Oxygen-vacancy-rich P,Mn_0.3-CoNi/MoO₄ for electrocatalytic oxidation of methanol to assist energy-saving hydrogen...

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,Mn_0.3-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 (O_V) 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,Mn_0.3-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 O_V concentration induced by P/Mn doping promotes charge transfer and enhances conductivity. Furthermore, the synergy between P/Mn and O_V 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.