Electrochemical Activity of Titanium Dioxide Toward Oxygen Reduction and Evolution Reactions

We report on the electrochemical activity of TiO₂ polymorphs toward oxygen reduction and evolution reactions in a CsH₂PO₄ solid acid electrochemical system. Oxygen reduction and evolution are catalytically challenging reactions relevant to the fuel cell and water splitting applications. Because of the strong O=O bond, oxygen reduction is a slow reaction even on a Pt surface. In fuel cells, the oxygen reduction reaction (ORR) requires high loadings of the precious Pt catalyst. Even at the operating temperature of the super-protonic CsH₂PO₄ solid acid, ca. 240 °C, the ORR remains sluggish.

Titanium dioxide has been studied extensively as a promising, low cost (photo)catalyst for water splitting. TiO₂ activity toward oxygen led us to examine its catalytic performance for the oxygen reactions in the CsH₂PO₄ electrochemical system. Solid state TiO₂ catalysts on carbon based supports show a range of activity depending on the relative ratio of the rutile to anatase polymorphs. Rutile phase exhibits a lower overpotential for the ORR. The activity of the catalysts are also controlled by the type of the carbon based interconnects used in the fabrication of the composite electrodes. Interconnects facilitate the interaction between CsH₂PO₄ and TiO₂ particles. Catalysis only occurs on TiO₂ particles that are connected to the CsH₂PO₄ electrolyte, and are also accessible to the O₂ gas. We will discuss the selective activity of pure and mixed phases of TiO₂ rutile and anatase polymorphs toward oxygen reduction and evolution reactions.