Phase Dependent Selectivity of Electrochemical CO2 Conversion to Fuels on TiO2 nanoparticles

We report the activity and selectivity of electrochemical CO₂ reduction to carbon monoxide and formate on rutile (110) and anatase (101) TiO₂. Our studies show that the rutile TiO₂ phase was found to be more selective, with Faradaic efficiencies of ~ 15% and ~ 18% for CO and formate, while the anatase efficiencies were less than ~2%.  The phase dependent efficiency exhibited by the electrochemical reaction is opposite to previously reported photochemical CO₂ reduction efficiency, which showed a greater activity from anatase TiO₂. In order to evaluate the role of oxygen vacancy and Ti³⁺ sites in the catalytic activity XPS was performed on the catalysts after CO₂ reduction. The XPS showed oxygen vacancies and Ti³⁺ defects in both the anatase and rutile phases. This implies that while the presence of surface defects may be necessary for the electro reduction of CO₂ on TiO₂ the efficiency determining property is the catalyst’s underlying atomic structure. Our recent results using DFT to elucidate a potential mechanism for this phenomenon, comparing the binding energies of CO₂ reduction adsorbates on rutile and anatase TiO₂, will also be discussed.