Engineering electron redistribution in the Ni₃Fe alloy through Ru doping for efficient water splitting

Developing efficient and durable bifunctional electrocatalysts is crucial for promoting the development of water splitting. In the alkaline oxygen evolution reaction (OER), the surface of the Ni₃Fe alloy is oxidized to the active component Ni/FeOOH, whereas its internal properties still retain high electrical conductivity. Consequently, the Ni₃Fe alloy demonstrates outstanding oxygen evolution activity. Nevertheless, Ni₃Fe has a high dissociation energy barrier for H₂O in the hydrogen evolution reaction (HER) and strong adsorption of the H intermediate, which restricts its application as an independent HER catalyst. Herein, a ruthenium-doped Ni₃Fe electrocatalyst supported on nickel foam (Ru-Ni₃Fe/NF) was successfully fabricated through a one-step hydrothermal process combined with a subsequent reduction procedure. In alkaline media, the HER overpotential of the composite was significantly decreased from 191 mV to 63 mV at 10 mA cm^-2 by doping Ru atoms, and the composite presented an OER overpotential of 289 mV at 50 mA cm^-2. Ru-Ni₃Fe/NF maintained 90.0% and 92.0% of its initial activity for the HER and OER, respectively, indicative of superior long-term stability. The reason why the catalyst shows excellent electrochemical performance includes: (i) Ru is doped into the Ni₃Fe alloy through the bulk phase, which can adjust the microelectronic structure of the alloy, promote the formation of Ni/FeOOH active sites, and accelerate the OER reaction kinetics. (ii) The interaction between Ru and the Ni₃Fe alloy optimizes the hydrogen evolution intermediate, and Ru acts as a new hydrogen evolution active site, thus accelerating the HER kinetics. This study offers a promising approach for the rational design of high-performance and durable bifunctional electrocatalysts derived from transition metal alloys.