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

Abstract

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.