Interfacial C-S Bonding Stabilizes Phase-Tailored Ni Heterosulfides on Carbon Nanofibers for Bifunctional Electrolytic Water Splitting

The development of efficient and cost-effective electrocatalysts is critical for advancing durable water-splitting systems. Special attention must be given to catalyst design, functionality, and interface regulation strategy to create synergistic effects that enhance electrocatalytic performance. We present a rational design of non-precious optimized heterojunction electrocatalysts comprising face-centered cubic nickel metal, cubic Ni₃S₄, and hexagonal NiS phases, supported on a 3D cross-linked carbon nanofiber (CNF) network. Detailed characterization reveals lattice-matching heterojunctions between Ni₃S₄, NiS, and Ni, where strong C-S bonding stabilizes the heterojunction and ensures effective electronic coupling. These heterogeneous interfaces serve as highly electroactive regions, significantly enhancing charge transfer, structural stability, and reaction kinetics. The optimized Ni₃S₄/NiS/Ni@CNF composite demonstrates exceptional bifunctional performance, achieving a low hydrogen evolution reaction overpotential of 88 mV at 10 mA/cm² with a Tafel slope of 34 mV/dec and an oxygen evolution reaction overpotential of 330 mV at 10 mA/cm² with a Tafel slope of 45 mV/dec, alongside excellent durability. The superior electrocatalytic performance is attributed to synergistic interactions at the Ni₃S₄, NiS, Ni, and CNF heterointerfaces, enhanced electronic conductivity, increased catalytic site exposure, and efficient interfacial charge transfer. This work offers a new strategy for the rational design of heterojunction-based materials with superior electrochemical performance in water-splitting applications.