bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrocatalytic Activities of High-Entropy Oxides for the Oxygen Evolution Reaction
Authors: Choi Yun-Hyuk
Published: February 2024

Electrocatalytic water-splitting hydrogen generation consists of the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER), where the four-electron-relevant OER is the rate-determining step. So far, there have been many efforts to substitute for the highly expensive noble-metal electrocatalysts (platinum, ruthenium or rhodium oxides, etc.). Transition-metal oxides based on Co, Ni, Mn, and V have been suggested as such alternatives, due to their low cost, high efficiency, and high stability. Recently, since the compositional diversity can provide a new breakthrough in that area, a high-entropy oxide (HEO) with five transition-metal cations has been suggested as a promising electrocatalyst toward the OER. In our studies, two kinds of HEOs were prepared and their OER activities were investigated. To begin with, for the (Mg0.2Fe0.2Co0.2Ni0.2Cu0.2)O, the effect of constituent cations on the OER activity was unveiled. Furthermore, a core cation driving the high OER activity was found. For it, the medium-entropy oxides (MEOs) with four cations are prepared by subtracting each cation (Mg, Fe, Co, Ni, or Cu) from the HEO, exhibiting homogeneous morphology, equiatomic composition, and single-phase rocksalt structure. As a result, it is found that the highest concentration of Co3+ in the MEO (w/o Cu) leads to the best OER activity, and thus Co3+ is the core ion driving the high OER activity. Furthermore, it is regarded that Cu2+ ions prevent the conversion of Co or Fe cations from 2+ to 3+ in the HEO and MEOs. Accordingly, maximizing the concentration of Co3+ within electrocatalysts is suggested as an effective design strategy for the high-efficiency electrocatalysts based on high or medium entropy materials. Secondly, the relationship between structure and OER activity was elucidated for the (Mg0.2Fe0.2Co0.2Zn0.2Cu0.2)O with a temperature-dependent rocksalt-to-spinel transition.
Highly Exposed MoS2 Nanosheets Grown Under pH Modulated Non-Equilibrium Hydrothermal Route and Its Electrocatalytic Hydrogen Evolution Performance
Authors: Shaikh Naznin , Mukhopadhyay Indrajit , Ray Abhijit
Published: February 2024

Abstract: Molybdenum disulfide (MoS2) has emerged as a highly potential noble metal-free electrocatalyst for the Hydrogen Evolution Reaction (HER). However, edge sites of MoS2 created by sulphur non-stoichiometry play a prominent role in influencing the HER activity. In this work we adopt a simple hydrothermal route under a non-equilibrium condition with in-situ pH modulation, to synthesize its highly exposed edge sites MoS2 which have not been reported so far, and study the variation of its physio-chemical properties that enable an efficient electrocatalytic activity. Electrochemical measurements and impedance studies are conducted to understand harmonic morphology, and structural and composition variation, which were responsible for the activity. Additionally, the Density Functional Theory is adopted to support the enhanced hydrogen absorption and desorption processes in synchronous with various non-stoichiometric structures.
Charge Carrier Trapping in the Surface Region of BiVO4 Photoanodes
Authors: Kaya Sarp
Published: February 2024

Photoelectrochemical water splitting is a promising method for converting solar energy into chemical energy stored in molecular hydrogen and oxygen. However, the efficiency of this process is heavily dependent on the properties of the photoelectrode materials used. Metal oxide semiconductors, such as BiVO4, are commonly used as photoanode materials, but they have poor charge transport properties and surface catalytic activity, which can limit their efficiency.

To address these limitations, catalysts are often incorporated onto the surface of the photoanode to improve its surface activity. However, the overall efficiency of the photoelectrochemical process is also influenced by charged defect sites present both in the bulk and on the surface of the semiconductor. These defect sites can trap charges and hamper the kinetics of the process in the millisecond time scale. To address this issue, covalently coordinated catalyst layers and surface doping can be used to eliminate these trapped charges. Moreover, the bulk charge carriers are not entirely decoupled from the surface processes and can be influenced by surface treatments. Therefore, a multi-folded approach that considers both the surface and bulk properties of the photoanode, as well as the role of the catalysts, is necessary to improve the overall efficiency of photoelectrochemical water splitting.

We have investigated interfacial charge trapping and transfer processes through a CoOx catalyst layer deposited on BiVO4 by atomic layer deposition (ALD) and cobalt incorporated into the subsurface region. We have shown, by the combination of activity studies and spectroscopy investigations, that oxygen vacancies modified by cobalt incorporation have a remarkable impact on the water oxidation activity and charge injection efficiency. We further demonstrated by transient photocurrent measurements performed by fast LED light pulses (within ms time scale) that the CoOx catalyst layer reduced the number of trapped electrons and improved the rate of charge utilization. Cobalt ions in the subsurface region on the other did not act as catalytic centers but they eliminated the trapping process. We have also confirmed these observations by transient absorption spectroscopy investigations and showed that cobalt incorporation had a much bigger effect on the charge recombination lifetime.
Nanostructured Fe-Doped Nickel Sulfide on Ni Foam As Electrocatalyst for Oxygen Evolution Reaction
Authors: Zhu Jiahui , Pescarmona Paolo. P.
Published: February 2024

In recent years, with the increasing demand for clean and renewable energy, growing research efforts have been dedicated to the generation of hydrogen through water electrolysis [1,2]. To industrialize hydrogen production, it is important to find low-cost and high-activity electrocatalysts for hydrogen evolution reaction (HER) and, especially, oxygen evolution reaction (OER) [3]. OER is more challenging because it involves a four-electron transfer process, while HER is a two-electron transfer process. In this study, Ni3S2 nanorods were synthesized on Ni foam (NiS/Ni foam, Fig. 1a) by a new one-step solvothermal reaction, with S powder as the sulfur source and Ni foam as the nickel source. Experimental results indicated that the NiS/Ni foam electrocatalyst had an overpotential of 276 mV at 10 mA/cm2 for OER in 1 M KOH electrolyte. To boost the electrocatalytic activity of Ni3S2, we developed an effective method of doping with Fe via hydrothermal reaction. The obtained nanostructured Fe-doped Ni3S2 on Ni foam (Fe-NiS/Ni foam, see Fig. 1b) achieved OER at an extremely low overpotential of 218 mV at 10 mA/cm2. Remarkably, Fe-NiS/Ni foam exhibited high stability at an industrially-relevant high current density (500 mA/cm2 for 24h). Currently, we are studying its phase transfer process with in situ XPS.

REFERENCES

Jiao, S., et al., Energy & Environmental Science, 2021. 14(4): p. 1722-1770.

Boppella, R., et al., Coordination Chemistry Reviews, 2021. 427.

Du, J., F. Li, and L. Sun, Chem Soc Rev, 2021. 50(4): p. 2663-2695.

Figure 1
Copper-Based Catalyst Yields Unusual Ammonia Yield in Nitrate Electroreduction
Authors: Kumar Abhishek , Garg Abhishek
Published: February 2024

The electrochemical reduction of nitrate (NO3
-) ions into ammonia (NH3) provides an alternative method to produce highly valuable NH3 as well as eliminating harmful NO3
- pollutants. A variety of catalysts have been explored in recent times, however the NH3 production rate is far behind that of industrial Haber Bosch process which poses a major challenge for large scale synthesis. Herein, we have adopted an electrochemical synthetic route to produce highly porous copper nanoparticle enriched with (100) facets over copper foil containing which efficiently catalyzes NO3
- to NH3. Cu(100) rich electrocatalyst shows a significantly high NH3 production rate of greater than 1.0 mmol h-1 cm-2 even in the dilute NO3
- concentration of 14 mM, which is 4 to 5 times higher than the best reported values. Increasing the NO3
-concentration to 140 mM resulted in an NH3 production rate greater than 3.0 mmol h-1 cm-2, demonstrating that the catalyst is active in a wide range of NO3
- concentrations. Furthermore, durability test conducted in a flow system shows more than 100 h stability while maintaining a faradaic efficiency of greater than 98 %. Thus, we have successfully demonstrated the suitability of our catalyst at an industrially relevant scale.

References:

Patil, S. B.; Liu, T.-R.; Chou, H.-L.; Huang, Y.-B.; Chang, C.-C.; Chen, Y.-C.; Lin, Y.-S.; Li, H.; Lee, Y.-C.; Chang, Y. J., Electrocatalytic reduction of NO3
- to ultrapure ammonia on {200} facet dominant Cu nanodendrites with high conversion faradaic efficiency. The Journal of Physical Chemistry Letters
2021,
12 (33), 8121-8128.

Hu, Q.; Qin, Y.; Wang, X.; Wang, Z.; Huang, X.; Zheng, H.; Gao, K.; Yang, H.; Zhang, P.; Shao, M., Reaction intermediate-mediated electrocatalyst synthesis favors specified facet and defect exposure for efficient nitrate–ammonia conversion. Energy & Environmental Science
2021,
14 (9), 4989-4997.

He, W.; Zhang, J.; Dieckhöfer, S.; Varhade, S.; Brix, A. C.; Lielpetere, A.; Seisel, S.; Junqueira, J. R.; Schuhmann, W., Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia. Nature Communications
2022,
13 (1), 1129.
Understanding Performance Limitations in Water Splitting Photoelectrodes at the Nanoscale
Authors: Wolz Lukas , Balakrishnan Harishankar , Zhou Guanda , Sharp Ian D. , Hartschuh Achim , Eichhorn Johanna
Published: February 2024

Photoelectrochemical (PEC) water splitting is a promising route for efficient conversion of solar energy into chemical fuels. In this context, economically viable photosystems are often based of semiconductor thin films which are polycrystalline or nanostructured with highly complex architectures e.g. with boundaries between differently orientated grains, different crystal facet orientations, as well as locally varying composition or phase. These nano- to micrometer properties often control critical processes, such as efficiency and stability, of the macroscale system. To understand the impact of nanoscale properties on the macroscopic performance, we aim at resolving local structural, chemical, and optoelectronic heterogeneities and at elucidating their effect on light-driven processes.

In this work, we use a correlative approach to elucidate the nanoscale properties of polycrystalline BiVO4 thin films – a promising material for solar water splitting. Mapping of the local charge transport properties by photoconductive atomic force microscopy (pc-AFM) reveals the tolerance to grain boundaries.[1] Interestingly, scanning nearfield infrared microscopy shows strongly varying absorption from VO4 stretching modes between grains and at grain boundaries which correlate with the heterogeneities in the local photoconductivity across the polycrystalline thin films. Furthermore, local temperature-dependent current-voltage spectroscopy show that the low intrinsic bulk conductivity of BiVO4 limits the electron transport through the film, and that the transport mechanism can be attributed to space charge limited current (SCLC) in the presence of trap states.[1] Performing the same measurements in-situ in controlled gas-phase environment reveals the influence of chemical interactions of adsorbed oxygen and water on charge transport and interfacial charge transfer.[2] For BiVO4, we demonstrate that adsorbed oxygen acts as a surface trap state for electrons, which enhances the built-in potential and depletes the BiVO4 layer. Overall, combining insights from different nanoscale techniques generates a comprehensive picture of charge separation, transport, and transfer at the nanoscale. The gained nanoscale understanding of energy materials enables the rational design of durable and efficient solar fuel devices.

[1] Eichhorn et al., Nat. Commun. 9, 2597(2018).

[2] Eichhorn et al., ACS Appl. Mater. Interfaces, 10, 41, 35129 (2018).
Electrochemical Method for Detection and Quantification of Lead Particulate in Tap Water
Authors: Alvarez Noe T , Huseinov Artur , Dangel Gabrielle R.
Published: February 2024

Quantification of lead particulates requires laborious sample acidification and/or digestion in acidic environment, therefore lead quantification is limited to laboratories with trained personnel and expensive instrumentation. These technologies are not easily accessible to the public, and the large number of portable methods available to public today are characterized by their qualitative nature, and requirement of additional reagents. Unlike labor intense expensive instruments, electrochemical methods are inexpensive, fast and portable but they are blind to non-electroactive lead species or particulate forms of lead. They are limited to the detection of ionic or electroactive analytes. This talk will report an electrochemical method for the detection and quantification of lead contaminant in drinking waters that results from particulate forms of lead, mostly present as scales. We will present the fundamentals of membrane electrolysis for reagent-free sample preparation and detection of Pb2+. Also, we will present the characterization of real particulates/scales extracted from lead service lines from the Cincinnati area. We think this method will contribute to the development of on-site, quantitative methods of lead detection, and can assist to the research and understanding of drinking water contamination. Perhaps it could help to determine what triggers lead intermittent release to residential tap water. This work has the potential to address the lack of that instrumentation because it employs a robust technology based on anionic exchange membrane and controlled electrolysis for in-situ generation of nitric acid, that eliminates the need of external reagent or sample treatments. For its trace detection, it employs a well stablished Anodic Striping Voltammetry method.
Direct Electroreduction of Carbonate to Formate
Authors: Ma Hai-bin , Ibáñez Alé Enric , López Nuria , Yeo Boon Siang Jason
Published: February 2024

A cause of losses in energy and carbon conversion efficiencies during the electrochemical CO2 reduction reaction (eCO2RR) can be attributed to the formation of carbonates (CO3
2–), which is generally considered to be an electrochemically-inert species. Herein, we employ in-situ electrochemical Raman spectroscopy, liquid chromatography, nuclear magnetic resonance spectroscopy, 13C isotope-labelling and density functional theory (DFT) simulations to understand the role of carbonate species formed on copper catalysts during eCO2RR, and its ability to reduce to formate. Direct carbonate-to-formate conversion was confirmed by the the direct reduction of CuCO3, and by pulse reduction of N2-saturated K2CO3 electrolyte on Cu,. DFT simulations elucidated the nature of the active sites generating the Cu-CO3
2– species and revealed the mechanism for the pulse-enabled carbonate reduction to formate. Combining both experimental and computational results, we proposed that a dynamic carbonate intermediate was constantly formed on Cu during eCO2RR, that further evolves to formate between –0.4 to –1.2 VRHE on Cu. Control systems using Pb, Ag and Au electrodes were also studied.
Carbon and Energy Efficient Ethanol Electrosynthesis By Acidic CO2 Reduction
Authors: Shayesteh Ali , Li Feng , Alkayyali Tartela , Shirzadi Erfan , Arabyarmohammadi Fatemeh , Dorakhan Roham , O'Brien Colin P. , Gabardo Christine M. , Ozden Adnan , Zargartalebi Mohammad , Fan Lizhou , Papangelakis Panagiotis , Zhao Yong , Sargent Edward H. , Sinton David
Published: February 2024

The electrochemical CO2 reduction reaction (CO2RR) is one way of mitigating the rising levels of anthropogenic CO2 emissions. Most of the advancements in the CO2RR field have been implemented in basic or neutral electrolytes where a major fraction of the input CO2 converts to carbonate ions through reaction with OH– (Science 360, 783-787 (2018); Nat. Catal. 5, 564-570 (2022)). These approaches result in low carbon efficiency (the percentage of CO2 converted per total CO2 input), typically below 20% toward multicarbon products, resulting in severe energy and cost penalty (Nat. Sustain. 5, 563-573 (2022)).

Performing CO2RR in acidic conditions reduces reactant loss to carbonates. In this condition, the (bi)carbonate ion crossover/formation is countered by the high proton concentration in the electrolyte. However, the unshielded cathode surface favors the hydrogen evolution reaction (HER) over CO2RR due to the high availability of protons and the fast kinetics of the HER (Science 372, 1074-1078, (2021); Nat. Catal. 4, 654-662 (2021)).

Here, we have developed an interfacial cation matrix (ICM) to modulate the local microenvironment on the cathode surface. The ICM increases the local pH and electric field, promoting multicarbon production. Additionally, we have designed a Copper-Silver catalyst to tune the selectivity towards alcohol production. We improved the ethanol FE to 45% at 200 mA/cm2, which, to our knowledge, represents the highestethanol FE in membrane electrode assembly literature. The system maintains a high carbon efficiency (60%) resulting in a total energy cost of 263 GJ/tonne ethanol, which is the lowest value among current ethanol-producing CO2 electrolysers.
In Situ Investigation of Electrochemically Mediated Carbon Capture and Release Via Quinone Chemistry in Aqueous Media
Authors: Amini Kiana , Cochard Thomas , Jing Yan , Sosa Jordan D. , Xi Dawei , Alberts Maia , Gordon Roy G. , Aziz Michael J.
Published: February 2024

The development of devices capable of capturing and sequestering carbon dioxide emissions directly from air or at point sources is motivated by mitigating climate change. Electrochemically driven carbon capture and release at ambient temperature and pressure through the formation of complexes with organic redox active molecules [1,2] or via pH swing caused by proton-coupled electron transfer during molecular redox events [3,4] has shown promising results for carbon capture and release in terms of energy cost, scalability and safety compared to the state of the art amine scrubbing technologies [5].

Quinones are organic molecules containing an unsaturated six-member ring with two carbonyl groups. They exhibit two potential mechanisms of CO2 capture. (a) Upon electrochemical reduction, the carbonyl groups within quinones provide sites for nucleophilic addition of carbon dioxide which results in the formation of a quinone-CO2 adduct (CO2reversibly bound by quinones). (b) Depending on the pKa of the quinone and the local pH, the electrochemical reduction of the compound can be proton-coupled, creating hydroxide, which captures CO2 as carbonate or bicarbonate.

In this work, we introduce in situ electrochemical characterization and in situ fluorescence microscopy to separately quantify the two aforementioned contributions toward capture of CO2 at partial pressures ranging from 0.1 bar to 0.4 mbar. The non-invasive in situ analytical methods introduced in this work are used to distinguish, with sub-second time resolution, between the oxidized, reduced and adduct species by their electrochemical and fluorescence signatures. The results of this study permits us to understand the underlying simultaneous contributions of quinone-CO2 adduct path and the pH-swing path toward carbon capture and release and, additionally, introduces powerful non-invasive methods for gathering insights on similar systems.

1X. Li, X. Zhao, Y. Liu, T.A. Hatton, and Y. Liu, "Redox-tunable lewis bases for electrochemical carbon dioxide capture", Nature Energy
7, 1065 (2022).

2Y. Liu, H.Z. Ye, K.M. Diederichsen, T. Van Voorhis, and T.A. Hatton, "Electrochemically mediated carbon dioxide separation with quinone chemistry in salt-concentrated aqueous media", Nat Commun
11, 2278 (2020).

3S. Jin, M. Wu, Y. Jing, R.G. Gordon, and M.J. Aziz, "Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing", Nat Commun
13, 2140 (2022).

4S. Jin, M. Wu, R.G. Gordon, M.J. Aziz, and D.G. Kwabi, "pH swing cycle for CO2 capture electrochemically driven through proton-coupled electron transfer", Energy & Environmental Science
13, 3706 (2020).

5G.T. Rochelle, "Amine scrubbing for CO2 capture", Science
325, 1652.
Visualizing pH and Mass Transport at Hydrogen Evolving Electrodes with Fluorescence Lifetime Microscopy
Authors: Bleeker Jorrit , Vermaas David , Jager Wolter
Published: February 2024

The chemical industry needs electrochemical solutions to avoid large CO₂ emissions. However, many of these electrochemical processes suffer from poor mass transport around the catalyst. To optimize these technologies, we need to gain a better understanding of the local processes at the electrode. This could give us ideas of new catalyst and reactor designs to enhance mass transport.

The pH is a parameter that helps us to understand these processes. This is because the catalyst stability and selectivity of many reactions is strongly dependent on the local pH. You need a non-invasive technique to measure in operando spatial maps of pH. Optical techniques are a logical route for this.

Fluorescence Lifetime Imaging Microscopy (FLIM) is a technique that measures the fluorescence lifetime of a probe molecule. It is friendly to use, as it is self-referencing (i.e. you do not need to calibrate your system for every new measurement). Many electrochemical applications, like seawater electrolysis, CO2 reduction and alkaline water electrolysis, tend to work in alkaline conditions (pH >8). Unfortunately commercial FLIM probes are only available in neutral and mildly acidic pH (4 to 8), owing to their use in biological systems.

We have developed new fluorescence lifetime probes based on the 1-methyl-7-amino-quinolinium fluorophore molecules, that allow pH measurements in the range of pH 5.5-13. We have used the probes to visualise the local pH around a hydrogen evolving electrode and can show the boundary layer that forms close to the electrode and investigate how it is disturbed by gas bubbles at a rate of 3 fps and resolution of 4 μm.

Figure 1
Probing of Near-Surface Cations during the Oxygen Evolution Reaction (OER) Using Operando XAS
Authors: Deka Nipon , Mom Rik
Published: February 2024

Electrified solid-liquid interfaces are ubiquitous in technologies ranging from colloidal science to electrochemistry. Hence, an atomic-level characterization of the electrode-electrolyte interface is crucial for total control and optimization of the processes involved. While the electrode side of the interface has been quite extensively studied, the electrolyte side is comparatively poorly understood1. Specifically probing the near-surface electrolyte species during an electrochemical reaction is a major technical challenge in the field of catalysis and surface chemistry.

We have developed an interface-sensitive X-ray absorption spectroscopy (XAS) approach which allows us to directly probe the near-surface cations and anions of the electrolyte under applied potentials. In this approach, we employ a mesoporous electrocatalyst film coated on a 𝑆𝑖𝑁𝑥 X-ray window. These mesoporous films exhibit an extremely high electrode-electrolyte interface area, enabling us to specifically probe the behaviour of interfacial ions via their K-edge spectra. Using this approach, we have recently investigated the interaction of Na+ cations with IrOx during the oxygen evolution reaction (OER), which is a bottleneck in major electrochemical processes like green hydrogen production and CO2 reduction. The cations and anions of the electrolyte reportedly influence the OER activity of electrodes during OER2,3. We used operando Na K-edge XAS to directly probe the concentration and coordination environment of the near-surface Na+ cations. Simultaneously, operando O K-edge XAS monitored the interfacial water structure and the evolution of catalyst’s surface structure. Contrary to expectations, we discovered that the positively charged Na+ ions are drawn to the IrOx surface by more positive potentials only at alkaline pH. This finding cannot be explained by any of the electrolyte theories4 put up thus far, emphasizing the necessity of a detailed investigation of interfacial electrolyte structures.

References:

Arminio-Ravelo et al.
ChemPhysChem
20, (2019).

Tymoczko et al.
Catal. Today
244, (2015).

Ganassin et al.
Phys. Chem. Chem. Phys.
17, (2015).

Waegele et al.
J. Chem. Phys.
151, (2019).

Figure 1
An Electrochemical Cell for Operando Grazing-Incidence X-Ray Absorption Spectroscopic Studies of Low-Loaded Electrodes
Authors: Winzely Maximilian , Diercks Justus S. , Safonova Olga V. , Rüttimann Peter , Clark Adam Hugh , Leidinger Paul Maurice , Phadke Sumant , Nachtegaal Maarten , Schmidt Thomas J. , Herranz Juan
Published: February 2024

X-ray absorption spectroscopy (XAS) is a powerful technique that can provide element specific information on the local electronic and structural properties of newly developed electrocatalysts, especially when performed under operating conditions (i.e., operando). However, the large amounts of catalyst typically needed to achieve sufficiently high spectral quality and temporal resolution can result in working electrodes of several micrometers in thickness. This can in turn lead to an inhomogeneous potential distribution across the electrode, delamination and/or incomplete utilization of the catalyst layer, severe bubble formation and accumulation due to poor mass transport properties.[1, 2] In addition, the activity and selectivity of a catalyst are often measured in a different cell geometry (e.g., using rotating disk electrodes (RDEs)), leading to uncertainties in comparison with the results inferred from spectroscopic data.[3]

To tackle these problems we have developed a new spectroelectrochemical XAS flow cell that enables spectral acquisition in fluorescence mode using an X-ray beam incidence angle of ≤ 0.1° with regards to the working electrode’s substrate plane, i.e., in a so called grazing incidence (GI) configuration (see Figure 1). In this acquisition configuration we successfully tracked the formation of palladium hydride with a time resolution of 10 seconds per spectrum while using a Pd-loading as low as 50 µgPd∙cm-2. Moreover, the careful design of the working electrode flow field allows the study of faradaic processes (e.g., O2-reduction) under mass-transport controlled conditions entailing currents comparable to those attained in RDE measurements (≤ 10 mA∙cm−2). The combination of these features with an ion-conductive membrane to separate the working- and counter-electrode compartments additionally enables the detection of gaseous products (e.g., from CO2-electroreduction) by degassing them out of the electrolyte and analyzing them in time-resolved fashion by means of mass spectrometry.[4]

References

Diklić, N., et al., Potential Pitfalls in the Operando XAS Study of Oxygen Evolution Electrocatalysts. ACS Energy Letters, 2022. 7(5): p. 1735-1740.

Diercks, J.S., et al., Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements. Angew Chem Int Ed Engl, 2023: p. e202216633.

Diercks, J.S., et al., Interplay between Surface-Adsorbed CO and Bulk Pd Hydride under CO2-Electroreduction Conditions. ACS Catalysis, 2022: p. 10727-10741.

Khanipour, P., et al., Electrochemical Real-Time Mass Spectrometry (EC-RTMS): Monitoring Electrochemical Reaction Products in Real Time. Angew Chem Int Ed Engl, 2019. 58(22): p. 7273-7277

Figure 1
Operando x-Ray Absorption Spectroscopy Investigation of Secondary Metal Doping into Iron-Nitrogen-Carbon Catalysts for Oxygen Electroreduction
Authors: Luo Fang , Roy Aaron , Sougrati Moulay-Tahar , Khan Anastassiya , Cullen David A. , Wang Xingli , Primbs Mathias , Zitolo Andrea , Jaouen Frederic , Strasser Peter
Published: February 2024

Oxygen reduction reaction (ORR) plays a key role in the development of fuel cell technology, and great efforts have been made to reduce the amount of platinum, required to speed up this sluggish reaction, or, even more desirable, to use efficient electrocatalysts based on earth-abundant metals. To date, numerous single-atom catalysts in the form of metal-doped carbon-nitrogen materials (MNC) have proved to be a promising alternative to ORR Pt-based materials. [1-3]

In this study we employed advanced spectroscopic techniques, namely Mössbauer spectroscopy and operando X-ray absorption (XAS) spectroscopy, to understand the structural and electronic factors underlying an increase in the catalytic turn over frequency (TOF) of bimetallic FeSnNC and FeCoNC catalysts, relative to the parent FeNC materials. In particular, 57Fe Mössbauer spectroscopy identified a larger ratio of D1/D2 species in both bimetallic catalysts, supporting a larger ratio of Fe(III)-Nx/Fe(II)-Nx sites. The combination of extended X-ray absorption fine structure (EXAFS) modeling, and the analysis of operando X-ray absorption near-edge spectroscopy (XANES) spectra revealed a disordered carbon structure around FeNx active sites, and variations in the iron oxidation state that can be linked to the enhanced intrinsic catalytic reactivity (TOF). This talk is therefore intended to draw attention to the potential of the XAS technique, especially when applied to in-situ/operando studies in the field of electrocatalysis.

References

F. Luo, A. Roy, L. Silvioli, D.A. Cullen, A. Zitolo, M.T. Sougrati, I.C. Oguz, T. Mineva, D. Teschner, S. Wagner, J. Wen, F. Dionigi, U.I. Kramm, J. Rossmeisl, F. Jaouen and P. Strasser. P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction. Nature Materials
2020, 19, 1215-1223

A. Zitolo, N. Ranjbar, T. Mineva, J. Li, Q. Jia, S. Stamatin, G.F. Harrington, S.M. Lyth, P. Krtil, S. Mukerjee, E. Fonda, F. Jaouen. Identification of catalytic sites in cobalt-nitrogen-carbon materials for the oxygen reduction reaction. Nature Communications
2017, 8(1), 957

A. Zitolo, V. Goellner, V. Armel, M. T. Sougrati, T. Mineva, L. Stievano, E. Fonda, F. Jaouen. Identification of catalytic sites for oxygen reduction in iron and nitrogen doped graphene materials. Nature Materials
2015, 14, 937-942
Hydrous Iridium Oxide Thin Films: Revealing the Structure of a Highly Active Model Catalyst By in-Situ Ir L
3-Edge XANES and EXAFS
Authors: van der Merwe Marianne , Lee Yonyhyuk , Garcia-Diez Raul , Wibowo Enggar , Kokumai Tathiana , Efimenko Anna , Arce Mauricio D. , Jiménez Catalina Elena , Steigert Alexander , Schuck Götz , Sear Michael J. , Clark Pip , Favaro Marco , Starr David , Scheurer Christoph , Bär Marcus
Published: February 2024

Currently, only iridium oxide shows favourable activity and stability under the harsh oxygen evolution reaction (OER) conditions for application in proton exchange membrane water electrolysis (PEM-WE) [1-3]. There is a well established inverse relationship between OER activity and stability of iridium oxide-based OER catalysts given its degree of crystallinity and hydration [4-6]. Crystalline, anhydrous iridium oxides are more stable but have diminished OER activity compared to amorphous, hydrous iridium oxides, which are more active. Different OER mechanisms have been theorized to occur on these materials, explaining their difference in performance [6]. Several spectroscopic investigations have been performed to explore the properties of such different iridium oxides, in particular to identify the chemical and electronic state of their active sites. However, a consensus regarding the active site structure and OER mechanism has yet to be reached [7-10].

Using scanning electron microscopy, x-ray photoelectron spectroscopy, and combining in-situ Ir L
3-edge x-ray absorption spectroscopy with density functional theory (DFT) calculations and ab initio thermodynamics, we have investigated in-situ electrochemically grown porous hydrous iridium oxide thin films (HIROF) as a model system to examine the chemical and electronic structure of the highly active, hydrous iridium oxide species. In-situ extended x-ray absorption fine structure(EXAFS) results show that HIROF grows preferentially in a form most often associated with the OER catalytically active site of hydrous iridium oxides. Calculations over different possible structures allowed us to identify a unique structural group with enhanced hydrogenation that best fits the EXAFS data. In-situ x-ray absorption near edge structure (XANES) results reveal a lower onset potential for the redox behaviour of HIROF compared to rutile IrO2. Based on this study, we propose a new structural model explaining the high activity and poorer stability of hydrous iridium oxides compared to crystalline IrO2.

References: [1] A. Buttler and H. Spliethoff, Renew. Sustain. Energy Rev., 2018, 82, pp. 2440-2454. [2] Schlögl, ChemSusChem, 2010, 3, pp. 209-222. [3] M. Schalenbach, J. Electrochem. Soc., 2016, 163, pp. F3197-P3208. [4] S. Cherevko, Electrochem. Commun., 2014, 48, pp. 81-85. [5] S. Cherevko, J. Electroanal. Chem., 2016(1), 773, pp 69-78. [6] S. Cherevko, J. Electroanal. Chem., 2016(2), 774, pp 102-110. [7] V. Pfeifer. Surf. Interface Anal., 2016, 48, pp. 261-273. [8] A. Minguzzi, Chem. Sci., 2014, 5, pp- 3591-3597. [9] A.H. Reksten, Phys. Chem. Chem. Phys., 2020, 22, pp. 18868-18881. [10] J.J. Veslasco-Vélez, J. Am. Chem. Soc., 2021, 143, pp. 12524-12534.
(Digital Presentation) Electrochemical Hydrogen Production and Charge Storage Mechanisms on Mxenes Via in-Situ/Operando Raman Spectroelectrochemistry
Authors: Johnson Denis , Yoo Ray , Djire Abdoulaye
Published: February 2024

The production of hydrogen fuel from water splitting through the hydrogen evolution reaction (HER) has been investigated for more than a century; yet, there exists no commercial water splitting device because of the lack of an efficient and cost-effective electrocatalyst. This scientific gap can be filled by the new class of two-dimensional carbides and nitrides, known as MXenes, if their mechanisms of electrocatalysis can be understood. Herein, we report on the electrocatalytic properties of MXenes and elucidate their mechanisms of electrocatalysis and charge storage. More specifically, we report on the detailed mechanisms of HER electrocatalysis and charge storage on the benchmark Ti3C2 carbide MXene in acidic (HCl) and neutral (Na2SO4) electrolytes using an in-situ/operando Raman spectroelectrochemical approach. This approach allows us to monitor, in real time, the structural behavior of the materials under operating conditions. The correlation between the Raman shifts and the current density provides insights into the mechanism of HER. In acidic electrolyte, we found that the HER mechanism proceeds through a surface protonation mechanism due to termination group changes, whereas neutral electrolyte HER undergoes an overcharging mechanism prior to splitting water to form hydrogen gas. For capacitive charge storage, we found that acidic electrolytes allow for pseudocapacitive behavior to take place in a similar surface protonation mechanism as for HER. In neutral electrolytes, the charge storage mechanism follows a purely double layer capacitance mechanism with sodium ions adsorbing and desorbing from the surface. The new knowledge from this work can be applied to a broad class of materials and systems to advance the field of energy conversion and storage.
Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy
Authors: Ikezawa Atsunori , Kida Juri , Shimizu Shugo , Arai Hajime
Published: February 2024

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).

CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.

References

[1] D. Bayer et al., Int. J. Hydrog. Energy, 35, 12660 (2010).

[2] S. Möller et al., Angew. Chem. Int. Ed.,
59, 1585 (2020).

[3] E. L. Clark et al., Anal. Chem.,
87, 8013 (2015).

Figure 1
The Influence of the Interfacial pH on the Electrochemical CO2 Reduction Towards Formate on Cu Electrodes
Authors: Katsoukis Georgios , Heida Hilbert C , Gutgesell Merlin , Mul Guido
Published: February 2024

The electrochemical reduction of CO2 (CO2RR) using renewable electricity is considered a promising way to replace fossil fuels as feedstock. In aqueous media, the activity and selectivity for the CO2RR is strongly influenced by electrolyte composition at the solid-electrolyte interface. Due to competing H+ reduction, the interfacial pH is strongly affected by the applied potential which in turn determines the balance between CO2, HCO3
-, and CO3
2-. The Bicarbonate equilibrium and cation-hydroxide interactions are directly connected to the CO2RR and HER rate.[1]

To learn more about the impact of the electrolyte composition within the double layer on the CO2RR mechanism we deploy time-resolved (sub-second) FT-IR reflection-absorption spectro-electrochemistry at grazing angle using polarized light. This allows us to differentiate conversions at the electrode-electrolyte interface (i.e. CO2RR) from the diffuse double layer (i.e. pH effects). Herein, we elucidate the electrochemical CO2RR towards formate on polycrystalline Cu in aqueous bicarbonate electrolyte. We compare the rate of CH formation to the interfacial pH changes determined by the ratio between the intensity of the CO2, HCO3
-, and CO3
2- bands. We discuss how potential steps and sweeps relate to interfacial pH and CO2RR.

By applying a ‘pre’potential more positive from the open circuit potential (OCP: ca. +0.5 V vs. RHE) before stepping to -0.9 V vs. RHE, the interfacial pH decreases due to the oxidation of Cu. As a result, the rate of C-H formation is initially hindered for several seconds before setting off. Likewise, an applied ‘pre’potential more negative from the OCP results into poor C-H formation kinetics.

Reference:

[1] Liu, X.; Monteiro, M.C.O.; Koper, M. T. M. Phys. Chem. Chem. Phys. 2023, advance article.

Figure 1
(Invited) Neutrons as a Powerful Tool for Better Understanding Electrochemistry on Various Length and Time Scales
Authors: Gilles Ralph
Published: February 2024

Today, sophisticated methods are applied to gain a deeper understanding of processes in in-situ electrochemistry. There are few ways to study electrochemically relevant processes on different length and/or time scales without affecting the processes themselves. Probes that cover a sufficient volume of the sample non-destructively and are sensitive to the important charge carriers are in great demand. For such purposes, neutrons are an ideal candidate to perform this task because they have relatively high sensitivity to the light chemical elements, can distinguish neighboring elements of the periodic table, have a large beam cross-section, and possess high penetration depth for many types of materials.

Therefore, many open questions are addressed to unique neutron techniques tailored to solve the open problems. This article gives an overview of some examples to show the advantages of using neutrons for special questions on different length and time scales [1]. For surface investigations of electrodes, the neutron depth profiling method (NDP) is suitable for characterizing the Li distribution up to the nano range [2]. Neutron diffraction is a powerful tool to better understand cylindrical cells at the atomic level, e.g. during the intercalation process [3]. Another strong field of neutrons is the monitoring of the wetting process during the electrolyte filling of prismatic hard case cells on the macroscopic length scale using the neutron imaging technique [4].

References:

[1] R. Gilles, How neutrons facilitate research into gas turbines and batteries from development to engineering applications, Journal of Surface Investigations: X-Ray, Synchrotron and Neutron Techniques, (2020), 14, Suppl. 1, S69.

[2] M. Trunk, L. Werner, R. Gernhäuser, B. Märkisch, Z. Revay, H. A. Gasteiger, M. Wetjen, R. Gilles, Materials science application of neutron depth profiling at the Prompt Gamma-ray Activation Analysis (PGAA) of Heinz Maier-Leibnitz Zentrum, Materials Characterization (2018), 146, 127.

[3] J. Wilhelm, S. Seidlmayer, S. Erhard, M. Hofmann, R. Gilles, A. Jossen, In situ neutron diffraction study of lithium gradients in graphite anodes during discharge and relaxation, Journal of the Electrochemical Society (2018), 165(9), A1846.

[4] F.J. Günter, J. Keilhofer, C. Rauch, S. Rössler, M. Schulz, W. Braunwarth, R. Gilles, R. Daub,G. Reinhart, Influence of pressure and temperature on the electrolyte filling of lithium-ion cells: Experiment, model, method, Journal of Power Sources (2022), 517, 230668.
Designing a Novel Setup for High-Throughput Investigations of Electrochemical Reactions in Real Time
Authors: Cuomo Angelina , Nikolaienko Pavlo , Mayrhofer Karl J. J.
Published: February 2024

With the great interest in new electrochemical processes, fast screening of various reaction parameters is highly desirable. For this purpose, differential electrochemical mass spectrometry (DEMS) and membrane-inlet mass spectrometry (MIMS) have been established to enable real-time monitoring of volatile compounds. However, the analysis of non-volatile compounds is commonly limited by the temporal resolution of traditional quantification methods such as NMR, GC-MS, or LC-MS. While ambient ionization mass spectrometry (AIMS) generally enables time-resolved monitoring of non-volatile compounds, electrolyte salts can lead to ionization suppression. The latter can decrease the sensitivity of product detection and the reliability of quantitative data. Therefore, a suitable reaction setup and thorough investigations are needed when utilizing AIMS. Nonetheless, in recent efforts, an electrochemical flow cell was coupled with such a technique to provide a method for on-line monitoring of non-voltile reaction products in aqueous electrolytes. To keep up with the increasing interest in electrosynthesis in organic media, we now present a new setup that is also applicable to non-aqueous media. It pairs a novel and versatile electrochemical cell with an AIMS and DEMS for highly sensitive detection of reaction products. Moreover, various reaction parameters such as electrode material, electrolyte, and temperature can be investigated in high-throughput.

Key words: Electrocatalysis, Electrosynthesis, Real-time, On-line monitoring, High-throughput
Synchrotron Capabilities in a Laboratory Setting: In Situ X-Ray Absorption Spectroscopy of Disordered Vanadium Ferrite Electrodes for Lithium-Ion Batteries
Authors: DeBlock Ryan H. , Ford Hunter O. , Chervin Christopher N. , Rolison Debra R. , Johannes Michelle D. , Long Jeffrey W.
Published: February 2024

X-ray absorption spectroscopy (XAS) provides important information on metal oxidation state and

element-specific coordination, but data collection has historically required the energy specificity

and brilliance of a synchrotron facility. Recent developments in detectors and optics are now

bringing XAS capabilities to the laboratory setting through multiple commercially available

instruments. At the U.S. Naval Research Laboratory, we use laboratory-based XAS to explore the

local electronic and atomic structure of a class of disordered vanadium ferrite (VFe2Ox) aerogels

that exhibit promising performance for electrochemical energy-storage applications such as

rechargeable lithium-ion batteries.1,2 These materials are synthesized by an epoxide-promoted sol–

gel reaction of iron chloride and vanadium isopropoxide, with the resulting fluid-filled gels

rendered as high surface area aerogels via supercritical-CO2 drying. During the initial sol–gel

synthesis, electroinactive metals such as aluminum, zinc, and zirconium may also be substituted

for vanadium and iron to alter the local electronic environment and corresponding electrochemical

performance of VFe2Ox. Heat treatment of as-dried VFe2Ox aerogels under either O2-containing

or inert atmosphere yields disordered or nanocrystalline variants, respectively. The resulting series

of native and substituted VFe2Ox materials are evaluated as powder-composite cathodes versus

lithium metal in coin cells with conventional nonaqueous lithium-ion electrolyte. We correlate

such critical battery-performance parameters as total specific capacity, high-rate capability, and

cycle life as a function of VFe2Ox composition and its degree of structural order/disorder, as

measured with in-situ XANES and EXAFS. In parallel with experimental observations,

calculations on VFe2Ox reveal that V incorporates into the defective spinel structure at tetrahedral

sites and that both disorder induced by vacancies and Fe/V tetrahedral occupation lowers the

overall energy and opens an electronic energy gap that establishes the redox sequence during

lithiation.

1. C. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T.

Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison,

and J. W. Long, J. Mater. Chem. A 3, 12059 (2015).

2. C. N. Chervin, R. H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison,

and J. W. Long, RSC Adv. 11, 14495 (2021).