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

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.