Synchronous construction of Cu and Ni single-atom sites in ordered porous TiO2 for enhanced photo-conversion of CO2 and H2O to methane

The solar-powered conversion of CO2 and H2O to hydrocarbons is highly compelling but remains a significant challenge because both CO2 reduction and H2O oxidation are thermodynamically unfavorable. Herein, the synchronous incorporation of Cu and Ni single-atom sites into ordered porous TiO2 was accomplished through a template-assisted calcination process, resulting in a series of Cu-Ni/TiO2 catalysts for photocatalytic CO2 reduction using H2O as a hydrogen source. The formation of Cu and Ni single atoms was verified by X-ray absorption fine structure (XAFS) spectroscopy. The optimal Cu-Ni/TiO2 photocatalyst exhibited excellent performance to reach a CH4 production rate of 63.88 μmol g−1 h−1 with a high selectivity of 96.4% under simulated sunlight, in the absence of sacrificial agents. The presence of Cu and Ni single atoms not only provided effective active sites for adsorption and activation of CO2 and H2O but also facilitated separation and transfer of photogenerated charge carriers. In situ spectroscopic analyses revealed that CO2 was adsorbed on the catalyst as bicarbonates, followed by the multistep reduction into CH4 via the electron-proton transfer processes, while the photogenerated holes were consumed by H2O oxidation to generate H2O2. The simultaneous enhancement of both H2O and CO2 activation guarantees excellent photocatalytic performance towards CH4 production. This study provides guidance on developing highly efficient photocatalysts by engineering active sites as well as insights into enhancing CO2 photoreduction.