Performance and Limitations of Nickel-Doped Chromite Anodes in Electrolyte-Supported Solid Oxide Fuel Cells

Ni-doped chromite anodes were integrated into electrolyte-supported cells (ESC) with 5x5 cm2 size and investigated in fuel cell mode with H2/H2O fuel gas. Both a stoichiometric and a nominally A-site deficient chromite anode material showed promising performance at 860 °C approaching the ones of state-of-the-art Ni/Gd-doped ceria (CGO) anodes. While the difference in polarization resistance was small, an increased ohmic resistance of the perovskite anodes was observed, which is related to limited electronic conductivity of the perovskites. Increasing the chromite electrode thickness was shown to enhance performance and stability considerably. Degradation increased with current density, suggesting its dependency on the electrode potential, and could be reversed by redox cycling. Sulfur poisoning with 20 ppm hydrogen sulfide led to rapid voltage drops for the chromite anodes. It is discussed that Ni nanoparticle exsolution facilitates hydrogen dissociation to the extent that it is not rate-limiting at the investigated temperature unless an insufficiently thick electrode thickness is employed or sulfur impurities are present in the feed gas

Synthesis and Evaluation of the A–site Deficient Perovskite La0.65Sr0.3Cr0.85Ni0.15O3-δ as Fuel Electrode for High Temperature Co–electrolysis Enhanced by In Situ Exsolution of Ni Nanoparticles

In this work, we focused on the lanthanum strontium chromite (LSC) matrix with the purpose to partially substitute the B-site with an electrocatalytic reducible transition metal that could be exsolved in situ. Therefore, nickel was considered at a substitution level of 15%. In addition, an A-site deficiency was formulated in order to enhance the exsolution capability of the electrocatalyst. A precursor was synthesized by wet-chemical method and further calcined in air. Single phase was obtained with the formulation La0.65Sr0.3Cr0.85Ni0.15O3-δ (L65SCN) which was characterized by X–ray diffraction (XRD) and Rietveld refinement analyses. Exsolution was investigated by means of thermogravimetric analysis (TGA) under reducing conditions and temperature-programmed reduction (TPR). Scanning electron microscopy (SEM) was used to study the particle morphology and its evolution. Ni particle exsolution was observed after exposure to a reducing atmosphere. The behaviour of the L65SCN perovskite was compared with the stoichiometric La0.70Sr0.3Cr0.85Ni0.15O3-δ (L70SCN). Aiming at evaluating the electrochemical performance, electrolyte-supported cells were manufactured by screen printing and sintering of composite L65SCN/CGO as fuel electrode and La0.58Sr0.4Fe0.8Co0.2O3-δ (LSCF) as air electrode on CGO-3YSZ-CGO substrates. The produced cells were tested in electrolysis and co–electrolysis mode and characterized by means of Electrochemical Impedance Spectroscopy (EIS) and polarization curves. Results will be presented with the perspective of SOEC applications

Performance and Limitations of Nickel-Doped Chromite Anodes in Electrolyte-Supported Solid Oxide Fuel Cells

Ni-doped chromite anodes were integrated into electrolyte-supported cells (ESC) with 5x5 cm2 size and investigated in fuel cell mode with H2/H2O fuel gas. Both a stoichiometric and a nominally A-site deficient chromite anode material showed promising performance at 860 °C approaching the ones of state-of-the-art Ni/Gd-doped ceria (CGO) anodes. While the difference in polarization resistance was small, an increased ohmic resistance of the perovskite anodes was observed, which is related to limited electronic conductivity of the perovskites. Increasing the chromite electrode thickness was shown to enhance performance and stability considerably. Degradation increased with current density, suggesting its dependency on the electrode potential, and could be reversed by redox cycling. Sulfur poisoning with 20 ppm hydrogen sulfide led to rapid voltage drops for the chromite anodes. It is discussed that Ni nanoparticle exsolution facilitates hydrogen dissociation to the extent that it is not rate-limiting at the investigated temperature unless an insufficiently thick electrode thickness is employed or sulfur impurities are present in the feed gas

Performance and Limitations of Nickel‐Doped Chromite Anodes in Electrolyte‐Supported Solid Oxide Fuel Cells

Ni‐doped chromite anodes were integrated into electrolyte‐supported cells (ESC) with 5×5 cm(2) size and investigated in fuel cell mode with H(2)/H(2)O fuel gas. Both a stoichiometric and a nominally A‐site deficient chromite anode material showed promising performance at 860 °C approaching the ones of state‐of‐the‐art Ni/Gd‐doped ceria (CGO) anodes. While the difference in polarization resistance was small, an increased ohmic resistance of the perovskite anodes was observed, which is related to their limited electronic conductivity. Increasing the chromite electrode thickness was shown to enhance performance and stability considerably. Degradation increased with current density, suggesting its dependency on the electrode potential, and could be reversed by redox cycling. Sulfur poisoning with 20 ppm hydrogen sulfide led to rapid voltage drops for the chromite anodes. It is discussed that Ni nanoparticle exsolution facilitates hydrogen dissociation to the extent that it is not rate‐limiting at the investigated temperature unless an insufficiently thick electrode thickness is employed or sulfur impurities are present in the feed gas

Solid Oxide Cells for Power-to-X: Materials, Applications & Challenges

In a context of climate change, the need for more carbon efficient technologies for energy storage and energy efficiency is pressing. Owing to high temperature operation and fast electrode kinetics reaction Solid Oxide Cells (SOC) present the unique feature, to be capable of reversible operation, meaning fuel cell mode and electrolysis mode. While the latter allows primarily efficient conversion of steam into Hydrogen, it also presents the huge benefit of allowing co-electrolysis of CO2 and H2O into a synthetic gas made of CO and H2 that can be processed downstream into valuable chemicals via the Fischer-Tropsch process. As practical operation requires a stable operation, it is of crucial importance to understand the behavior of those cells. The technology is mature for fuel cell mode, however operating in electrolysis mode implies new boundary conditions that may trigger novel degradation mechanism to be understood and mitigated in order to develop efficient and durable solid oxide cells for Power-to-X applications. In this presentation, the behaviour of SOC electrolysis and co-electrolysis and reversible operation is shown for operation up to 10 000 hours. The most significant degradation phenomena specific to electrolysis operation and that affect the durability of electrochemical cells (for instance: nickel migration phenomena, microstructure alteration, poisons…) are presented in terms of physico-chemical, materials and microstructural aspects and discussed. The relative sensitivity of the different cell architectures to the various degradation phenomena that are monitored and reported in this presentation is discussed. Finally, some new materials combinations candidate for the next generation SOC with improved performance and characteristics, will be presented

Formulations of LSFN and LSCN as fuel electrode materials for high temperature co-electrolysis cells

The efficient utilization of CO2 and its conversion into CO has received great interest since it is considered a suitable path for decarbonisation of human activity and a promising climate protection measure. Solid Oxide Electrolysis Cells (SOECs) offer a single step conversion by electrolysing simultaneously H2O and CO2 to obtain syngas (H2 + CO). This can subsequently be used as feedstock in the Fischer – Tropsch process to yield liquid synthetic fuels. In contrast to the syngas obtained by steam reforming of methane, high temperature co-electrolysis is advantageous since it enables fuel production without consuming non-renewable fossil fuels. In addition, SOEC operation at high temperatures, favours electrode reaction kinetics and decreases the electrolyte resistance, thereby decreasing the required electrical energy for co-electrolysis. State-of-the-art Ni-based cermets have been widely studied as fuel electrode materials due to their high catalytic properties towards H2O/CO2 splitting, as well as for their high electrical conductivity. However, they are susceptible to impurities and irreversible degradation in operation, e.g. by nickel depletion in the functional fuel electrode at high over-potential, as one of several effects. Therefore, further investigations are needed in order to propose mitigation strategies based on detailed understanding of degradation mechanisms. As an alternative, Perovskite-based oxides are promising electrode materials for SOECs due to their catalytic activity and stability in dual atmospheres, besides of being potentially resistant towards migration phenomena. With the aim to implement perovskite-based materials for the fuel electrode of a SOEC, lanthanum-transition-metal perovskites were investigated: (La0.6-x Sr0.4) Fe0.8Ni0.2O3 and (La0.7-x Sr0.3)Cr0.85Ni0.15O3. These precursors were produced by soft chemistry methods by varying their A-site deficiency stoichiometry. Particle morphologies were characterized by SEM and formation of crystalline phases were corroborated by XRD and TGA. Results are presented and discussed with the perspective of SOEC application