Combined effects of the hetero-interface of NiSe2–Ni3Se4 and Fe doping markedly boost the electrocatalytic overall water splitting performance of a self-supported nanosheet array electrode†

Optimizing the intrinsic activity of nickel selenide (Ni_xSe_y)-based electrocatalysts is crucial yet extremely challenging for enhancing catalytic reactivity in hydrogen evolution, oxygen evolution, and overall water splitting (HER/OER/OWS). In this work, by skillfully leveraging the adjustable property of the BDC precursor component and precisely controlling the addition amount of the second metal, Fe, a series of self-supported Fe–NiSe₂–Ni₃Se₄/NF-x (x = 1, 2, and 3) electrodes with unique composition and structure was obtained through one-step selenization by combining the effects of Fe doping, the hetero-interface of NiSe₂–Ni₃Se₄ and the nanosheet array structure. Studies have demonstrated that when the molar ratio of Fe to Ni is 3/7, the resulting Fe–NiSe₂–Ni₃Se₄/NF-2 electrode exhibits optimal electrocatalytic activities in the HER (91 mV at 10 mA cm⁻²), OER (161 mV at 10 mA cm⁻²) and OWS (1.51 V at 10 mA cm⁻²) along with long-term stability. The main reasons are as follows: the interfacial electron effect from the NiSe₂–Ni₃Se₄ hetero-interface combined with optimal iron doping can doubly regulate the electronic structure and optimize the adsorption free energy of key intermediates, thereby enhancing inherent catalysis. Meanwhile, the well-dispersed nanosheet array provides as many active sites as possible and accelerates the permeation of electrolytes and the release of bubbles. This work emphasizes the importance of optimizing intrinsic catalytic activity and provides insights for designing advanced Ni_xSe_y-based bifunctional catalysts.