(345g) Insights Into the Performance of Cu2O in Photocatalytic CO2 Conversion

Photocatalytic conversion of CO₂ to methanol requires new, efficient, and low-cost catalytic materials for this process to be a cost-effective source of fuel. Cu₂O is one attractive semiconductor with many optimal properties for this application. The limitations of Cu₂O as a photocatalytic material can be better understood through theoretical studies of its physical, electrical, chemical, and optical properties. By identifying the source of the limitations, the possibility of rational design is created, allowing for the study of how modifications to its composition may improve its performance.

We use density functional theory (DFT) +U and hybrid-DFT to evaluate many of the properties of Cu₂O that are essential factors in its functionality as a photocatalyst. The need for DFT+U and hybrid-DFT is first established by a comparison to conventional DFT in the prediction of Cu₂O bulk properties. We then use a hybrid-DFT/G₀W₀ approach to evaluate the Cu₂O band gap and band edge potentials, which define the material’s sunlight absorption efficiency and its thermodynamic ability to catalyze redox reactions. A combination of DFT+U and HSE is used to examine the energetics and electronic structure of trap states and delocalized hole states created by intrinsic bulk cation vacancies. Trap states are detrimental to photoconductivity by promoting carrier recombination, and inhibiting trap states will help to optimize of Cu₂O as a photocatalyst. Based on our observations, we suggest doping with Li as a method to prevent deleterious trap state formation. Finally, we use DFT+U to analyze reactant adsorption on the Cu₂O(111) surface, and show the importance of the coordinatively unsaturated surface copper atom as the adsorption site.