Synergistic modulation of inverse spinel Fe₃O₄ by doping with chromium and nitrogen for efficient electrocatalytic water splitting

Earth-abundant Fe-based oxides have drawn less attention in electrocatalytic water splitting owing to the inferior intrinsic activity and poor conductivity. Therefore, developing an effective method to increase the catalytic performance of Fe-based oxides is of great importance for the practical application. Herein, a novel Cr/N co-doped Fe₃O₄ electrocatalyst (denoted as Cr-Fe₃O₄-N/NF) is designed and prepared by a simple immersion treatment followed by a calcination method for efficient water splitting. The resultant Cr-Fe₃O₄-N/NF shows significant catalytic activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with overpotentials of 218 and 95 mV at 10 mA cm^-2. Furthermore, the water splitting system using Cr-Fe₃O₄-N/NF could afford a current density of 10 mA cm^-2 at 1.53 V, which is superior to two-electrode system composed of Pt/C and RuO₂. The high activities are attributed to the synergistic effect between Cr and N element doping. Specifically, the introduction of electron-deficient Cr is conductive to accelerate the dissociation process of water, adsorption process of intermediates, adjust the electronic structure. Simultaneously, N doping can increase the adsorption of H intermediates, provide more active sites for hydrogen absorption, and improve the electrical conductivity. This study provides a new strategy for Cr and N co-doped metal oxides electrocatalysts for high-performance water splitting.