In Situ Polysulfide Intercalation for Graphene-Encapsulated Co–Ni Sulfide Electrocatalysts in Overall Water Splitting

The development of highly efficient and durable bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for advancing sustainable energy technologies. In this work, we present an in situ intercalation strategy utilizing polysulfides as a sulfur source to construct graphene oxide (GO)-encapsulated cobalt-nickel bimetallic sulfide (GO@Co₂NiS₄-PDA/NF) with a unique sea urchin-like architecture on nickel foam. The synergistic integration of the three-dimensional (3D) hierarchical morphology, conductive GO encapsulation, and polysulfide-derived active sites not only maximizes the electrochemically active surface area but also facilitates rapid charge transfer and gas diffusion. As a result, the optimized catalyst delivers exceptional bifunctional performance in alkaline media, achieving a low HER overpotential of 172 mV at -10 mA cm^-2 and outstanding OER overpotentials of 153.5 mV (η₅₀) and 227.9 mV (η₁₀₀). Furthermore, the robust GO coating and well-engineered nanostructure ensure remarkable long-term stability under continuous electrocatalytic operation. This work presents a scalable approach for designing high-performance electrocatalysts, demonstrating promising performance in overall water splitting.