Effects of hydrothermal treatment on the catalytic activity of cobalt-doped catalysts for oxygen reduction reaction

A series of cobalt-doped catalysts (Co–PPy/BP) is synthesized by hydrothermal treatment of polypyrrole-modified BP2000 in cobalt nitride solution. The hydrothermal temperature is varied from 80 °C to 180 °C to investigate the effect of treatment temperature on the catalytic site formation for oxygen reduction reaction (ORR). Treatment temperature is found to slightly affect the structure and morphology of the synthesized catalysts. However, the catalytic activity of the synthesized Co–PPy/BP increases with increased treatment temperature up to 160 °C because higher treatment temperatures promote pyrrolic-N conversion to Co–Nx. Co–Nx catalyzes H2O2 electroreduction reaction, which increases the number of electrons transferred during ORR. However, the hydrothermal treatment at 180 °C leads to decreased pyrrolic-N and Co–Nx contents, which results in decreased catalytic activity of the synthesized Co–PPy/BP.