Detailed experimental analysis of solid oxide cells degradation due to frequent fuel cell/electrolyser switch

Energy storage systems are key for the transition to a net-zero carbon society, for they mitigate the great uncertainty and intermittence of renewable energy sources and add more flexibility of regulation by connecting electric and energy grids. Solid Oxide Cells are a type of electrochemical energy conversion technology that can function as both a power generator (fuel cell) and as part of an energy storage system (electrolyser), thus enabling renewable electricity storage in a chemical energy vector, namely hydrogen, and vice-versa. Despite being considered reversible, frequent switching between fuel cell and electrolyser modes may eventually lead to reduced reversibility and efficiency after a certain number of operation cycles. This study aims to examine the impact of two primary process variables, namely the frequency of fuel cell/ electrolyser switches (commutation time) and the reactant gases utilization rate on the performance of Solid Oxide Cells for 500 h. Through operando measurement of electrochemical impedance and ex-post circuital analysis (equivalent circuit model: LRel(RctC)GRW), the study provides a systematic analysis of the cell state of health and polarization resistances evolution, contributing to the field of Solid Oxide Cells research thereby. This study finds that the ageing effect ascribed to the electrolyte resistance decreases with lower commutation times, and high reactant gases utilization rates imply lower variation of the electrolyte resistance, yet a sharper increase of the air electrode impedance.