Relaxation of Electrochemically Induced Intermediate States Under Non-Operando Conditions

Abstract

Electrochemical polarization under oxygen evolution conditions often induces structural reconstruction from the parent phase in transition-metal-based catalysts, which are frequently interpreted as active intermediate species. Here, we investigate the relaxation behavior of electrochemically induced intermediates in spinel and hydroxide catalysts at controlled non-operando conditions by correlated spectroscopy and microscopy techniques. The oxyhydroxide phase formed at high anodic potentials remains stable after potential removal as long as electrochemical environments are maintained. In contrast, once the electrode is disconnected and the electrolyte is gradually removed, the intermediate state progressively relaxes back to the parent structure. Further drying treatments reveal that decreasing electrolyte activity markedly accelerates such structural recovery. These findings demonstrate that electrochemically induced intermediate structures should be regarded as boundary-condition-dependent states rather than intrinsically stable phases, highlighting the strong environment dependence of catalyst structural insights obtained under non-operando conditions.