Abstract
To improve the water electrolysis performance of unitized regenerative fuel cells, ultrafine 
powder was synthesized from colloidal precursors, and an active electrode for oxygen evolution and reduction was prepared by mixing the 
powder and Pt black. Analysis showed that the surface area of the synthesized 
was higher than that of high‐surface‐area Pt black. During fuel cell operation, 
increased the overpotential slightly; however during water electrolysis, the mixed 
electrocatalyst had a considerably higher activity for oxygen evolution. The addition of only a small amount of 
to the oxygen electrode was sufficient for the unitized regenerative fuel cell. © 2000 The Electrochemical Society. All rights reserved.