Photochemical Reduction of CO2 Using Delafossite Oxides

The photochemical reduction of CO₂ in the presence of H₂O to form CO, CH₄ and other light gases with industrial value is an interesting approach for dealing with CO₂ emissions. This approach can generate tangible revenue to help offset carbon capture and storage costs by generating a product stream with industrial demand from a CO₂ feedstock. Delafossite materials of the general stoichiometry ABO₂ are a new class of photocatalysts being considered for this application. Recent theoretical calculations have indicated that B-site alloying in these systems breaks the inversion symmetry of the crystal giving rise to symmetry forbidden optical transitions across the band structure of the material. B-site alloying can also be used to modulate the delafossite band structure to create new, low energy band gaps, as well as to align band edge positions for the photochemical redox reactions needed specifically for CO₂ applications. The photochemical activity of CuAlO₂, CuAl_0.9Fe_0.1O₂, CuGaO₂ and CuGa_1-xFe_xO₂ (x=0.05, 0.1, 0.15, 0.2) for the reduction of CO₂ will be presented. The photoreduction of CO₂ in the presence of H₂O vapor using CuAlO₂, CuAl_0.9Fe_0.1O₂, CuGaO₂ and CuGa_1-xFe_xO₂ produces CO with little evidence for other products such as H₂ or hydrocarbons.  The observed optical spectra will be compared to the theoretical band structure in these systems to better understand how B-site alloying can be used to control the optical activity of this material for photochemical applications.  Additionally, the calculated band edge positions will be compared to CO₂ reduction and H₂O oxidation potentials to better understand the reaction products and yields observed experimentally.