Effect of Added Elements into TiO2 on Oxygen Reduction Activity in Acid Media

Abstract

In order to develop stable non-platinum cathodes based on titanium oxides, we investigated the effect of added elements into titanium oxide and heat-treatment temperature under reductive atmosphere on the catalytic activity of oxygen reduction reaction (ORR) in acidic media. Non-, niobium-, tantalum- and zirconium-added titanium oxides heat-treated at different temperature for 10 min under Ar containing 4% hydrogen without carbon materials were prepared to reveal the dependence of ORR activity on added elements and heat-treatment temperature. We investigated the relationship between ORR activity and physico-chemical properties such as conductivity, BET surface area, crystalline structure and electronic state. We added an appropriate mixture of the Ketjenblack with the oxide catalysts led to the electrochemical activation of the oxide surface by the formation of electron conduction networks. We revealed that the density of the low-valence state of titanium ions, Ti3+, affected ORR activity in case of niobium- and tantalum-added TiO2. In addition, crystalline distortion of anatase phase with the existence of Ti3+ of niobium- and tantalum-added TiO2 might be essential in order to show ORR activity.