Dual Electronic Modulations on NiFeV Hydroxide@FeO_x Boost Electrochemical Overall Water Splitting

Abstract Nickel‐iron based hydroxides have been proven to be excellent oxygen evolution reaction (OER) electrocatalysts, whereas they are inactive toward hydrogen evolution reaction (HER), which severely limits their large‐scale applications in electrochemical water splitting. Herein, a heterostructure consisted of NiFeV hydroxide and iron oxide supported on iron foam (NiFeV@FeO_x/IF) has been designed as a highly efficient bifunctional (OER and HER) electrocatalyst. The V doping and intimate contact between NiFeV hydroxide and FeO_x not only improve the entire electrical conductivity of the catalyst but also afford more high‐valence Ni which serves as active sites for OER. Meanwhile, the introduction of V and FeO_x reduces the electron density on lattice oxygen, which greatly facilitates desorption of H_ads. All of these endow the NiFeV@FeO_x/IF with exceptionally low overpotentials of 218 and 105 mV to achieve a current density of 100 mA cm⁻² for OER and HER, respectively. More impressively, the electrolyzer requires an ultra‐low cell voltage of 1.57 V to achieve 100 mA cm⁻² and displays superior electrochemical stability for 180 h, which outperforms commercial RuO₂||Pt/C and most of the representative catalysts reported to date. This work provides a unique route for developing high‐efficiency electrocatalyst for overall water splitting.