Highly Durable and Efficient Ni-FeO<i>_x</i>/FeNi₃ Electrocatalysts Synthesized by a Facile <i>In Situ</i> Combustion-Based Method for Overall Water Splitting with Large Current Densities

Abstract

Ni-/Fe-based materials are promising electrocatalysts for the oxygen evolution reaction (OER) but usually are not suitable for the hydrogen evolution reaction (HER). Herein, a durable and bifunctional catalyst consisting of Ni-FeO<i>_x</i> and FeNi₃ is prepared on nickel foam (Ni-FeO<i>_x</i>/FeNi₃/NF) by <i>in situ</i> solution combustion and subsequent calcination to accomplish efficient alkaline water splitting. Density functional theory (DFT) calculation shows that the high HER activity is attributed to the strong electronic coupling effects between FeO<i>_x</i> and FeNi₃ in the Janus nanoparticles by modulating Δ<i>G</i>_H* and electronic states. Consequently, small overpotentials (η) of 71 and 272 mV in HER and 269 and 405 mV in OER yield current densities (<i>j</i>) of 50 and 1000 mA cm^-2, respectively. The catalyst shows outstanding stability for 280 and 200 h in HER and OER at a <i>j</i> of ∼50 mA cm^-2. Also, the robustness and mechanical stability of the electrode at an elevated <i>j</i> of ∼500 mA cm^-2 are excellent. Moreover, Ni-FeO<i>_x</i>/FeNi₃/NF shows excellent water splitting activities as a bifunctional catalyst as exemplified by <i>j</i> of 50 and 500 mA cm^-2 at cell voltages of 1.58 and 1.80 V, respectively. The Ni-FeO<i>_x</i>/FeNi₃/NF structure synthesized by the novel, simple, and scalable strategy has large potential in commercial water electrolysis, and the <i>in situ</i> combustion method holds great promise in the fabrication of thin-film electrodes for different applications.