Dependence of the Electrocatalytic Activity Towards CO2 Reduction on the Crystal Structure of TiO2

Titanium dioxide (TiO₂) has been investigated as a possible electrocatalyst for CO₂ reduction in a polymer exchange membrane fuel cell (PEMFC) based full electrochemical cell. The electrocatalytic activity of TiO₂ for CO₂ reduction is discovered to strongly depend on the crystal structure. Interestingly, rutile phase shows a much higher activity for CO₂ reduction than anatase, in contradiction to widely reported higher photocatalytic activity of anatase than rutile. Carbon monoxide (CO), methane (CH₄), formate (HCOO^-) are observed as major CO₂ reduction products with ethanol (C₂H₅OH) in traces for rutile TiO₂. This observed much higher electrocatalytic activity of rutile than anatase is mainly attributed to the exposed (110) surfaces for the case of rutile TiO₂. X-ray photoelectron spectroscopy (XPS) measurements of the TiO₂ gas diffusion electrodes (GDEs) before and after electrolysis also suggest the presence of  surface defects such as Ti³⁺ and oxygen vacancies which significantly influence the electrocatalytic activity for CO₂ reduction.