Dual Roles of High-Valence Mo Cation on the Enhanced Electrocatalytic OER Performance of Mixed Multimetal (FeCoNiZrMo) Compounds: Experiment and DFT Insights

The incorporation of high-valence metals into FeCoNi-based oxides is a well-established strategy to enhance the alkaline oxygen evolution reaction (OER). However, the intrinsic mechanism by which high-valence metal cations improve the catalytic activity in materials remains poorly understood. This study explores the dual roles of high-valence Mo cations in boosting the electrocatalytic OER performance of FeCoNiZrMo-based materials (denoted as MMC-Mo_n, with n = 0.0, 0.5, 1.0, 1.5, and 2.0 mmol MoCl₅ reagent). A combination of selected area electron diffraction, X-ray spectroscopy analyses, and first-principles calculations reveals that Mo cations facilitate phase transformation and electro-dissolution, which effectively modify the local atomic and electronic structures of the Fe, Co, and Ni active sites. These structural modifications led to a substantial improvement in the OER activity. Notably, the optimized MMC-Mo_1.0 specimen exhibited an overpotential of 253 mV at 10 mA/cm², along with a 6-fold enhancement in turnover frequency compared to MMC-Mo_0.0 at 1.53 V. These findings highlight the dual roles of high-valence Mo cations in enhancing catalytic performance and provide valuable insights into the rational design of high-performance electrocatalysts.