Hierarchical MXene@Ni3S4/Co3S4 heterostructures with dual-interfacial electronic coupling for efficient and durable water splitting.

A fundamental challenge in alkaline oxygen evolution reaction (OER) is optimizing the adsorption energetics of oxygenated intermediates while accelerating reaction kinetics. Herein, we report a hierarchical MXene@Ni3S4/Co3S4 heterostructure on nickel foam via an interfacial electronic engineering strategy. The Ni3S4/Co3S4 heterojunction induces d-orbital hybridization and charge redistribution between Ni and Co, generating electronically modulated Co active centers with optimized adsorption behavior. Meanwhile, MXene serves as a conductive scaffold and forms TiS interfacial bonds with the sulfides, promoting electron delocalization and further regulating the electronic structure of the active centers. Density functional theory calculations on the sulfide pre-catalyst model reveal a reduced limiting Gibbs free-energy change for the potential-determining step of 0.744 eV and an enhanced density of states near the Fermi level, providing theoretical insights into the intrinsic electronic properties of the pre-catalyst prior to surface reconstruction. Consequently, the catalyst exhibits excellent bifunctional activity in 1.0 M KOH, requiring overpotentials of 251 mV at 100 mA cm-2 for OER and 173 mV at 50 mA cm-2 for HER. A laboratory two-electrode electrolyzer assembled with the catalyst as both the anode and cathode requires only 1.53 V to achieve 10 mA cm-2. Furthermore, an anion exchange membrane water electrolyzer (AEMWE) incorporating the catalyst operates stably for 200 h at 1 A cm-2. This work demonstrates the electronic regulation of active centers via a sulfide/sulfide heterojunction in synergy with TiS interfacial coupling and provides a practical strategy for designing efficient and durable water-splitting electrocatalysts.