Bimetallic sites and coordination effects: electronic structure engineering of NiCo-based sulfide for 5-hydroxymethylfurfural electrooxidation

Abstract

Bimetallic-sites construction and coordination species tuning are considered as effective strategies to improve electrocatalytic performance of 5-hydroxymethylfurfural (HMF) oxidation. However, it remains a challenging issue to clarify the roles of dual-sites and coordinating anions through optimized electronic structure. Herein, hierarchical NiCo-based sulfide (NiCo–S) nanosheets are reported to disclose the composition-dependent activity at the atomic level. X-ray absorption spectroscopy (XAS) evaluates the tuned electronic configuration. Electrochemical experimental and theoretical results manifest that Ni–Co dual sites synergistically participate in HMF oxidation, where Co sites promote the transformation of the aldehyde (CHO) group to the carboxyl group with the strong diatomic adsorption (O and C atoms) on the CHO group of HMF, while Ni sites speed up the reaction rate of 2,5-furandicarboxylic acid (FDCA) generation. Meanwhile, the coordinating S species also contributes to the formation of strong diatomic adsorption with the CHO group of HMF, and a larger density of state (DOS) of NiCo–S at the Fermi level demonstrates a higher conductivity for carrier transfer compared with NiCo–O. All the above studies confirm the effects of the Ni–Co dual-sites and S coordination on accelerating reactions and lowering energy barriers, thus facilitating the catalytic activity (98.0% selectivity and 97.1% yield for FDCA) with rapid reaction kinetics and low onset potential (1.2 V vs. RHE).