In situ regulating intimately connected heterostructure by decomposition of solid solution oxides toward high-efficient water oxidation

Heterogeneous interfaces produced by inter-domain interactions on a nanoscale performs a crucial role in boosting the properties of an electrocatalyst toward oxygen evolution reaction (OER) process. Herein, a series of dual-phase electrodes with intimately connected heterointerfaces are prepared by in situ decomposing solid solution oxide of Ni_xCo_yFe_100−x−yO, which grew on Ni foam massively via an ultrafast combustion approach. Particularly, with high-reaction kinetics caused by the reduction treatment at 450 °C, the less electronegative Fe and Co are more oxyphilic than Ni, which facilitated their co-exsolution and formation of CoFe₂O₄/NiO oxide with enriched oxygen vacancies. Benefiting from the nanoporous framework, heterojunction structure, and oxygen defects, the self-supporting electrodes present rapid charge/mass transmission and provide abundant active sites for OER. The optimized sample (R-SNCF4.5) shows low overpotentials of 226 and 324 mV at 10 and 100 mA·cm⁻², a small Tafel slope (46.7 mV·dec⁻¹), and excellent stability. The assembled R-SNCF4.5//Pt/C/NF electrolyzer demonstrates continuous electrolysis over 50 h at a current density of 10 mA·cm⁻², under 1.51 V. Density functional theory (DFT) calculations verify that the strong electronic modulation plays a critical part in the CoFe₂O₄/NiO hybrid by lowering the energy barriers for the rate-determining steps, and Fe sites are the most active OER sites.