Water electrolysis is an essential technology for realizing the renewable energy society. PEM electrolysis, in particular, is promising because of its high power density despite its high cost per unit active area. Its OER catalyst often contains Ir or Ru (or both) because of their high OER activities and durabilities. Although the current prices of these two metals are not extremely high compared with other precious metals because of their relatively low demand, Ir and Ru are, however, ones of the scarcest elements on earth and this extreme scarcity could be a major obstacle for wide distribution of PEM electrolysis technology.

Recently we have started fundamental studies on mixed oxides of platinum so called "platinum bronze" (Bronze in this context means mixed oxides with metallic sheen) consisting of platinum, oxygen and other metal ions (such as Li, Na, Mg, Ca, Zn, Cd, Co, Ni [1]) as a versatile electrocatalyst for ORR, OER and HOR.

Co-Pt bronze was prepared according to the literature [1] with some modifications. Platinum oxide and Co(NO₃)₂·6H₂O powders were mixed and heat-treated under air conditions at 650 ºC for 5 hours. The obtained powder was washed with heated (80 °C) aqua regia for 3 times and the remaining powder was then thoroughly rinsed with pure water.

The electronic conductivity of the bronze measured with a compression cell was compared in Fig. 1 with those of Vulcan XC-72 (a typical conductive carbon black), IrO₂ (a typical OER catalyst) and PtO₂. The Co-Pt bronze showed a comparable conductivity with XC-72 and IrO₂, which is much higher than that of PtO₂, an insulator.

OER activities were measured by potential sweep and potential hold experiments. The electrodes were prepared by depositing the catalysts on a glassy carbon disk electrode. Fig. 2 a) and b) show that the Co-Pt bronze has a similarly active and stable OER activity with IrO₂ not like Pt black and Pt/Vulcan, which show rapid decay of OER current due to formation of PtO₂.

This study is financially support by the New Energy and Industrial Technology Development Organization.

References

[1] R.D. Shannon, et al., Inorg. Chem., 21, 3372 (1982)