Electrochemical characterization of p- and n-type Perovskites in Solid Oxide Electrolysis

Kurzfassung

Mixed ionic and electronic conductive (MIEC) perovskites - in contrast to state-of-the-art Nickel-cermets, are not limited to triple-phase-boundary activity. MIEC use their complete surface for the reaction and can host catalytically active exsolved metals in the form of nanoparticles (NPs) which enables performances comparable to cermet FEs at a significantly lower Nickel content. By means of redox cycling, where catalyst NPs may be dissolved and re-exsolved from the perovskite, these electrodes yield an operando healing mechanism against various kinds of catalyst related degradation, which may be a significant advantage in the future. Drawbacks are the generally lower electrical conductivity of perovskites, their limited chemical compatibility with common electrolyte- and contacting materials, the sensibility of their defect chemistry towards surrounding oxygen partial pressure and their generally not guaranteed redox stability. This work aims to address these challenges by first identifying the degradation mechanisms and then derive mitigation strategies. The focus here is on the investigation of different n-type titanate- and p-type chromo-manganite-based fuel electrodes (FEs). Emphasize is set on the impact of the exsolved transition metals on the defect chemistry and the cell performance. Various FEs based on perovskites such as (La, Sr, Ca)Ti0.95Ni0.05O3 and (La, Sr)Cr0.5Mn0.45(Fe, Ni, Mn)0.05O3 are screen-printed onto electrolyte supported solid oxide cells (SOCs). Their operando behaviors are investigated by means of electrochemical impedance spectroscopy (EIS) during 500 h of steam electrolysis operation.