Ni₃S₂–Co₉S₈ Heterojunction Integrated within Cobalt Layered Double Hydroxide Nanosheets for 5-Hydroxymethylfurfural Oxidation and Oxygen Evolution Reaction

Metal sulfides are regarded as promising candidates for electrocatalytic applications owing to their highly conductive metal sulfide frameworks serving as the core and high-valence metal active layers functioning as the shell during the electrooxidation process. However, the catalytic ability of a single metal sulfide still needs to be optimized. Herein, a straightforward hydrothermal sulfidation approach was employed to fabricate a uniquely structured electrode composed of Ni3S2–Co9S8 heterojunction embedded in interconnected cobalt layered double hydroxide nanosheets grown on nickel foam (NF) (Ni3S2–Co9S8/Co LDH/NF). The Ni3S2–Co9S8/Co LDH/NF electrode demonstrated a low overpotential (240 mV at 10 mA cm–2) and a small Tafel slope (35.1 mV/dec) in the oxygen evolution reaction (OER). Furthermore, it exhibited a small Tafel slope (15.5 mV/dec) in the 5-hydroxymethylfurfural (HMF) oxidation reaction, achieving nearly 100% conversion of HMF and an approximately 86% yield of 2,5-furandicarboxylic acid (FDCA). The synthesis of Co LDH nanostructure on nickel foam facilitated the dispersion of the Ni3S2–Co9S8 heterojunction, thereby exposing more active sites and enhancing the mass transfer. Additionally, experimental results revealed that the electronic interactions at interfaces enabled precise adjustment of the electronic structure while promoting the formation of high-valence nickel species. Electrochemical measurements verified that the multiphase composite structure fabricated by interface engineering effectively reduced the interfacial impedances and charge transfer resistances, which in turn improved electrocatalytic performances for the OER and HMF oxidation reaction. This research provides a method for constructing a structure-optimized metal sulfide-based electrocatalyst, which can efficiently drive both the OER and oxidative HMF valorization.