Tantalum-induced reconstruction of nickel sulfide for enhanced bifunctional water splitting: Separate activation of the lattice oxygen oxidation and hydrogen spillover

Designing highly active and stable bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under alkaline conditions is crucial for sustainable overall water splitting. Herein, we present a targeted reconstruction of Ni₃S₂ by introducing tantalum, achieving remarkable overall water splitting performance through the separate activation of the lattice oxygen mechanism and hydrogen spillover. Electrochemical Mass Spectrometry and in-situ Raman spectroscopy reveal that tantalum induces Ni₃S₂ to reconstruct into nickel hydroxide during OER, thereby enhancing catalytic activity via the activation of the lattice oxygen mechanism. In the corresponding HER, tantalum promotes the reconstruction of Ni₃S₂ into oxysulfide, facilitates hydrogen spillover, and acts as an anchor to shorten the spillover distance, improving the HER catalytic performance, as verified by the kinetic isotope effect and theoretical calculations. Therefore, the catalyst-based anion exchange membrane water electrolyzer system achieves a current density of 1 A cm^-2 at just 1.97 V, maintaining continuous operation for 500 h. This study offers new insights into the design of bifunctional catalysts, advancing the development of efficient and robust overall water splitting catalysts.