Engineering carbon nanofiber-supported NiCo/CoNi₂S₄ Mott-Schottky heterostructure with robust interfacial electric...

The sluggish kinetics of the oxygen evolution reaction (OER) remains a critical bottleneck for efficient electrochemical water splitting. Herein, we overcome this challenge through rational heterostructure engineering by constructing a novel sandwich-like Mott-Schottky heterojunction composed of NiCo alloy encapsulated within carbon nanofibers (CNF) and decorated with CoNi₂S₄ nanoparticles (NiCo@CNF/CoNi₂S₄). The built-in electric field formed at the NiCo/CoNi2S4 interface effectively modulates the electronic structure, optimizing the adsorption energetics of OER intermediates. Moreover, the intermediate CNF layer serves as a physical and chemical barrier, preventing corrosive ion penetration and inhibiting mutual diffusion of active components, thereby significantly enhancing structural stability. The optimized NiCo@CNF/CoNi₂S₄ catalyst exhibits exceptional OER performance, requiring a low overpotential of only 252 mV to achieve 10 mA cm^-2 and a small Tafel slope of 68.96 mV dec^-1 in 1.0 M KOH. Remarkably, it demonstrates outstanding long-term durability, maintaining stable operation at 100 mA cm^-2 for 1000 h without significant degradation. In situ Raman spectroscopy reveals that CoNi₂S₄ undergoes surface self-reconstruction to form Ni(Co)OOH as the true catalytically active species. Density functional theory (DFT) calculations further elucidate that the Mott-Schottky heterojunction optimizes the interfacial electronic distribution, lowers the Gibbs free-energy barrier for the rate-determining *O to *OOH step, and strengthens Ni/Co 3d-O 2p orbital hybridization. This work highlights the efficacy of interface engineering in constructing robust Mott-Schottky heterostructures and provides a viable strategy for designing high-performance OER electrocatalysts for sustainable energy conversion technologies.