High‐Spin Cobalt Oxyhydroxide Enhancing Electrocatalytic Oxidation of 5‐Hydroxymethylfurfural to FDCA

Abstract The oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA) is governed by the high‐valence metal ion in the catalysts. Spin regulation can modulate the electronic structure of active metal centers and influence the formation of metal‐oxo species. In this work, we synthesized cobalt oxyhydroxide enriched with high‐spin Co by molybdenum dissolution from the CoMoO 4 precursor. We found that such a formed catalyst has a high content (28.3%) of high‐spin cobalt ( h ‐CoOOH). Compared to low‐spin cobalt ( l ‐CoOOH) synthesized by the electrodeposition method, h ‐CoOOH exhibits enhanced HMFOR performance (21.9 times higher current density at 1.2 V versus RHE) and excellent FDCA Faraday efficiency (> 98%). High‐spin Co 3+ facilitates cobalt‐oxo formation, accelerating the kinetics of HMF nucleophilic oxidation. In situ Raman and X‐ray absorption fine structure (XAFS) reveal that high‐spin Co 3+ induces octahedral distortion, promoting the formation of Co 4+ ‐oxo (Co 4+ ═O) species. Based on the 18 O labeling experiment, an HMFOR reaction pathway via h ‐CoOOH in HMFOR was proposed.