Voltage-controlled reconstruction of NiSx for enhanced electrocatalytic oxidation of 5-Hydroxymethylfurfural

The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) represents a pivotal step in facilitating the industrialization of bio-based polyesters. While nickel sulfides are widely regarded as promising electrode materials for HMF oxidation (HMFOR), systematic research regarding their structural stability under anodic conditions and the identification of their true active species remains insufficient. Herein, we employ cyclic voltammetry (CV) pretreatment as a controllable strategy to investigate the electrochemical oxidative reconstruction of NiS x in an alkaline environment by regulating the upper-potential (ranging from 0.9–1.4 to 0.9–1.8 V vs. RHE). This approach elucidates the structure-activity relationship between the degree of reconstruction and HMFOR performance. The results demonstrate that NiS x undergoes surface sulfur oxidation even at relatively mild potentials. As the upper potential increases, the initial spherical structure gradually reconstructs into NiO x -rich nonosheet structures, accompanied by an increased population of Ni 3+ species, accelerated charge transfer kinetics and significantly enhanced electrochemically active surface area. Specifically, moderate reconstruction (e.g., at an upper potential of 1.7 V) achieves an optimal balance between structural stability and the abundance of Ni 3+ active sites, thereby yielding superior HMF conversion efficiency and FDCA selectivity. Conversely, insufficient or excessive potentials result in a scarcity of active sites or structural collapse, respectively. These findings provide fresh insights into the evolutionary mechanism of sulfide-based catalysts during anodic reactions and offer an effective strategy for constructing high-performance HMFOR electrocatalytic systems via potential-regulated reconstruction.