Influence of sputtering power on oxygen reduction reaction activity of zirconium oxides prepared by radio frequency reactive sputtering

Zirconium oxides (ZrO2−x) have been investigated as new cathodes for direct methanol fuel cells without platinum. ZrO2−x films were prepared using a radio frequency (RF) magnetron sputtering at RF powers from 75 to 175 W. The influence of the RF power on the catalytic activity for the oxygen reduction reaction (ORR) and properties of the ZrO2−x films were examined. The ORR activity of the ZrO2−x catalyst increased with the RF power in the range we studied. The onset potential for ORR over ZrO2−x deposited at 175 W was 0.88 V vs RHE. In addition, the relationship between the ORR activity and the composition, crystallinity, electric conductivity, as well as the ionization potential has been investigated. The zirconium oxide with an oxygen defected state and the higher electric conductivity showed the higher ORR activity, and the electrocatalytic activity for ORR increased with the decreasing in the ionization potential of the ZrO2−x catalyst.