Ternary doping of phosphorus, nitrogen, and sulfur into porous carbon for enhancing electrocatalytic oxygen reduction

We report a synthesis of phosphorus (P), nitrogen (N) and sulfur (S) ternary co-doped porous carbon (PNS-PC) which acts as efficient metal-free electrocatalyst for the ORR. PNS-PC has been fabricated via an electrostatic assembly method followed by a carbonization process. Tetraphenylphosphonium bromide is employed as carbon and phosphorus source and ammonium persulfate as nitrogen and sulfur source. The as-prepared PNS-PC possesses high BET specific surface area (>580 m2 g−1). The most active PNS-PC that containing 1.44 at.% P, 2.96 at.% N and 2.65 at.% S exhibits much enhanced electrocatalytic activity for the ORR compared to solely P-doped carbon (P-C) in alkaline media. This PNS-PC shows an onset potential of 0.905 V (vs. RHE), which is 120 mV higher than that of P-C. A negative shift of only about 68 mV in the half-wave potential of the PNS-PC as compared to commercial Pt/C (20 wt.% Pt on Vulcan XC-72, Johnson Matthey) is achieved. The high electrocatalytic activity of the PNS-PC is primarily attributed to the synergistic effect of P, N and S ternary doping in carbon and its hierarchical porous structure. The results demonstrate that multiple element doping is an efficient way for enhancing the electrocatalytic activity of carbon for ORR.