(Invited) Photocatalytic CO2 reduction with Water By Cu/TiO2: Mechanistic Studies Using in Situ XAS and FTIR

Cu/TiO2 photocatalysts are extensively studied for CO2 photoreduction with H2O, but the roles of Cu species and the photocatalyst deactivation mechanism are not well understood. In this work, we have employed in situ X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), to explore the surface chemistry of various Cu/TiO2 under CO2 photoreduction environment. We found that H2 reduced Cu/TiO2 exhibited 50% higher activity of CO production than air-calcined Cu/TiO2, resulting from the synergy of OH groups, Cu+ and oxygen vacancies that can provide CO2 adsorption sites, act as hole scavengers, and facilitate the activation of adsorbed CO2. Meanwhile, the consumption of OH groups and Cu+ active sites by holes may result in catalyst deactivation, correlated to the change of oxidation state from Cu+ to Cu2+ and increased coordination number. Strategies to maintain the more active Cu+ species for more stable CO2 photoreduction activity is also discussed.