Steering the methanol oxidation pathway via interfacial microenvironment engineering: NiCr mixed hydroxide composite on conductive MXene scaffolds.

Abstract

In sustainable energy conversion, developing methanol oxidation reaction (MOR) electrocatalysts that combine high activity with cost-effectiveness is both scientifically and practically significant. Under alkaline conditions, the MOR involves a multi-proton-coupled electron transfer (PCET) process. Conventional nickel-based catalysts exhibit limited capability in adsorbing hydroxyl species (*OH), resulting in a sluggish MOR kinetics. Herein, this work reports the facile synthesis of a NiCr mixed hydroxide catalyst supported on MXene (Cr(OH)xNi(OH)y@MXene) for electrocatalytic methanol oxidation to produce formate. Cr(OH)3 compounding into the Ni(OH)2 enhances current density at low overpotentials, while the MXene support further amplifies current response and modulates interfacial electron transfer. This synergy broadens the operating potential window and promotes OH- adsorption. The catalyst achieves 100 mA cm-2 at 1.44 V vs Reversible Hydrogen Electrode (RHE) with a Tafel slope of 55.74 mV dec-1. And under low methanol concentrations, the reaction potential window reaches 0.33 V. Faradaic efficiency reaches 91.15% at 1.55 V. The catalyst maintained stable performance for 50 h at a constant potential of 1.55 V vs. RHE. Spectroelectrochemical and density functional theory (DFT) analyses reveal that Cr-MXene synergy enriches interfacial *OH, selectively favoring the CH dehydrogenation pathway:*CH3OH → *CH2OH over the OH dehydrogenation pathway:*CH3OH → CH3O*. This work offers mechanistic insights into surface microenvironment regulation and provides a strategic framework for designing amorphous or weakly crystalline mixed-metal hydroxide active phases.

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