High-density triple-phase contact points for enhanced photocatalytic CO2 reduction to methanol

Abstract

The efficiency of photocatalytic CO2 reduction reaction (PCRR) is restricted by the low solubility and mobility of CO2 in water, poor CO2 adsorption capacity of catalyst, and competition with hydrogen evolution reaction (HER). Recently, hydrophobic modification of the catalyst surface has been proposed as a potential solution to induce the formation of triple-phase contact points (TPCPs) of CO2 (gas phase), H2O (liquid phase), and catalysts (solid phase) near the surface of the catalyst, enabling direct delivery of highly concentrated CO2 molecules to the active reaction sites, resulting in higher CO2 and lower H+ surface concentrations. The TPCPs thus act as the ideal reaction points with enhanced PCRR and suppressed HER. However, the initial synthesis of triple-phase photocatalysts tends to possess a lower bulk density of TPCPs due to the simple structure leading to limited active points and CO2 adsorption sites. Here, based on constructing a hydrophobic hierarchical porous TiO2 (o-HPT) with interconnected macropores and mesopores structure, we have significantly increased the density of TPCPs in a unit volume of the photocatalyst. Compared with hydrophobic macroporous TiO2 (o-MacPT) or mesoporous TiO2 (o-MesPT), the o-HPT with increased TPCP density leads to enhanced photoactivity, enabling a high methanol production rate with 1111.5 µmol g−1 h−1 from PCRR. These results emphasize the significance of high-density TPCPs design and propose a potential path for developing efficient PCRR systems.