bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Characterization of Catalyst Layers in Polymer Electrolyte Membrane Electrolyzers
Authors: Stelmacovich Genevieve , van Eijk Lonneke , Foster Jayson , Pylypenko Svitlana
Published: December 2024

Polymer electrolyte membrane water electrolyzers (PEMWEs) play a vital role in promoting the widespread adoption of renewable hydrogen. To successfully fabricate and integrate components, develop scalable manufacturing techniques, understand degradation mechanisms, and devise strategies to mitigate degradation, it is essential to thoroughly characterize materials and components in these devices. Due to the complexity of these systems and various interconnected problems, as well as the multitude of relevant scales, the use of multi-technique characterization and the development of novel characterization approaches and methods are crucial.

This talk will highlight the complementary nature of electron and X-ray microscopy and spectroscopy methods for investigating surfaces, interfaces, and interactions with focus on catalyst layers (CLs) with an emphasis on analysis of as-prepared, tested and degraded samples. Micro X-ray computed tomography (XCT) provides both 2D and 3D analysis, but its resolution is not sufficient to identify catalyst layer features with enough detail, especially when Pt PTL coatings and low Ir-based catalyst loadings are used. On the other hand, Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDS) provides superior resolution and enables the differentiation of PTL coatings and catalysts. Although SEM-EDS provides only 2D information, by employing a combination of top-down and cross-sectional analysis, a comprehensive understanding of catalyst distribution within the PTL can be attained, facilitating the initial assessment of PTLs and PTEs. The parameters extracted from SEM-EDS data can be used for a comprehensive quantitative assessment of the composition and distribution of catalysts, highlighting the differences between fabricated samples across a wide range of fabrication variables. Transmission Electron Microscopy (TEM) in tandem with EDS is also essential for nanoscale analysis of CLs, and PTEs. However, it is limited by its focus on small areas and necessitates complex sample preparation, especially for degraded samples. To complement these techniques, Time-of-Flight Secondary Mass Spectrometry (ToF-SIMS) has been developed as a promising complementary method to offer chemical insights, particularly valuable in analyzing protective coatings, catalyst layers, and interfaces between different layers. Furthermore, X-ray photoelectron spectroscopy (XPS) has high sensitivity in discerning catalyst evolution and subtle variations at the catalyst-ionomer interface, highlighting its complementary role in elemental and chemical composition analysis, especially in the context of tested and degraded samples.
A “Ship-in-a-Bottle” Method for Hydrogen Crossover Mitigation in PEM Water Electrolyzers
Authors: Yang Fan , Sun Qiang , Mittelsteadt Cortney
Published: December 2024

This work presents a new approach to address hydrogen crossover in proton exchange membrane water electrolyzers (PEMWEs), a pivotal challenge that not only compromises safety but also affects the system’s compatibility, especially when integrated with fluctuating renewable energy sources like wind turbines and solar panels. Platinum (Pt), a critical component for recombination reaction in PEMWEs, is traditionally integrated into ionomers through mechanical processing methods such as ball milling, sonication, or inline milling. These processes disperse Pt particles directly within ionomer dispersions1, but they have limitations in terms of efficiency and cost. Our "ship-in-a-bottle" method involves introducing Pt ions into the ionomer substrate, which are subsequently chemically reduced to form Pt nanocrystals within the polymer matrix. It offers numerous benefits over traditional routes, including a more uniform distribution of Pt nanocrystals within the hydrogen channels of the polymer network. This leads to significantly enhanced recombination efficiency and allows for the use of thinner membranes, production of high-pressure H2, reducing the quantity of platinum required, and consequently lowering the cost of the PEMWE technology.

Moreover, our research delves into the creation of a unique recombination layer within membrane electrode assemblies (MEAs), significantly curtailing hydrogen crossover, especially at low turn-down ratio—a persistent issue in PEMWE industry. Utilizing the non-conductive PTFE backbone of PFSA ionomers to isolate well dispersed Pt nanocrystals from areas of high voltage, our approach markedly increases efficiency of hydrogen crossover mitigation. The result not only improves the safety and operational flexibility of PEMWEs but also underscores a shift towards a more economical, safe, and adaptable hydrogen production methodology. By addressing key challenges associated with hydrogen crossover, this study lays the groundwork for transformative changes in the green hydrogen sector, emphasizing a sustainable future powered by renewable energy sources.

Klose et al 2018 J. Electrochem. Soc. 165 F1271
From Structure to Performance: Insights into the Role of Porous Transport Layers in PEM Water Electrolysis via Electrode Engineering
Authors: Goswami Navneet , Diaz-Abad Sergio , Komini Babu Siddharth , Spendelow Jacob S. , Kort-Kamp Wilton
Published: December 2024

Proton Exchange Membrane Water Electrolyzers (PEMWEs) are a promising technology to combat the deleterious effects of climate change [1]. It uses intermittent electricity from sustainable energy sources to electrochemically generate green hydrogen – a carbon-free energy carrier. Most importantly, the integration of water electrolyzers with fuel cells into a single reversible system is an enabler to achieving hydrogen-based long-duration energy storage. To make PEMWE systems more cost-competitive and technologically viable, it is essential to control the ohmic and mass transport limitations, a significant contribution of which stems from the fibrous porous transport layers (PTLs). In this work, we present a multiscale framework to investigate the effect of PTL electrode parameters on the electrochemical response of the PEMWE. Our starting point is stochastically generated PTL configurations with a host of microstructural features such as fiber diameter, porosity, fiber orientation, etc. The salient morphology-dependent transport properties like tortuosities, effective electronic conductivities, and two-phase permeabilities are then evaluated by employing pore-network modeling [2]. These are subsequently deployed to a physics-based multiphase reactive transport model [3] of the electrolyzer to quantify the concomitant overpotential modes. The interplay of operating regimes and PTL structural parameters on the resistive signature is further delineated. An optimization of the PTL architecture along with its pore size distribution investigated in this study can guide the design of experiments towards high-performing PEMWEs with enhanced catalyst utilization and mass transport.

References:

[1] Pham, Chuyen Van, et al. "Essentials of high performance water electrolyzers–from catalyst layer materials to electrode engineering." Advanced energy materials 11.44 (2021): 2101998.

[2] Gostick, Jeff, et al. "OpenPNM: a pore network modeling package." Computing in Science & Engineering 18.4 (2016): 60-74.

[3] García-Salaberri, Pablo A. "1D two-phase, non-isothermal modeling of a proton exchange membrane water electrolyzer: An optimization perspective." Journal of Power Sources 521 (2022): 230915.
Fibrous Electrodes for Alkaline Electrolysis
Authors: Russo Andrea , Jensen Jens Oluf , Kraglund Mikkel Rykær , Zhang Wenjing (Angela) , Cho EunAe
Published: December 2024

The development of thin alkaline ion-conducting membranes with low internal resistance has highlighted the potential to reach high current densities in conventional alkaline electrolyzers. As membrane resistances drop with new novel separators, the necessity of using high surface area 3D porous electrodes without inactive regions in the form of large holes becomes evident, to be able to reach performances comparable to PEM or AEM systems.

To improve electrodes many researchers are moving towards high surface area nickel foams, as opposed to more conventional mesh or perforated plate-based electrode materials. While nickel foams have more surface area compared with their mesh counterparts, the specific surface areas are is still relatively low unless further surface enhancements are carried out in the form of rough coatings. Additionally, the total electrode thickness remains substantial, potentially resulting in mass transport issues, gas entrapment, and additional ionic ohmic losses within the porous structure. However, the absence of blind spots should lead to a significant increase in active catalytic area, corresponding to a higher performance.

This work demonstrates how to take the supporting structural morphology to the next step, by developing finely porous electrodes based on a polymer skeleton, coated with a thin homogenous layer of nickel phosphorous. This approach both enhances the accessible electrochemical surface area and reduces the environmental impact as the amount of nickel used is significantly decreased. The developed finely porous structures result in an order of magnitude larger surface area, at approximately one-tenth of the electrode thickness.

As an additional benefit, the diffusion path length for the evolved gasses is reduced, promoting mass transport properties, and helping to avoid commonly labeled bubble resistances, as well as potentially suppressing supersaturation effects.
Anion Exchange Membrane Water Electrolyzer Accelerated Durability Assessment Using Potential Cycling
Authors: Ul Hassan Noor , Volk Emily K. , Kreider Melissa , Dinh Huyen N , Pivovar Bryan S. , Alia Shaun M
Published: December 2024

Anion exchange membrane water electrolyzers (AEMWEs) have shown remarkable progress in terms of voltage efficiency and achievable current density in the past few years. Various methods are employed to assess the durability of AEMWEs at component and cell level, and include constant and cycled current/potential, start/stop cycles, and open-circuit-voltage (OCV) holds. Each technique may impose different levels of stress on individual components, and in cases have aimed to accelerate polymer degradation or to stress the catalyst or catalyst layer integrity. Particularly due to the more fundamental technology readiness level of AEMWE, it is essential to understand the degradation mechanism and failure modes at membrane electrode assembly (MEA) level.

In this study, commercial AEM, ionomer, Co3O4 as anode and PtC as cathode catalysts were employed for fabricating MEAs. Square-wave and triangular-wave potential cycling were applied as operational-based stress tests to understand the impact of load cycling on degradation. Square-wave potential cycling appeared to accelerate catalyst layer degradation through ionomer oxidation, which lessened catalyst site-access and enhanced kinetics. On the other hand, triangular-wave potential cycling seemed to stress membrane (thinning) reducing the high frequency resistance (HFR). In both cycling patterns, the dissolution of cobalt (catalyst) and nickel from the porous transport layer (PTL) were observed by inductively coupled plasma-mass spectrometry (ICP-MS) analysis of the feed liquid. Moreover, a slight decrease in double layer capacitance supports degradation of catalyst layer. The motivation of this investigation was to mimic closely representative operation when directly integrated with renewable energy sources. The results discussed here may provide insight as to lifetime differences between different electrolysis technologies and provide pathways to develop stress tests for AEMWE systems and improve cell level durability.

Figure 1
Investigation of Degradation Mechanism of Liquid Alkaline Water Electrolyzer Under Dynamic Operation Condition
Authors: Wang Guanzhi , Mukundan Rangachary , Peng Xiong
Published: December 2024

Abstract:

Liquid alkaline water electrolyzers (LAWEs) occupy a pivotal position in the realm of large-scale green hydrogen production1. However, LAWEs face a notable challenge in terms of pronounced electrode degradation under dynamic operating conditions, particularly the induced reverse current phenomenon experienced during transit start-up/shut-down operation2. In this study, in order to comprehend the degradation mechanism of LAWE under dynamic operational conditions, a three-electrode LAWE membrane electrode assembly (MEA) setup is designed to decouple the anode and cathode polarization behavior and track the anode/cathode performance during reverse current operation. Combined with post-mortem characterization, it is demonstrated that the anode performance is improved during reverse current operation due to the continuous formation of OER-active species NiOOH/Ni(OH)2. While severe cathode degradation is found, resulting from the irreversible oxidation of Ni metal to Ni(OH)2, which leads to worsened activity towards HER, decreased conductivity and significant strain-induced mechanical degradation. This research offers a comprehensive examination of the electrode degradation mechanism in LAWE, providing valuable insights to enhance its adaptability to dynamic operations, and contribute to the widespread application of green hydrogen production through electrolysis.

Acknowledgement

The authors acknowledge the Department of Energy-Office of Energy Efficiency and Renewable Energy-Hydrogen and Fuel Cell Technologies Office (DOE-EERE-HFTO) and the H2 from Next-generation Electrolyzers of Water (H2NEW) consortium for funding under Contact Number DE-AC02-05CH11231.

References:

Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annu. Rev. Chem. Biomol.
Eng. 2019, 10, 219-239.

Kim, S. Jung, K. Kim, H. Kim, J. Kwon, J. Lee, H. Cho, Y. Kim, JACS Au, 2022, 2, 2491-2500.
(Invited) Ionomer-Free Nano-Channeled Electrodes for Proton-Exchange-Membrane Water Electrolyzers
Authors: Lee Keonhag , Babbe Finn , Wang Guanzhi , Tricker Andrew , Mukundan Rangachary , Weber Adam Z. , Peng Xiong
Published: December 2024

Clean hydrogen, produced through water electrolysis using renewables, is a promising means of decarbonization for hard-to-abate sectors, including transportation, industry, and chemical sectors. Proton-exchange-membrane (PEM) water electrolyzers are one of the leading electrolysis technologies amongst other types of electrolyzers available today with their compact design and rapid response time, which align well with the requirements of renewable energy integration. However, cost remains a major challenge in further adoption of this technology. Specifically, the high cost and limited availability of iridium catalysts used in the anode for oxygen evolution reaction are predicted to become the bottleneck at the gaga-watt (GW) scale, necessitating catalyst loading reduction and recycling processes. In this work, we present the ionomer-free nano-channeled porous transport electrodes (PTEs) aimed at reducing the cost of PEM water electrolyzers. The nano-channeled PTEs demonstrate superior current density (> 9 A/cm2 below 3 V) and reduces overpotential by 190 mV compared to baseline ionomer-free PTEs. In addition, nano-channeled electrodes show minimal degradation after 100k cycles of accelerated stress tests. Decay rate of 11.66 µV/h was achieved over 2000 h operation at 1.8 A/cm2. These results highlight the significance of the localized transport dynamics at the electrode interface in PEM water electrolyzers.
Numerical Investigation on Two-Phase Flow Pressure Drop in Cathode Channels of Proton Exchange Membrane Fuel Cells
Authors: Yang Danan , Garg Himani , Andersson Martin
Published: December 2024

Water management remains a critical challenge in proton exchange membrane (PEM) fuel cells, particularly concerning flooding under high-current density and prolonged operation. Dynamic water distribution directly affects gas phase transport, encompassing convection within gas channels (GCs) and diffusion through porous electrodes. The fluctuation of pressure drop has been highlighted in previous studies [1-3], which is more frequent when compared with that when only single-phase flow in the channel is considered. A reasonable cathode channel pressure drop can benefit fuel cell performance [1] and energy efficiency [4]. Although pressure drop correlations have been conducted experimentally and numerically [5], the pressure drop prediction still needs to be improved, for example, involving the liquid transport from gas diffusion layers (GDLs) [6]. In this study, two-phase flow simulations in an assembled GC and fibrous GDL are conducted by the volume of fluid method in OpenFOAM. To utilize the fibrous GDL structures to mimic the natural breakthrough water, different GDLs are stochastically reconstructed using straight- and curved- cylinders (regarded as carbon fibers) and keeping the same bulk porosity and fiber diameter, as shown in Figure 1. The GC pressure drop is studied in local and total regions in different scenarios, e.g, different GDL structures (see Figure 1(c)), different surface wettability, and different air flow rates. Preliminary results show that the pressure drop does not exhibit a direct correlation with the liquid amount present in the GC, suggesting a multifaceted relationship that extends beyond mere liquid content, as shown in Figure 2. Therefore, it is imperative to explore additional factors that may influence this critical parameter. Figure 3 displays the spatial and temporal distribution of pressure and water cross-section area of 23 cross-section along the GC length direction in 13.5 ms in Case A and B. The breakthrough types in the GDL/GC interface and drainage flow types in GCs are found to relate more to the pressure drop. In future work, we aim to explore all the above scenarios to gain deeper insights into their impact on pressure drop behavior and ultimately enhance our understanding of the complex interactions governing two-phase flow in PEM fuel cell systems.

References

Li, P. Pei, Z. Wu, H. Xu, D. Chen and S. Huang, Applied Energy, 190, 713 (2017).

Liu, L. Guo, R. Zhang, L. Chen and W.-Q. Tao, Applied Energy, 302, 117625 (2021).

Zhang, S. Liu, Z. Wang, R. Li and Q. Zhang, International Journal of Hydrogen Energy, 47, 17713 (2022).

S. Ijaodola, Z. El- Hassan, E. Ogungbemi, F. N. Khatib, T. Wilberforce, J. Thompson and A. G. Olabi, Energy, 179, 246 (2019).

Li, H. Zhou, C. Li, Z. Liu, P. Zhang and C. Lu, Experimental Thermal and Fluid Science, 155, 111198 (2024).

Mortazavi and K. Tajiri, Renewable and Sustainable Energy Reviews, 45, 296 (2015).

Figure 1
Novel Approaches for a Time and Cost Efficient Activation of Polymer Electrolyte Membrane Fuel Cell Stacks
Authors: Zink Stefan , Joerissen Ludwig
Published: December 2024

Towards a CO2 free energy supply, hydrogen plays an important role as a chemical energy storage capable of storing renewable energy in large dimensions. In this context, fuel cells, such as e.g. polymer electrolyte membrane fuel cells (PEMFC) are going to evolve to a key technology for the conversion of the chemically stored energy back to usable electric energy. Therefore, after decades of fuel cell research, the phase of industrialization of fuel cells has begun recently to provide fuel cells in large quantity for a variety of applications, such as e.g. to power heavy duty vehicles, ships and even airplanes or as stationary power plants.

For PEMFC mass production, the optimization of the manufacturing process of fuel cells is important to decrease the manufacturing time and costs. One of the most time and cost consuming steps during the production of fuel cells is the first time activation. During the so-called break-in, the fuel cell is operated for the first time in order to activate the membrane electrode assembly (MEA). During break-in, the proton conductivity of the membrane is established and the catalyst is activated, but also chemical residues of the production of the fuel cell components were removed. This procedure is necessary for a fuel cell stack to provide its maximum power output and maximum robustness of all single cells. Furthermore, the successful activation of the PEMFC strongly affects the overall lifetime of a fuel cell stack.

To date, a typical break-in of a fuel cell stack takes in between 2 and 8 hours of time, in which a considerable amount of hydrogen and air is required. Thereby, the stack is commonly operated at a high relative humidity doing several cycles of current ramps from minimum to medium or high load interrupted by shutdowns, whereby the first current ramp is usually performed very slowly. Besides the media consumption, the rather long state-of-the-art break-in time calls for a high degree of parallelization of break-in stations at each production line to reach a reasonable output of fuel cell stacks, which is related to high investment costs. An optimization of the break-in process in respect to the necessary time and media consumption significantly reduces the production costs of a PEMFC stack. In this work, several new approaches to activate PEMFCs were introduced in order to decrease the duration and media consumption of the break-in process. Thereby, the common break-in doing several current ramps was replaced by more efficient and promising approaches, such as e.g., hydrogen starvation events or hydrogen pumping. This break-in experiments were performed in short stacks of small scale as well as automotive scale. Finally, the influence of each break-in variation on the performance and durability of the PEMFC was investigated.
Performance of Pt-Free Catalysts in a Fuel Cell Vehicle
Authors: Santos Andrade Tatiana , Thiringer Torbjörn
Published: December 2024

Fuel cell vehicles have been pointed out as a promising green transportation alternative in the current energy transition scenario. However, the use of Pt-based catalysts adds relevant costs to the proton exchange membrane (PEM) fuel cell technologies that limit the spread commercialization of those vehicles. Therefore, Pt-free catalysts have been strongly investigated for PEM fuel cell stacks. However, those catalysts usually face a performance-durability trade-off that is a challenge to overcome. In recent years, significant improvements have been reported for those catalysts. Thus, catalysts that reach encouraging criteria for single fuel cell experiments aiming at vehicle propulsion were reported which supports a positive direction for the application of those materials in fuel cell vehicles. Modeling these novel materials as stacks in a fuel cell vehicle and comparing them to conventional fuel cell vehicles is a relevant step to investigate the potential and limitations of those catalysts aiming at vehicle propulsion technologies. Thus, in this work, we aim to evaluate how novel Pt-free catalysts would impact the fuel cell vehicle performance in comparison to the current fuel cell stacks. For that, reported experimental data of single Pt-free fuel cells were used as a reference. The data were scaled up to a fuel cell stack based on the stack size of a commercial fuel cell vehicle. Further, the designed stack is integrated into a fuel cell vehicle model and simulated for a driving cycle using MATLAB. The vehicle model has similar parameters to a high-performance fuel cell vehicle and comprises the following components besides the fuel cell stack: the wheels, a single-step gear, an 8-pole PMSM motor, a 3-phase IGBT inverter, and a small lithium-ion battery. Results indicate that despite the low performance at high power, the vehicle comprising a Pt-free fuel cell could achieve promising car efficiency compared to the vehicle comprising conventional Pt loading due to its performance at low power values. Establishing strict limits in the fuel cell operation and increasing the number of cells could favor the integration of Pt-free catalysts into fuel cell vehicles supporting the development of more cost-competitive fuel cell vehicles.
Development of a Dynamic Model for a Shell-and-Tube Type Gas-to-Gas Polysulfone Hollow Fiber Membrane Humidifier and Optimization of Operating Conditions and Fiber Dimensions to Maximize PEMFC Stack Power in Hydrogen Fuel Cell Vehicles
Authors: Kim Jiwoong , Kim Sehyeon , Chun Hyunsoo , Kang Sanggyu , Min Kyoungdoug
Published: December 2024

In polymer electrolyte membrane fuel cell (PEMFC) systems, effective water management is key to enhancing both efficiency and lifespan of the system. The necessity of keeping the system optimally hydrated to improve proton conductivity, while avoiding the issue of water flooding, emphasizes the crucial role of humidification technologies. In this study, the permeation characteristics of polysulfone hollow fiber membranes for transferring water vapor from moist air were experimentally and theoretically investigated. Experiments were conducted to assess the effect of operating conditions (e.g., inlet temperature, relative humidity, and temperature differences) on the performance of the humidifier under various feed flow rates using the membrane humidifier module in a hydrogen fuel cell vehicle. Additionally, detailed theoretical analyses were undertaken to comprehend the permeation phenomena of air through the membrane, which were correlated with experimental data to validate the model (relative error of <5%). The developed model incorporates transport equations for species, mass, momentum, and energy balances across both bulk streams, taking into consideration the heat and concentration boundary layer near the membrane. Furthermore, it introduces a new dual-mode sorption model that incorporates temperature dependence into the solution-diffusion mechanism across the membrane. The performance of the humidifier in two different flow configurations, counter and parallel-flow, was compared to illustrate the spatial variations in heat and mass transfer rates. To investigate the dynamic behavior of the PEMFC system, a system model integrating of a lumped dynamic model of an air compressor, a one-dimensional dynamic model of an intercooler (i.e., heat exchanger), and a one-dimensional dynamic model of a PEMFC stack was developed, as well as a dynamic model of a membrane humidifier. To maximize stack power in a PEMFC system, using a Pareto chart and response surface methodology, the degree of influence of valuables of the membrane humidifier was determined, and optimal operating points and geometric designs of the humidifier for enhanced efficiency and PEMFC stack performance were systematically identified.
Low-Temperature Cation Ordering in Ce0.5-XZr0.5+XO2 Under Precisely Controlled P(O2)
Authors: Okazaki Yume , Ishii Akihiro , Oikawa Itaru , Takamura Hitoshi
Published: December 2024

CeO2-ZrO2 solid solutions (CZ) with a high oxygen storage capacity (OSC), owing to the valence change of Ce ions upon reduction, have been utilized to control the P(O2) of automobile exhaust purification systems. In the CeO2-ZrO2 system, cation-ordered κ-Ce2Zr2O8 shows the highest OSC; however, cation ordering requires high-temperature heat treatment, typically higher than 1200 °C, under a reducing atmosphere [1], which leads to grain growth and a decrease in OSC. Our previous study revealed that the addition of a small amount of Fe2O3 reduces the cation-ordering temperature to 800 °C, although the mechanism is unknown [2]. In this study, in-situ high-temperature XRD revealed that Fe2O3 plays an important role in cation ordering by precisely controlling P(O2), which assists the nucleation of the ordered phase. Furthermore, the effect of the Ce/Zr ratio on the ordering behavior was investigated because Zr-rich CZ (Ce0.5-xZr0.5+xO2) with a high proportion of Zr is expected to suppress grain growth, thereby improving the specific surface area and OSC. Thus, this study discusses the mechanism of low-temperature cation ordering of Zr-rich CZ solid solutions by Fe2O3 addition and evaluates their OSC.

DFT-based first-principles calculations revealed that Zr-rich Ce0.375Zr0.625O2 was less likely to be ordered than Ce0.5Zr0.5O2 (Ce/Zr=1) because the energy gain resulting from cation ordering was smaller by 0.35 eV/f.u. Meanwhile, in the disordered phases, the oxygen vacancy formation energy was negatively larger by 0.12 eV/f.u. in the Zr-rich CZ than in Ce0.5Zr0.5O2, suggesting that the Zr-rich CZ was more readily reduced. The in-situ high-temperature XRD revealed that Fe2O3-added Zr-rich Ce0.5-xZr0.5+xO2 (0.05 < x < 0.1) was not ordered under dry 10%H2-N2; however, surprisingly, it was successfully ordered under wet 4.5%H2-N2, which provides a weak reducing atmosphere. It should also be noted that Zr-rich CZ without Fe2O3 addition was not ordered, regardless of the gas composition. In addition, the Zr-rich CZ embedded in the mixture of Fe2O3 and Fe3O4 powders and heat-treated at 900 °C showed significant grain growth, which seems to be related to the initial stage of cation ordering. Based on these results, a moderately reducing atmosphere rather than a highly reducing one leads to a deeper reduction of the Zr-rich CZ, which triggers cation ordering. A more detailed thermodynamic discussion is also provided. The cation-ordered Zr-rich κ-Ce1.79Zr2.21O8 showed an excellent OSC of 688 μmol-O2/g at 400 °C excluding the reduction amount of Fe2O3 added, which is 96±6 % of the theoretical OSC, even without precious metal group catalysts.

References

[1] Y. Nagai et al., Catalysis Today, 74 (2002), 225-234.

[2] K. Murakami, J. Mater. Chem. A, 10 (2022), 21291-21299.
Towards Ultrahigh Osmotic Energy Harvesting By Covalent-Organic Framework Based Ionic Diode Membranes
Authors: Yeh Li-Hsien
Published: December 2024

The chemical energy stored between seawater and river water, the so-called osmotic energy (or blue energy), can be harvested by an ion-selective membrane. However, previously reported membranes suffer from insufficient ion selectivity and inferior transmembrane ionic flux (low conductance), thus impeding practical application. For example, the output osmotic power density reported by most of existing ion selective membranes is typically below the commercial benchmark (5 W/m2). Taking the inspiration from electrocytes in electric eel, which consist of a large number of sub-nanoscale rectified ion channels that allow unidirectional ion transport with amplified flux, we engineered a sub-2 nm-scale covalent-organic framework (COF)-based ionic diode membrane (IDM) for highly efficient osmotic energy harvesting (Fig. 1). We show that the proposed IDM can rectify ionic current even in high salt concentration, which was supported by our simulations based on the Poisson-Nernst-Planck model. We also probe application of this membrane in harvesting energy from salinity gradients. Notably, in addition to ultrahigh ion selectivity, these sub-2 nm-scale ionic diode membranes can achieve an unprecedented power density, higher than the commercial benchmark bandgap. Impressively, the exploited IDM can produce an ultrahigh power density as high as 27.8 W/m2 by mixing artificial salt-lake water and river water, outperforming all the state-of-the-art ion selective membranes under the same testing condition. Our work would open up new avenues of using pinhole-free COF membranes towards next-generation highly selective and ultrahigh-performance sustainable energy harvesting.
Dissociative Oxygen Adsorption and Incorporation in Co3O4-Dispersed BaZr0.9Sc0.1O2.95 for a PCFC Cathode
Authors: Kamohara Shinnosuke , Ishii Akihiro , Oikawa Itaru , Takamura Hitoshi
Published: December 2024

Proton-conducting fuel cells (PCFCs), which operate at lower temperatures than conventional solid oxide fuel cells (SOFCs) using an oxide-ion conductor, have attracted considerable attention owing to their high energy-conversion efficiency. Even with mobile protons, oxygen reduction reactions at the cathode limit the performance of PCFCs. To improve their cathode properties, a variety of functional oxides, including the so-called triple conductors, which have mobile oxide ions, protons, and holes, have been developed. Our group has focused on the excellent catalytic activity of Co3O4 for the dissociative adsorption of oxygen at elevated temperatures, which is comparable to that of Co-containing mixed conductors with a perovskite-type structure [1,2]. In this study, Co3O4-dispersed proton-conducting oxides, BaZr0.9Sc0.1O2.95, were prepared for use as composite-type cathodes, and their surface oxygen exchange behavior was investigated using the pulse isotopic exchange (PIE) technique.

BaZr0.9Sc0.1O2.95 (BZS10) was prepared using a solid-state reaction method by sintering at 1300 °C for 10 h. To prepare the composite powders, BZS10 powders were ball-milled with x vol%Co3O4 (x = 1, 3, 5, 10, and 50). Prior to PIE, their specific surface area was determined by a BET method for the sample powder heat-treated at 880 °C, which is slightly higher than the highest PIE temperature to avoid morphological and compositional change during PIE. The PIE was performed at 800–200 °C under a 10%O2 atmosphere.

Based on the almost constant lattice constants, regardless of the Co3O4 volume fractions, the composites were successfully prepared as a dual-phase state, unlike Co-doped BZS10 prepared at 1225 °C, which showed a decrease in the lattice constant [3]. At 500 °C, the surface oxygen exchange rate R0
of BZS10 without Co3O4 particles was 4.0×10-6 mol/m2·s. R0
was surprisingly enhanced by an order of magnitude with the addition of only 1 vol%Co3O4. Further addition of Co3O4 exceeding 10 vol% reduced R0
. This trend indicates that the optimum amount of Co3O4 provided sufficient dissociated oxygen on BZS10, which was readily incorporated into BZS10. Their electrochemical properties and detailed microstructural analyses are also discussed.

[1] Y. Tomura et al., J. Mater. Chem. A, 8 (2022) 21634–21641.

[2] A. Ishii et al., ACS Appl. Mater. Interfaces, 15 (2023) 34809−34817.

[3] H. Uehara et al., Int. J. Hydrogen Energy, 47 (2022) 5577−5584.
Modeling Oxygen Partial Pressure in Solid Oxide Electrolysis Cells: The Microstructure Effect
Authors: Lei Yinkai , Cheng Tianle , Xue FEI , Epting William K. , Abernathy Harry W. , Wen You-Hai
Published: December 2024

Oxygen partial pressure is an important thermodynamic state variable that affects both the performance and degradation of solid oxide electrolysis cells. In this work, a three-dimensional model developed from Virkar’s one-dimensional model has been applied to reconstructed and synthetic microstructures of solid oxide cells with hydrogen electrodes made from Ni and yttria stabilized zirconia (YSZ), and with oxygen electrodes made of gadolinium doped ceria (GDC) and lanthanum strontium cobalt ferrite (LSCF). The effect of microstructures, including the thickness of the YSZ and GDC layer, and the compositions of the hydrogen and oxygen electrodes on the distribution of oxygen partial pressure was investigated. The results show that the maximum oxygen partial pressure occurs on the interface between the GDC and YSZ layers. Under the constant current mode, a thicker GDC layer may decrease or increase the maximum oxygen partial pressure in the cell, depending on the rate of oxygen ion exchange between GDC and YSZ. A thicker YSZ layer lowers the maximum oxygen partial pressure in the hydrogen electrode but increases the maximum oxygen partial pressure in the cell. In addition, the Ni:YSZ/LSCF:GDC ratio and porosity also affect the distribution of oxygen partial pressure. These findings provide insights on mitigating degradation in solid oxide electrolysis cells by tuning the cell microstructures.
Solid State YSZ Electrolyte Oxygen Partial Pressure Under Dynamic Operation
Authors: Hartvigsen Jeremy , Zhang Qian , Casteel Micah , Kane Nicholas , Wang Lucun , Priest Cameron , Gomez Joshua , Ding Dong
Published: December 2024

Idaho National Lab has developed a time dependent model of oxygen partial pressure in the electrolyte of a solid oxide cell. This model is of a standard cell used commonly throughout literature and is the reference cell of the H2New consortium. The cell is composed of a generic material set for solid oxide electrolysis. The electrolyte is a 7 micron thick layer of YSZ, 5 micron thick barrier layer of GDC, and an electrode layer of LSCF. During cell operation, there is a slow increase of oxygen partial pressure in the electrolyte. This can be observed to reach a critical threshold which induces micro-cracking. This is one of the underlying degradation mechanisms of solid oxide cells. At high current, the time to reach the threshold changes. By switching between a safe threshold and an unsafe threshold, a meta-stable relaxation and redistribution of oxygen partial pressure avoids reaching the critical threshold. The time scale of the threshold can be between seconds and hours depending on the current and voltage applied. Models have been developed to reduce the impact of oxygen partial pressure using different cycling timescales, as well as identifying safe short-term overproduction rates.
Theoretical Analysis of Carbon Deposition in the Fuel Electrode of a Reversible Solid Oxide Cell
Authors: Yang Gang , Leger Jeremy Joseph , Wang Yudong , Xu Nengneng , Zhou Xiao-Dong
Published: December 2024

In this presentation, we aim at analyzing the changes of Gibbs free energy of carbon deposition reactions in a reversible solid oxide cell (RSOC) that utilizes a mixture of CO and CO2 in its fuel electrode compartment, operating either in fuel cell or electrolysis mode. The thermodynamics analysis was carried out by using oxygen chemical potential at the interface between the electrolyte and fuel electrode, µO2
FE|EL
, and a 1-dimensional model is established to calculate µO2
FE|EL
. From the thermodynamic calculation, we find that the higher µO2
FE|EL
, the greater the Gibbs free energy. The change of Gibbs free energy of two possible carbon deposition reactions: CO electroreduction reaction and Boudouard reaction, are compared. Gibbs free energy changes of CO reduction reaction are evaluated based on different RSOC cell parameters as well as operating conditions, including cell voltage, current density, electrolyte thickness, electronic and ionic conductivity of electrolyte and electrodes interfaces. In this research we found that:

CO can still be electrochemically reduced even the Boudouard reaction is absent in the fuel electrode. Therefore, suppressing CO electrochemical reduction reaction is critical to eliminate carbon deposition in RSOC.

The RSOC is prone to carbon deposition under high cell voltages . Therefore, carbon deposition tends to occur in electrolysis mode rather than in fuel cells mode when CO concentration and cell parameters are the same. High CO concentration in the fuel mixture also facilitates carbon deposition.

A thin electrolyte layer significantly increases oxygen chemical potential µO2
FE|EL
at the interface of fuel electrode and electrolyte thus fabricating thin electrolyte is critical for eliminating carbon deposition. What is more, carbon deposition can be suppressed with an electrolyte exhibiting a high electronic conductivity σe
EL
and/or a low low ionic conductivity σi
EL
, indicating that increasing σe
EL
by doping elements such as Ce into YSZ electrolyte can help prevent carbon deposition.

Modifying the interfacial area specific electronic resistance re
FE|EL
and ionic resistance ri
FE|EL
across fuel electrode and electrolyte also contribute to carbon deposition prevention. Increasing re
FE|EL
or reducing ri
FE|EL
is beneficial to suppress carbon deposition.

Contrary to the the interface between fuel electrode and electrolyte, low interfacial area specific electronic resistance re
OE|EL
and high interfacial area specific ionic resistance ri
OE|EL
is in favor of suppressing carbon deposition. However, a relatively lower ri
OE|EL
is also required to obtain an outstanding RSOC electrochemical performance.
In-Situ Exsolved Nico Alloy Nano Catalyst for Direct Utilization of Ammonia Fuel in Solid Oxide Fuel Cells
Authors: Jeong Hyeongwon , Kim Yo Han , Won Bo-Ram , Park Dayoung , Myung Jae-Ha
Published: December 2024

Ammonia (NH3) is regarded as an innovative hydrogen (H2) carrier for diverse energy conversion systems with its clean nature, high energy density, and widespread availability. Solid oxide fuel cells (SOFCs) are attracting attention for direct utilization of NH3 fuel due to thier high temperature operating (~900 oC) and conversion efficiency. The electrode materials for direct NH3 SOFCs (DA-SOFCs) are still limited to traditional Ni-based cermet materials. These materials suffer from additional overpotential during NH3 decomposition steps and the potential nitriding of pure Ni metal catalysts. In this study, we suggest in-situ prepared single and alloy nano metal catalysts exsolved from La0.43Ca0.37M1-xO3-d (M: Ni, Co, Fe, NiCo, NiFe, and CoFe) perovskite electrodes. Homogenously distributed NiCo alloy nano exsolution catalyst exhibits synergistically enhanced powder density under both H2 and NH3 fuel conditions, compared to that of single Ni exsolution and conventional Ni-YSZ electrode. Hydrogen production efficiencies of exsolution catalysts via NH3 decomposition reaction are characterized to determine the optimal composition of exsolution catalysts for DA-SOFCs electrode design. The electrochemical properties of different catalytic materials and fuels are also investigated to understand the effect of exsolution catalysts under DA-SOFCs operating conditions. The results obtained here are expected to improve the catalytic activity and durability of electrode materials for DA-SOFCs applications.
Optimum Operating Conditions By Co-Electrolysis in Solid Oxide Cell for Fischer-Tropsch Synthesis
Authors: Imabayashi Takumi , Ozeki Takayuki , Asano Koichi
Published: December 2024

Highly efficient liquid fuel production can be expected by integrating the Fischer-Tropsch (FT) synthesis process at the latter stage of the solid oxide electrolysis cell (SOEC) process and integrating the heat transfer between the processes. However, it is difficult to achieve the high efficiency and durability conditions in SOEC process with the high-yield conditions in FT synthesis process. In this study, the SOEC operating conditions were investigated to improve the efficiency and durability of the integrated production process by thermodynamic equilibrium calculations of the gas composition at the SOEC outlet (FT synthesis inlet) and experiments using a single cell.

Gas compositions of H2/CO=2.0 and high H2 and CO production are favorable for FT synthesis. To achieve these conditions at the SOEC outlet, the SOEC inlet gas must be close to (H2+H2O)/CO2=2.0, and reactant utilization must be high. However, these conditions are likely to cause carbon deposition in SOEC, which can lead to cell damage. An effective way to prevent carbon deposition is to increase the cell temperature because carbon deposition is an exothermic reaction. High temperature conditions have the advantage of lowering the cell voltage in co-electrolysis and preventing carbon deposition, but the life of the cell components may be shortened. Promoting methanation was also an effective way to prevent carbon deposition because of consuming CO, but it may cause lower yields of liquid fuel from FT synthesis. Under pressurized conditions, the volume reduction reaction which includes methanation and carbon deposition is accelerated Therefore, the risk of carbon deposition under pressurized conditions has become highly dependent on the SOEC operating conditions which determine whether methanation or carbon deposition is more promoted. These results clarify the risks associated with changing the operating conditions by co-electrolysis in SOEC and can be used to guide the optimum operating conditions.
Fabrication of Dense Electrolyte for Metal-Supported Solid Oxide Fuel Cells By Plasma Spray Method
Authors: Yashiro Keiji , Matsui Toshiaki , Yamaguchi Mina , Fujisaki Takaya , Kawada Tatsuya
Published: December 2024

Metal-supported SOFCs (MS-SOFCs) have attracted attention because of their potential for low cost and high mechanical robustness. However, the conventional cell fabrication process is not easily applied to MS-SOFCs. The difficulty of MS-SOFC fabrication is especially to form a dense electrolyte without oxidation and diffusion of the metal support. We’ve tried to use a plasma spray method to prepare the metal supported cells. Then, apparently dense electrolyte layer could be fabricated using doped lanthanum gallate instead of yttria stabilized zirconia. In this paper, electrochemical performance and gas tightness of the cells were evaluated to consider the applicability of plasma spray for MS-SOFC fabrication.

A prepared MS-SOFC consists of porous metal substrate (SUS430), NiO-YSZ anode, Sr-, Mg-doped lanthanum gallate (LSGM9182), and conventional cathode (LSCF6428). The cell components, except for the porous substrate, were deposited by atmospheric pressure plasma spray (APS). Gas tightness of the cell was confirmed by open circuit voltage (OCV) measurement. Cell performance was evaluated by current-voltage measurement and impedance measurement. Post-analysis of the cell was conducted by SEM/EDS.

The measured OCV was confirmed to be equivalent to theoretical value in humidified hydrogen at 973 K. It means the fully dense electrolyte layer could be prepared by plasma spray. Current density of I-V measurement was 0.6 Acm-2 at 0.5 V at 973 K. The impedance results showed larger over potential of anode reaction. This might be caused by anode electrochemical reaction and gas diffusion through anode and substrate layer. Further development of plasma spray anode is necessary for practical application; however, this study confirmed the possibility of the plasma spray method to fabricate the dense electrolyte for MS-SOFCs.

This research was financially supported by NEDO.