Electrochemical Activity of Titanium Dioxide Toward Oxygen Reduction and Evolution Reactions

Wednesday, 27 May 2015: 11:50
Williford Room C (Hilton Chicago)
H. Tavassol (California Institute of Technology) and S. M. Haile (Northwestern University)
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.