Rational design of oxygen vacancy-rich self-supporting NiCo(OH)2 electrode for efficient biomass upgrading

Transition metal-based electrocatalysts are a promising alternative to noble metal catalysts for electrochemical upgrading of biomass-derived 5-hydroxymethylfurfural (HMF) into high-value 2,5-furandicarboxylic acid (FDCA). However, the rational design of efficient electrocatalysts with precisely tailored structure–activity correlations remains a critical challenge. Herein, we report a hierarchically structured self-supporting electrode (Vo-NiCo(OH)₂-NF) synthesized through in situ electrochemical reconstruction of NiCo-Prussian blue analogue (NiCo-PBA) precursor, in which oxygen vacancy (Vo)-rich Co-doped Ni(OH)₂ nanosheet arrays are vertically aligned on nickel foam (NF), creating an interconnected conductive network. When evaluated for the HMF oxidation reaction (HMFOR), Vo-NiCo(OH)₂-NF exhibits exceptional electrochemical performance, achieving near-complete HMF conversion (99%), ultrahigh FDCA Faradaic efficiency (97.5%), and remarkable product yield (96.2%) at 1.45 V, outperforming conventional Co-doped Ni(OH)₂ (NiCo(OH)₂-NF) and pristine Ni(OH)₂ (Ni(OH)₂-NF) electrodes. By combining in situ spectroscopic characterization and theoretical calculations, we elucidate that the synergistic effects of Co-doping and oxygen vacancy engineering effectively modulate the electronic structure of Ni active centers, favor the formation of high-valent Ni³⁺ species, and optimize HMF adsorption, thereby improving the HMFOR performance. This work provides valuable mechanistic insights for catalyst design and may inspire the development of advanced transition metal-based electrodes for efficient biomass conversion systems.