Vacancy induced dissociation of hydrogenized CO2 for promoted CH4 production in MBenes

Abstract

In the electrocatalytic CO₂ reduction reaction, the first hydrogenation step only forms *COOH or *HCOO, which often limits the catalytic efficiency. Herein, we have extensively investigated the effect of transition metal atom vacancies in a series of M₂B₂ (M = Mo, Ti, V, Cr, Fe, Hf) MBenes on the catalytic performance of the CO₂RR. Our results suggest that an active microregion formed by the Mo vacancy in Mo₂B₂ directly facilitates the cleavage of the C–O bond in *CO₂ during the first hydrogenation step, leading to the formation of *CO/*OH intermediates, resulting in high selectivity for CH₄ production (U_L = −0.49 V). The modulation mechanism is illustrated by the vacancy-induced local electronic structure reconstruction, which leads to differences in electron filling of the d orbitals of Mo near the vacancy. This facilitates a unique *CO₂ adsorption configuration, in which the orbital is fully occupied, significantly weakening the C–O bond. And due to the lower energy barrier for hydrogenation occurring on the O atom, the first protonation step leads to the cleavage of *CO₂, creating a new CO₂RR pathway. This phenomenon expands the methods of CO₂ activation and CO₂RR pathways, paving the way for constructing vacancies as co-catalytic sites to enhance product selectivity.