Ti2O3/TiO2 heterophase junctions with enhanced charge separation and spatially separated active sites for photocatalytic CO2 reduction

Abstract

It is strongly desired to develop highly active photocatalysts for CO₂ reduction by accelerating charge separation and realizing spatially separated active sites. In this work, Ti₂O₃/TiO₂ heterophase junctions with enhanced charge separation and spatially separated active sites were facilely prepared via in situ thermal oxidation of commercial Ti₂O₃ in air at an appropriate annealing temperature. The as-prepared Ti₂O₃/TiO₂ heterophase junctions, especially the temperature-optimized T550 sample, displayed high photocatalytic activity for CO₂ reduction to yield CH₄ (∼0.65 μmol g⁻¹ h⁻¹), CO (∼2.64 μmol g⁻¹ h⁻¹) and O₂ (∼5.66 μmol g⁻¹ h⁻¹), which was 4 times higher than that of bulk Ti₂O₃ and nearly 2 times higher than that of rutile TiO₂. Based on the surface photovoltage spectra, related produced OH radical measurement and electrochemical reduction, the high photoactivity could be attributed to the metallic Ti₂O₃, which trapped the photogenerated electrons from TiO₂ through the formed Ti₂O₃/TiO₂ heterophase junctions to enhance charge separation. Remarkably, it was confirmed from theoretical calculations based on density functional theory, Kelvin probe and CO₂-TPD measurements that the Ti₂O₃/TiO₂ heterophase junction possesses spatially separated active sites for CO₂ reduction and water oxidation. Metallic Ti₂O₃ as a reduction site activated and catalyzed CO₂ to produce solar fuels such as CO and CH₄, while TiO₂ as an oxidation site oxidized H₂O to produce O₂ and protons. The designed concept of heterophase junctions and simultaneously activating CO₂ and H₂O at different spatial sites may offer a new strategy to suppress the reverse reactions during photocatalysis for efficient solar energy conversion.