Anionic defects engineering of NiCo₂O₄ for 5-hydroxymethylfurfural electrooxidation

Biomass electrooxidation reaction (BEOR) attracts worldwide attention due to its sustainable and carbon–neutral nature. The practical application of BEOR is, nevertheless, limited by the lack of electrocatalysts with high activity and selectivity. In this study, we demonstrate anionic defect engineering as an effective strategy to activate spinel NiCo₂O₄ to achieve outstanding performance towards 5-hydroxymethylfurfural electrooxidation reaction (HMFOR). F-dopants are successfully introduced into NiCo₂O₄, which spontaneously trigger oxygen vacancies formation in the lattice during synthesis. These anionic defects in NiCo₂O₄ result in the expansion of crystal structure, the increase of electron density and the weakened metal-O bond. The F-doped NiCo₂O₄ displays a 2,5-furandicarboxylic acid (FDCA) selectivity of 97% and Faradaic efficiency of 96.5%, which are noticeably higher than the pristine NiCo₂O₄. The strongly enhanced intrinsic activity is mainly attributed to the defect-facilitated adsorption of HMF. Our results provide critical insight into the role of anionic defects in determining the HMFOR activity, and the strategy can be applied for synthesizing high-performance electrocatalyst for other BEOR.