N,P-Codoped Graphdiyne as Efficient Metal-free Catalysts for Oxygen Reduction Reaction

The carbon-based metal-free catalyst is one of the ideal alternatives to Pt as electrocatalysts for oxygen reduction reaction, which can reduce the cost of fuel cells and zinc-air batteries. Here, graphdiyne(GDY), a carbon material with uneven charge distribution, was used as substrate. By doping nitrogen and phosphorus, a N-P-GDY catalyst was prepared, which further regulated the electron structure of GDY. The sheet-like morphology of GDY was preserved in N-P-GDY. The N and P were distributed uniformly in the catalyst, whereas defects and active sites were created by doping N and P, as demonstrated by the element mapping images and Raman spectra. X-Ray photoelectron spectroscopy results indicated N and P existed in many forms in N-P-GDY. The N-P-GDY exhibited higher activity for ORR than only N or P doped GDY, due to the synergistic effect of N and P in N-P-GDY. Moreover, the activity of N-P-GDY changed little after a long time cyclic voltammetry test or injecting methanol in the electrolyte. Besides, the four electrons transfer reaction to produce water was the main process for ORR on N-P-GDY catalysts.