Oxygen Reduction Reaction Studies of Phosphorus and Nitrogen Co-Doped Mesoporous Carbon Synthesized via Microwave Technique

Metal-free mesoporous P and N co-doped carbon (PNDC) composites are evaluated for their electrocatalytic activity towards the oxygen reduction reaction (ORR). Carbonization of melamine and hexamine-modified tannin in the presence of polyphosophoric acid produces PNDCs with prominent oxygen reduction properties in alkaline media. The effect of the P and N content in the carbon material is evaluated in terms of the ORR activity. The compound containing a high amount of N (8.3 atom%) and P (6.8 atom%), denoted PNDC-1, shows high electrocatalytic activity, stability, durability, and selectivity towards the ORR. PNDC-1 has an onset potential of 0.10 V versus a reversible hydrogen reference electrode and shows a significantly improved performance in comparison to the carbon materials containing less P and N dopant atoms. PNDCs exhibit superior ORR current densities to that of the 20% Pt/C catalyst because of the synergetic effect of P and N co-doping. X-ray photoelectron spectroscopy studies indicate the presence of pyridinic and graphitic N species, which are responsible for oxygen reduction that results in higher current densities. Rotating disk electrode and rotating ring-disk electrode studies support a four electron oxygen reduction to water, with negligible generation of hydrogen peroxide.