Improvement of ORR Activity of Monoclinic Zirconium Oxides by Fe and F Co-addition for PEFC Cathodes (Supporting Information)

We investigated the effect of adding Fe and F in the synthesis of zirconium-oxide-based cathode precursors to enhance the catalytic activity in the oxygen reduction reaction (ORR) in acidic media. In particular, we focused on adding F, and an ORR onset potential of 0.88 V was achieved by optimizing the amount of F added and heat treatment conditions contrary to a reversible hydrogen electrode. Additionally, a positive linear relationship was observed between the ORR onset potential and integrated intensity ratio of the monoclinic phase of ZrO₂ in the catalysts. This suggests that the monoclinic phase is fundamentally involved in the formation of active sites in the ORR in zirconium oxide-based cathodes.