Performance Of Solid Oxide Electrolysis Cells Research Articles

EReaxFF force field development for BaZr0.8Y0.2O3-δ solid oxide electrolysis cells applications

The use of solid-oxide materials in electrocatalysis applications, especially in hydrogen-evolution reactions, is promising. However, further improvements are warranted to overcome the fundamental bottlenecks to enhancing the performance of solid-oxide electrolysis cells (SOECs), which is directly linked to the more-refined fundamental understanding of complex physical and chemical phenomena and mass exchanges that take place at the surfaces and in the bulk of electrocatalysis materials. Here, we developed an eReaxFF force field for barium zirconate doped with 20 mol% of yttrium, BaZr0.8Y0.2O3-δ (BZY20) to enable a systematic, large-length-scale, and longer-timescale atomistic simulation of solid-oxide electrocatalysis for hydrogen generation. All parameters for the eReaxFF were optimized to reproduce quantum-mechanical (QM) calculations on relevant condensed phase and cluster systems describing oxygen vacancies, vacancy migrations, electron localization, water adsorption, water splitting, and hydrogen generation on the surfaces of the BZY20 solid oxide. Using the developed force field, we performed both zero-voltage (excess electrons absent) and non-zero-voltage (excess electrons present) molecular dynamics simulations to observe water adsorption, water splitting, proton migration, oxygen-vacancy migrations, and eventual hydrogen-production reactions. Based on investigations offered in the present study, we conclude that the eReaxFF force field-based approach can enable computationally efficient simulations for electron conductivity, electron leakage, and other non-zero-voltage effects on the solid oxide materials using the explicit-electron concept. Moreover, we demonstrate how the eReaxFF force field-based atomistic-simulation approach can enhance our understanding of processes in SOEC applications and potentially other renewable-energy applications.

Current-Voltage (i-V) characteristics of electrolyte-supported (NiO-YSZ/NiO-SDC/ScSZ/LSCF-GDC/LSCF) solid oxide electrolysis cell during CO2/H2O co-electrolysis

Solid oxide electrolysis cells (SOECs) stabilize CO2 emissions by converting CO2/H2O into synfuel. Current-Voltage (i-V) characteristics of an electrolyte-supported button cell (NiO-YSZ/NiO-SDC/ScSZ/LSCF-GDC/LSCF) were measured as a function of temperature, water vapor concentration, and CO2 gas concentrations. The cell microstructure was characterized by the Field Emission Scanning Electron Microscope (FE-SEM). FE-SEM micrographs depict that the electrolyte layer is relatively dense, and porous fuel and air electrode layers are well adhered to the electrolyte. The i-V curves were obtained at a scan rate of 0.02 Vs−1 from 0.3 to 1.5 V. Electrolysis current density increases as the temperature increases. SOEC performance increases, but SOFC performance decreases with increased water vapor concentration. Electrolysis current densities decrease as the CO2 concentration increases. The i-V characteristics show only ohmic polarization under fuel-lean and fuel-rich conditions. At optimal conditions, current density values at 800 °C/1.5 V are -174, -187, and -195 mA cm−2 for 5 %H2O, 30 %CO2, and 30 %CO2/5 %H2O co-electrolysis. At 800 °C, open-circuit voltage (OCV) values for H2O, CO2, and co-electrolysis are 0.906, 0.891, and 0.885 V, respectively. The electrolysis area-specific resistances (ASRs) give information on the reduction of CO2 or H2O, forming CO or H2, respectively. At optimal conditions, ASR values are 3.43, 3.29, and 3.18 Ω cm2 for H2O, CO2, and co-electrolysis, respectively. Co-electrolysis has a lower ASR value than pure H2O and CO2 electrolysis, indicating that H2O and CO2 are involved in the electrochemical processes.

Effect of cell sintering temperature on the performance of non-noble metal loaded cerium oxide SOEC anodes

Abstract Introducing methane oxidation reaction into the anode of the high-temperature solid oxide electrolysis cell (SOEC) can reduce the power consumption for water electrolysis. Compared to the traditional conditions of methane oxidation, the methane oxidation catalyst sintered at the SOEC anode, which is closely related to the cell sintering process. This study uses non-noble metals as active sites for methane oxidation, zirconia, and samarium oxides doped ceria as catalyst support and oxygen ion conductors. The effects of anode sintering temperature on the electrochemical performance of SOEC assisted by methane oxidation were investigated. The results indicate that the high-temperature sintering process promotes the performance of the SOEC anode with Ni as the active site, while high temperature harms the performance of the Co-loaded anode. The sintering temperature exhibits a poor effect on the Fe-loaded anode. The Ni exhibits good enhancement of methane oxidation on reducing the electrolysis voltage of SOEC, while Co only exhibits methane oxidation assistance at low-temperature sintering. Differently, Fe has almost no obvious methane oxidation assistance for SOEC, which mainly represents good oxygen evolution performance.

Integrated Thermodynamic Analysis and Channel Variation Effects on Solid Oxide Electrolysis for Efficient Hydrogen Generation

This study delves into the intricate dynamics of Solid Oxide Electrolysis Cells (SOECs) using comprehensive simulation and analysis. By exploring the effects of temperature, pressure, and geometrical variations, we reveal valuable insights into the behavior of these cells. Our findings encompass diverse aspects, including the distribution of velocity magnitudes, density patterns, and dynamic viscosity within the cell. Notably, varying cell geometries lead to distinct velocity magnitude distributions, shedding light on the fluid dynamics complexities at play. The density distribution analysis underscores the influences of temperature, pressure, and hydrogen concentration on mass transport behavior. Dynamic viscosity profiles further contribute to our understanding of fluid flow characteristics and their relevance to electrochemical reaction rates. Moreover, our study examines the interplay between voltage efficiency, current density, and operating conditions. Intriguingly, we identify scenarios where voltage efficiency surpasses 100%, suggesting potential energy gains from hydrogen production. These intricate relationships emphasize the significance of optimizing SOEC performance for diverse applications. In essence, this research offers a comprehensive view of SOEC behavior, providing insights crucial for enhancing their design and operation. The study's outcomes contribute to the advancement of sustainable hydrogen production through informed decision-making and efficient operational strategies.

Sulfur poisoning on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ fuel electrode for direct electrochemical CO2 reduction in solid oxide electrolysis cells

As a promising energy conversion technology, solid oxide electrolysis cells (SOECs) can efficiently convert CO2 to CO by utilizing renewable energy sources and industrial waste heat. Sulfur poisoning of fuel electrode is a significant drawback to the electrochemical activity and long-term electrolysis performance of SOECs using sulfur-containing fuels. Traditional Ni-based cermet electrodes are susceptible to sulfur poisoning due to the low activation barrier and large enthalpy of the adsorbed sulfur species on the Ni surface. La0.75Sr0.25Cr0.5Mn0.5O3-δ-based materials which exhibit excellent redox stability have been considered as the promising candidates for substitution of Ni-based cermet electrodes. Herein, the sulfur poisoning behavior on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ (LSCM-GDC) fuel electrode under CO2–SO2 condition and the mechanism of sulfur poisoning are investigated. The results show that the LSCM-GDC fuel electrode possesses stable electrocatalytic activity as SO2 content up to 10 ppm. With increasing of SO2 content, metallic sulfide, amorphous sulfur and sulfate impurities can be detected on the electrode surface, which decrease the reactive sites and hinder the charge transfer and oxygen ions transport pathway, leading to degradation of the electrolysis performance. The plausible sulfur poisoning mechanism is divided into two categories, namely, thermodynamic and electrochemical processes. For thermodynamic process, SO2 molecules adsorb into oxygen vacancies and couple to coordinated oxygen lattices to form sulfates; for electrochemical process, the formation of amorphous sulfur and metallic sulfide impurities is caused by the binding of SO2 molecules to surface polarons at three phase boundaries under cathodic polarization. This work provides new insights into sulfur poisoning effect on the perovskite oxide electrodes.

Optimizing water electrolysis activity in Mo-doped Sr2FeCoO6-δ perovskites by balancing oxygen vacancies and structural stability

Perovskite-based solid oxide electrolysis cells (SOECs) are promising for efficacious hydrogen production. This work explored how varying molybdenum (Mo) content impacts the structure and performance of Sr2FeCo1-xMoxO6-δ (SFCMx) perovskites for SOEC water electrolysis. SFCMx (x = 0.1–0.5) were synthesized via sol-gel method and incorporated into symmetrical cells. Electrolysis testing showed SFCM0.3 had the highest activity, achieving 2.09 A cm−2 at 2.0 V and 800 °C, compared to 0.964 and 0.847 A cm−2 for SFCM0.1 and SFCM0.5 respectively. This optimal performance with 0.3 Mo doping was put down to simultaneous variations in oxygen vacancy concentration and crystalline structure stability. Lower Mo doping accelerated charge transfer but destabilized the structure, while higher doping stabilized the cubic perovskite structure but reduced vacancies and electrocatalytic activity. This work demonstrates that balancing activity and stability by optimizing dopant concentration is critical to maximize SOEC performance. This provides new insights for enhancing water electrolysis through controlled doping and tuning of the perovskite structure.

Performance optimization of solid oxide electrolysis cell for syngas production by high temperature co-electrolysis via differential evolution algorithm with practical constraints

Co-electrolysis of water and carbon dioxide using solid oxide electrolysis cell combined with the catalytic reactor to produce renewable synthesis fuel is considered as a promising strategy for carbon dioxide utilization. However, in order to achieve a target product with a remarkable system-level efficiency, a certain proportion of carbon monoxide and hydrogen from solid oxide electrolysis cell must be sent to the catalytic reactor directly, which imposes practical constraints on the solid oxide electrolysis cell performance. Take this constraint into consideration, we proposed a performance design methodology that enables a rapid and effective optimization of the solid oxide electrolysis cell operating conditions. Firstly, a physical model is developed by integrating chemical equilibrium, electrochemistry, and energy conservation involved in the solid oxide electrolysis cell. Secondly, a physical model is utilized to generate a dataset for the development of neural network model and optimization algorithm. This approach allows for the efficient determination of optimal conditions while considering practical constraints. In the case study, under the constraint that the desired fuel is a long carbon chain fuel with a carbon dioxide conversion rate ranging from 80 % to 90 %, the highest efficiency achieved by the solid oxide electrolysis cell is optimized to 66.75 %. Moreover, this approach is extended to other two target fuels (dimethyl ether and methane) under different carbon dioxide conversion rate, and the optimal performance is designed. According to the results, there is a trade-off between high efficiency and high carbon dioxide conversion rate, as the low carbon dioxide conversion rate often leads to higher efficiency. This method allows for flexible design of operating conditions to meet different fuel requirements and guide practical applications.

Effects of structural parameters of double-layer electrode on co-electrolysis in a solid oxide electrolysis cell

The advantages of double-layer electrode are available in the literature about single electrolysis of H2O and CO2 using solid oxide electrolysis cell (SOEC). However, for the co-electrolysis of CO2 and H2O, the influence of the structural parameters of the double-layer electrode on the co-electrolysis performance has been still unclear. In this study, a multi-scale model describing the co-electrolysis process of CO2 and H2O in SOEC is adopted. After model validation, a comparison of the performance of SOEC between a single-layer cathode and a double-layer cathode is conducted with different inlet flow rates. Moreover, parametric analyses are performed to investigate the effects of the thickness and porosity of cathode diffusion layer (CDL) and the internal composition of cathode function layer (CFL). The results show that when the CDL porosity increases from 0.45 to 0.65, the conversion ratio of H2 and CO increase by 10.17 % and 10.24 %, respectively. The optimal thickness of CDL (200 μm) for enhancing the durability of the cell and the preferable internal composition of CFL for improving the co-electrolysis performance are found within the scope of this study. This numerical analysis can provide guidance for the design of the double-layer cathode and the optimization of the co-electrolysis performance.

CO2 conversion improvement of solid-oxide electrolysis cells by inserting buffer layers between MFe2O4 (M = Ni, Cu, Co, Fe) cathode and electrolyte

This study investigated the potential of spinel-structured materials (MFe2O4; M = Ni, Cu, Co, and Fe) as cathodes of solid oxide electrolysis cells (SOECs); at the same time, it revealed that the La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) blocking layers would improve the performance of SOECs by interposing between MFe2O4 and the Sm0.2Ce0.8O2-δ (SDC) electrolytes. The fabricated SOECs were tested under 39% CO2-1% CO-60% He up to 800 °C. Our results showed that the Faradaic efficiency for CO2 reduction was significantly improved and approached the theoretical production rate after the insertion of LSGM blocking layers. In addition, the LSGM barrier layers effectively prevent the short-circuit effect between MFe2O4 and SDC, allowing the open-circuit voltage (OCV) to increase from ∼0.56 V to ∼0.77 V, which dramatically improved the gas generation efficiency of SOECs. According to our optimized SOEC structure, NiFe2O4 and CuFe2O4 exhibited superior electrolytic performance and maintained stable electrolysis after 10 h without degradation. In summary, the inserted LSGM layers would gently modify the interfacial contact and address the mismatch between the spinel-structured materials and SDC to avoid the performance degradation caused by electrode detachment and achieve higher durability than the SOECs without LSGM layers.

Structural Reliability Analysis of Large Planar Steam Solid Oxide Electrolysis Cells

Solid oxide electrolysis cells (SOEC) have been receiving significant attention recently because of their high energy efficiency and fast hydrogen production. In our previous study, a multi-physics modeling framework to simulate the SOEC performance and structural reliability of planar SOEC design was developed and demonstrated. The electrochemical reactions, fluid dynamics, species transport, electron transfer, and heat transfer were modeled in the commercial computational fluid dynamics (CFD) software STAR-CCM+. The thermomechanical analysis and the associated structural reliability evaluations were conducted using the commercial finite element analysis software ANSYS. The electrochemistry model was validated by using the experimentally obtained current-voltage (I-V) characteristics of the electrode-supported SOECs. In this study, this framework was applied on a large 300 cm2 steam planar SOEC design, and systematically studied the structural reliability under combinations of cell operating conditions, with cell voltage 1-1.5 V, steam fraction in fuel inlet 0.7-0.9, air inlet flow rate 0-10 L/min, fuel inlet flow rate 2.5-12.5 L/min, and inlet temperature 600-900 C. In the modeling framework, all the cells were investigated under the adiabatic thermal conditions, which is equivalent to packing the cell in an insulated container. This induced the relatively larger temperature variation than in the smaller cell designs. This cell internal temperature non-uniformity may further enhance the spatial variations of open circuit voltage, activation loss, and ionic conductivity in the cell, which all influence the overall cell performance. This situation is more obvious when the cell voltage is higher than 1.35V, under which the cell is significantly heated along the steam flow direction. Traditionally, it is assumed that the cell internal temperature spatial variation plays an important role on cell structural reliability. However, because it was assumed that all the components in cell are stress free at 850 , the cell temperature deviation from 850 is more critical to the stress distribution and structural reliability in the cell. For the investigated cells in the practical conditions, like 750 C inlet temperature and varying voltage from 1.05 to 1.5 V, the highest first principal stress is always in the air side electrode, which is around 45 MPa. This is explained by the higher coefficient of thermal expansion of LSCF-GDC with respect to the other layers. This may indicate that the failure would possibly occur in the air side electrode, but at low risk due to the relatively higher Weibull characteristic strength.

Co-Electrolysis Performance and Process Analyses for Synthetic Liquid Fuel Production

To achieve carbon neutrality in 2050, carbon recycle technology is attracting much attention coupled with renewable power and electrolyzers to produce “green” fuels such as methane and synthetic oil. We have just started a new NEDO project (FY2020-2024) in Japan for synthetic liquid fuel production using solid oxide electrolysis cells (SOECs) and Fischer-Tropsch (FT) synthesis, which will give higher efficiencies compared to one with water electrolysis at low temperatures. In particular, the project aims at FT oil production from gasoline to diesel fractions (C5-C19) to avoid wax production. We are responsible for R&D of co-electrolysis process for the FT synthesis, cell/stack performance evaluation for the co-electrolysis, and evaluate state-of-the-art commercial single cells and stack that are developed for fuel cell application. Since carbon deposition at higher H2O/CO2 utilization is of concern, material analysis of such cells/stacks will be also carried out to elucidate optimal electrolysis operative conditions and to suggest cell and peripheral components design optimal to syngas production (H2/CO ~ 2.0). In the conference, we will report that developed SOEC performance evaluation methods for co-electrolysis which precisely control steam flowrate, giving cell voltage stability at ± 0.1 mV level. I-V characteristics of commercial cells and 1-2 kW class stack will also be presented at various operative conditions in combination of post-test analysis after the short-term cell/stack evaluation to discuss carbon deposition conditions for syngas production for FT synthesis. Furthermore, numerical process simulation results will be presented to discuss possible energy efficiency of the combined system with SOEC and FT synthesis.

Evaluation and Upscaling of Impregnated La0.20Sr0.25Ca0.45TiO3 Fuel Electrodes for Solid Oxide Electrolysis Cells Under H2O, CO2 and Co-Electrolysis Conditions

As a result of a successful collaboration between the University of St Andrews and HEXIS AG over the past >10 years, an alternative solid oxide fuel cell (SOFC) fuel electrode material (to the state-of-the-art Ni/CGO fuel electrode) has been intensively researched and developed 1 at a button cell scale (1 cm2 active area), 2 tested under harsh operating conditions and upscaled to short stack scale (5 cells each of 100 cm2 active area), 1,3 in addition to being integrated into full combined heat and power units (60 cells each of 100 cm2 active area) with nominal 1-1.5 kW power outputs. 3,4 This highly robust fuel electrode comprises a La0.20Sr0.25Ca0.45TiO3 (LSCTA-) ‘backbone’ with cerium gadolinium oxide (CGO) and Rh impregnates, offering stability toward redox/thermoredox/thermal cycling, overload or stress testing, degradation comparable to the state-of-the-art SOFCs and exposure to sulphurised natural gas. 1 This material, therefore, addresses many of the challenges presented by the Ni/CGO fuel electrodes.Given the success of this material as a SOFC fuel electrode and the growing demand for production of ‘green’ hydrogen and synthesis gas through high-temperature electrolysis, 5 it is also desirable to assess its performance in solid oxide electrolysis cells (SOECs). In this paper, the authors present a comprehensive study of the performance of SOECs containing the aforementioned titanate-based fuel electrodes.Firstly, testing of button cell scale SOECs (1 cm2 active area) in pure CO2 and H2O/H2 mixtures, carried out at the University of St Andrews and HEXIS AG, will be outlined, including promising initial test data from VI curves and AC impedance spectroscopic analysis. Subsequently, information on durability testing of the aforementioned SOECs will be provided. This data indicates that high degradation is observed during testing in H2O/H2/N2 mixtures when employing a LSM-YSZ/LSM air electrode, most likely due to delamination caused by oxygen evolution at the triple phase boundary between LSM and YSZ particles and at the air electrode-electrolyte interface, which is significantly minimised by replacement with a LSCF-CGO air electrode. Finally, upscaling of this technology to a 5 x 5 cm footprint SOEC (16 cm2 active area) containing the aforementioned fuel electrode, a stabilised zirconia electrolyte and a LSCF-CGO air electrode will be outlined. Encouraging results from a ~600 hour test at 850 °C will be presented, including operation in 54 % H2O:46 % CO2 and pure CO2 at 1.47 V, as well as in 51 % H2O:49 % N2 at 1.29 V (without the use of a reducing gas). References 1 R. Price, M. Cassidy, J. G. Grolig, G. Longo, U. Weissen, A. Mai and J. T. S. Irvine, Advanced Energy Materials, 2021, 11, 2003951.2 R. Price, M. Cassidy, J. G. Grolig, A. Mai and J. T. S. Irvine, J. Electrochem. Soc., 2019, 166, F343–F349.3 M. C. Verbraeken, B. Iwanschitz, E. Stefan, M. Cassidy, U. Weissen, A. Mai and J. T. S. Irvine, Fuel Cells, 2015, 5, 682–688.4 R. Price, H. Bausinger, G. Longo, U. Weissen, M. Cassidy, J. G. Grolig, A. Mai and J. T. S. Irvine, In Preparation, 2022.5 J. B. Hansen, Faraday Discuss., 2015, 182, 9 – 48.

Influence of Process Parameters on SOEC Performance

Solid oxide electrolysis cells (SOECs) are highlighted as futuristic Power-to-gas (P2G) devices that can provide reliable supply of hydrogen gas as a renewable energy carrier. Despite the great potential of SOECs there are many challenges facing their commercialization. In this work we investigated the influence of fuel electrode and process parameters on initial SOEC performance (500 hours). Electrolysis experiments were performed with both GDC (gadolinia doped ceria)-infiltrated and un-infiltrated Ni-YSZ fuel electrode under various hydrogen flow rates with different ratios of H2-H2O mix, and current density including open circuit conditions. All cells marginally improve in performance initially, then undergo a brief period of rapid decay followed by a stable performance. The observed three stages of variations in cell performance, in terms of length of time and rate of change, are dependent on the type of fuel electrode and experimental process parameters used. These are investigated employing I-V measurements, electrochemical impedance spectroscopy (EIS), distribution of relaxation time (DRT), and microstructural characterization. The role of GDC infiltration and process parameters driving these performance variations and efficiency of hydrogen generation is analyzed in this work.

Numerical simulation of flow channel geometries optimization for the planar solid oxide electrolysis cell

In a solid oxide electrolysis cell (SOEC), the flow channel design influences the gas distribution, mass transfer, temperature distribution, and electrochemical properties significantly. This study evaluates the overall performance of SOECs with rectangular, triangular, trapezoidal, and semicircular flow channels and examines the effect of the geometry of the flow channel cross-section on the electrolysis process, gas flow, and material distribution. The trapezoidal flow channel shows the best electrochemical performance, but requires a high power and high pressure drop; the triangular flow channel has the most uniform gas velocity and distribution; and the semicircular flow channel shows the maximum gas velocity. The trapezoidal shape is found to be the optimal shape. Sensitivity analysis of the SOEC with the trapezoidal flow channel indicates that increasing the operating temperature improves the electrochemical performance, and reducing the inlet gas's steam volume fraction increases the gas conversion rate and decreases the electrolysis voltage.

Enhancing Electrochemical CO2 Reduction on Perovskite Oxide for Solid Oxide Electrolysis Cells through In Situ A-Site Deficiencies and Surface Carbonate Deposition Induced by Lithium Cation Doping and Exsolution.

Solid oxide electrolysis cells (SOECs) hold enormous potential for efficient conversion of CO2 to CO at low cost and high reaction kinetics. The identification of active cathodes is highly desirable to promote the SOEC's performance. This study explores a lithium-doped perovskite La0.6- x Lix Sr0.4 Co0.7 Mn0.3 O3-δ (x = 0, 0.025 0.05, and 0.10) material with in situ generated A-site deficiency and surface carbonate as SOEC cathodes for CO2 reduction. The experimental results indicate that the SOEC with the La0.55 Li0.05 Sr0.4 Co0.7 Mn0.3 O3-δ cathode exhibits a current density of 0.991 A cm-2 at 1.5V/800°C, which is an improvement of ≈30% over the pristine sample. Furthermore, SOECs based on the proposed cathode demonstrate excellent stability over 300 h for pure CO2 electrolysis. The addition of lithium with high basicity, low valance, and small radius, coupled with A-site deficiency, promotes the formation of oxygen vacancy and modifies the electronic structure of active sites, thus enhancing CO2 adsorption, dissociation process, and CO desorption steps as corroborated by the experimental analysis and the density functional theory calculation. It is further confirmed that Li-ion migration to the cathode surface forms carbonate and consequently provides the perovskite cathode with an impressive anti-carbon deposition capability, as well as electrolysis activity.

Total Energy for the SOFC and SOEC

The Solid Oxide Fuel Cell (SOFC) Program at the National Energy Technology Laboratory (NETL) managed by the U.S. Department of Energy (DOE) Office of Fossil Energy and Carbon Management (FECM) is currently developing low-cost SOFC and Solid Oxide Electrolysis Cell (SOEC) systems. This paper develops the Total Energy (TE) (kilowatt-hours per kilogram hydrogen, kWh/kgH2 ) for the SOEC and SOFC. The Total Energy includes heat input, exergetic flows, enthalpy of vaporization, pressurization, heat loss, area specific resistance, etc. The SOEC Total Energy developed at NETL, as it would happen, correlates well with the Idaho National Laboratory (INL) proven SOEC performance of forty-five kilowatt-hours per kilogram hydrogen at twenty bars, 1.3 volt and 725oC. Total Energy is necessary for designing, predicting, and planning for SOEC and SOFC performance and cost.

Influence of Process Parameters on SOEC Performance

Solid oxide electrolysis cells (SOECs) are highlighted as promising power-to-gas (P2G) devices that can provide a reliable supply of hydrogen gas to store renewable energy. Despite the potential of SOECs, there are many challenges facing their commercialization. In this work, the influence of process parameters and fuel electrode optimization on initial SOEC performance (500 hours) is investigated. Electrolysis experiments were performed with both GDC (gadolinia doped ceria)-infiltrated and uninfiltrated Ni-YSZ (yttria stabilized zirconia) fuel electrodes under various hydrogen flow rates with different ratios of H2-H2O and current densities. All cells marginally improve in performance initially, then undergo a brief period of rapid performance degradation followed by stabilization. The observed three stages of cell performance, in terms of length of time and rate of change, are found to be dependent on the type of fuel electrode and experimental process parameters used.

Performance study of proton conducting electrolytes based on BaZr1−xYxO3-δ for solid oxide electrolysis cell

For the purpose of realizing the high-performance BaZr1−xYxO3-δ (BZY) proton electrolyte materials for solid oxide electrolysis cell (SOEC), the influence of different contents of the transition metal oxide NiO on the performance of proton electrolyte BZY was studied. Specifically, BZY-x mol. % NiO (x = 0, 0.5, 1, 2 and 3, named as BZY, BZY+0.5NiO, BZY+1NiO, BZY+2NiO and BZY+3NiO, respectively) composite electrolyte materials were prepared, as well as and their crystal structure, morphology and electrochemical properties were characterized. The results demonstrate that the composite NiO contributes to the effective improvement of the density of BZY prepared at 1400 ℃, significantly improving the proton conductivity of BZY, and facilitating the performance of BZY-based SOECs. Among them, 2 mol. % NiO-BZY has the optimal performance, the highest density, and the lowest electrochemical impedance. The SOEC based on BZY+ 2NiO electrolyte possesses the most satisfying electrochemical performance, indicating the optimum content of 2 mol. % NiO in this case.

Towards strategies to mitigate degradation and regenerate performance of a solid oxide electrolyzer during co-electrolysis operation

One of the main objectives towards the broad commercialization of solid oxide electrolysis cells (SOEC) is to reduce the effects of degradation and extend the lifetime of the technology. Special industrially relevant operating conditions can, however, amplify and accelerate the degradation of SOECs, thus significantly reducing the lifetime of the technology. Nevertheless, not all degradation processes are completely irreversible, especially if they are detected at an early stage. In order to develop strategies to mitigate degradation and to regenerate performance, several experiments were performed on a five-layer SOEC stack operating in steam and co-electrolysis mode. The experiments were performed at different industrially relevant gas mixtures, reactant conversion rates and operating temperatures. The experimental results revealed different types and degrees of effects of the degradation, mitigation and regeneration strategies on the performance of the stack, which were analyzed in detail and linked to the underlying mechanisms and processes. As a result, promising strategies for mitigating degradation and regenerating the performance of SOECs could be derived and optimized. In addition, this study provides a set of recommendations for safe and stable operation of SOECs under various operating conditions.

Experimental investigation of segmented SOECs: Locally-resolved impedance and degradation characteristics

High temperature solid oxide electrolysis cells (SOEC) provide an innovative solution for direct conversion of steam and electricity to hydrogen with the additional capability of adding CO2 to produce syngas. However, specific operating conditions can have a negative impact on the performance and lifetime of SOECs. In this context, the distributions of operational parameters such as gas species, temperature and current density within the cell structure influence local transport processes and reaction kinetics and can lead to locally different electrochemical potentials and thus degradation phenomena. This study focuses on experimental investigations of steam-electrode supported SOECs with segmented air electrodes with the main objective to measure EIS and thus identify locally-resolved impedance and degradation characteristics caused by different operating conditions in steam and co-electrolysis mode. Thereby, significant correlations between operating conditions, local effects, electrode processes and degradation mechanisms were observed and analyzed in detail using EIS, DRT and SEM.