S-Species-Evoked High-Valence Ni 2+ δ of the Evolved β-Ni(OH) 2 Electrode for Selective Oxidation of 5-Hydroxymethylfurfural.

An efficient NiS x -modified β-Ni(OH) 2 electrode is reported for the selective oxidation reaction of 5-hydroxymethylfurfural (HMFOR) with excellent electrocatalytic 5-hydroxymethylfurfural (HMF) selectivity (99.4%), conversion (97.7%), and Faradaic efficiency (98.3%). The decoration of NiS x will evoke high-valence Ni 2+ δ species in the reconstructed β-Ni(OH) 2 electrode, which are the real active species for HMFOR. The generated NiS x /Ni(OH)O modulates the proton-coupled electron-transfer (PCET) process of HMFOR, where the electrocatalytically generated Ni(OH)O can effectively trap the protons from the CHO end in HMF to realize electron transfer. The oxygen evolution reaction (OER) competes with the HMFOR when NiS x /Ni(OH)O continues to accumulate, to generate the NiS x /NiO x (OH) y intermediate. Density functional theory (DFT) calculations and experimental results verify that the adsorption energy of HMF can be optimized through the increased NiS x composition for more efficient capture of protons and electrons in the HMFOR.