bluuebunny/crossref_metadata_2025 huggingface dataset:
Hole Extraction Beyond the Depletion Layer in Ge-Doped Hematite Photoanode
Authors: Leite Edson Roberto , Rodrigues Murillo Henrique De H.M. , Junior Joao
Published: February 2024

As extensively discussed in the literature, photoelectrochemistry water splitting has enormous potential for the generation of green hydrogen. However, to obtain an efficient and economically viable photoelectrochemistry cell, it is necessary to use efficient semiconductor materials from the photogenerated charge separation point of view. In n-type semiconductors, based on transition metal oxides, where the diffusion length (Lp) is small compared to the absorption depth (α-1), i.e., αLp<< 1, the charge separation process will occur in the depletion layer region. Since this layer is typically tens of nanometers in size, only a fraction of the material exposed to light will contribute to the water photo-oxidation process, thus drastically restricting the efficiency of these semiconductor oxides. Hematite (α-Fe2O3) is an n-type semiconductor oxide widely explored as a photoanode for water photo-oxidation and is known to be a material dominated by the charge separation process in the depletion layer, following the Gartner-Butler model. In this way, we will only have photocurrent in Vappl>Vfb (Vappl is the applied potential, and Vfb is the flat band potential). Here we will explore the possibility of extracting holes at potentials smaller than Vfb in Ge-doped hematite photoanodes through rigorous measurements of Vfb and absorbed photon-to-current conversion efficiency (APCE) as a function of Vappl. We determined Vfb based on the Gartner–Butler analysis in the presence of a sacrificial reagent (H2O2) under different wavelength excitation and observed a dependence of the Vfb with the wavelength. The APCE measurements as a function of Vappl-Vfb clearly show the existence of photocurrent at potentials below Vfb, strongly suggesting that we are extracting holes even before the formation of the depletion layer (before the band bending). We estimate that the holes arrive from a region approximately 3nm close to the electrolyte-semiconductor interface. This phenomenon was only observed for Ge-doped hematite and not for pristine hematite.
Interface and Structural Engineering of Cr Doped Zinc Oxide/Graphene Photoanode with Enhanced Photoelectrochemical Water Splitting
Authors: Tamboli Mohaseen , Park Hyeonwook , Park Chinho
Published: February 2024

The low-cost hydrogen (H2) generation from solar energy is one of the attractive and promising methods for clean and sustainable energy. It is challenging to boost global, renewable H2 energy mission. Until now, no catalytic system has been realized with viable efficiency and stability with reasonable manufacturing cost. Herein, we demonstrate a facile synthesis of chromium doped zinc oxide/graphene (Cr-doped ZnO@Graphene) as multicomponent photoanode using simple, inexpensive hydrothermal method. We investigated that graphene layer beneath ZnO can act in a different way, while salient features of controllable graphene concentration and appropriate Cr doping clearly displayed profound influence on photoelectrochemical water splitting reaction which is due to promoted electron transfer at interface. The detailed computational study was done by density functional theory (DFT) calculations. A photoelectrochemical cell was assembled with optimized photoanode displayed 4-fold increase in photocurrent density as compared to pristine ZnO. The improved PEC performance is attributed to the synergistic effects, where the presence of Cr dopant improves the charge carrier density and enhanced electronic conductivity, and graphene has increased the carrier transport and collection efficiency. Overall, this study provides valuable insights into the development of (Cr-doped ZnO@Graphene) as a highly efficient and stable photoelectrode for practical applications in solar water splitting and renewable energy conversion.
(Invited) Computational and Experimental Studies of Solar Water Splitting Technologies
Authors: Ogitsu Tadashi
Published: February 2024

Solar water splitting technologies are attractive in that intermittent solar energy is directly converted to hydrogen as economically scalable energy storage. In this presentation, we will overview various types of solar water splitting such as III-V, chalcopyrite, and nano particle based z-scheme where trade offs unique to each technologies will be discussed. While remedies will be also unique to the technology, there are some common factors in the approaches. These differences and commonality will discussed based on our own experiences in the past 12 years. Part of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Integrated Capture and Electrochemical Conversion of CO2 into CO
Authors: Xiao Yurou Celine , Gabardo Christine M. , Liu Shijie , Lee Geonhui , Zhao Yong , O'Brien Colin P. , Miao Rui Kai , Xu Yi , Edwards Jonathan P. , Fan Mengyang , Huang Jianan Erick , Li Jun , Papangelakis Panagiotis , Alkayyali Tartela , Sedighian Rasouli Armin , Zhang Jinqiang , Sargent Edward H. , Sinton David
Published: February 2024

The capture and electrochemical conversion of CO2, powered by renewable electricity, is an attractive method of sustainably producing valuable chemicals and fuels (e.g. carbon monoxide (CO)), reducing atmospheric CO2, and storing intermittent renewable energy. Integrated capture and conversion (reactive capture) of CO2 presents a CO2-to-CO electrolysis pathway that eliminates most of the upstream capital and energy costs by releasing CO2 directly inside the electrolyzer using an internal pH-swing. The reactive capture system readily allows for the collection of produced gas products via phase separation, thus minimizing downstream separation costs.

Industrial-scale integration of reactive capture systems with upgrading processes require a pure and consistent product stream. Previous studies using bicarbonate electrolytes have demonstrated high selectivity towards CO. However, the limited CO2 capture capacity of bicarbonate electrolytes dilute the cathode product gas stream with excess CO2. This mandates a secondary CO2 capture unit and increases the cost of downstream separation. Other studies using carbonate or carbamate electrolyte as the inlet feed did not simultaneously achieve high CO selectivity and long-term stability.

This study sought to improve the Faradaic efficiency (FE) toward CO in our carbonate electrolysis system by engineering a novel membrane electrode assembly structure. We designed a composite CO2 diffusion layer (CDL) between the cathode and the membrane that attains high CO selectivity by simultaneously achieving high alkalinity and sufficient CO2 availability at the cathode. We determined that the thickness, wettability, and permeability of the CDL affected species transport and were important optimization parameters. Applying this strategy, we produced syngas, a mixture of CO and hydrogen (H2), with an industrial H2/CO ratio of 1.16 at 200 mA cm-2. This corresponded to a CO Faradaic efficiency (FE) of 46% and energy intensity of 52 GJ tsyngas-1. The syngas produced in this system was not diluted by CO2 and contained sufficient CO content to meet industrial standards. We further increased the FE towards CO by exploring different capture solutions and designing selective catalysts for energy efficient CO production. System parameters such as temperature and pressure effects were also investigated to improve the CO2 concentration at the cathode. This study illustrated the potential for the industrial implementation of an energy efficient and capital cost effective CO2-to-CO pathway via reactive capture.
Investigation of Aliovalent Substitution in the Solid Sodium Ion Electrolyte Na2ZrCl6
Authors: Guo Hao , Bianchini Matteo
Published: February 2024

The research community is working hard on the development of solid-state batteries (SSB) as an alternative to commercialized lithium-ion batteries, due to their higher energy density and enhanced safety. One of the core research areas of SSBs is the solid-state electrolyte (SE), which should fit the demand for high ionic conductivity and electrochemical stability at the same time. Recently, halide SEs have emerged because they are mechanochemical processable, similar to sulfidic SEs, but halide SEs exhibit excellent electrochemical oxidation stability compared to sulfidic SEs [1,2].

However, the relatively low ionic conductivity at room temperature still hinders the application of halide SE in SSBs. Aliovalent substitution is a very widely used method to improve the ionic conductivity of SEs [3,4]. We are also motivated by the application of earth-abundance elements to reduce raw material costs.

Recently, significant focus has been gained by Zr-based compounds such as Na2ZrCl6. We investigate here such compounds, focusing on elemental substitutions to gain increased ionic conductivity and on gaining insight into the influence of synthesis on SE crystal structure and electrochemical properties.

In our work, different amounts of elemental substitutions are investigated, and the related materials are synthesized at different temperatures. In particular, the influence of a series of subsequent heating temperatures on the structure of the binary system is studied through XRD diffraction analysis and further refinement. The Ionic diffusion paths are also estimated through the band valence sum approach, in order to validate the electrochemical impedance spectroscopy (EIS) results.

In summary, we report our early results on the development of novel solid electrolytes for Na-based solid-state batteries.

REFERENCES

[1] Kwak, H.; Lyoo, J.; Park, J.; Han, Y.; Asakura, R.; Remhof, A.; Battaglia, C.; Kim, H.; Hong, S.-T.; Jung, Y. S. Na2ZrCl6 enabling highly stable 3 V all-solid-state Na-ion batteries. Energy Storage Mater. 2021, 37, 47−54.

[2] Tong Zhao, Alexander N. Sobolev, Roman Schlem, Bianca Helm, Marvin A. Kraft and Wolfgang G. Zeier. Synthesis-Controlled Cation Solubility in Solid Sodium Ion Conductors Na2+xZr1
-
xInxCl6.
ACS Appl. Energy Mater. 2023, XXXX, XXX, XXX-XXX.

[3] Schlem, R.; Banik, A.; Eckardt, M.; Zobel, M.; Zeier, W. G. Na3-xEr1-xZrxCl6-A Halide-Based Fast Sodium-Ion Conductor with Vacancy-Driven Ionic Transport. ACS Appl. Energy Mater. 2020, 3, 10164−10173.

[4] Wu, E. A.; Banerjee, S.; Tang, H.; Richardson, P. M.; Doux, J.M.; Qi, J.; Zhu, Z.; Grenier, A.;Li, Y.; Zhao, E.; Deysher, G.; Sebti, E.;Nguyen, H.; Stephens, R.; Verbist, G.; Chapman, K. W.; Clement, R.J.; Banerjee, A.; Meng, Y. S.; Ong, S. P. A stable cathode-solid electrolyte composite for high-voltage, long-cycle-life solid-state sodium-ion batteries. Nat. Commun. 2021, 12, 1256.
Binderless Sheet-Type Oxide-Sulfide Composite Solid Electrolyte for All-Solid-State Batteries
Authors: Kim A-yeon , Jung Hun-Gi , Shin Hyeon-Ji , Kim Jun tae
Published: February 2024

Lithium-ion batteries have been used as energy sources not only for small electronic devices but also for high-capacity and high-energy-density applications such as electric vehicles. However, the use of flammable organic liquid electrolytes in lithium-ion batteries has raised safety concerns in various applications. Therefore, solid-state batteries using flame-retardant inorganic materials are considered a more reasonable direction for future energy sources due to their high safety and high energy density. Solid electrolytes(SEs) are divided into oxide-based, sulfide-based, and polymer-based. Each solid electrolyte has its own advantages and disadvantages. Oxide-based solid electrolytes (e.g., Li7La3Zr2O12 (LLZO), Li3xLa2/3-xTiO3 (LLTO), Li1.3Al0.3Ti1.7(PO4)3 (LATP)) are air-stable and exhibit excellent electrochemical properties over a wide potential range. However, their high interfacial resistance may limit their practical application as batteries. Sulfide-based solid electrolytes (e.g., Li6PS5X (X=Cl, Br, I), Li10GeP2S12, (100-x)Li2S-xP2S5)) have high ionic conductivity, ductile properties, low interfacial resistance, and good room temperature workability. However, they are vulnerable to atmospheric instability, which can produce toxic gases such as H2S, and are relatively electrochemically unstable with Li metal. Polymer-based solid electrolytes, such as those made from polymers like PEO, PVDF, PAN, etc. that are compounded with other solid electrolytes (oxides, sulfides, etc.), offer the advantage of being able to form solid electrolyte membranes over large areas. But they have low ionic conductivity and weak mechanical properties of the polymer itself, limiting their practical application.

To apply solid-state batteries to practical high-energy density energy storage devices such as electric vehicles, high ion conductivity, electrochemical stability, high mechanical properties, and large area formation of the electrolyte layer are essential. Solid electrolytes are mainly formed in powder form, and without a polymer binder, it is limited to apply as a film for large-capacity storage devices. Here, we fabricated a freestanding sheet-type Al-LLZO oxide-based solid electrolyte that forms a 3D network without a polymer material using an electrospinning method. In addition, we prepared a oxide-sulfide composite solid electrolyte membrane by impregnating LPSCl sulfide-based solid electrolyte into the Al-LLZO solid electrolyte sheet. As a result, This process removed the polymer and improved both the ionic conductivity and mechanical properties. Furthermore, it was possible to achieve both large-area and film characteristics without the need for a polymer.
Development of Moisture Absorbent Ceramic-Coated Separators for Advanced Lithium-Ion Batteries
Authors: Choi Sinho , KIM Tae-Hee
Published: February 2024

In the present human life, various electric devices and machines are worked by lithium-ion batteries (LIBs). The batteries have still remained challenges such as, the low cycling stability due to side reactions during charge-discharge cycling and the weak thermal stability at high temperatures. Accordingly, research on improving resistance to high temperatures and impregnability by coating ceramic particles and polymer binders on the surface of the separator is being conducted. The ceramic coating separator is manufactured by connecting small-sized inorganic particles to each other using a small amount of binder. The inorganic particles have high hydrophilicity and high specific surface area, so the ceramic separator has excellent wettability to the electrolyte. As a ceramic coating, alumina is currently commercialized, and a slurry is prepared by mixing a binder, etc., and then coated on a separator and then dried. LG Energy Solutions has commercialized a ceramic composite separator called SRS (Safety-reinforcing separator) and is applying it to batteries. By introducing a ceramic layer on the surface of a polyolefin-based separator, the heat resistance and mechanical strength of the separator have been greatly improved, and it has been widely used in high-capacity and large-sized batteries. when the temperature of the LIBs rises and the separator shrinks or ruptures, a large amount of lithium ions may move, making control difficult and creating a risk of explosion. Therefore, shutdown occurs, but a separator with good shape retention at high temperature is required. Accordingly, research on improving resistance to high temperatures by coating ceramic particles and a polymer binder on the surface of the separator is being conducted. In this work, Ceramic-coated separator membrane film was fabricated using aluminum fluoride (AlF3) materials for a powerful moisture (H2O) scavenger. Accordingly, research on improving high temperature resistance and impregnation property by coating ceramic particles and a polymer binder on the surface of the separator is in progress. First of all, a-AlF₃ nanorods with an average length of 1.882 μm and a diameter of 320 nm were synthesized under low supersaturation conditions. Then, PVdF-HFP [Poly(vinylidene fluoride-co-hexafluoropropylene)]-acetone solution was mixed and coated on a polypropylene membrane. The AlF₃-coated separator exhibited thermal shrinkage of 4%, 8%, and 18% at 130, 140, and 150°C, respectively, confirming that thermal stability was improved. In addition, as a result of the impregnation test, it was confirmed that the impregnation property of the coated separator was improved compared to the existing polypropylene separator. In addition, it was confirmed that the full cell manufactured using the a-AlF₃-coated membrane film has improved cycle stability and high-speed, high-capacity compared to the full cell manufactured using the existing non-coated separator.
Ceramic Composite Gel Polymer Electrolyte for Aqueous Zinc-Ion Battery
Authors: You Seungmin , Kang Chaeeun , Park Jooeun , Kim Jae-Kwang
Published: February 2024

As the most extreme application of electrical energy storage devices, lithium-ion batteries (LIBs) not only have the high energy density, but also show long charge/discharge life cycles. Nevertheless, some inherent issues hinder its widespread application, such as the safety problems, lithium metal extrusion, dendrite growth, and the high cost, together with the limited resources of lithium metal. As one of the next-generation batteries, zinc-ion battery (ZIB) is a promising candidate to solve the above problems, due to their high theoretical capacity, low cost, high abundance, low potential, high energy density, and intrinsic safety. Three-types electrolytes, liquid-state, solid-state, and gel-state, are included in ZIBs. The aqueous ZIBs with liquid-state electrolytes are usually considered as ultra-intrinsic batteries. However, various side reactions of dendrite growth, oxygen evolution reaction, hydrogen evolution reaction, and metal Zn corrosion deteriorate the electrochemical reaction of ZIB.

Herein, ceramic composite gel polymer electrolytes preparing by electrospinning process were applied to improve the electrochemical properties of ZIB. The gel polymer electrolytes containing amounts of aqueous liquid electrolytes have the activity of water, which can extend the electrochemical stability window and provide good ﬂexibility and H+ insertion/extraction during charge/discharge process for high capacity and good cyclic stability.
Modelling Ca2+ Mobility and Dynamics in Solvent-Free Molten Salt Electrolytes for Calcium Batteries
Authors: Cruz Carolina , Johansson Patrik
Published: February 2024

Multivalent elements based batteries using earth-abundant minerals is a route with promises, not only from a performance but also from a supply and cost point of view; this is not the last true for calcium (Ca) batteries since Ca is the fifth most abundant element in the Earth's crust [1,2,3]. There is, however, no functional electrolyte available yet for Ca batteries, calling for early modelling to be made to map the influence of different Ca-salts and salt concentrations on electrolyte physicochemical properties such as density, viscosity, ionic conductivity, charge carrier dynamics and diffusivity [3, 4].

One particular route little trodden is molten salt electrolytes (MSEs), materials that consist of ions with different valences in direct contact with each other due to the complete absence of any solvent. In practice, MSEs are multicomponent salt mixtures with reduced melting points with respect to the ingoing components and furthermore they also expand the operating temperature range upwards as compared to conventional liquid electrolytes. Moreover, MSEs have high ionic conductivities due to their intrinsically high ionic content and ionic mobility. Additionally, MSEs exhibit wide electrochemical stability windows, non-flammability, and non-toxicity [5, 6].

We have investigated MSEs composed of Ca(FSI)2, LiFSI, NaFSI, and KFSI, by molecular dynamics (MD) simulations. Apart from the basic properties, we focus on the relative dynamical properties of the different cations in the MSEs in order to obtain a fundamental understanding of the systems’ behaviour, both globally and locally, but for natural reasons with special emphasis on the Ca2+ ions.

References

[1] M. E. Arroyo-de Dompablo, A. Ponrouch, P. Johansson, and M. R. Palacín, “Achievements, Challenges, and Prospects of Calcium Batteries,” Chem. Rev., 120, 6331–6357 (2020). doi: 10.1021/acs.chemrev.9b00339.

[2] D. Monti, A. Ponrouch, R. B. Araujo, F. Barde, P. Johansson, and M. R. Palacín, “Multivalent Batteries—Prospects for High Energy Density: Ca Batteries,” Front. Chem., 7 (2019). doi: 10.3389/fchem.2019.00079.

[3] I. D. Hosein, “The Promise of Calcium Batteries: Open Perspectives and Fair Comparisons,” ACS Energy Lett., 6, 1560–1565 (2021). doi: 10.1021/acsenergylett.1c00593.

[4] M. Shakourian-Fard, G. Kamath, S. M. Taimoory, and J. F. Trant, “Calcium-Ion Batteries: Identifying Ideal Electrolytes for Next-Generation Energy Storage Using Computational Analysis,” J. Phys. Chem. C, 123, 15885–15896 (2019). doi: 10.1021/acs.jpcc.9b01655.

[5] K. Wang et al., “Molten salt electrolytes for electrochemical capacitors with energy densities exceeding 50 Wh kg−1,” Energy Environ. Sci., 15, 5229–5239 (2022). doi: 10.1039/D2EE01969H.

[6] P. Masset and R. A. Guidotti, “Thermal activated (thermal) battery technology,” J. Power Sources, 164, 397– 414 (2007). doi: 10.1016/j.jpowsour.2006.10.080.
Improving Structural and Chemical Stability of O3-Type Sodium Layered Oxide Cathode Via Fluorination
Authors: Yu Tae-Yeon , Park Seong-Eun , Sun Yang-Kook
Published: February 2024

A spherical O3-type layered oxide cathode, composed of compactly‐packed nanosized primary particles, is synthesized by the coprecipitation method so that the high tap density of the cathode ensures increased volumetric energy density for energy storage applications. However, drastic volume changes in the deeply charged states contribute to structural degradation, by inducing mechanical stress and the eventual disintegration of the cathode particles by the formation of microcrack. The microcrack traversing the entire secondary particle compromise the mechanical integrity of the cathode and accelerate electrolyte infiltration into the particle interior, causing the subsequent degradation of the exposed internal surfaces. In this study, we suggested a promising fluorination strategy to extend the cycle life of the O3‐type Na[Ni0.5Mn0.5]O2 cathode by improving their mechanical integrity and protecting their surfaces against electrolyte attack. Fluorination not only inhibits the microcracking of cathode secondary particles but also suppresses surface degradation, i.e., the formation of an electrochemically inactive NiO-like rock salt phase and dissolution of transition metals into electrolyte solution.
Conduction/Densification Enhancement of Na1+X
Zr2Si
x
P3-X
O12 Nasicon Solid Electrolyte for Solid-State Na Batteries
Authors: Fung Kuan-Zong , Tsai Shu-Yi , Liu I-Chun
Published: February 2024

Due to the better safety feature, replacing organic liquid electrolyte with ceramic solid electrolytes (SE) may effectively suppress the fire incidents caused by conventional rechargeable batteries. Recently, solid-state batteries using Na+ ion conductors tend to receive much attention because the abundance of Na in earth’s crust. However, solid-state batteries (SSBs) have been suffered by the relatively high interface polarization between electrode and SE. For higher Na+ conductivity, Na1+x
Zr2Si
x
P3-x
O12 with NASICON (Na Super Ionic Conductor) structure is selected for this study. Although solid state reaction is adopted, it is believed the selection of precursors may be critical for better crystallization and densification of Na1+x
Zr2Si
x
P3-x
O12. For instance, adequate amount of Na2CO3 may be used as the Na source as well as flux for densification. Thus, the objectives of this study is to (1) to identify the role of precursors such as Na2CO3 for conduction/densification of NASICON, (2) to search the appropriate temperature for synthesis/crystallization of NASICON, (3) to investigate the factors, such as crystallinity/density, affecting the ionic conductivity. During the different stages of processing, the structural, microstructural and electrical properties of decomposed precursors and resultant NASICON will be examined using XRD, SEM and DC/AC impedance measurements.
Bridging Aqueous and Organic Electrolytes: Intercalation Mechanism of TiS2 in Sustainable Aqueous Li-Ion Batteries
Authors: Zhang Leiting , Kühling Franziska Maria , Mattsson Agnes-Matilda , Hou Xu , Zhang Chao , Brant William Robert , Edström Kristina , Berg Erik J.
Published: February 2024

Aqueous Li-ion batteries (ALiBs) are a promising alternative for large-scale grid storage owing to water's non-flammability, low cost, and ease of purification. However, the narrow electrochemical stability window (ESW) of water (1.23 V) significantly limits the energy density of ALiBs, compared to their non-aqueous counterpart. The use of a highly concentrated electrolyte, such as 21 mol kg-1 (molality, m) of LiTFSI in water, known as the “water-in-salt” (WiS) electrolyte, can widen the water ESW to ~3 V, but its high cost and low environmental sustainability hinder the commercialization of ALiBs. Therefore, we explored the feasibility of cycling layered TiS2 anodes in ALiBs containing dilute electrolytes (i.e. 2 m LiTFSI in water).

We obtained a reversible discharge capacity of ca. 80 mAh g-1 at a current density of 50 mA g-1. By employing three-electrode cycling with online electrochemical mass spectrometry, we identified potential-dependent gas evolution from the cell triggered by multiple chemical/electrochemical reactions, such as (1) solvent co-intercalation, (2) partial TiS2 exfoliation, and (3) TiS2-catalyzed water splitting in dilute aqueous electrolytes. We also identified a completely different potential profile of TiS2, when cycled in an aqueous electrolyte, with two distinct redox plateaus at 2.95 V and 2.88 V, followed by a sloping region until 2.3 V (all vs. Li+/Li0). Recall that in classic non-aqueous electrolytes, TiS2 shows a characteristic sloping profile centered at ca. 2.2 V, the peculiar potential profile suggests a different intercalation mechanism of TiS2 in aqueous electrolytes.

In this presentation, we will share our latest findings from complementary physicochemical and computational methods to tackle the complex interfacial reactivity between layered anodes and aqueous electrolytes. Operando synchrotron X-ray diffraction data revealed the reversible uptake-release of water molecules between TiS2 layers, which was also confirmed energetically favorable by theoretical modeling. By introducing triethyl phosphate (TEP) as a co-solvent, we successfully tuned the electrochemical intercalation behavior of TiS2 from purely Li-intercalation (as in non-aqueous systems, when using only TEP as the solvent) to hydrated-Li-intercalation (as in concentrated and dilute aqueous electrolytes, when using water/TEP mixtures as the solvent). These findings suggest that solvent co-intercalation can be a promising strategy for ALiBs. The general implication of these results on the electrode-electrolyte interface and interphase in aqueous batteries will be systematically discussed in the talk. Overall, our work provides new perspectives on developing sustainable energy storage technologies.

Figure 1
Unraveling the Synthesis of Positive Electrodes for Na-Ion Batteries by in Situ XRD
Authors: Xu Mingfeng , Laurier Jade , Akhtar Mainul , Bianchini Matteo
Published: February 2024

In situ diffraction studies can capture transient crystalline phases forming during chemical reactions. Whether the reaction is a chemical solid-state synthesis, or an electrochemical intercalation process within typical active compounds used as battery electrodes, proper sample environments allow nowadays to perform in situ diffraction experiments with high temporal and angular resolution even when using laboratory diffractometers. In both cases, the time-resolved nature of the experiments allows to obtain a greatly increased amount of information. For example, in the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase [1]. On the other hand, often stable compounds cannot be synthesized. To rationalize that, the competition between thermodynamics and kinetics occurring during the process need to be investigated in real time. Fully determining the reaction pathway is a key requirement to achieve the rational synthesis of target materials [2, 3]. In this presentation, recent unpublished examples will be reported from our work applying in situ XRD to understand the synthesis of cathode materials for Na-ion batteries. We focus on layered materials and on the relationship between P2 and P3 polymorphs in series of samples of the same composition NaxDyNizMn1-y-zO2 (where D is a substitutional element and Ni and Mn are in divalent and tetravalent oxidation state, respectively) and highlight the transformation of a phase into the other during calcination. Moreover, we provide electrochemical and morphologic characterizations of the target compounds, aiming to answer the question: does one or the other polymorph offer better performances? The charge compensation mechanism, involving Ni redox but also O redox, will be reported. Finally, the presentation will also briefly cover the investigation of novel solid-state synthesis routes for cathodes of the fluorophosphate Na3V2(PO4)2F3-xOx family.

References:

[1] M. Aykol et al., Science Advances, 2018, 4 (4), 148.

[2] Z. Jiang et al., Journal of Materials Chemistry C,
2017, 5 (23), 5709-5717.

[3] M. Bianchini, J. Wang et al., Nature Materials. 2020, 19 (10), 1088-1095.

Figure 1
(Invited) Accelerating Electrocatalysts’ Activity and Stability Assessments
Authors: Cherevko Serhiy , Jenewein Ken , Geuß Moritz
Published: February 2024

The standard approach to new electrocatalysts development and testing is prohibitively slow. Moreover, it fails to meet the complexity of real devices. As a rule, it consists of routinely repeated steps, including synthesis, physicochemical characterization, and electrochemical measurements. The latter is typically based on the application of rotating disk electrodes (RDE) as conductive solid support to carry electrocatalysts and bulk electrochemical cells with liquid electrolytes as the reaction media.

The current work will contain two main parts presenting our recent approaches to tackling the abovementioned limitations of the classical electrochemical test systems. As a representative example, oxygen evolution reaction (OER) electrocatalysis in electrolytes of different pH is taken. It will be shown that bearing in mind the intrinsic limitations of the aqueous mode systems (AMSs), significant acceleration of electrocatalysts’ activity and stability measurements can be achieved by using coupled techniques based on different scanning flow cells.1, 2 This approach is ideal for quick multidimensional parameter space screening. However, further tests in real systems are necessary after identifying promising candidates. It will be shown that also this step can be accelerated using model gas diffusion electrode (GDE)-based setups.3, 4 Moreover, qualitatively different information, e.g. electrocatalyst dissolution assessment, can be achieved using GDE setups coupled to external analytics like inductively coupled plasma mass spectrometry (on-line ICP-MS). While it will be shown that using two approaches, facile screening and real-device level proof tests, are feasible, limitations and challenges will also be discussed, together with further directions to develop these techniques.

References:

A. Kormányos, K. J. Jenewein and S. Cherevko, Trends in Chemistry, 4, 475 (2022).

K. J. Jenewein, G. D. Akkoc, A. Kormányos and S. Cherevko, Chem Catalysis, 2, 2778 (2022).

Y.-P. Ku, K. Ehelebe, A. Hutzler, M. Bierling, T. Böhm, A. Zitolo, M. Vorokhta, N. Bibent, F. D. Speck, D. Seeberger, I. Khalakhan, K. J. J. Mayrhofer, S. Thiele, F. Jaouen and S. Cherevko, Journal of the American Chemical Society, 144, 9753 (2022).

K. Ehelebe, J. Knoppel, M. Bierling, B. Mayerhofer, T. Bohm, N. Kulyk, S. Thiele, K. J. J. Mayrhofer and S. Cherevko, Angew Chem Int Ed Engl, 60, 8882 (2021).
(Invited) Developing Catalysts and Interfaces for Hydrogen Production By Water Electrolysis and Solar Photoelectrochemistry
Authors: Jaramillo Thomas F.
Published: February 2024

Hydrogen is one of the most important molecular commodities in the fuels and chemicals sectors. Developing new pathways to hydrogen production by means of renewable resources could play an important role in meeting global sustainability goals. This paper will focus on the design and development of catalysts and interfaces for hydrogen production. This includes catalysts for hydrogen evolution and oxygen evolution, as well as interfacing those materials within the context of devices for water electrolysis and solar photoelectrochemical (PEC) hydrogen producing systems.
(Invited) Solar Fuel Processing: Performance and Longevity Requirements and Trends
Authors: Haussener Sophia
Published: February 2024

I present the learnings from the Solar Fuels Database (SolarFuelsDB) and the review of the different solar fuels approaches [1] in terms of performance and longevity. The SolarFuelsDB is an open database for experimental demonstrations of solar to fuel devices (photoelectrochemical and solar thermochemical for water splitting and/or CO2 reduction) based on the FAIR principles. The database and the review aim to accelerate the development of such technologies. Utilizing this dataset and the review, I present a comprehensive review of photo-electrochemical and solar thermochemical devices, identify notable trends categorized by device taxonomy, architecture, and materials, and provide a second law analysis in order to identify potential of the various material systems and approaches.

References

[1] S. Haussener, Solar Energy, 10.1016/j.solener.2022.09.019, 2022.
(Invited) Crosscutting Materials Innovation for Transformational Chemical and Electrochemical Energy Conversion Technologies—Solid Oxide Cells
Authors: Njodzefon Jean-Claude , Sauter Ulrich , Weber Andre
Published: February 2024

The Solid Oxide Cell (SOC) primarily operated as Solid Oxide Fuel Cell (SOFC) converts the chemical energy of a fuel such as hydrogen directly into electricity with very high efficiencies. Reverse operation of the exact same SOCs—as Solid Oxide Electrolysis Cells (SOEC) converts electrical energy into chemical energy by using the electricity to split chemical molecules such as steam, carbon dioxide or mixtures of both into hydrogen, carbon monoxide or mixtures of both respectively.

The SOC is basically a gas-tight and oxide-ion conducting solid electrolyte, sandwiched between porous oxide ion – and electron-conducting electrode materials—the oxygen electrode and the fuel electrode where the electrochemical conversions occur.

Irrespective of operation mode, the choice of SOC materials and processing routes generally aim for maximum performance and lifetime at chosen conversion rate and efficiency at nominal operation. This is as much as the technology can intrinsically offer and by far not enough to guarantee either profitable production of electricity or chemicals hydrogen, carbon monoxide or both. Ultimately the materials and manufacturing costs of the cell, stack, module, and system play a key role in the involved invest. Generally, operation costs such as cost of natural gas or electricity as well as maintenance costs are much more significant in determining the profitability of the technology than the investment costs. These technology-independent factors can in turn orientate the technologist to optimize the cell for either for maximum efficiency or conversion rate capability.

In this talk we will discuss specific SOC materials such as doped zirconia, doped ceria, manganates, cobaltites, and titanates. Intrinsic limitations and advantages with respect to performance, durability and costs; how they are withstanding the test of time and the ever decreasing operation temperature from micro/nano structuration, infiltration and exsolution of electrocatalysts through switching of cell supports. We will give a perspective on the dependency of cell material choices based on technology use cases and boundary conditions

Figure 1
Process Intensification and Performance Assessment of Sputtered Gadolinium Doped Ceria (GDC) Barrier Layer in Large-Area Solid Oxide Fuel Cell Short Stack
Authors: Sami ur rehman Hafiz , Coppola Nunzia , Singh Arpana , Polverino Pierpaolo , Carapella Giovanni , Montinaro Dario , Martinelli Francesca , Granata Veronica , Galdi Alice , Maritato Luigi , Pianese Cesare , Braglia Luca , Torelli Piero , Aruta Carmela
Published: February 2024

In recent years, Gadolinium Doped Ceria (GDC) barrier layers have been reported to enhance the performance of Solid Oxide Fuel Cells (SOFCs)by reducing cathode/electrolyte interface diffusion and improving ionic conductivity. Prior investigations have demonstrated that GDC thin film sputtered at room-temperature yields substantial enhancements in Solid Oxide Fuel Cells (SOFCs).This enhancement is evidenced by a noteworthy increase in output current (+78%) and a considerable reduction in ohmic resistance (up to -42%), compared to conventionally screen-printed industrial SOFCs. To probe the intricate interplay between morphology and stoichiometry, which fundamentally determines the Ce3+/Ce4+ ratio governing both ionic and electronic conductivity, this study utilized quantitative X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) techniques. Results revealed that annealing parameters played a role in the number of available oxygen vacancies in the oxygen-reduction reaction (ORR), inducing different changes in the investigated samples. Non-destructive investigations utilizing Distribution of Relaxation Time (DRT) analysis were conducted on two short stacks with varying thickness, employing different sputtering Modalities. These studies revealed that thickness significantly influences the ultimate performance.
Systematic First-Principles Calculations of Ce3+-Dopant in Garnet-Type Oxide Phosphors
Authors: Mohd Razip Nora Izzati Binti Binti , Novita Mega , Ogasawara Kazuyoshi
Published: February 2024

A study of Ce3+-doped oxide phosphors was performed using first-principles calculations based on the relativistic DV-Xα method. In particular, we focused on the Ce3+-doped garnet-type oxides, which have potential applications in solid-state lighting and display devices. The electronic structure and optical properties of the phosphors were analyzed. The energy levels of the Ce3+ ions were affected by the coordination number and the crystal field strength of the surrounding oxygen ions. In addition, the crystal structure of the material had a significant impact on the energy levels of the Ce3+ ions, with different crystal structures leading to different energy levels.

The Ce3+ ion is substitutionally incorporated in the garnet lattice, and the 4f electron of Ce3+ plays an important role in the luminescence of the material. The emission wavelengths of the 5d-4f transition energy of Ce3+ can be tailored by varying the crystal structure and the composition. The 5d orbitals of Ce3+ are substantially affected by the crystal field splitting while the amplitude of crystal field splitting (εcfs) is caused by many parameters: coordination number, symmetry of Ce3+ site, and bond lengths between the Ce3+ ion and the oxygen ions (O2-). This study incorporated the following computational conditions: i) lattice relaxation, ii) the choice of the exchange-correlation potential, and iii) Slater’s transition state method. The effects of these conditions were analyzed. In addition, the correlations among physical properties and electronic structure parameters were also investigated in detail.

The first-principles calculation results were compared to the experimental data to validate the accuracy of the theoretical models, which showed a good agreement between the experimental and predicted values.
Theoretical Analysis of Anomalous Emission of Eu2+ in Crystals By First-Principles Calculation
Authors: Okamura Tatsunori , Ogasawara Kazuyoshi
Published: February 2024

The 5d-4f transition energies of lanthanides are very versatile, especially the 4f65d1-4f75d0 transition energy of Eu2+ has high luminescence efficiency and is used in various luminescent materials such as phosphors like SrxCa1-xAlSiN3: Eu2+, scintillators, and solid-state lasers, etc. However, there are materials that do not undergo pure 5d-4f transitions, showing the so-called anomalous luminescence instead. The anomalous luminescence is caused by the formation of excitons due to the overlap of the 5d level of Eu2+ with the conduction band and the transition of electrons from the conduction band to the 4f level, resulting in a shift to a lower energy than the general 5d-4f transition energy. A more detailed analysis of this phenomenon is important for the development of novel luminescent materials using Eu2+.

In this study, we aimed to theoretically analyze the anomalous luminescence based on first-principles electronic structure calculations. The model clusters of Eu2+-doped crystals consisting of Eu2+ at the substitution site and the surrounding ions were created. Then molecular orbital calculations were performed by the relativistic discrete-variational Xα (DV-Xα) method and subsequently multiplet calculations were performed by the relativistic discrete-variational multi-electron (DVME) method. These first-principles calculations were carried out for Eu2+-doped crystals that show anomalous luminescence and those that do not show anomalous luminescence, and the electronic states of these materials were compared in detail.
First-Principles Calculations of the Optical Spectra of Uranium Ions in Oxide Crystals
Authors: Masago Toshiki , Ogasawara Kazuyoshi
Published: February 2024

Recently U6+-doped phosphors are attracting attentions as potential green phosphors for the white LED application. However, the origins of the peaks in the optical spectra in some U-doped phosphors have not been clarified yet. For the development of the novel uranium phosphors, detailed analysis of the absorption and emission mechanisms of these materials is indispensable.

In this study, we have performed the first-principles electronic structure calculations of U in oxide crystals using the relativistic discrete-variational multi-electron (DVME) code which is a configuration-interaction calculation program based on the four-component fully relativistic wave functions obtained by the relativistic discrete-variational Xα (DV-Xα) molecular orbital method. The optical spectra due to the charge transfer transitions of U6+ in oxides were calculated using the explicitly obtained many-electron wave functions. For comparison, the 5f-6d transitions of U3+ in oxide crystals were also calculated and the influence of the valency was investigated. The theoretical spectra were compared with the experimental spectra and the origins of the peaks were clarified based on the configuration analysis of the corresponding relativistic many-electron wave functions.
(Keynote) Metallaelectro-Catalyzed Bond Activations
Authors: Ackermann Lutz
Published: February 2024

Oxidative C–H activation has emerged as an increasingly powerful tool in molecular syntheses.[
1] Despite major progress towards atom and step economy, these transformations largely rely on precious metal catalysts and stoichiometric amounts of toxic metal oxidants, compromising the overall sustainability of the C–H activation strategy. In contrast, employing electrooxidation in lieu of reactive chemical oxidants prevents undesired waste formation through oxidant economyand offers efficient use of renewable energies from sustainable sources for chemical bond formation.[2] Inexpensive Earth-abundant 3d metal[3] cobaltaelectrocatalysis set the stage for molecular syntheses at a unique level of resource economy.[4] Our studies towards metallaelectrocatalytic C–H and C–C activation will be discussed, with a topical focus on sustainable base metals.[5]

References

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[2] a) P. Gandeepan, L. H. Finger, T. H. Meyer, L. Ackermann, Chem. Soc. Rev.
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[3] P. Gandeepan, T. Müller, D. Zell, G. Cera, S. Warratz, L. Ackermann, Chem. Rev.
2019, 111, 2192–2452.

[4] Y. Qiu, M. Stangier, T. H. Meyer, J. C. A. Oliveira, L. Ackermann, Angew. Chem. Int. Ed.
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57, 14179–14183; b) Y. Qiu, W.-J. Kong, J. Struwe, N. Sauermann, T. Rogge, A. Scheremetjew, L. Ackermann, Angew. Chem. Int. Ed.
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[5] a) R. Mei, N. Sauermann, J. C. A. Oliveira, L. Ackermann, J. Am. Chem. Soc.
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140, 7913–7921;N. Sauermann, T. H. Meyer, C. Tian, L. Ackermann, J. Am.
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Figure 1
Biogas-Upgrading of Anaerobic Digestion Effluent CO2 into CH4 Using a Microbial Electrosynthesis Cell
Authors: KIM Minsoo , Li Shuwei , Kim Eunseo , Song Young Eun , Lee Dong-Yeol , Kim Jeom-Soo , Kim Jung Rae
Published: February 2024

Upgrading anaerobic digestion (AD) biogas has been highlighted to secure an alternative renewable energy source. The CO2 content of AD effluent is over 40%, thus it is necessary to separate and/or increase CH4 content up to 95%. This study examines a microbial electrosynthesis (MES) to directly convert CO2 into CH4 by cathode attached cell. The MES with −1.0V (vs. Ag/AgCl) applied cathodic potential presented a maximum rate of 10.55L CH4/ m2 cat/ day and achieve 96% of final CH4 content. The next-generation sequencing indicates the most methanogens attached to the cathode surface rather than suspension. These results suggest that cathode attached cells play a major role in the biogas-upgrading of CO2 into CH4 in the MES system.