Synthesis and Electrocatalytic Activity of Nitrogen and Phosphorus Co-Doped Graphene for Oxygen Reduction
Authors: Yang Ruizhi , Wu Jiao , Zheng Xiangjun , Zhang Na 
Published: February 2020

The oxygen reduction reaction (ORR) at the cathode plays an important role in the performance of fuel cells and metal-air batteries. Due to the high cost and scarcity of Pt-based electrocatalysts, intensive efforts have been focused on reducing or replacing Pt catalyst in fuel cells and metal-air batteries. [1-4]
Graphene, single-atom-thick layer of sp2-hybridized carbon atoms packed into two-dimension hexagonal lattice, has been rapidly developed in recent years. Recently, both theoretical and experimental studies show that the electrical and physicochemical properties of graphene can be significantly modified by incorporation foreign atoms into graphene. [5-8] Especially for catalytic applications, doping pristine graphene with heteroatoms, such as N, B, S, I and P, is an effcient approch to alter the electron-donor property and consequently increase the electrocatalytic performance for ORR. [9-12] Particularly, co-doping multiple heteroatoms endows graphene much imrpoved ORR activity than doping with single atom. Such multiple-doped graphene can create a unique electronic structure with a synergistic effect in these heteroatoms, efficiently enhancing the ORR activity.
In this work, for the first time, we have successfully synthesized P and N binary-doped graphene (PNG) through a facile thermal annealing method by using urea and tetraphenylphosphonium bromide (C24H20BrP) as N and P precursors, respectively. The as-prepared PNG catalysts with a large specific surface area up to 1207.03 m2 g-1 act as efficient metal-free electrocatalysts for ORR, showing remarkable electrocatalytic activity and excellent long-term stability as well as high tolerance to methanol in alkaline solution. The content of N and P has a significant impact on the activity of the PNG as shown in Figure 1.The outstanding electrocatalytic activity and long-term durability of PNG toward ORR are primarily attributed to the synergetic effect arising from co-doping graphene with both P and N. This work may provide an efficient approach for the synthesis of heteroatom multiple-doped graphene.

Acknowledgements

This work is supported by National Natural Science Foundation of China (Nos.51272167, 21206101 and 51572181 ).

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Figure 1. Linear sweeping voltammograms of the ORR on the P and N binary-doped graphene (PNG) in 0.1 M NaOH solution with a rotating speed of 1600 rpm.

Figure 1