Carbonized-Wood-Supported Ni3Fe@Ni Core–Shell Nanoparticles as Integrated Catalysts for Highly Efficient Water Splitting

The oxygen evolution reaction (OER) is a crucial half-reaction in water electrolysis. Currently, the sluggish kinetics of the OER limit the efficiency of water electrolysis, making the development of advanced OER catalysts imperative. Herein, utilizing carbonized wood (CW) as a self-supporting conductive substrate, we synthesized ultrafine Ni3Fe@Ni core–shell nanoparticles featuring a surface Ni3Fe alloy on unalloyed Ni nanoparticles. Ni3Fe@Ni/CW exhibits a low overpotential of 290 mV at 100 mA cm–2 with excellent stability, outperforming Ni3Fe/CW, Ni/CW, and RuO2/CW. In an overall water splitting electrolyzer, Ni3Fe@Ni/CW delivers a low cell voltage of only 1.74 V at 100 mA cm–2 with outstanding long-term stability. This unique surface-interior heterostructure, where the unalloyed Ni nanoparticles modulate both the geometric configuration and d-band center of the surface Ni3Fe alloy, optimizes the adsorption energetics of oxygen intermediates. Accordingly, for both Ni3Fe/CW and Ni/CW, the rate-determining step (RDS) is the conversion of O* to OOH*. In contrast, the RDS for Ni3Fe@Ni/CW is the OOH* to O2 step with a significantly lower energy barrier, accounting for its excellent OER performance. This work highlights the immense potential of surface-interior engineering for the rational design of high-performance OER catalysts.