Most nonplatinum group metal (non-PGM) catalysts for polymer electrolyte fuel cell cathodes have so far been limited to iron(cobalt)/nitrogen/carbon [Fe(Co)/N/C] composites owing to their high activity in both half-cell and single-cell cathode processes. Group IV and V metal oxides, another class of non-PGM catalysts, are stable in acidic media; however, their activities have been mostly evaluated for half-cells, with no single-cell performances comparable to those of Fe/N/C composites reported to date. Herein, we report successful syntheses of zirconium oxynitride catalysts on multiwalled carbon nanotubes, which show the highest oxygen reduction reaction activity among oxide-based catalysts. The single-cell performance of these catalysts reached 10 mA cm –2 at 0.9 V, being comparable to that of state-of-the-art Fe/N/C catalysts. This new record opens up a new pathway for reaching the year 2020 target set by the U.S. Department of Energy, that is, 44 mA cm –2 at 0.9 V.

In order to make the PEFC gain in popularity, we are working on preparing the non-precious metal catalysts for the cathode oxygen reduction reaction (ORR). Our researches are focus on the oxide-based compounds of group 4 and 5 metals. We have reported that the oxide-based compounds, in particular, partially oxidized carbonitrides of Zr1 Nb2, and Ta3 had high stability and high catalytic activity for the ORR in acidic solution. But it is hard to prepare the fine particle catalysts to improve the ORR activity by using carbonitrides compounds. So we tried to prepare the oxide-based compounds by different starting material.

In order to develop a non-precious metal cathode for PEFCs, we have tried Zr oxide based materials. To synthesize fine particles, we used oxy-zirconium phthalocyanine (ZrOPc) as a starting material. ZrOPc was placed on multi-walled carbon nanotube (MWCNT) and treated under 0.005～0.5%O2 + 2%H2 – N2 and 4%H2 – N2 atmosphere at 900oC. The slow scan voltammetry (SSV) was performed to evaluate the catalytic activity for the oxygen reduction reaction (ORR) under nitrogen and oxygen atmosphere separately in 0.1 mol dm-3 H2SO4 at 30oC. The XRD analysis of these catalysts showed tetragonal ZrO2. The particle size was about 10 nm. The maximum ORR current was up to 300 mA g-1 Cat / C at 0.8 V. This value was 300 times higher than Zr-CNO(CN) we reported before.

In order to develop a non-precious metal cathode for PEFCs, we have tried to improving oxygen reduction activity of Zr oxide-based cathodes. We succeeded to prepare Zr oxide-based cathodes with fine primary particles using zirconium oxy-phthalocyanine as a starting material. However, secondary particle size was very large, resulting that the activity was insufficient. Therefore, we performed ball mill to crack secondary particles for increasing the actual surface area. In addition, nitridation of oxide-based compounds was performed to increase the active sites for oxygen reduction reaction such as oxygen defects and/or nitrogen atoms including oxide lattice.

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