The Role of Nonstoichiometry on the Electrocatalytic Properties of TiO2-δ towards the Conversion of Carbon Dioxide to Fuels

Crystalline titanium oxide (TiO₂), which exists in the three ubiquitous phases: rutile, anatase and brookite, possesses a direct wide band gap (E_g ~ 3.3 eV at 300 K) similar to that of GaN (E_g ~ 3.4 eV at 300 K), is under consideration as an alternative material to replace GaN for optoelectronic applications.  It's known that reduced titanium dioxides (TiO_2-x and TiO) exhibit some unique chemical activities towards water oxidation.  In this presentation, we will report our recent studies of using TiO_2-x and TiO as the electrocatalysts to convert carbon dioxide to fuels by incorporating the electrocatalysts into a polymer exchange membrane fuel cell (PEMFC) based full electrochemical cell.  Nonstoichiometric Ti₃O₅ was prepared by reducing TiO₂ at high temperature in the presence of high pressure hydrogen.  X-ray diffraction and thermogravimetric analysis were used to analyze the phase and nonstoichiometry of TiO and Ti₃O₅.  Ti₃O₅ exhibits the highest Faradaic efficiency (~ 12%) towards the formation of formate, comparing to < 2% for both TiO and TiO₂ P25.  X-ray photoelectron spectroscopy (XPS) measurements of the Ti₃O₅ 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.