Harnessing non-reducible Ga2O3 hydroxyls to modulate proton delivery for highly selective electrochemical CO2 methanation

The CuO/Ga 2 O 3 –550 catalyst achieves a high CH 4 Faradaic efficiency of 72.1%. • Hydroxyl-rich Ga 2 O 3 support modulates interfacial proton delivery. • Surface hydroxyls accelerate H 2 O dissociation and lower the *CO 2 − to *COOH energy barrier. • Hydroxyl-mediated water activation and *CO stabilization contribute to deep methanation. Electrochemical reduction of CO 2 (CO 2 RR) to methane (CH 4 ) provides a sustainable pathway for the green and efficient CO 2 conversion, yet it is hindered by the competing hydrogen evolution reaction and poorly regulated interfacial proton microenvironments. This work establishes hydroxyl-content modulation on gallium oxide (Ga 2 O 3 ) supports as a robust strategy for CuO/Ga 2 O 3 catalyst fabrication and CO 2 RR to CH 4 optimization. Notably, the CuO/Ga 2 O 3 –550 catalyst with a moderate hydroxyl content exhibits excellent performance, achieving a Faradaic efficiency of 72.1% at −1.5  V vs. RHE for CH 4 production. The kinetic isotope effect (KIE) result reveals that surface hydroxyl groups significantly accelerate *H transfer dynamics. In situ spectroscopy and DFT calculations clarify that surface hydroxyl groups on Ga 2 O 3 not only promote the CO 2 reduction pathway by lowering the energy barrier for CO 2 -to-*COOH conversion, but also optimize *CO adsorption on Cu sites and stabilize *CHO intermediates. Moreover, hydroxyl-mediated water molecular activation reduces the energy barriers for H 2 O dissociation, generates abundant active hydrogen groups, thereby promotes proton-coupled electron transfer toward deep methanation. This study underscores the great potential of support hydroxyl engineering to regulate local proton environments for the selective electroreduction of CO 2 to CH 4 . Surface hydroxyl groups on Ga 2 O 3 regulate the local interfacial microenvironment around Cu active sites and promote H 2 O dissociation, thereby providing accessible proton sources for CO 2 electroreduction. The hydroxyl-mediated proton delivery mechanism facilitates proton delivery on Cu sites, increases *CO coverage, promotes the formation of the *CHO intermediate, and suppresses the competing HER process. Download: Download high-res image (175KB) Download: Download full-size image