Tracing defect-driven stepwise reconstruction of FeCoNi-MOF for enhanced oxygen evolution performance

To tackle the challenge of developing efficient and stable electrocatalysts for the oxygen evolution reaction (OER), we report a defect-driven, CV-induced stepwise reconstruction process of FeCoNi-based metal-organic frameworks (MOFs), which enables the formation of highly active oxyhydroxide working states. By resolving the electrochemical evolution at different CV stages, the rapid reconstruction of FeCoNi-MOF is traced from the initial MOF structure, through an FeOOH intermediate, to a highly active CoFe/NiFeOOH phase. Comprehensive characterization reveals that this transformation involves ligand dissociation, metal ion leaching, and the creation of oxygen vacancies, collectively optimizing the adsorption behavior of oxygen intermediates. The activated catalyst exhibits exceptional OER activity, requiring an overpotential of only 284 mV to reach 1000 mA cm⁻² in 1.0 M KOH, with a Tafel slope of 31.88 mV dec⁻¹, surpassing the performance of control samples and most state-of-the-art MOF-based catalysts. Density functional theory calculations indicate that the introduced oxygen vacancies modulate the electronic structure of Fe sites, thereby reducing the energy barrier of the rate-determining step. Furthermore, in a practical anion exchange membrane (AEM) water electrolyzer using 0.1 M KOH at 50 °C, the catalyst achieves an industrial-relevant current density of 500 mA cm⁻² at 1.75 V with remarkable stability exceeding 400 h. This study provides deeper insights into the rapid electrochemical reconstruction of MOF-derived precatalysts and clarifies the formation of intermediate species and active oxyhydroxide phases under OER conditions.