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

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 − . By doping transition metals into CoO x , we can regulate the deintercalation capacity of OH − . The CoCuO x with enriched oxygen vacancies allowed the optimization of the competitive adsorption between HMF and OH − , and accelerated the kinetics of HMFOR.