Synergetic regulation of Ce doping and Zn vacancy on Co₂FeO₄ spinel for promoting large-current hydrogen evolution

Co-Fe spinel oxides are attractive alternatives to noble metal-based electrocatalysts for water splitting due to their abundant reserves, unique electrochemical redox characteristics and inherent stability. However, their alkaline HER performance under high-current conditions remains limited by inefficient water adsorption/dissociation and suboptimal hydrogen adsorption balance. Herein, a 600-cm² amorphous Ce-doped Co₂FeO₄ cathode with Zn vacancies (Ce, Zn_v-Co₂FeO₄) were synthesized by electrodeposition and alkaline etching method. It exhibits exceptional alkaline HER performance with low overpotentials of 47.5 and 247.5 mV at 10 and 1000 mA cm⁻², meanwhile maintaining high stability over 500 h at 1000 mA cm⁻² with a potential retention rate of 96.5 %. The resulting water electrolyzer with Ce, Zn_v-Co₂FeO₄ as cathode only needs a cell voltage of 1.90 V at 1000 mA cm⁻² for overall water splitting. In-situ electrochemical tests and density functional theory (DFT) calculations demonstrate that the synergistic effect of Ce doping and Zn vacancies in Co₂FeO₄ leads to a 50 % reduction in bandgap, thereby enhancing conductivity. It also facilitates spontaneous water adsorption and dissociation, reduces the energy barrier by 46 %, and optimizes the balance of hydrogen adsorption/desorption, thereby ultimately enhancing HER activity. This study presents a potential strategy to address the performance limitations of spinel-based HER catalysts.