Oxygen electrocatalysis under fuel cell conditions: behaviour of cobalt porphyrins and tetraazaannulene analogues

Under fuel cell conditions, using a protonic conductor Nafion® electrolyte, active cobalt porphyrins (TpOCH3PPCo or CoTMPP and derivatives) and cobalt tetraazaannulene (CoTAA) supported on an active charcoal were investigated towards oxygen reduction to test their activity and stability. Over a 200 h period, performances were found almost constant with CoTAA after an 800°C heat treatment (HT 800), whereas performances with different substituted phenyl porphyrins declined. XPS analyses were also carried out on these electrodes. On all samples they displayed a complete loss of cobalt within the measurement accuracy. Heat treatment temperature effects were visible on the Nls spectra for the CoTAA samples, the most stable and active samples presenting the lowest oxidation state after current drain application.