Direct Observation of Rate Determining Step for Nd[2]NiO[4+δ] SOFC Cathode Reaction by operando Electrochemical XAS

Abstract

The oxygen chemical potential of dense Nd[2]NiO[4+δ] thin films on Zr[0.92]Y[0.08]O[1.96] electrolyte was investigated by operando X-ray absorption spectroscopy (XAS) measurements. Operando XAS at the Ni K-edge was measured under an applied voltage and various oxygen partial pressures at high temperature to simulate the operating conditions of solid oxide fuel cells (SOFCs). The absorption edge energy under various polarizations is similar to those measured under equivalent oxygen partial pressures under open circuit condition. Thus, the oxygen chemical potential changes drastically at the electrode/gas interface and the rate-determining step of this model system is the surface reaction. This study provides direct evidence for the rate-determining step of the SOFC cathode reaction.