Greatly enhanced CO₂ electrocatalytic reduction performance of Ag₂Se nanocatalyst via phase-engineering

Crystal phase of semiconductor nanocatalysts has a great influence on their catalytic performance. Ag-based nanomaterials are fascinating electrocatalysts for CO₂ reduction reaction (CO₂RR) toward CO formation. However, the phase-dependent catalytic behavior of Ag-based electrocatalysts has not been studied so far. Herein, we report a crystal phase-dependent catalytic behavior of Ag₂Se nanoparticles based on the successful synthesis of monoclinic (m-Ag₂Se) and orthorhombic (o-Ag₂Se). Remarkably, m-Ag₂Se nanoparticles deliver an enhanced CO Faradic efficiency up to 98.1 % at −0.90 V vs. RHE as well as the long-term stability under an extremely high current density, far exceeding that of o-Ag₂Se. Theoretical simulations reveal that m-Ag₂Se surface not only facilitates the adsorption and stabilization of *COOH species, but also tends to inhibit HER, thus accounting for the high activity and selectivity for CO formation during CO₂RR. This work offers new insights into the facile design of electrocatalysts in catalysis via crystal phase structure regulation.