Nitrogen and phosphorus co-doped hierarchically porous carbons derived from cattle bones as efficient metal-free electrocatalysts for the oxygen reduction reaction
The development of highly efficient metal-free electrocatalysts towards the oxygen reduction reaction (ORR) is of vital importance for the large-scale application of fuel cell technologies. Herein, we demonstrate a facile and effective strategy for the controllable synthesis of nitrogen and phosphorus co-doped hierarchically porous carbon (N,P-HPC) electrocatalysts by pyrolyzing phytic acid (PA) and dicyandiamide (DCDA) with nitrogen-doped hierarchically porous carbon (NHPC) derived from cattle bones. The results show that optimal N and P co-doping plays an important role in enhancing the ORR catalytic activity of carbon-based electrocatalysts. The optimized N,P-HPC with a high content of N (3.2 at%) and P (4.0 at%) exhibits remarkable ORR activity with an onset potential of 0.924 V (comparable to commercial Pt/C), a half-wave potential of 0.853 V (12 mV higher than that of Pt/C) and a kinetic current density of 38.2 mA cm−2 at 0.8 V (1.9-times that of Pt/C) in alkaline electrolyte. Furthermore, the N,P-HPC electrocatalyst also demonstrates superior electrochemical stability and methanol tolerance in comparison with Pt/C. The excellent ORR performance of N,P-HPC can be attributed to the increased number of active sites, the favorable three-dimensional hierarchically porous structure and the large specific surface area (1516 m2 g−1). This attractive strategy opens a new avenue for the synthesis of highly efficient metal-free electrocatalysts for the ORR.