Temperature Solid Oxide Electrolysis Cells Research Articles

(Invited) The SOFC Program at the DOE’s Office of Fossil Energy and Carbon Management (FECM) and National Energy Technology Laboratory (NETL)

The Solid Oxide Fuel Cell (SOFC) Program, managed by the U.S. Department of Energy (DOE) Office of Fossil Energy (FE) and administered by the FE’s National Energy Technology Laboratory (NETL) is currently developing low-cost SOFC power generation systems. SOFC power systems have the potential to achieve greater than 60 percent efficiency. The SOFC’s operating temperature is lower than combustion-based processes and precludes NOx formation. In addition, there are near-zero emissions of CO2, criteria pollutants, and particulates. Furthermore, SOFC power systems require approximately one-third the amount of water relative to conventional combustion-based power systems. The Program includes the testing of SOFC with natural gas in distributed applications, including data centers. In addition to SOFC, there are several projects on various aspects of high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water. The development of efficient systems for hydrogen production is very interesting, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants.

A 3D Simulation of DC-Biased Electrochemical Impedance of Solid Oxide Electrolysis Cell: Effects of Delamination

The demand for green energy sources with near zero-carbon footprints is rising owing to global warming, pollution and increasing world population. Hydrogen is one of the capable energy sources with higher gravimetric energy density than conventional gasoline fuel. Clean hydrogen production can be achieved through water splitting electrolysis processes. High temperature solid oxide electrolysis cells (SOEC) have higher efficiency, which requires less overall electric power compared to other electrolysis cells [1]. Hitherto, SOEC has not been commercialized due to their faster degradation under higher current densities, compared against its performance in fuel cell mode [2]. Delamination of oxygen electrode (OE) from the electrolyzer (EL) is the major reason for the cell degradation [3,4].Half-cell configuration is simulated to understand the delamination of OE coupled with experimental results observed during polarization test ran for 1000 hours. The OE used here is a composite of La1-xSrxCo1-yFeyO3-δ (LSCF) and Gadolinium-doped Ceria (GDC). A buffer layer (GDC) is introduced between the electrolyte (EL) made of 8 mol% Y2O3 doped ZrO2 (YSZ) and composite OE. The OE, buffer layer and EL diameter are 7, 10 and 10 mm with thicknesses of 30, 1 and 10 μm, respectively. The oxygen evolution reaction here is considered as multi-step charge transfer reaction at two phase boundaries (2PB) accompanied by triple phase boundary (3PB) intersection of OE, EL and gas phase [5]. Charged species like vacancies, holes, and electrons in OE, especially inside LSCF, are solved using Nernst-Planck transport equations. Gas diffusion in pores is simulated by Fick’s law. The charge transfer in the transport pathways (2PB and 3PB) are given by Butler-Volmer model [6]. Eventually, the perturbation form and the steady state form of the physics-based model will be coupled to simulate DC-biased impedance under various operating current densities. We will use the model to study the evolution of impedance when the OE/EL interface delamination propagates under long-term tests.The preliminary steady state results are shown in Figure 1, operated at 1 A/cm2. The electronic potential distribution in LSCF can be seen in Figure 1a. This potential is close enough to the applied voltage and the variation of potential along the thickness is negligible. The trend of ionic potential along the half-cell thickness is illustrated in Figure 1b. The linearity in potential is changed to exponential correlation when we move from EL to OE region, which is because of 2PB and 3PB current contribution to GDC. The variation in the vacancy is also minimal in OE, owing to its micro scale dimension. The oxygen partial pressure is maximum at OE-Buffer layer interface due to oxygen evolution. All these trends are plotted as a function of cell thickness along its axis. We will validate the model by both the experimentally measured voltage-current curve and electrochemical impedance spectra (EIS) under DC bias. This study will unveil the underlying degradation mechanism of SOEC by relating EIS with delamination of SOEC under long-term tests.

Co nanoparticles decorated with in-situ exsolved oxygen-storage CeO2 for an efficient and stable electrolysis of pure CO2

The valorization of the CO2 greenhouse gas is important in decarbonization using the renewable energies. Intermediate temperature solid oxide electrolysis cells (SOEC) working at around 800 °C can be useful in activating the strong CO bond (799 kJ mol−1) in CO2 for the production of CO and decreasing the precious electricity by partially using the heat instead. Ceria/Co doping on the stable chromite is employed to design a composite oxide/metal cathode with a unique ceria decorating Co0 for the direct CO2 electrolysis. The in situ outgrowth of Co0 from the B site activates the ceria exsolution from the A site, or vice versa, producing a well-adhered heterojunction for the activation of CO2. A high current and stable density above 1 Acm−2 for 300 h is obtained at a bias of 1.3 V for the CO2 at a Faraday efficiency close to unity. The higher electrochemical performance of the cell with Ce/Co0 codoped cathode is explained by the oxygen storage property of the ceria rather than the direct activation of CO2 over ceria. This work presents a novel method of constructing metal/oxide cathode for efficient CO2 analysis and in-depth mechanistic explanation for the metal/oxide hetero-structure in CO2 activation.

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.

Synthesis of Yttrium Doped Barium Zirconate/Cerate Electrolyte Materials and Densification Using Conventional and Cold-Sintering Processes

Compared to high temperature solid oxide electrolysis cell, usually based on Yttrium stabilized Zirconia electrolytes, intermediate temperature proton conducting electrolysis cell, allows the production of water free hydrogen and a better chemical stability. Proton conducting perovskite materials, such as Barium Indates, Zirconates or Cerates are nearly commercial electrolytes for such devices. At intermediate temperature and under humid atmosphere, hydration process allows diffusion of protonic charges. Such electrolyte material combines a low thermal expansion coefficient and a high protonic conductivity. and The Zirconium rich material BaZr0.7Ce0.2Y0.1O3-δ that shows a conductivity around 10-2 S.cm-1 at 500°C will be compared to the Cerium rich BaZr0.3Ce0.6Y0.1O3-δ material that shows conductivities around 10-4 S.cm-1 at the same temperature.

Modeling Electrokinetics of Oxygen Electrodes in Solid Oxide Electrolyzer Cells

High temperature solid oxide electrolyzers operated at >600oC are advantageous from a thermodynamic perspective since heat (TDS) can be converted into chemical energy (DH) [1]. This additional heat reduces the overall electrical power (DG) requirement, allowing an electrolysis cell to achieve ~100% efficient H2 production [1]. Since the thermal energy contribution to the electrolysis reaction can also be obtained from sensible Joule heating produced within the cell, the electrical energy demand is further reduced which decreases the H2 production price. The bulk of the heat can be provided by an external source such as nuclear power, solar thermal power, or waste heat from a chemical plant. Theoretically, there is no external heat requirement if the electrolyzers operate at the thermoneutral voltage. Due to the above advantages, the research and development on solid oxide-based water electrolyzers have received significant attention [1–6].This work focuses on physics-based modeling of high temperature solid oxide electrolysis cells (SOEC). A microscale model is presented to simulate electrode kinetics of the oxygen electrode in a solid oxide electrolyzer cell (SOEC). Two mixed ionic/electronic conducting structures are examined for the oxygen producing electrode in this work: single layer porous lanthanum strontium cobalt ferrite (LSCF), and bilayer LSCF/SCT (strontium cobalt tantalum oxide) structures. An yttrium-stabilized zirconia (YSZ) electrolyte separates the hydrogen and oxygen electrodes, as well as a gadolinium doped-ceria (GDC) buffer layer on the oxygen electrode side. Electrochemical reactions [7-8] occurring at the two-phase boundaries (2PBs) and three-phase boundaries (3PBs) of single-layer LSCF and bilayer LSCF/SCT oxygen electrodes are modeled under various SOEC voltages with lattice oxygen stoichiometry as the key output. The results reveal that there exists a competition in electrode kinetics between 2PBs and 3PBs, but 3PBs are the primary reactive sites for single-layer LSCF oxygen electrode under high voltages. These locations experience the greatest oxygen stoichiometry variations and are therefore the most likely locations for dimensional changes. By applying an active SCT layer over LSCF, the 2PBs become activated to compete with the 3PBs, thus alleviating oxygen stoichiometry variations and reducing the likelihood of dimensional change. This strategy could reduce lattice structural expansion, proving to be valuable for electrode-electrolyte delamination prevention and will be the focus of future work. Figure 1

Reactive Molecular Dynamics Study for CO2 Electrocatalytic Conversion on Lmfcr (M= Sr, Ca) Perovskite-Based Solid Oxides

Due to their mixed conducting properties as well as their electronic, crystallographic, and chemical versatility, perovskite-based oxides have been shown to be very promising electrocatalysts for CO2 conversion to syngas in high temperature (600 – 1000 °C) solid oxide electrolysis cells (SOECs) integrated with renewable energy resources. In addition to generating fuels and value-added chemicals, CO2 reduction (CO2RR) in SOECs serves to lower atmospheric CO2 emissions. La-based (1) perovskite oxides have been intensively used instead of precious metals and metal-cermet materials (e.g., Ni-YSZ, Ni-GDC) for CO2 electrolysis in high temperature SOECs. The effect of the dopant cations on the electrocatalytic performance and degradation have also been investigated since the segregation of dopants can reconstruct the surface (2). Our team has been actively developing the family of La0.3a0.7Fe0.7Cr0.3O3−δ (LMFCr, where M = Ca or Sr) for CO2 reduction (3,4) showing that CO2RR is more active than CO oxidation, and that the catalyst is also highly active on the air side. More recently, we have shown that Fe-Ni exsolved LCFCr significantly improves the rate of CO oxidation (5), while hardly changed CO2RR. However, a full atomistic scale understanding of the CO2 reduction mechanism and related degradation issues, such as dynamic changes of the surface composition as a function of operating conditions, does not yet exist. The oxygen vacancy concentration (V0) and surface termination of the perovskite material are important factors that affect the CO2RR, as shown recently (6) utilizing DFT methods.In this study, we used Density Functional Theory (DFT) to explore the energetics of the catalytic conversion of CO2 to CO on LMFCr (M = Sr, Ca) perovskite surfaces. The DFT calculations were then used to generate datasets of optimized lattice structures, including point defects, equations of state, surface energies, and surface CO2/CO interactions in order to develop reactive force fields (ReaxFF). The datasets were optimized by using an evolutionary algorithm, CMA-ES, and validated in order to explore the dynamics of the catalytic conversion process under varying conditions, such as temperature, inlet CO2/CO gas ratio, the perovskite surface composition and applied electrical field.Our results have shed light on reaction steps involving adsorption of CO2 at high temperatures, C=O bond activation, and the dominant intermediates as transition states during the conversion process and their role in generating CO. These observations will serve as a foundation to determine the elementary reaction steps involved in the CO2 splitting mechanism on LMFCr at high temperatures. Furthermore, this study will enable us to determine the optimal conditions for the reaction to occur and shed light on possible surface degradation mechanisms, allowing future optimization of the stability and catalytic activity of these promising perovskites.ACKNOWLEDGMENTSThis computational research was supported by the Canada First Research Excellence Fund (CFREF), while the platforms for this computational work were provided by Westgrid (https://www.westgrid.ca) and Compute Canada (https://www.computecanada.ca). Thanks are also extended to Oliver Calderon and Misha Pidburtnyi for helpful discussions.References Cao, Z., Wei, B., Miao, J., Wang, Z., Lü, Z., Li, W., Zhang, Y., Huang, X., Zhu, X., Feng, Q. and Sui, Y., (2016). Efficient electrolysis in symmetrical solid oxide electrolysis cell with highly active 3Sr0.7Fe0.7Ti0.3O3 electrode material. Electrochemistry Communications, 69, 80-83.Zhang, Y. Q., Li, J. H., Sun, Y. F., Hua, B., & Luo, J. L. (2016). Highly active and redox-stable Ce-doped LaSrCrFeO-based cathode catalyst for CO2 SOECs. ACS Applied Materials & Interfaces,, 8(10), 6457-6463.Addo, P. K., Molero‐Sanchez, B., Chen, M., Paulson, S., & Birss, V. (2015). CO/CO2 study of high performance La0. 3Sr0. 7Fe0. 7Cr0. 3O3–δ reversible SOFC electrodes. Fuel Cells, 15(5), 689-696.Molero-Sánchez, B., Morán, E., & Birss, V. (2017). Rapid and Low-Energy Fabrication of Symmetrical Solid Oxide Cells by Microwave Methods. ACS Omega, 2(7), 3716-3723.Ansari, H. M., Bass, A. S., Ahmad, N., & Birss, V. I. (2022). Unraveling the evolution of exsolved Fe–Ni alloy nanoparticles in Ni-doped La 0.3 Ca 0.7 Fe 0.7 Cr 0.3 O 3− δ and their role in enhancing CO 2–CO electrocatalysis. Journal of Materials Chemistry A.Kozokaro, V. F., Addo, P. K., Ansari, H. M., Birss, V. I., & Toroker, M. C. (2020). Optimal Oxygen Vacancy Concentration for CO2 Reduction in LSFCr Perovskite: A Combined Density Functional Theory and Thermogravimetric Analysis Measurement Study. The Journal of Physical Chemistry C, 124(50), 27453-27466.

Three-Dimensional Modeling and Performance Study of High Temperature Solid Oxide Electrolysis Cell with Metal Foam

Optimizing the flow field of solid oxide electrolysis cells (SOECs) has a significant effect on improving performance. In this study, the effect of metal foam in high temperature SOEC electrolysis steam is investigated by a three-dimensional model. The simulation results show that the SOEC performance is improved by using metal foam as a gas flow field. The steam conversion rate of the SOEC increases from 72.21% to 76.18% and the diffusion flux of steam increases from 2.3 × 10−4 kg/(m2∙s) to 2.5 × 10−4 kg/(m2∙s) at 10,000 A/m2. In addition, the permeability, temperature, steam mole fraction, and gas utilization are investigated to understand the effect of the improved performance of the SOEC with metal foam. The results of this study provide a baseline for the optimal design of SOECs with metal foam.

Electroreduction of CO2/CO to C2 Products: Process Modeling, Downstream Separation, System Integration, and Economic Analysis.

Direct electrochemical reduction of CO2 to C2 products such as ethylene is more efficient in alkaline media, but it suffers from parasitic loss of reactants due to (bi)carbonate formation. A two-step process where the CO2 is first electrochemically reduced to CO and subsequently converted to desired C2 products has the potential to overcome the limitations posed by direct CO2 electroreduction. In this study, we investigated the technical and economic feasibility of the direct and indirect CO2 conversion routes to C2 products. For the indirect route, CO2 to CO conversion in a high temperature solid oxide electrolysis cell (SOEC) or a low temperature electrolyzer has been considered. The product distribution, conversion, selectivities, current densities, and cell potentials are different for both CO2 conversion routes, which affects the downstream processing and the economics. A detailed process design and techno-economic analysis of both CO2 conversion pathways are presented, which includes CO2 capture, CO2 (and CO) conversion, CO2 (and CO) recycling, and product separation. Our economic analysis shows that both conversion routes are not profitable under the base case scenario, but the economics can be improved significantly by reducing the cell voltage, the capital cost of the electrolyzers, and the electricity price. For both routes, a cell voltage of 2.5 V, a capital cost of $10,000/m2, and an electricity price of <$20/MWh will yield a positive net present value and payback times of less than 15 years. Overall, the high temperature (SOEC-based) two-step conversion process has a greater potential for scale-up than the direct electrochemical conversion route. Strategies for integrating the electrochemical CO2/CO conversion process into the existing gas and oil infrastructure are outlined. Current barriers for industrialization of CO2 electrolyzers and possible solutions are discussed as well.

(Plenary) Update on the SOFC Program at the DOE’s National Energy Technology Laboratory

The Solid Oxide Fuel Cell (SOFC) Program, managed by the U.S. Department of Energy (DOE) Office of Fossil Energy (FE) and administered by the FE’s National Energy Technology Laboratory (NETL) is currently developing low-cost SOFC power generation systems. SOFC power systems have the potential to achieve greater than 60 percent efficiency. The SOFC’s operating temperature is lower than combustion-based processes and precludes NOx formation; there are near-zero emissions of CO2, criteria pollutants, and particulates. Furthermore, SOFC power systems require approximately one-third the amount of water relative to conventional combustion-based power systems. The Program includes the testing of SOFC with natural gas in distributed applications, including data centers. In addition to SOFC, there are several projects on various aspects of high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water. The development of efficient systems for hydrogen production is very interesting, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants.

Research Needs for the Solid Oxide Electrolyzer (SOEC) with a Proton-Conducting SOEC (H-SOEC) Electrochemical Hydrogen Compressor (EHC) Energy Conversion Network (ECN)

A high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water is paired with a H-SOEC for hydrogen compression. SOEC and EHC have been integrated into an ECN in a series configuration and then simulated and analyzed. Adding heat and minimizing area specific resistance (ASR) would be highly desirable for further developing highly-efficient SOEC H-SOEC EHC ECN’s. It is important to note there is a maximum possible heat generation rate with a given ASR when operated below the thermoneutral point. There is a maximal heat addition rate for optimal efficiency of the SOEC, and it is not at thermoneutral. Many developers have expressed interest in the thermal management of electrolyzer cells and in the possible existence such an optimum. It is important to understand in general that heat removal can allow increase hydrogen production rate over the thermoneutral path at constant temperature. For this reason, the SOEC H-SOEC EHC ECN was simulated over a range of currents and ASR’s to determine the heat addition or removal required. If the internal resistance of an SOEC could be lowered sufficiently via the development of new, high-performing materials, the efficiency of hydrogen production could be very high, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants. It is remarkable that a quarter to a third of the energy for the combined high-temperature electrolysis and hydrogen compression system could be provided by solar, nuclear or geothermal energy. The goal of HT electrolysis research and development should be to lower ASR and improve heat conduction or heat transfer into and out of the SOEC. The promise of the H-SOEC electrochemical hydrogen compressors depends on its stability, durability and improved transference numbers. The goal of future research should be to improve the potential of this new SOEC H-SOEC EHC ECN.

Research Needs for the Solid Oxide Electrolyzer (SOEC) with a Proton-Conducting SOEC (H-SOEC) Electrochemical Hydrogen Compressor (EHC) Energy Conversion Network (ECN)

A high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water is paired with a H-SOEC for hydrogen compression (EHC). SOEC and EHC have been integrated into an electrochemical network (ECN) in a flow-series configuration and then simulated and analyzed. Adding heat and minimizing area specific resistance (ASR) would be highly desirable for further developing highly-efficient SOEC+EHC ECN’s. It is important to note there is a maximum possible heat generation rate with a given ASR when operated below the thermoneutral point. There is a maximal heat addition rate for optimal efficiency of the SOEC, and it is not at thermoneutral. Many developers have expressed interest in the thermal management of electrolyzer cells and in the possible existence of such an optimum. It is important to understand in general that heat removal can allow an increased hydrogen production rate over the thermoneutral path at constant temperature. For this reason, the SOEC+EHC ECN was simulated over a range of currents and ASR’s to determine the heat addition or removal required. If the internal resistance of an SOEC could be lowered sufficiently via the development of new, high-performing materials, the efficiency of hydrogen production could be very high, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants. It is remarkable that a quarter to a third of the energy for the combined high-temperature electrolysis and hydrogen compression system could be provided by solar, nuclear, or coal.

(Plenary) Update on the SOFC Program at the DOE’s National Energy Technology Laboratory

The Solid Oxide Fuel Cell (SOFC) Program, managed by the U.S. Department of Energy (DOE) Office of Fossil Energy (FE) and administered by the FE’s National Energy Technology Laboratory (NETL), is currently developing low-cost SOFC power generation systems. SOFC power systems have the potential to achieve greater than 60 percent efficiency. The SOFC’s operating temperature is lower than combustion-based processes and precludes NOx formation; there are near-zero emissions of CO2, criteria pollutants, and particulates. Furthermore, SOFC power systems require approximately one-third the amount of water relative to conventional combustion-based power systems. The Program includes the testing of SOFC with natural gas in distributed applications, including data centers. In addition to SOFC, there are several new projects on various aspects of high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water. The development of efficient systems for hydrogen production is very interesting, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants.

Plasma-Enhanced High Temperature Solid-Oxide Electrolysis Cells: The Search for Synergy

High temperature solid-oxide electrolysis cells (SOECs) are a promising conversion technology to produce energy-rich molecules such as CO from CO2 [Song2019]. The high energy efficiency and separation of product streams intrinsic to oxygen ion-conducting electrolyte materials are desirable for renewable synthetic fuel and value-added chemical production at industrial scale.While most improvement in SOEC performance in recent years has been achieved by advancements in electrode materials and cell design, the use of plasmas to enhance SOEC performance also shows potential [Mori2017, Patel2019]. It is reported that the oxygen exchange rate for yttria-stabilized zirconia (YSZ) is 100 times higher simply by exposure to plasma [Rohnke2004]. Despite the apparent synergy in such plasma-SOEC approaches, the underlying mechanisms of plasma and surface processes are presently not well understood. A common explanation is that plasma-activated species (e.g., by vibrational excitation, plasma-dissociation and ionization) support the reduction kinetics on the surface. The effects of plasma-induced surface charging and local fields on, for instance, the vacancy concentration and exchange kinetics may also play a significant role. Dedicated experiments aimed to distinguish between these underlying mechanisms are essential to reveal the true nature of the synergy.In this contribution, we will present our novel hybrid plasma-SOEC reactor aimed at investigating fundamental aspects of SOEC-plasma synergy. The plasma is generated in a brushed electrode discharge in the quiescent region [Ratynskaia2015], which provides a highly stable, homogeneous and field-free plasma environment well suited for a controlled exposure of the SOEC. Langmuir probe measurements will help to obtain insights into the plasma properties, complemented with 1D plasma-kinetic modelling of the plasma bulk and wall region. With this combined experimental-modeling approach, we intend not only to quantify the plasma-effect on SOEC performance, but also to develop insights into the rate-limiting kinetics. We will share our first experimental results on plasma-enhanced oxygen pumping in an O2/He plasma environment.Song, Y., Zhang, X., Xie, K., Wang, G., & Bao, X. (2019). High-Temperature CO2 Electrolysis in Solid Oxide Electrolysis Cells: Developments, Challenges, and Prospects. Advanced MaterialsMori, S., & Tun, L. L. (2017). Synergistic CO2 conversion by hybridization of dielectric barrier discharge and solid oxide electrolyser cell. Plasma Processes and Polymers, 14(6), 1600153.Patel, H., Sharma, R. K., Kyriakou, V., Pandiyan, A., Welzel, S., Van De Sanden, M. C. M., & Tsampas, M. N. (2019). Plasma-Activated Electrolysis for Cogeneration of Nitric Oxide and Hydrogen from Water and Nitrogen. ACS Energy Letters, 4(9), 2091–2095.Rohnke, M., Janek, J., Kilner, J. A., & Chater, R. J. (2004). Surface oxygen exchange between yttria-stabilised zirconia and a low-temperature oxygen rf-plasma. Solid State Ionics, 166(1–2), 89–102.Ratynskaia, S., Dilecce, G., & Tolias, P. (2015). BABE – a brush cathode discharge for thermal fluctuation measurements. J. Plasma Physics, 81(2), 345810202.

Improved performance of a samarium-doped ceria interlayer of intermediate temperature solid oxide electrolysis cells by doping the transition metal oxide Fe2O3.

The ionic conductivity of the interlayer in the intermediate temperature solid oxide electrolysis cell (IT-SOEC) affects the polarization resistance of the oxygen electrode. Improving the ionic conductivity of the interlayer can improve the performance of the oxygen electrode. In this work, the ionic conductivity of a samarium-doped ceria (SDC) interlayer is improved by doping the transition metal oxide Fe2O3. The experimental results show that the oxygen electrode polarization resistance of the symmetrical cell based on the SDC-Fe2O3 interlayer is 0.09 Ω cm−2 at 800 °C and under the open circuit voltage, which is obviously lower than that of the symmetrical cell based on an SDC interlayer (0.22 Ω cm−2). Besides, the electrolysis current of the SOEC based on the SDC-Fe2O3 interlayer is 0.5 A cm−2 at 800 °C and 1.5 V, which is higher than that of the SOEC based on the SDC interlayer (0.3 A cm−2). The above results show that improving the ionic conductivity of the SDC interlayer in the SOEC by doping Fe2O3 can reduce the polarization resistance of the oxygen electrode and enhance the performance of the SOEC. Thus, this work provides an effective way for improving the performance of the SDC interlayer in the IT-SOEC.

Cobalt substituted Pr2Ni1-xCoxO4+δ (x = 0, 0.1, 0.2) oxygen electrodes: Impact on electrochemical performance and durability of solid oxide electrolysis cells

This study is focused on the development of layered perovskites based alternative oxygen electrodes for high temperature Solid Oxide Electrolysis Cells (SOECs). In this respect, rare earth nickelates Ln2NiO4+δ (Ln = La, Pr or Nd) have taken considerable attention due to their good electrochemical properties resulting from high oxide ion diffusivity and a large surface exchange rate. Among them, Pr2NiO4+δ (PNO) shows the best electrochemical properties, however, it displays relatively higher degradation rate under SOEC operation at high current density. Therefore, in this work, we perform further modification by substituting nickel by cobalt in order to enhance the physico-chemical properties, electrochemical performance and most importantly the durability of SOECs. Three compositions (x = 0.0, 0.1 and 0.2) are prepared and characterized using different techniques. The electrochemical measurements are performed with symmetrical as well as single cells using DC- and AC-techniques in the 700–900 °C temperature range. The electrode reaction mechanism is also examined by recording the impedance spectra at different pO2. An improvement in electrochemical performance as well as lower degradation rate is observed with cobalt substitution, during short term SOEC operation at −1 A⋅cm−2 current density at 800 °C with 50% H2 and 50% H2O feed gas mixture.

High-performance composite cathode for electrolysis of CO2 in tubular solid oxide electrolysis cells: A pathway for efficient CO2 utilization

High temperature solid oxide electrolysis cells (SOECs) have a tremendous potential to provide a practical pathway for onsite on demand production of high purity CO by recycling waste CO2 at industry relevant production scale. CO is an important feedstock for production of numerous chemicals required for the pharmaceutical, food and plastics industry. Recently, SOECs are also being developed to produce renewable fuels and energy carriers to allow transport and storage of renewable energy. Despite promising pre-commercial demonstrations, some key technical challenges need to be addressed to make this technology economically feasible. These include lowering capital costs with low cost materials and cell designs, and improvements in the electrode performance and lifetime, the cathode. The conventional Nickel-YSZ cathode is found to be promising in terms of performance during initial operation; however, a continuous supply of valuable reducing gas is needed to prevent oxidation of Ni to NiO, and accelerated degradation has been observed due to Ni migration and deactivation. In the present study we have evaluated the performance of A-site deficient doped lanthanum ferrites ((La0.60Sr0.40)0.95Co0.20Fe0.80O3-x) - Gd0.20Ce0.80O1.95) dual phase mixed ionic and electronic conducting cathode for CO2 electrolysis in a symmetrical tubular cell without the addition of reductant or protective gas during the cell operation. A polarization resistance as low as 0.36 ohm-cm2 was observed at 1.2 V after 350 h of CO2 electrolysis at 800 °C. The electrochemical performance of the electrode is also compared with state-of-the-art Ni-YSZ cathode using similar cells and experimental conditions.

Tri-Doped BaCeO3-BaZrO3 as a Chemically Stable Electrolyte with High Proton-Conductivity for Intermediate Temperature Solid Oxide Electrolysis Cells (SOECs).

Solid oxide electrolysis cells (SOECs) are devices that enable economically viable production of clean fuel such as hydrogen gas, which can be used in many industrial applications and serving as an energy carrier for renewable energy sources. Operation of SOEC at intermediate temperature (IT) range (400 to 600 °C) is highly attractive because many unexploited heat sources from industries can be utilized. Proton conducting SOECs based on barium-zirconium-cerate electrolytes show great potential for operating at this temperature range due to their high proton conductivity at reduced temperatures. In this study, a new tridoped BaCe0.5Zr0.2Y0.1Yb0.1Gd0.1O3-δ (BCZYYbGd) electrolyte with very high chemical stability and proton conductivity is coupled with a PrNi0.5Co0.5O3-δ steam electrode and a Ni-BCYYbGd hydrogen electrode for IT-SOEC operation. The dopants of the electrolyte were carefully designed to obtain the optimum stability and conductivity for IT-SOEC. The BCYYbGd electrolyte was stable over 200 h at 50 vol % steam in argon and at 600 °C, and a very high electrolysis current density of 2.405 A cm-2 was obtained at 600 °C and 1.6 V at 20 vol % of steam in argon. This system was also found to be highly reversible, exhibiting very high performance in SOFC mode and suggesting a potential candidate for next generation proton conducting electrolyte.

Moisture-dependent electrochemical characterization of Ba0.2Sr1.8Fe1.5Mo0.5O6-δ as the fuel electrode for solid oxide electrolysis cells (SOECs)

Barium-doped strontium ferrite oxide is a double perovskite where Ba dopant replaces A-site cation to give better electrochemical performance by means of lattice expansion, and therefore can potentially be a stable fuel electrode for high temperature solid oxide electrolysis cells. Ba0.2Sr1.8Fe1.5Mo0.5O6-δ (B2SFMO) double perovskite as fuel electrode was prepared by solution combustion synthesis with the calcination temperature of 1100 °C. Three-electrode half cell was used to evaluate its electrochemical performance under various steam contents in hydrogen atmosphere both under fuel cell mode and electrolysis mode. Electrochemical impedance spectroscopy demonstrated that hydrogen oxidation reaction involved gaseous adsorption/desorption, oxide transport, and charge transfer processes whereas the oxide transport process in water reduction reaction was split into faster and slower processes at low steam-content region. Polarization study showed the monotonously decreased current density in SOFC mode with the increase in the steam content but it displayed the opposite trend in the current density in SOEC mode with the suitable steam content at 20%.

Advanced Electrochemical System for Energy Storage through CO2 conversion

The extensive usage of fossil fuel as energy source has led to the increased atmospheric concentration of CO2, which is mainly responsible for the negatively intensified greenhouse effect upon our living habitat. Various pathways have been studied in order to alleviate the negative effects of CO2 emission; electrochemical reduction of CO2 is considered as one of the promising method to effectively reduce CO2 emission. The process involves the conversion of CO2 to useful chemicals and fuels using high temperature solid oxide electrolysis cells (SOECs), these devices can run in the opposite direction in solid oxide fuel cells but utilize similar concepts, and involve materials challenges and operating conditions to achieve ‘Power to Fuels’. It is well known that CO2 molecules are very stable so that high energy input is required for cathodic reaction to proceed. The cathodic reaction, therefore, plays a vital role in the overall cell performance and so far, extensive investigations have been conducted to develop the advanced cathode materials with high catalytic activity and stability.Among various types of catalysts for SOECs, perovskite-based materials have attracted world wide research efforts as the mixed ionic and electronic conductors through introducing proper doping elements into perovskite lattice during synthesis process. Nonetheless, the cathodic material thus developed still suffer from relatively lower catalytic activity compared to conventional nickel-based cermets. In this work, three strategies are adopted to improve their performance of CO2 electrochemical reduction. It has been demonstrated that the perovskites with exsolved nanoparticles anchored on the surface of matrix exhibit excellent catalytic activity in comparison with the conventional ones. As a facile in-situ process, exsolution can significantly increase the number of reaction sites by forming uniformly dispersed active nanoparticles and at the same time, can efficiently impede agglomeration of nanoparticles under high temperature. Therefore, the perovskite with exsolved nanoparticles is a promising cathode material that can enhance the overall performance of CO2 reduction in an electrochemical cell.