Electrocatalytic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) presents a promising pathway for synthesizing the value-added chemical, 2,5-furandicarboxylic acid (FDCA). However, it is still lack of scalable strategies to fabricate electrocatalysts with high activity and selectivity. Herein, a bayberry-like Ni@Ni3S2 core–shell catalyst is prepared via a spontaneous corrosion strategy for HMF electro-oxidation. The Ni3S2 shells with abundant electron-deficient Ni sites facilitate the generation of high-valence Ni3+OOH active species. Additionally, the in situ oxidation of S2− to SO42− enhances the electron and proton transport capacity. Both high-performance liquid chromatography (HPLC) and density functional theory (DFT) analyses reveal that Ni@Ni3S2 preferentially selects the 2,5-dicarboxyfurylfuran (DFF) pathway due to the lower reaction energy barrier from HMF to DFF, and the rate-determining step of DFF oxidation to generate 5-formylfuran-2-carboxylic acid (FFCA) is significantly accelerated. Consequently, the yield of FDCA and Faraday efficiency are found to be 99.20% and 99.35%, respectively, and they still reach 88.79% and 90.33% after ten cycles, showing excellent stability. Moreover, a mass production of 13.97 g Ni@Ni3S2 is successfully synthesized using the spontaneous corrosion strategy. This work offers a valuable reference for designing scalable and high-performance catalysts by manipulating reaction routes to achieve efficient biomass conversion.