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

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 CoOx doped with the desired transition metals M (M = Mn, Fe, Co, Ni, Cu, and Zn) (denoted as CoMOx) by co-precipitation and electrooxidation methods. The HMFOR activity of CoMOx displayed a volcanic curve trend, in which the CoCuOx showed the most remarkable HMFOR activity with an onset potential of 1.2 V and a current density approximately 7 times that of CoOx. Moreover, the CoCuOx 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 CoCuOx and enhanced the deintercalation capacity of OH-, with the lowest number of Co-O coordination sites compared to other CoMOx. 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-.