Ga-induced electronic structure engineering of NiFe2O4 nanosheet arrays for stable and efficient oxygen evolution

Abstract

Developing highly efficient and stable electrocatalysts toward the oxygen evolution reaction (OER) is essential for water-splitting technologies. Herein, hierarchical gallium (Ga)-doped NiFe₂O₄ (Ga-NiFe₂O₄) nanosheet arrays grown on nickel foam (NF) were successfully fabricated by a straightforward hydrothermal method as three-dimensional (3D) electrodes for the OER. The Ga doping regulated the electronic structure of NiFe₂O₄ and produced oxygen vacancies, tuning the adsorption energies of the oxygen intermediate species. Thanks to the unique 3D nanosheet arrays and Ga doping, the optimal Ga-NiFe₂O₄ displayed superior OER activity with ultralow overpotentials of 218 and 250 mV at 10 and 100 mA cm⁻² in alkaline media, respectively. The robust electrocatalytic durability of Ga-NiFe₂O₄ at a large current density was also demonstrated. Furthermore, the voltage of Ga-NiFe₂O₄ at 10 mA cm⁻² was 1.59 V in overall water splitting, and it also demomstrated remarkable stability. Based on systematic experiments, the outstanding OER properties of Ga-NiFe₂O₄ could be attributed to the optimized electronics, rich oxygen vacancies, and 3D nanosheet array structure. Moreover, density functional theory (DFT) calculations further revealed that the enhancements in conducting capacity and binding energy of the oxygen-containing intermediates could be ascribed to Ga doping, which optimized the electronic configuration of NiFe₂O₄, leading to an improvement in the OER performance. This study provides insights for the fabrication of advanced electrocatalysts.