Revising the role of chromium on the surface of perovskite electrodes: Poison or promoter for the solid oxide electrolysis cell performance?

Abstract

Perovskite materials are typically used as oxygen electrodes of solid oxide fuel and electrolysis cells (SOC). The high stability of the perovskite structure in oxidative environments makes it a good candidate as a cathode electrode for steam electrolysis SOC as well. In this work, we investigate SOC with La0.75Sr0.25Cr0.9Fe0.1O3 perovskite cathodes employing near ambient pressure X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopies combined with online electrochemical measurements. Based on operando experimental evidences the surface state of the perovskite electrode is directly associated with the electrocatalytic performance of the cell. The results indicate that under steam electrolysis operating conditions the well-known Sr surface enrichment is accompanied by Cr segregation and formation of SrCrO4-like oxide. In contrast to the common perception of the role of surface chromites, we show here that its presence does not induce cell deactivation, but on the contrary, is beneficial for cell performance.