Oxygen-vacancy-rich P,Mn0.3-CoNi/MoO4 for electrocatalytic oxidation of methanol to assist energy-saving hydrogen production.

The preparation of bifunctional catalysts for energy-efficient hydrogen production by coupling the methanol oxidation reaction (MOR) and the hydrogen evolution reaction (HER) remains a significant challenge. In this work, the P,Mn0.3-CoNi/MoO4 composite (0.3 and CoNi/MoO4 represent the amount of manganese and the composite compound composed of CoMoO4 and NiMoO4, respectively) with abundant oxygen vacancies (OV) fabricated by the hydrothermal coupling phosphating method exhibits remarkable MOR (1.281 V vs. RHE@10 mA cm-2) and HER (-47 mV vs. RHE@10 mA cm-2) performance, and has exceptionally high formic acid selectivity. At a current density (j) of 100 mA cm-2, the voltage (1.522 V) required for the methanol electrolytic cell is 200 mV lower than that needed for the traditional overall water splitting. After consecutive 500 h of chronopotentiometry (CP) at a higher j (100 mA cm-2), the voltage of the methanol electrolytic cell increased by only 3.3% from the initial value. The excellent performance of the P,Mn0.3-CoNi/MoO4 composite mainly results from the following: the layered nanosheets formed by Mn induction facilitate the diffusion of the electrolyte and the release of gases; P optimizes the electronic density and promotes surface reconstruction of the composite, thus accelerating the formation of the NiCoOOH active phase, as confirmed by in situ electrochemical Raman spectroscopy; and the increased OV concentration induced by P/Mn doping promotes charge transfer and enhances conductivity. Furthermore, the synergy between P/Mn and OV facilitates the HER kinetics by optimizing H2O dissociation and H⁎ adsorption and reduces the energy barrier of the MOR rate-limiting step (CH3O⁎ → CH2O⁎), as confirmed by the results of density functional theory (DFT) calculations.