Oxygen reduction reaction on a polypyrrole-modified, carbon-supported cobalt hydroxide catalyst

A series of polypyrrole (PPY)-modified carbon-supported Co(OH)(2) catalysts [Co(OH)(2)-PPY-C] with different types of carbon supports and the PPY and Co(OH)(2) contents are synthesized to investigate the effect of the Co-Nx and -C=N-C= sites on the oxygen reduction reaction (ORR). X-ray photoemission spectroscopy results reveal that the Co-Nx and -C=N-C= sites dominate the four- and two-electron transfer ORR, respectively. The carbon support and the PPY and Co(OH)(2) contents of the catalysts determine the distribution of the Co-Nx and -C=N-C= sites. The competition between these two sites determines the overall electron number of the ORR. A direct borohydride fuel cell using an optimal Co(OH)(2)-PPY-C as the cathode catalyst exhibits a maximum power density of 550 mW cm(-2) at 80 degrees C. (C) 2012 Elsevier B.V. All rights reserved.