Taming *OH intermediates via defect engineering to suppress oxygen evolution for efficient glycerol electrooxidation-coupled hydrogen production

Abstract

Replacing the kinetically sluggish oxygen evolution reaction (OER) with the thermodynamically favorable glycerol oxidation reaction (GOR) offers an effective strategy for energy-saving hydrogen production. However, the strong adsorption of *OH intermediates and the rapid kinetics of the OER lead to competition between the GOR and OER at high potentials. Herein, we propose a facile approach involving Dy and S co-doped NiMoO₄, in which S vacancies are introduced via argon plasma etching to modulate the adsorption of *OH intermediates. This resulting catalyst, bouquet-like Dy and S co-doped NiMoO₄ with S vacancies (Sv/Dy-NiMoO₄/NF), demonstrates remarkable performance in the GOR-coupled hydrogen production, achieving an exceptionally low hydrogen evolution overpotential of merely 29 mV at a current density of 10 mA cm⁻². Simultaneously, this catalyst maintains a cell voltage as low as 1.39 V during operation in a membrane electrode assembly. This configuration provides a potential reduction of 260 mV compared to conventional overall water splitting while also enabling the co-production of high-value formate as oxidation products. Both experimental and theoretical analyses reveal that the S vacancies optimize the electronic structure of the catalyst, thereby activating additional reaction sites, specifically those associated with Dy and its neighboring Mo and Ni, for better adsorption of *glycerol. Furthermore, the OER is effectively inhibited due to the diminished binding with *OH intermediates. This work not only advances the design of highly efficient electrocatalysts for energy-saving hydrogen production but also establishes a sustainable pathway for the concurrent generation of valuable chemicals.