Large enhancement of electrochemical biomass oxidation by optimizing the competitive adsorption of HMF and OH− on doped CoOx

Abstract

Cobalt-based catalysts have shown great potential in the 5-hydroxymethylfurfural oxidation reaction (HMFOR), which is often hindered by the competitive adsorption and coupling process of HMF and OH⁻, leading to reduced catalytic efficiency. Here, we report the successful fabrication of CoO_x doped with the desired transition metals M (M = Mn, Fe, Co, Ni, Cu, and Zn) (denoted as CoMO_x) by co-precipitation and electrooxidation methods. The HMFOR activity of CoMO_x displayed a volcanic curve trend, in which the CoCuO_x showed the most remarkable HMFOR activity with an onset potential of 1.2 V and a current density approximately 7 times that of CoO_x. Moreover, the CoCuO_x exhibited an outstanding FDCA yield of 99.8% and FE of 97.7%. In situ EIS and XAFS revealed that the incorporation of Cu reduced the charge transfer resistance of CoCuO_x and enhanced the deintercalation capacity of OH⁻, with the lowest number of Co–O coordination sites compared to other CoMO_x. This enabled more unsaturated Co sites to capture OH⁻ ions and participate in the dehydrogenation process of HMF in the form of lattice OH⁻, thus optimizing the competitive adsorption between HMF and OH⁻.