Porous SiO2 Encapsulation for Selective Suppression of Hydrogen Evolution in Photocatalytic CO2 Reduction

Photocatalytic carbon dioxide reduction reaction (CO2RR) represents a promising route for sustainable energy conversion. However, in conventional solid-liquid-gas reaction systems, inefficient CO2 diffusion to the catalyst surface often leads to dominant hydrogen evolution reaction (HER), limiting CO2 conversion efficiency and product selectivity. Herein, we propose a catalyst encapsulation strategy using porous silicon dioxide (SiO2) to spatially control molecular transport toward the active sites. By encapsulating Ag-modified titanium dioxide within a porous SiO2 layer, we effectively restrict water access to the catalytic interface while facilitating CO2 permeation. As a result, the parasitic HER is significantly suppressed, enabling an exceptional 100% selectivity for CO production from photocatalytic CO2 reduction in pure water, which is a dramatic improvement from the mere 5.9% CO selectivity of the unencapsulated Ag-TiO2 catalyst. This design achieves near-complete suppression of HER and 100% selectivity toward CO production under photocatalytic conditions. Our work provides a versatile interfacial engineering approach to overcome mass transfer limitations in three-phase photocatalytic systems, opening avenues for efficient gas-involving photoreactions.