Enhanced electrocatalytic activity due to additional phosphorous doping in nitrogen and sulfur-doped graphene: A comprehensive study

Effect on oxygen reduction reaction (ORR) of ternary-doped reduced graphene oxide (RGO) as an electrocatalyst is evaluated by employing thiourea as a single source of nitrogen (N) and sulfur (S), and triphenylphosphine for phosphorous (P) as precursors for heteroatom doping. The topographical studies show that by doping the RGO, disruption in surface charge and spin asymmetry is introduced into the carbon matrix due to the difference in the bond length and electronegativity between carbon and heteroatoms, which makes carbon lattice ORR active. Ternary (N, S and P)-doped RGO shows excellent ORR activity, which is ∼2 times better than that of binary (N and S)-doped RGO, and ∼5 times better than that of single (P)-doped RGO. The catalytic activity of the ternary-doped carbon even exceeds the commercial Pt in alkaline medium. Additional P doping causes remarkable synergistic effect on binary N and S-doped RGO by generating active P-N species, improving graphitic order and increasing surface area as well as mesopore volume, which in turn enhances the ORR activity.