Forschungszentrum Jülich – Current Activities in SOC Development

Abstract

Understanding degradation mechanisms in SOCs remains an ongoing issue for its mitigation and to reach levels that will bring the technology closer to commercialization. Benefiting from our experience in performing long-term tests on stacks (up to 100,000 h) post-test examination of the components of several of these stacks gave a better understanding about various degradation effects. Among others the chromium poisoning of La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) and La0.6Sr0.4CoO3-δ (LSC) air electrodes used over the past decade in the cells will be presented.In parallel alternative air electrode materials for low-temperature application based on La2Ni1-xCoxO4+δ (LNCO) are being developed and the influence of A- and B-site substitution on the structural, physico-chemical and electrochemical properties of the materials is investigated. First promising results of a short-stack with Ni/YSZ substrate cells with La2Ni0.8Co0.2O4+δ air electrodes will be presented.Based on the earlier experience obtained from the operation of a 5 kW (in FC-mode) reversible system (rSOC), stacks and supporting components were adapted to scale-up to a 10/40 kW (FC/EL)-class system. This included among others the development of a scalable steam generator of which a prototype was tested separately. This allows for the optimization of the efficiency of the system, especially in electrolysis mode. The 10/40 kW class rSOC system will contain four 20-layer sub-stacks in the planar-type window frame stack-design, each with four standard-sized cells (10 × 10 cm²) in a 2 × 2 array per layer.Our activities focus more and more on investigating high-temperature electrolysis as a first step in future Power-to-X value chains using renewable energies, focusing on CO2-valorization through co-electrolysis of H2O and CO2 for syngas production as well as pure CO2-electrolysis. The performance and stability of cells and short-stacks were investigated with DC and AC techniques for various feed gas compositions. Especially the analysis of the Electrochemical Impedance Spectroscopy (EIS) measurements performed on State-of-the-Art cells in the boundary region between pure CO2-electrolysis and co-electrolysis with low steam content in the feed gas led to a better insight in the role of the reverse water gas shift reaction (RWGS) in the conversion of CO2 under these conditions.For the (co-)electrolysis case a model of the multi-physics phenomena occurring on cell level was developed using the COMSOL platform. The model is fully coupled including electrochemical, chemical, heat and transport phenomena occurring at single cell level. On stack level a steady-state, 3-D, non-isothermal, and homogenized model for rSOC stacks has been developed from an extension of previous studies and implemented into the open-source library OpenFOAM.