Three-Dimensional Phosphorus-Doped Graphitic-C₃N₄ Self-Assembly with NH₂-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 -C 3 N 4 @NH 2 –CB) for the highly efficient ORR catalyst. P- g -C 3 N 4 @NH 2 –CB was prepared by mixing phosphorus-doped graphitic carbon nitride nanosheets (P- g -C 3 N 4 NSs) with NH 2 -functionalized carbon black (NH 2 –CB) via a novel self-assembly approach. The NH 2 –CB was rationally chosen as the spacer that enables the self-assembled with the P- g -C 3 N 4 NSs driven by the electrostatic interaction. The intercalation of NH 2 –CB induces the transformation of 2-D P- g -C 3 N 4 NSs into a 3-D composites material of higher surface area, thereby exposing more ORR active sites. The P- g -C 3 N 4 @NH 2 –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 NH 2 –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 -C 3 N 4 and NH 2 –CB.