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

Liu, Chaofan; Shi, Xue-Rong; Yue, Kaihang; Wang, Peijie; Zhan, Ke; Wang, Xianying; Xia, Bao Yu; Yan, Ya · Adv Mater · 2023

basic_science · Level V

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Abstract

An efficient NiS<sub>x</sub> -modified β-Ni(OH)<sub>2</sub> 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<sub>x</sub> will evoke high-valence Ni<sup>2+</sup> <sup>δ</sup> species in the reconstructed β-Ni(OH)<sub>2</sub> electrode, which are the real active species for HMFOR. The generated NiS<sub>x</sub> /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<sub>x</sub> /Ni(OH)O continues to accumulate, to generate the NiS<sub>x</sub> /NiO<sub>x</sub> (OH)<sub>y</sub> intermediate. Density functional theory (DFT) calculations and experimental results verify that the adsorption energy of HMF can be optimized through the increased NiS<sub>x</sub> composition for more efficient capture of protons and electrons in the HMFOR.