Three-Dimensional Phosphorus-Doped Graphitic-C 3 N 4 Self-Assembly with NH 2 -Functionalized Carbon Composite Materials for Enhanced Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the major reaction that occurs at the cathodes of fuel cells and metal-air batteries. Development of inexpensive, active, and durable heteroatom doped carbon-based ORR catalysts can lead to significant cost reduction of these electrochemical energy devices, which therefore has recently attracted enormous research attentions. This work reports a three-dimensional porous composite (P-g-C3 N4 @NH2 -CB) for the highly efficient ORR catalyst. P-g-C3 N4 @NH2 -CB was prepared by mixing phosphorus-doped graphitic carbon nitride nanosheets (P-g-C3 N4 NSs) with NH2 -functionalized carbon black (NH2 -CB) via a novel self-assembly approach. The NH2 -CB was rationally chosen as the spacer that enables the self-assembled with the P-g-C3 N4 NSs driven by the electrostatic interaction. The intercalation of NH2 -CB induces the transformation of 2-D P-g-C3 N4 NSs into a 3-D composites material of higher surface area, thereby exposing more ORR active sites. The P-g-C3 N4 @NH2 -CB exhibited a remarkable ORR activity with an electron transfer number of 3.83 and Tafel slope of 89 mV dec-1 in alkaline electrolyte, which is comparable to the ORR performance on Pt/Vulcan XC-72. It is found that the incorporated P atoms as well as employing NH2 -CB spacer not only reduces the overpotential of ORR, but also enhances the ORR activity of carbon nitride-based materials, owing to the synergistic effect between P and N in tri-s-triazine rings of carbon nitrides and the optimum interaction between the oppositely charged P-g-C3 N4 and NH2 -CB.