.; Wagemaker, M. Direct view on the phase evolution in individual LiFePO4 nanoparticles during Li-ion battery cycling. *Nat. Commun.* **2015**, *6*, 8333.

(681) van Hulzen, M.; Ooms, F. G. B.; Wright, J. P.; Wagemaker, M. Revealing operando transformation dynamics in individual Li-ion electrode crystallites using X-Ray microbeam diffraction. *Front. Energy Res.* **2018**, *6*, Article 56.

(682) Ulvestad, A. P.; Singer, A.; Cho, H.-M.; Clark, J. N.; Harder, R.; Maser, J.; Meng, Y. S.; Shpyrko, O. G. Single particle nanomechanics in operando batteries via lensless strain mapping. *Nano Lett.* **2014**, *14*, 5123-5127.

(683) Assefa, T. A.; Suzana, A. F.; Wu, L.; Koch, R. J.; Li, L.; Cha, W.; Harder, R. J.; Bozin, E. S.; Wang, F.; Robinson, I. K. Imaging the phase transformation in single particles of the lithium titanate anode for lithium-ion batteries. *ACS Appl. Energy Mater.* **2021**, *4*, 111–118.

(684) Liu, T. et al. Origin of structural degradation in Li-rich layered oxide cathode. *Nature* **2022**, *606*, 305–312.

(685) Chao, S.-C.; Yen, Y.-C.; Song, Y.-F.; Chen, Y.-M.; Wu, H.-C.; Wu, N.-L. A study on the interior microstructures of working Sn particle electrode of Li-ion batteries by in situ X-ray transmission microscopy. *Electrochem. Commun.* **2010**, *12*, 234–237.

(686) Cahn, J. W.; Hilliard, J. E. Free energy of a nonuniform system. I. Interfacial free energy. *J. Chem. Phys.* **1958**, *28*, 258.

(687) Van der Ven, A.; Ceder, G. Lithium diffusion in layered $Li_xCoO_2$. *Electrochem. Solid-State Lett.* **1999**, *3*, 301.

(688) Gorobtsov, O. et al. Interaction and transformation of metastable defects

in intercalation materials. *arXiv* **2021**, *2106*, 12145.

(689) Choi, S. et al. In situ strain svolution on Pt nanoparticles during hydrogen peroxide decomposition. *Nano Lett.* **2020**, *20*, 8541–8548.

(690) Kawaguchi, T.; Komanicky, V.; Latyshev, V.; Cha, W.; Maxey, E. R.; Harder, R.; Ichitsubo, T.; You, H. Electrochemically induced strain evolution in Pt–Ni alloy nanoparticles observed by Bragg coherent diffraction imaging. *Nano Lett.* **2021**, *21*, 5945–5951.

(691) Dupraz, M. et al. Imaging the facet surface strain state of supported multi-faceted Pt nanoparticles during reaction. *Nat. Commun.* **2022**, *13*, 3003.

(692) Sheyfer, D.; Mariano, R. G.; Kawaguchi, T.; Cha, W.; Harder, R. J.; Kanan, M. W.; Hruszkewycz, S. O.; You, H.; Highland, M. J. Operando nanoscale imaging of electrochemically induced strain in a locally polarized Pt grain. *Nano Lett.* **2022**, *23*, 1–7.

(693) Hirayama, M.; Sakamoto, K.; Hiraiide, T.; Mori, D.; Yamada, A.; Kanno, R.; Sonoyama, N.; Tamura, K.; Mizuki, J. Characterization of electrode/electrolyte interface using in situ X-ray reflectometry and $LiNi_0.8Co_0.2O_2$ epitaxial film electrode synthesized by pulsed laser deposition method. *Electrochim. Acta* **2007**, *53*, 871–881.

(694) Hirayama, M. et al. Characterization of electrode/electrolyte interface for lithium batteries using in situ synchrotron X-ray reflectometry—A new experimental technique for $LiCoO_2$ model electrode. *J. Power Sources* **2007**, *168*, 493–500.

(695) Hirayama, M.; Sonoyama, N.; Ito, M.; Minoura, M.; Mori, D.; Yamada, A.; Tamura, K.; Mizuki, J.; Kanno, R. Characterization of electrode/electrolyte interface with X-ray reflectometry and
epitaxial-film LiMn₂O₄ electrode. *J. Electrochem. Soc.* **2007**, *154*, A1065.

(696) Hirayama, M.; Ido, H.; Kim, K.; Cho, W.; Tamura, K.; Mizuki, J.; Kanno, R. Dynamic structural changes at LiMn2O4/electrolyte interface during lithium battery reaction. *J. Am. Chem. Soc.* **2010**, *132*, 15268–76.

(697) Yu, X.; Chen, X.; Buchholz, D. B.; Li, Q.; Wu, J.; Fenter, P. A.; Bedzyk, M. J.; Dravid, V. P.; Barnett, S. A. Pulsed laser deposition and characterization of het-eroepitaxial LiMn2O4/La0.5Sr0.5CoO3 bilayer thin films as model lithium ion battery cathodes. *ACS Appl. Nano* **2018**, *1*, 642–653.

(698) Chattopadhyay, S.; Lipson, A. L.; Karmel, H. J.; Emery, J. D.; Fister, T. T.; Fenter, P. A.; Hersam, M. C.; Bedzyk, M. J. In situ X-ray study of the solid electrolyte interphase (SEI) formation on graphene as a model Li-ion battery anode. *Chem. Mater.* **2012**, *24*, 3038–3043.

(699) Fister, T. T.; Long, B. R.; Gewirth, A. A.; Shi, B.; Assoufid, L.; Lee, S. S.; Fenter, P. Real-time observations of interfacial lithiation in a metal silicide thin film. *J. Phys. Chem. C* **2012**, *116*, 22341–22345.

(700) Fister, T. T.; Esbenshade, J.; Chen, X.; Long, B. R.; Shi, B.; Schlepuetz, C. M.; Gewirth, A. A.; Bedzyk, M. J.; Fenter, P. Lithium intercalation behavior in multilayer silicon electrodes. *Adv. Energy Mater.* **2014**, *4*, 1301494/1.

(701) Evmenenko, G.; Fister, T. T.; Buchholz, D. B.; Li, Q.; Chen, K.-S.; Wu, J.; Dravid, V. P.; Hersam, M. C.; Fenter, P.; Bedzyk, M. J. Morphological evolution of multilayer Ni/NiO thin film electrodes during lithiation. *ACS Appl. Mater. Interfaces* **2016**, *8*, 19979–19986.

(702) Fister, T. T. et al. Dimensionally controlled lithiation of chromium oxide. *Chem. Mater.* **2016**, *28*, 47–54.

(703) Chen, X.; Fister, T. T.; Esbenshade, J.; Shi, B.; Hu, X.; Wu, J.; Gewirth, A. A.; Bedzyk, M. J.; Fenter, P. Reversible Li-ion conversion reaction for a TixGe alloy in a Ti/Ge multilayer. *ACS Appl. Mater. Interfaces* **2017**, *9*, 8169–8176.

(704) Evmenenko, G.; Warburton, R. E.; Yildirim, H.; Greeley, J. P.; Chan, M. K. Y.; Buchholz, D. B.; Fenter, P.; Bedzyk, M. J.; Fister, T. T. Understanding the role of overpotentials in lithium ion conversion reactions: Visualizing the interface. *ACS Nano* **2019**, *13*, 7825–7832.

(705) Kim, J. J. et al. Structural changes during the conversion reaction of tungsten oxide electrodes with tailored, mesoscale porosity. *ACS Nano* **2022**, *16*, 5384–5392.

(706) Cao, C. T.; Steinruck, H. G.; Shyam, B.; Toney, M. F. The atomic scale electrochemical lithiation and delithiation process of silicon. *Adv. Mater. Interfaces* **2017**, *4*, 1700771.

(707) Cao, C. T.; Steinruck, H. G.; Shyam, B.; Stone, K. H.; Toney, M. F. In situ study of silicon electrode lithiation with X-ray reflectivity. *Nano Lett.* **2016**, *16*, 7394–7401.

(708) Cao, C. T.; Abate, I. I.; Sivonxay, E.; Shyam, B.; Jia, C. J.; Moritz, B.; Devereaux, T. P.; Persson, K. A.; Steinruck, H. G.; Toney, M. F. Solid electrolyte interphase on native oxide-terminated silicon anodes for Li-ion batteries. *Joule* **2019**, *3*, 762–781.

(709) Cao, C. T. et al. Toward unraveling the origin of lithium fluoride in the solid electrolyte interphase. *Chem. Mater.* **2021**, *33*, 7315–7336.
(710) Steinruck, H. G.; Cao, C. T.; Veith, G. M.; Toney, M. F. Toward quantifying capacity losses due to solid electrolyte interphase evolution in silicon thin film batteries. *J. Chem. Phys.* **2020**, *152*, 084702.

(711) Cao, C.; Shyam, B.; Wang, J.; Toney, M. F.; Steinruck, H. G. Shedding X-ray light on the interfacial electro-chemistry of silicon anodes for Li-ion batteries. *Acc. Chem. Res.* **2019**, *52*, 2673-2683.

(712) Linpe, W.; Harlow, G. S.; Larsson, A.; Abbondanza, G.; Ramisch, L.; Pfaff, S.; Zetterberg, J.; Evertsson, J.; Lundgren, E. An electrochemical cell for 2-dimensional surface optical reflectance during anodization and cyclic voltammetry. *Rev. Sci. Instrum.* **2020**, *91*, 044101.

(713) Linpe, W. et al. Revisiting optical reflectance from Au(111) electrode surfaces with combined high-energy surface X-ray diffraction. *J. Electrochem. Soc.* **2021**, *168*, 96511.

(714) Sokolowski-Tinten, K.; von der Linde, D. Ultrafast phase transitions and lattice dynamics probed using laser-produced x-ray pulses. *J. Condens. Matter Phys.* **2004**, *16*, R1517-R1536.

(715) Ihee, H.; Wulff, M.; Kim, J.; Adachi, S. Ultrafast X-ray scattering: structural dynamics from diatomic to protein molecules. *Int. Rev. Phys. Chem.* **2010**, *29*, 453-520.

(716) Hau-Riege, S. P. et al. Ultrafast transitions from solid to liquid and plasma states of graphite induced by X-ray free-electron laser pulses. *Phys. Rev. Lett.* **2012**, *108*, 217402.

(717) Singer, A. et al. Photoinduced enhancement of the charge density wave amplitude. *Phys. Rev. Lett.* **2016**, *117*, 056401-1-6.

(718) Wingert, J. et al. Direct time-domain determination of electron-phonon coupling strengths in chromium. *Phys. Rev. B* **2020**, *102*, 041101.
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