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

Cr-Fe3O4-N/NF nanoarray has abundant active sites and shows good catalytic performance for OER and HER in alkaline solution. [Display omitted] •A novel Cr/N dual-element co-doped Cr-Fe3O4-N electrocatalyst was designed for total water splitting.•The doping of Cr as an oxophilic site promotes the adsorption and dissociation of water, and can optimize the adsorption energy of the intermediate in the Fe site during the OER process.•Electronegativity N doping can provide more favorable active sites for the adsorption of hydrogen intermediates and can increase the strength of OH− adsorption.•The synergistic effect of the three sites of Cr, N and anti-spinel Fe further promotes the total water splitting catalytic activity.•The optimal Cr-Fe3O4-N/NF exhibited high electrocatalytic activity with overpotentials of 95 mV and 218 mV for HER and OER, respectively, at a current density of 10 mA cm–2. 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.