bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Gas Void Fraction on Electrode Performance in Industrial Alkaline Water Electrolysis
Authors: Gäde Felix , Möller Jonatan , Turek Thomas , Becker Maik
Published: December 2024

In alkaline water electrolysis cells with an electrolyte gap between the electrodes, the cell's internal resistance increases when the gas void fraction in the electrolyte rises (Figure 1 a). Bongenaar-Schlentner et al. [1] were able to show this in their work already in 1985. As laboratory cells are usually significantly lower in height than industrial cells and the flow velocities [2] are typically higher than during technical operation, the influence of the gas void fraction within the cell has been paid little attention to date.

Cell heights of more than 1 m with a zero-gap arrangement are currently used in the industry [3, 4]. The influence of the gas void fraction on the efficiency in this cell configuration needs further experimental investigations, as the gas evolves in the void of the cell and does not necessarily affect the area in between them. However, it can be expected that the gas void fraction and the bubble size distribution impair the wetting of the electrode, the detachment of gas bubbles, the mass transport to the electrode and the wetting of the separator, to name just a few of the possible effects.

To emulate these effects in a real industrial-scale cell, different gas void fractions were generated in a lab-scale cell through gas addition corresponding to the gas flow rate of the industrial-scale cell at variable heights (Figure 1 b). To evaluate the influence on the current density, chronoamperometry was applied. The inlet temperature and electrolyte flow rate were varied within industrially relevant operating conditions, and the effect of different cell internals was studied.

It was observed that the influence of the additional gas is considerable, decreasing the local cell current up to 20 % at high gas void fractions. The results obtained were compared with those of a pilot plant with full-size cells, showing significant electrode utilization differences over the cell height.

This experimental investigation is a good starting point for further investigations on the effect of the gas-void fraction on the electrode performance and can lead to improved cell designs.

References

[1] B. E. Bongenaar-Schlentner, L. J. J. Janssen, S. J. D. Van Stralen, E. Barenbrecht, Journal of Applied Electrochemistry. 1985, (15), 537–548.

[2] M. T. Groot, J. Kraakman, R. L. Garcia Barros, International Journal of Hydrogen Energy. 2022, (47), 34773-34783, DOI: https://doi.org/10.1016/j.ijhydene.2022.08.075.

[3] “Atmospheric Alkaline Electrolyser – Nel Display,” https://display.nelhydrogen.com/product/atmospheric-alkaline-electrolyser-a-series/ (Accessed on April 12, 2024), n.d.

[4] “WEW - water electrolysis works,” https://wewhydrogen.com (Accessed on April 16, 2024), n.d.

Figure 1
Experimentally-Validated CFD Model of an Anhydrous HCl Electrolyzer
Authors: Likit-anurak Kris , Teel Hunter , Shimpalee Sirivatch , Meekins Benjamin
Published: December 2024

Chlorine is an important chemical used in many everyday products1. Most Cl2 has been produced from brine by the chlor-alkaline process, which also produces NaOH and H2 as byproducts2,3. Not only can the chlor-alkaline process produce Cl2, but Cl2 can also be generated from electrolysis of HCl. Polybenzimidazole (PBI) membranes, which are high temperature proton exchange membranes, have been shown to decrease cell potential in the oxygen depolarized cathode (ODC) HCl electrolyzer compared to Nafion membrane4,5. Because PBI membranes are acid-tolerant and do not require humidity, they were used to develop a fully anhydrous HCl electrolyzer that could generate dry H2 and Cl2 from anhydrous HCl with a single pass conversion efficiency approaching 100%6. Anhydrous HCl is a highly corrosive and toxic gas which could injure researchers and damage equipment if it leaked during an experiment. This risk is especially prominent when using high HCl flow rates or applying back pressure to the electrolyzer. To eliminate the risk, computational fluid dynamics (CFD) software was used to enhance the understanding of the transport phenomena in the electrolyzer and aid improvement of the electrolyzer performance.

We will show the development of the CFD model of the fully anhydrous HCl electrolyzer based on experiments using gel-type PBI and densified PBI prepared two separate ways. The CFD model can accurately predict electrolyzer performance and guide optimization of the anhydrous HCl electrolyzer. We show that cell temperature, HCl flow rate, and cell back-pressure can be optimized to improve electrolyzer performance. We also discuss potential pitfalls of the electrolyzer, especially when considering scale-up to industrial processes.

Reference

EuroChlor, (2016) https://www.eurochlor.org/wp-content/uploads/2021/04/02-The-Chlorine-Tree-Infosheet.pdf.

P. Schmittinger, Chlorine: Principles & Industrial Practice, 1st ed., p. 254, Wiley-VCH, (2000).

EuroChlor, (2023) https://www.chlorineindustryreview.com/wp-content/uploads/2022/08/Industry-Review-2021-2022.pdf.

L. A. Murdock and B. C. Benicewicz, Macromolecules, 56, 2729–2735 (2023).

K. Likit-anurak et al., ACS Appl. Energy Mater., 6, 5429–5434 (2023).

K. Likit-anurak et al., Int. J. Hydrog. Energy, 47, 26859–26864 (2022).
High-Performance Fuel Cell with Integrated Flow Distribution in Porous Transport Layer for Heavy-Duty Vehicular Applications
Authors: Sharma Preetam , Owejan Jon , Esan Oladapo Christopher , Fields Garrett , Aaron Douglas S , Mench Matthew M
Published: December 2024

The U.S. Department of Energy (DOE) interim (2030) targets for polymer electrolyte fuel cells (PEFCs) in heavy duty vehicle applications call for reduced system cost (US $80/kW), increased peak efficiency (68%), and longer system lifetime (25,000 hrs) [1]. Designing high-performance, durable, low-temperature hydrogen fuel cells involves intricate trade-offs between cell-level geometries and materials, as well as considering system-level complexities and efficiencies. Optimal reactant gas management, particularly oxygen transport to the cathode, is a crucial part of the design process. Despite efforts to enhance convective mixing and reduce liquid water accumulation through novel flow distribution architectures, recent commercialization trends favor formed bipolar plates with a parallel/serpentine channel architecture. These plates with flow distribution channels prove to be the most cost-competitive for heavy-duty automotive applications. Porous and high-pressure-loss flow channel networks, while promising in performance under specific operating conditions, fall short in justifying the additional cost or parasitic power associated with implementation in commercial systems [2]. This study introduces a hybrid porous layer [3],[4] with organized convection pathways that significantly improves performance compared to conventional bipolar plates. Exceptional performance (see Figure 1) is demonstrated across diverse operating conditions (e.g. wet, cold conditions up to dry, hot). The results of this study offer the potential to achieve high performance with reduced weight, as well as manufacturing and assembly cost using this hybrid architecture.

References:

[1] D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers, and A. Kusoglu, “New roads and challenges for fuel cells in heavy-duty transportation,” Nat Energy, vol. 6, pp. 462–474, 2021, doi: 10.1038/s41560-021-00775-z.

[2] G. Zhang, Z. Qu, W. Q. Tao, X. Wang, L. Wu, S. Wu, X. Xie, C. Tongsh, W. Huo, Z. Bao, K. Jiao, and Y. Wang, “Porous Flow Field for Next-Generation Proton Exchange Membrane Fuel Cells: Materials, Characterization, Design, and Challenges,” Chemical Reviews, vol. 123, no. 3. American Chemical Society, pp. 989–1039, Feb. 08, 2023. doi: 10.1021/acs.chemrev.2c00539.

[3] P. Sharma, J. Owejan, D. Aaron, and M. M. Mench, “Porous Carbon Fiber Flow Fields for Heavy-Duty Polymer Electrolyte Fuel Cell (PEFC) Applications,” ECS Meeting Abstracts, vol. MA2023-01, no. 38, p. 2255, Aug. 2023, doi: 10.1149/MA2023-01382255mtgabs.

[4] J. P. Owejan and S. G. Goebel, “Performance evaluation of porous gas channel ribs in a polymer electrolyte fuel cell,” J Power Sources, vol. 494, May 2021, doi: 10.1016/j.jpowsour.2021.229740.

Figure 1
Numerical Modeling of a Polymer Electrolyte Membrane Fuel Cell for Electric Aircraft Propulsion
Authors: Oka Haruya , Katsuki Yusaku , Nakajima Hironori , Inoue Chihiro
Published: December 2024

Electrified propulsion systems with hydrogen-fueled fuel cells can potentially reduce carbon dioxide emissions from aircraft. However, achieving a substantial increase in the gravimetric/volumetric power density of fuel cell systems poses a considerable challenge. In this study, we focus on polymer electrolyte membrane fuel cells (PEMFCs) working between 100 and 200°C. To design an optimized PEMFC structure for an electric aircraft, we have developed a numerical model that employs the finite element method (FEM) (COMSOL Multiphysics) to couple electrochemistry, gas diffusive and convective transports, and heat transfer in fuel cell components such as separators, gas flow channels, gas diffusion layers, catalyst layers, and a PEM1)2). We thereby three-dimensionally visualized the current, hydrogen, oxygen, and water vapor concentration distributions, as well as the temperature distributions, assuming conditions in aircraft operations. Moreover, we developed a machine learning model from the data outputs of the FEM model, which serves as training data, to reduce the computational costs for the fuel cell stack design incorporated in a system-level numerical model.

Acknowledgement

This study is based on results obtained from a project, JPNP14004, commissioned by the New Energy and Industrial Technology Development (NEDO). We are indepted to Boeing Research & Technology, Boeing Japan for their support and discussions. We are also grateful to Professor Motoaki Kawase of Kyoto University for his fruitful suggestions. Thanks are offered to Professor Kohei Ito and Associate Professor Tatsumi Kitahara of Kyushu University for their valuable discussions.

References

1) Ö. Aydın, T. Ochiai, H. Nakajima, T. Kitahara, K. Ito, Y. Ogura, J. Shimano, Mass transport limitation in inlet periphery of fuel cells: Studied on a planar Solid Oxide Fuel Cell, Int. J. Hydrogen Energy, 43 (2018) 17420–17430. https://doi.org/10.1016/j.ijhydene.2018.07.030

2) X. Wang, H. Nakajima, Y. Iwanaga, K. Ito, Numerical and experimental investigation of a cathode-supported microtubular solid oxide electrolysis cell from current and temperature variations in-situ assessed with electrode-segmentation method, J. Energy Storage, 72 (2023) 108459. https://doi.org/10.1016/j.est.2023.108459
Preventing Electrode Degradation Against Reverse Current By Interrupting Ion Transfer during Shut-Down in Alkaline Water Electrolysis
Authors: Im Sejin , Kim Wan Sik , Tamboli Asiya M. , Sim Junseok , Jung Younghan , OH JunSeok , Kim Chang-Hee
Published: December 2024

The renewable energy integrated alkaline water electrolysis (AWE) is a potential candidate for large scale and economically viable technology for green hydrogen production. However, the periodic power off mode causes reverse current in alkaline electrolyzer, which is inevitable intermittent characteristics of renewable energy sources. The reverse current spontaneously occurs by potential difference between electrodes to release the accumulated charges of electrodes during shut-down state. It adversely affects to the performance and the lifetime of the AWE stacks by an irreversible phase change of the electrodes. To prevent degradation of electrodes against the reverse current, we designed a system interrupting ion transfer by significantly lowering ion conductivity of the electrolyte during power shut-down in the AWE stacks. Consequently, we verify the relationship between the ionic conductivity and reverse current by analyzing the decrease rates of each cell potential corresponding phase change in the AWE stacks during the shut-down state. Through this research, we anticipate providing fundamental solutions to prevent electrode degradation and enhance the durability of stacks for renewable energy integrated AWE system.
Diagnosing the Nature of Oxygen Site in Yttrium Doped Barium Calcium Niobates and Its Impact Towards Electrochemical Oxidative Coupling of Methane
Authors: Ramaiyan Kannan , Benavidez Angelica , Garzon Fernando H.
Published: December 2024

Effective conversion of methane into value added chemicals such as ethylene will help reduce its venting and flaring from oil and gas wells. Oxidative coupling of methane (OCM) is shown to produce ethylene although over oxidation products such as CO2 and CO reduce the C2 hydrocarbon selectivity. The industrial target for OCM process is a single pass conversion of at least 30% and a C2 selectivity around 80% although catalysts with satisfactory performance has not been identified yet despite four decades of intense research.1 Electrochemical OCM is recently gaining renewed interest due the ability to control the conversion rate and product selectivity though temperature and applied potential. We demonstrated a potential dependent C2 selectivity using Fe and Ca codoped barium niobates as E-OCM catalysts.2–4 However, introduction of yttrium as a dopant in barium calcium niobate (BCNY) resulted in a remarkable change in its electrical conductivity and methane activation properties. We present our results on BCNY’s methane activation properties and possible correlation between the nature of oxygen species in the BCNY crystal matrix. Electrical conductivity measurements, E-OCM measurements and temperature programed reactions in oxidizing and reducing conditions are utilized to establish the role of yttrium and compare with other transition metal dopants such as Fe and Ni.

References

Zavyalova U, Holena M, Schlögl R, Baerns M. Statistical Analysis of Past Catalytic Data on Oxidative Methane Coupling for New Insights into the Composition of High-Performance Catalysts. ChemCatChem. 2011;3(12):1935-1947. doi:10.1002/cctc.201100186

Ramaiyan K, Denoyer LH, Benavidez A, Garzon FH. Role of Dopants in Fine-Tuning the Electrical and Catalytic Properties of Barium Niobate Perovskites Towards High-Temperature Electrolyzer Application. ECS Trans. 2023;111(6):1139. doi:10.1149/11106.1139ecst

Denoyer LH, Benavidez A, Garzon FH, Ramaiyan KP. Highly Stable Doped Barium Niobate Based Electrocatalysts for Effective Electrochemical Coupling of Methane to Ethylene. Adv Mater Interfaces. 2022;9(27):2200796. doi:10.1002/admi.202200796

Denoyer LH, Benavidez A, Brearley A, Ramaiyan K, Garzon FH. Chemical Stability of BaMg0.33Nb0.67-XFexO3-δ in High Temperature Methane Conversion Environments. ECS Trans. 2023;111(6):587. doi:10.1149/11106.0587ecst
Resolving the Impact of Sr and Ni Diffusion on Moderate-Temperature Sintered BaZr0.44Ce0.36Y0.2O3/SrZr0.4Ce0.4Y0.1O3–NiO Half-Cells Interface for PCEC/PCFC
Authors: Kwati Leonard , Povstugar Ivan , Kindelmann Moritz , Meulenberg Wilhelm , Ishihara Tatsumi , Matsumoto Hiroshige
Published: December 2024

Proton-conducting solid oxide electrolytes are poised to play a transformative role in steam electrolysis (PCEC) and fuel cells (PCFC) application at moderate to low temperatures, given their high ionic conductivity and inherent advantages in the gas flow configuration over traditional solid oxide cells. However, their refractory nature necessitates high sintering temperatures to ensure sufficient densification which also compromises the protonic conductivity of the material. This paper investigates the impact of Sr and Ni segregation at the electrode/electrolyte interface in BaZr0.44Ce0.36Y0.2O3 (BZCY(54)8/92) proton conductinghalf-cells using a combination of high-resolution STEM-EDX, 3-dimensional atom probe tomography (APT), and Raman spectroscopy to understand structural modifications of the half-cells upon sintering at varying temperatures. Our half-cells are fabricated using an industrially established inverse tape-casting route with NiO-SrZr0.5Ce0.4Y0.1O3-δ as the substrate, ensuring minimal warping and no cracks in the end-fired state. After co-sintering at 1300 °C for 5 hours, the tri-layered green tapes achieved dense, gas-tight electrolyte layers with a He leakage rate well within the threshold necessary for cell operation (~5 × 10–5 hPa dm3 (s cm2)–1). Using Ba0.5La0.5CoO3−δ as the air electrode demonstrates remarkable capabilities and endurance within the 450-600°C temperature range, achieving a peak power density of 1.13 W cm-2 at 600 °C in the fuel cell mode and a high current density of 1.5 A cm-2 at 1.3 V in the electrolysis mode. Furthermore, It is apparent from the latter techniques that upon sintering above 1350 °C, the electrolyte material undergoes evident structural changes with new crystal defects that affect the perovskite host. Ni diffuses into the electrolyte layer and gets dissolved in the bulk while some segregate at the grain boundary, below monolayer coverage in either case (GNi 2.0 at%/nm2).

Acknowledgment: The authors gratefully acknowledge financial support through JSPS KAKENHI Grant-in-Aid for Scientific Research (C), No. 19K05672, NEDO (International collaboration) JPNP20005, JSPS Core-to-Core (Solid Oxide Interfaces for Faster Ion Transport) and WPI-I2CNER sponsored by the World Premier International Research Center Initiative (WPI), MEXT, Japan.
Proton-Conducting Solid Oxide Electrolysis Cells with Scandia-Doped Barium Zirconate Electrolytes
Authors: Naughton Matthew , Zhang Yuchen , Sun Quanwen , Zhao Zeyu , Wu Wei , Yan Yushan , Ding Dong
Published: December 2024

Proton-conducting solid oxide electrolysis cells (P-SOECs) leverage their low activation energy for proton-conduction to achieve high water electrolysis performance in the intermediate temperature regime (400-600°C). In this sought after temperature zone critical challenges that face high-temperature systems (>700°C) such as balance-of-plant costs, degradation, and oxidation may be alleviated while still retaining favorable reaction kinetics with earth-abundant materials. The electrolyte in P-SOECs plays a vital role in full cell performance and efficiency. P-SOEC electrolytes must have high ionic conductivity, low electronic conductivity, and exceptional durability in high steam atmospheres. Yttrium-doped barium zirconate (BZY) and yttrium/ytterbium co-doped barium cerate zirconate (BZCYYb) are the most widely used P-SOEC electrolyte materials to date. However, practical applications for these materials are in question due to the low protonic conductivity of BZY, poor durability of BZCYYb in high steam environments, and the depressed faradaic efficiencies achieved by P-SOECs utilizing these electrolytes. In this work we show that scandium-doped barium zirconate (BZSc) is a promising electrolyte material to produce P-SOECs with a combination of high performance, efficiency, and durability. Relevant electrolysis current densities were attained below 500°C and long-term durability is demonstrated. Cell architecture and operating conditions are optimized to maximize faradaic efficiency. Our results indicate that high proton concentrations in the electrolyte achieved through high dopant levels can boost performance in barium zirconate-based P-SOECs while preserving unrivalled durability. This work demonstrates the potential for BZSc as an effective P-SOEC electrolyte and we anticipate future studies to further characterize BZSc. Furthermore, this work opens the door for more research into proton conducting materials with dopant levels exceeding 20 mol%.
Influence of Local Environment Under Polarization on Wettability of Ni/YSZ Interface
Authors: Ihara Sota , Muroyama Hiroki , Matsui Toshiaki
Published: December 2024

In solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), degradation of hydrogen electrode during long–term operation is one of the issues to be solved. Migration and aggregation of Ni particles are major factors of this degradation, and especially after steam electrolysis operation, intense Ni migration has been observed at the hydrogen electrode/electrolyte interface [1]. This phenomenon is assumed to be related to the change in wettability of the Ni/electrolyte interface under polarization [2]. A quantitative measurement of interface wettability is the concept of contact angle. It is known that the contact angle is determined by the balance between the surface tension of contacting materials and the interfacial tension. Contact angle analysis is usually used for liquid–solid interfaces, but it has also been suggested to be useful for the characterization of solid metal–oxide interfaces [3]. Therefore, the aim of this study was to directly measure the contact angle between Ni and YSZ electrolyte under various conditions in order to quantify the changes in wettability at the interface.

Ni thin film electrodes were prepared by sputtering Ni on YSZ electrolyte. Using this model electrode, electrochemical measurements were performed under open circuit holding or a potentiostatic operation (SOFC operation or SOEC operation) at high temperatures. Subsequently, postmorterm analysis of the samples was performed using a Focused Ion Beam–Scanning Electron Microscope (FIB–SEM). Using the cross–sectional SEM images of the model electrode, the contact angle was calculated by distinguishing the three phases of Ni, YSZ, and pores based on the difference in contrast of each phase. The analysis revealed that the wettability of the Ni/YSZ electrolyte interface changed depending on the operation mode. Specifically, the contact angle after SOEC operation increased compared to values after open circuit holding or SOFC operation. This phenomenon is thought to be related to changes in oxygen potential.

Acknowledgements

This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

References

[1] M.B. Mogensen,
et al.
,
Fuel Cells
, 17, 434 (2017).

[2] Z. Jiao and N. Shikazono,
Acta Materialia
, 135, 124 (2017).

[3] H. Kishimoto,
et al.
,
Solid State Ion.
, 225, 65 (2012).
Functional Layer Optimization of Proton Conducting Electrochemical Cells
Authors: Zhang Yuchen , Sun Quanwen , Zhao Zeyu , Wu Wei , Tong Jianhua , Ding Dong
Published: December 2024

Proton conducting electrochemical cells (PCECs) are a promising device for hydrogen production and energy conversion, working at relatively low temperatures (400-600oC) with high energy efficiency. Addressing electrochemical performance limitations and structural defects in PCECs, the integration of functional layers was pursued to enhance electrolyte/electrode interfaces, thereby reducing total resistance, improving structural stability, and achieving greater activity at active reaction sites. However, in contrast to the extensive investigations into oxygen-ion conducting electrochemical cells, research on functional layer remains largely confined to achieving performance enhancements without comprehensive elucidation of their underlying operational mechanisms. Thus, we focus on manipulating functional layer properties through adjustments of relevant parameters and discerning their consequential impacts on electrochemical performance of PCECs. This study endeavors to offer insights towards the fabrication of an optimal fuel electrode functional layer, thereby fostering enhanced electrochemical performance and bolstering mechanical stability, with a view towards facilitating the scaling up of PCECs.
Surface Proton Conductivity of Sm-Doped SrCeO3-BaCeO3 Solid Solution Ceramic and Thin Film
Authors: Tabuchi Riku , Morizane Ryota , Notake Go , Higuchi Tohru
Published: December 2024

Solid oxide fuel cell (SOFC) device that generates electrical power by hydrogen or oxygen gas is one

of clean and renewable energy sources. SOFC at medium temperature (MT) range operating at 400-

600 °C is highly attractive because operating time become shorter than SOFC using YSZ ceramic

electrolyte. Although the ion conduction at MT been extensively studied in acceptor-doped BaCeO3

or BaZrO3 bulk ceramics, no practical ion conductivity has been achieved so far [1][2]. Although Y-SrCeO3 and Y-BaCeO3 have confirmed proton conductivity at medium temperature (MT), so we focused on SrCeO3 and BaCeO3, which are extremely chemically stable perovskite-type oxides [3][4].

In this study, we have prepared the Sm-doped BaCeO3-SrCeO3 (Sr0.7Ba0.3Ce0.8Sm0.2O3-δ: SBCS)

composite thin film on Al2O3 (0001) substrate with the aim of improving chemical stability and high conductivity, and investigated its ionic conduction [5].

The SBCS thin films were prepared on Al2O3 (0001) substrates by RF magnetron sputtering using ceramic targets. The flow rate of Ar gas controlled by a mass-flow controller was kept at approximately 2.81 sccm. The pressure of Ar gas was fixed at 3.5 × 10−3 Torr during the deposition. The prepared thin films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and A.C impedance method using a frequency response analyzer.

The XRD pattern results showed a 121 peak and a 242 peak, indicating successful crystallization of the films. The prepared thin films exhibit plane index of 121.

Figure 1 shows an Arrhenius plot of the conductivity of the wet-annealed SBCS thin films with various thicknesses. The conducting carrier is considered to be proton, although the contribution of oxide ion also exists. These conductivities exhibit relatively high conductivity in this temperature region. Moreover, the conductivity is enhanced by the addition of Ba, as indicated by the improved conductivity compared to SrCe0.8Sm0.2O3-δ (SCSO). A thinner film thickness results in higher conductivity. This is believed to be due to the contribution of surface proton conductivity.

Reference

[1] D.Pergolesi et al., NATURE MATERIALS, 9, (2010), 846-852

[2] T.Hibino et al. ,J Phys Chem,B ,Vol.105,No.46,2001

[3] S. Shin et al., Solid State Ionics (1990)

[4] T. Higuchi et al., Solid State Ionics, 270 (2015) 1-5.

[5] E. Gorbova,Journal of Power Sources,181,(2008)207

Figure 1
Mixed Protonic and Electronic Conduction in N-Type Oxide Semiconductor MgIn2O4 Under Hydrogen Atmosphere
Authors: Yamasaki Tomoyuki , Kudo Saki , Omata Takahisa
Published: December 2024

There is an emerging interest in mixed protonic-electronic conductors for use as hydrogen-permeable membranes and electrodes of fuel cell and water electrolyzer working at 300–500℃. Up to now, the research for mixed protonic-electronic conductors has been limited to a common approach: an acceptor cation is doped to a perovskite-type oxide, creating positively charged compensating defects, notably oxygen vacancy, then hydrate these1;

H2O(g) + VO
•• + OO
× → 2OHO
•.

Since the doped acceptor has an effective negative charge relative to the species they replace, the introduced protons are plausibly trapped surrounding the acceptors (proton trapping). Therefore, to achieve mixed protonic-electronic conductors with high proton conductivity at intermediate temperatures.

In n-type oxide semiconductors, such as In2O3, SnO2, and ZnO, hydrogen is a ubiquitous impurity that acts as an electron donor. Hydrogen is incorporated into interstitial sites and forms a shallow donor state2, according to

H2(g) → 2H
i

• + 2e’.

Here, we reveal that the interstitial proton introduced via this mechanism conducts through n-type conducting MgIn2O4
3 at intermediate temperatures. We show that hydrogen is incorporated into MgIn2O4 in a hydrogen atmosphere, leading to an increase in the electronic conductivity. To assess the partial proton conductivity of hydrogen-incorporated MgIn2O4, we prepared an electron-blocking cell. A MgIn2O4 thin film was deposited by RF magnetron sputtering on a proton-conducting phosphate glass4. We conducted chronoamperometry and electrochemical impedance spectroscopy for the electron-blocking cell. The proton partial conductivity of MgIn2O4 was determined as 1.1×10−6 Scm−1 at 250℃. In the presentation, the proton mobility of MgIn2O4 will be discussed in comparison with perovskite-type proton conductors, showing that n-type conducting oxides are promising for mixed protonic-electronic conductors.

References

Kreuer, K.-D. Proton Conductivity: Materials and Applications. Chem. Mater.
8, 610–641 (1996).

Kılıç, Ç. & Zunger, A. n-type doping of oxides by hydrogen. Appl. Phys. Lett.
81, 73–75 (2002).

Ueda, N. et al. New oxide phase with wide band gap and high electroconductivity, MgIn2O4. Appl. Phys. Lett.
61, 1954–1955 (1992).

Ishiyama, T. et al. Transport properties of proton conducting phosphate glass: An electrochemical hydrogen pump enabling the formation of dry hydrogen gas. Int. J. Hydrog. Energy
44, 24977–24984 (2019).
Evaluation of B-Site Doped Barium Niobate Perovskite Anodes for the Electrochemical Oxidative Coupling of Methane
Authors: Denoyer Luke H , Ramaiyan Kannan , Benavidez Angelica , Brearley Adrian , Garzon Fernando H.
Published: December 2024

More efficient usage of shale gas reserves and natural gas resources will allow for higher olefin yields and lower greenhouse gas emissions. The oxidative coupling of methane (OCM) is a direct pathway for converting methane to ethylene at temperatures >700 °C. OCM catalysts preferably avoid COx products and limit coke formation on the catalyst. Often, catalysts are analyzed via computationally expensive DFT computations in combination with experimental results leading to long lead times for catalyst development. Perovskite oxide catalysts are useful for OCM due to their flexible bond networks and varied properties (conductivity, selectivity, surface area) based on synthesis/doping. This work aims to illustrate the utility of the bond-valence bond-length model (ionic model)1
,2 in conjunction with gas reduction experiments for rapid structure evaluation of the co-doped perovskite BaMg0.33Nb0.67-xFexO3-δ (BMNF, x=0.17,0.25,0.33). This perovskite catalyst has previously been adopted as a CO2 sensing material3 and an active/stable anode for the electrochemical oxidative coupling of methane4 (E-OCM). Further evaluation of this perovskite by our group illustrated the unique stability of ionic Fe into the BMNF while performing the oxidative coupling of methane5. This work delves into the crystal structure of the BMNF material as well as its chemical stability validated using a much more facile computational methodology featuring the bond-valence bond-length method. XPS, XRD, and reduction/oxidation high temperature cycling are utilized in conjunction to illustrate the stabilizing mechanisms for cations within the BMNF perovskite when exposed to highly reducing environments.

References

(1) Pauling, L. "The principles determining the structure of complex ionic crystals."

J. Am. Chem. Soc. 1929, 51 1010-1026.

(2) Lufaso, M. W.; Woodward, P. M. Prediction of the Crystal Structures of Perovskites Using the Software Program SPuDS. Acta Crystallogr. B
2001, 57 (6), 725–738. https://doi.org/10.1107/S0108768101015282.

(3) Kannan, R.; Mulmi, S.; Thangadurai, V. Synthesis and Characterization of Perovskite-Type BaMg0.33Nb0.67−xFexO3−δ for Potential High Temperature CO2 Sensors Application. J. Mater. Chem. A
2013, 1 (23), 6874–6879. https://doi.org/10.1039/C3TA10572E.

(4) Denoyer, L. H.; Benavidez, A.; Garzon, F. H.; Ramaiyan, K. P. Highly Stable Doped Barium Niobate Based Electrocatalysts for Effective Electrochemical Coupling of Methane to Ethylene. Adv. Mater. Interfaces
2022, 9 (27), 2200796. https://doi.org/10.1002/admi.202200796.

(5) Denoyer, L. H.; Benavidez, A.; Garzon, F. H.; Electrochemical oxidative coupling of methane: deciphering the exceptional properties of BaMg0.33Nb0.67-xFexO3-δ for enhanced electrocatalysis and durable operation. Accepted by Energy & Fuels Feb.

2024
Development of Barium-Modified Anodes for Anode-Supported Solid Oxide Fuel Cells Fueled with Ammonia
Authors: Fujita Akinari , Muroyama Hiroki , Matsui Toshiaki
Published: December 2024

Solid oxide fuel cells (SOFCs) have attracted significant attention due to their high power generation efficiency and low pollutant emissions. Owing to the use of solid oxide electrolytes, SOFCs are usually operated at high temperatures of 600–800 oC, leading to favorable fuel flexibility. Although alternative fuels such as hydrocarbon fuels are superior to pure hydrogen in terms of storage, transportation, and energy density, by-products from the fuels, as exemplified by carbon, will deteriorate the performance and stability of anodes.

Ammonia is promising as a carbon-free fuel for SOFCs because of its low cost, high hydrogen content and volumetric energy density, and ease in liquefaction and transportation under mild conditions. In ammonia-fueled SOFCs, the following reactions occur on the anode.

2NH3 → N2 + 3H2 (1)

H2 + O2− → H2O + 2e− (2)

Ammonia is decomposed to form nitrogen and hydrogen (1) and then the produced hydrogen is electrochemically oxidized (2). Thus, the anode material has to be active for ammonia decomposition as well as electrochemical hydrogen oxidation. The conventional Ni–YSZ electrode, however, is known to have low activity for ammonia decomposition. Therefore, it is necessary to enhance the catalytic activity of Ni–YSZ-based anode.

It has been reported that the addition of basic components to Ni-based catalysts improve the ammonia decomposition activity. In this study, then, we modified the anode of a commercial anode-supported SOFC button cell (Elcogen, ASC–400B) with barium components by dropping a solution containing barium salts onto the electrode. The effect of additive component on the cell performance was evaluated.

An aqueous solution of 2.0 M Ba(CH3COO)2–0.7 M C2H5NO2 was dropped onto the anode of anode-supported cell, followed by the heat-treatment at 800 oC for 2 h. This series of process was repeated several times so that desired amounts of barium component were loaded. Performances of the as-received cell and the fabricated cells were evaluated under hydrogen- and ammonia-containing fuels at 600–750 oC. For the as-received cell, cell performances were comparable in both fuels at 700 oC, indicating that the ammonia decomposition proceeded over the anode, while the performance were much different between H2 fuel and NH3 fuel at lower temperatures. On the other hand, comparable performances were obtained under both fuels at all the temperatures investigated. This suggested that the barium component promoted the ammonia decomposition sufficiently over the anode even at 600 oC.

This work was supported by JST SICORP Program (Grant Number: JPMJSC2122).
Stabilization of a Hydride Superionic Conducting Phase Via Cation Substitution in Ba-Li Based Oxyhydride
Authors: Yaguchi Hiroshi , Okamoto Kei , Takeiri Fumitaka , Kobayashi Genki
Published: December 2024

Hydride ions (H–) are attractive charge carriers with basic characteristics suitable for fast ion conduction, including monovalence, moderate ionic size, and large polarizability. The strong reducing property based on the standard redox potential (Eº(H–/H2) = –2.3 V vs. SHE) can lead to high energy density in batteries and high efficiency in energy/material conversion devices. For H– conductors, mixed-anion compounds such as oxyhydrides are currently the primary targets of materials exploration. This is because, compared to simple metal hydrides, the coexistence of multiple anions facilitates the control of parameters essential for developing H– conductors, such as the H– concentration and configuration.

Recently, we reported H– conducting Ba-Li oxyhydrides (BLHO) with the K2NiF4-type structure [1]. BLHO has a stable composition of the highly vacant Ba1.75LiH2.7O0.9 under ambient pressure and forms the superlattice structure at low temperature due to the three types of long-range ordering, namely Heq/VH, Hap/Oap, and Ba/VBa (Heq, Oap, and V
M
represent hydrogen at equatorial anion sites, oxygen at apical anion sites, and a vacancy at M sites, respectively). These long-range orderings are successively disordered upon heating; Ba/VBa and Heq/VH at 300 ºC; Hap/Oap at 350 ºC (each phase is called b-, γ-, d-BLHO from the lower temperature side). The H– conductivity enhances after the β-γ transition to the so-called superionic conduction state, which exhibits conductivity over 10–2 S·cm–1 nearly independent of the temperature. The introduction of structural randomness into BLHO via elemental substitutions should stabilize the γ- and δ-phases at lower temperatures. In this study, we synthesized solid solutions of BLHO in which Li and Ba were partially substituted by cations with different sizes and valences, respectively, and investigated the impact of the elemental substitution on the phase transition behavior and H– conductivities [2 - 4].

[1] F. Takeiri, G. Kobayashi et al., Nat. Mater.,
21, 325–330 (2022)

[2] K. Okamoto, G. Kobayashi et al., J. Mater. Chem. A, 10, 23023-23027 (2022).

[3] K. Okamoto, G. Kobayashi et al., Adv. Sci., 10, 2203541 (2023).

[4] H. Yaguchi, G. Kobayashi et al., (in preparation).

Figure 1
Enhanced Reactivity and Stability in SOFC Cathodes via Thermal Reduction-Induced Surface Amorphization and Ex-Solution in Cu-Doped La0.6Sr0.4Co0.2Fe0.8O3-Δ
Authors: Jeon SungHyun , Jung Wan-Gil , Bae Hohan , Barnett Scott A , Seo Jongsu , Kim Bong-Joong , Jung WooChul
Published: December 2024

Numerous studies have shown a marked interest in the application of supported nanoparticles for chemical and electrochemical catalytic reactions. However, these discrete nanoparticles often exhibit limited reactivity within their immediate regions and are prone to aggregation at high operating temperatures. This poses significant challenges in maintaining their activity and enhancing the inherent properties of the host materials. In this study, we propose a straightforward method to boost both the reactivity and stability of the oxide support. This method involves a mild thermal reduction of the Co/Fe-based perovskite oxide, which exhibits dynamic redox properties, over an extended period. This process promotes the releases of sufficient amount of lattice oxygen, which in turn facilitates the development of an amorphous surface layer as well as a nanoparticle ex-solution. The surface amorphization. As a case study, we use Cu-substituted La0.6Sr0.4Co0.2Fe0.8O3-δ, a prime example of a solid oxide fuel cell cathode material. In situ environmental transmission electron microscopy demonstrates that surface amorphization and nanoparticle formation occur sequentially. Consequently, electrochemical measurements reveal that these structural transformations, i.e., surface amorphous layer and nanoparticle, significantly enhance the stability and activity of the oxygen reduction reaction, respectively. These findings offer a new perspective on designing catalyst surfaces for various high-temperature applications.
(Invited) Enabling Materials for Intermediate Temperature Solid Oxide Electrolyzers
Authors: Huang Kevin
Published: December 2024

High-efficiency and high-flux hydrogen production via electrolytic cells are of vital importance to the realization of a clean and sustainable hydrogen energy future. High-temperature solid oxide steam electrolyzer (SOEC) technology is thermodynamically and kinetically advantageous over its low-temperature counterparts. However, the commercial development of SOEC technology is severely challenged by the poor durability, largely attributed to the high operating temperature that triggers a wide range of materials degradation mechanisms. Therefore, reducing the operating temperature of SOEC from the current 750oC to 650oC, for example, is highly preferred to improve durability by mitigating or even completely shutting down the degradation mechanisms. Here in this presentation, materials options to enable the reduced operating temperature for SOEC are thoroughly discussed from a viewpoint of material properties. Several examples of cell materials well positioned for intermediate-temperature SOECs are illustrated. Future research directions in materials development for SOEC technology are suggested.
(Invited) Studying Ni-YSZ Fuel Electrode Microstructure and Characteristics Using Symmetric Cells
Authors: Pibulchinda Pattiya , Barnett Scott A
Published: December 2024

Electrode-supported solid oxide cell (SOC) performance, efficiency, and stability are largely dependent on their Ni-YSZ cermet electrodes and supports. The design variables for these Ni-YSZ layers include the Ni/YSZ ratio, pore former volume fraction/size, thicknesses, and the firing conditions that partly determine their microstructures. These parameters can be used to optimize the electrode by maximizing active triple phase boundary (TPB) density in the functional layer, maximizing gas transport through the support, achieving required conductivity, maintaining mechanical strength, and minimizing overall Ni content.

This study aims to investigate how Ni-YSZ characteristics affect overall electrochemical performance and mechanical strength. In the initial studies, Ni-YSZ electrode-supported symmetric cells with a single uniform Ni-YSZ layer without pore former were studied to focus on functional layer properties. Cells with different Ni contents were compared. Cells were manufactured by laminating tape-cast layers and co-sintering at high temperatures, with a YSZ electrolyte thickness of ~ 10 μm and Ni-YSZ thickness of ~ 150 μm. Initial NiO weight percentages in the NiO-YSZ slurries were varied from 45 to 70% in different cells. Although NiO-YSZ layers with different compositions are expected to have different shrinkages, we found that by sintering the symmetric cells at 1300°C, all cell configurations were free of defects, curvature, or delamination.

Flexural strengths of both the electrodes and symmetric cells were characterized at ambient temperature via three-point bending tests. The NiO-YSZ composite reduction to cermet Ni-YSZ decreases flexural strength. In addition, increases in Ni content decrease flexural strength. The flexural strength results will be compared with values expected based on classic laminate plate theory.

Electrochemical impedance spectroscopy measurements were taken at open circuit voltage in 97% H2-3% H2O at 650°C, 700°C, 750°C, and 800°C. The impedance results fitted well using an equivalent circuit model that includes Ohmic, transmission line, and Warburg resistance elements. The Warburg resistance, which corresponds to gas diffusion processes, decreases significantly with increasing Ni content since most of the porosity results from the reduction of NiO to Ni. In these low steam conditions, the Warburg resistance element dominates overall impedance in 45 to 65 NiO weight percent electrodes. The 50-weight percent NiO electrode was found to minimize transmission line model resistance. The correlation between impedance results and the measured electrode microstructure (e.g., porosity, tortuosity, and active TPB density) will be discussed.
Advances in Redox-Electrodialysis for Energy-Efficient Desalination
Authors: Su Xiao , Kim Nayeong , Elbert Johannes
Published: December 2024

Electrochemical separations have rapidly grown in recent years due to advances in functional materials as well as architecture design. By bridging the technologies between redox-based energy storage and desalination, redox-mediated electrodialysis (redox-ED) has been shown to achieve continuous desalination from brackish water to seawater, with reduced energy consumption. Here, we provide an overview the advances in redox-electrodialysis, in terms of materials design as well as electrochemical engineering.

First, by replacing costly and sensitive ion-exchange membranes (IEMs) with robust nanofiltration membranes (NFs), we enable the energy-efficient desalination and removal of organic contaminants.1 NF-enabled redox-polymer ED demonstrated desalination down to potable water (<500 μS/cm) in wastewater containing organic substances, while redox-ED with IEM suffered from significant membrane fouling and slower desalination rates.

Second, by combining the water-soluble redox polymers with NFs, we removed a variety of chain lengths of carboxylates and per- and polyfluorinated substances (PFAS), while preventing membrane fouling and polymer crossover into the feed solution. Finally, we discuss the application of redox-electrodialysis systems for facilitating downstream processing in biomanufacturing, through the retention of proteins and organic acids from complex food and fermentation streams. 2-4 In general, we envision redox-electrodialysis platforms to gain increased attention for both water purification and multicomponent industrial separations.

References

(1) Kim, N.; Elbert, J.; Kim, C.; Su, X. Redox-Copolymers for Nanofiltration-Enabled Electrodialysis. ACS Energy Letters
2023, 8 (5), 2097-2105.

(2) Kim, N.; Lee, J.; Su, X. Precision Tuning of Highly Selective Polyelectrolyte Membranes for Redox‐Mediated Electrochemical Separation of Organic Acids. Advanced Functional Materials
2023, 33 (12), 2211645.

(3) Kim, N.; Oh, W.; Knust, K. N.; Zazyki Galetto, F. b.; Su, X. Molecularly Selective Polymer Interfaces for Electrochemical Separations. Langmuir
2023, 39 (47), 16685-16700.

(4) Kim, N.; Jeon, J.; Elbert, J.; Kim, C.; Su, X. Redox-mediated electrochemical desalination for waste valorization in dairy production. Chemical Engineering Journal
2022, 428, 131082.
Atomically Dispersed Transition Metal Catalysts for Electrochemical Chlorine Evolution Reaction
Authors: Kim Jinjong , Joo Sang Hoon
Published: December 2024

Chlorine evolution reaction (CER) is a crucial anodic reaction in the chlor–alkali process. For 50 years, dimensionally stable anode (DSA) has been extensively used for CER. However, the DSA requires about 30 at% of precious metals, such as iridium and ruthenium, and also catalyzes oxygen evolution reaction as a parasitic reaction, invoking the cost and selectivity issues, respectively. In this work, we have synthesized atomically dispersed non-precious metal (M; M = Fe, Co, Ni, and Cu)-based CER catalysts to unravel their CER catalytic trends. The catalysts were synthesized by coating carbon nanotube (CNT) with polyaniline layers, adsorption of a metal precursor, silica layer overcoating, thermal annealing, followed by silica layer etching. The resulting M1/aniCNT catalysts showed over 90% CER selectivity. Among the catalysts, Ni1/aniCNT exhibited the best CER activity, surpassing that of DSA. The high CER activity of Ni1/aniCNT is attributed to the asymmetric Ni–N3 structure with Ni1+ oxidation state. This work highlights the dependency of activity on the structure of atomically dispersed catalysts and broadens the range of CER catalysts.
Innovative Anode Design Incorporating Sub-Catalyst Layer for Proton Exchange Membrane Water Electrolyzers with Ultra-Low Iridium Loading
Authors: Hsu Yu Wei , Chueh Lu Yu , Pan Yung-Tin
Published: December 2024

Proton exchange membrane water electrolyzers (PEMWE) have garnered increasing attention in recent years due to their capability to produce clean, high-purity hydrogen. The optimization of the catalyst layer structure within these systems is critical, particularly in reducing the loading of platinum-group metal (PGM) anode catalysts. Under conditions of ultralow iridium loading, ion and mass transport are severely impeded, which hampers the kinetic performance of oxygen evolution reaction (OER) catalysts.

In this study, we propose an innovative membrane electrode assembly (MEA) design for PEMWE, wherein an ultra-thin sub-catalyst layer is constructed atop the conventional catalyst layer. This sub-catalyst layer, fabricated via spray coating with an ultra-low iridium loading of less than 0.05 mg/cm², possesses a high surface area and is engineered to enhance the interfacial contact area between the catalyst layer and the porous transport layer. The integration of this sub-catalyst layer markedly reduces both kinetic and ohmic resistances, thereby lowering the overall overpotential.

Our findings demonstrate that this novel approach results in a significant increase in the current density of the electrolyzer by 400 mA/cm² and a reduction in high-frequency resistance (HFR) by 35 mΩ cm², when compared to the conventional MEA structure. This study highlights the potential of the proposed MEA design to improve the efficiency and performance of PEMWE systems, contributing to the advancement of clean hydrogen production technologies.