Heteroatom doped carbons prepared by the pyrolysis of bio-derived amino acids as highly active catalysts for oxygen electro-reduction reactions

Abstract

Heteroatom (nitrogen and sulfur)-doped carbons were synthesized via the pyrolysis of composites composed of iron chloride, cobalt chloride and five different amino acids (alanine, cysteine, glycine, niacine and valine), and their electrocatalytic activity towards oxygen reduction reactions (ORR) compared with each other for fuel cell applications. In all of the prepared catalysts, carbon was doped by nitrogen, and, in particular, a catalyst synthesized from cysteine was dual-doped with nitrogen and sulfur. Among all the catalysts, the dual-doped carbon showed the highest onset potential (0.55 V, vs. Ag/AgCl) and electrochemical activity in acidic media, -0.2 mA (at 0.2 V, vs. Ag/AgCl), which is about 43% of that of commercial Pt/C (40 wt%). XPS revealed that sulfur was doped in the carbon as sulfate or sulfonate, and it is surmised that not only nitrogen doping but also sulfur doping of carbon plays a key role in improving its electrocatalytic activity towards ORR.