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Silver Nanoparticles Encapsulated in an N‑Doped Porous Carbon Matrix as High-Active Catalysts toward Oxygen Reduction Reaction via Electron Transfer to Outer Graphene Shells

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journal contribution
posted on 13.09.2019, 20:44 by Minxue Huang, Shuai Liu, Shipeng Gong, Pengping Xu, Kang Yang, Shi Chen, Changlai Wang, Qianwang Chen
Graphene with an intrinsic sp2-conjugated carbon framework is inactive to the oxygen reduction reaction (ORR) because of the weak adsorption of oxygenated species at the electroneutral carbon site. The heteroatom doping such as N into graphene is an efficient strategy to facilitate it, but most N-doped electrocatalysts are still inferior to transition metal-based catalysts because it is difficult endowing them with enough electrons to achieve a superb performance. Herein, we successfully tune carbon atoms into near-optimal adsorption sites for ORR by injection of extra electrons from a combined electron-rich source to change the π electron occupancy at carbon sites in a rationally designed core–shell structure. Ag nanoparticles encapsulated in N-doped graphitized carbon shells exhibit an excellent performance of a half-wave potential of 906 mV and limited current density of 6.10 mA cm–2 in alkaline media, which is superior to most N-doped electrocatalysts. Density functional theory calculation shows that the degree of extra π electron occupancy at the carbon site is highly correlated to the adsorption strength of oxygenated species, and it proves that Ag is the optimal selection to transfer enough electrons to the outer carbon shells. The Ag@4C model in which every carbon site is activated by extra π electrons with transferred 0.0572 e shows the best performance among Ag@xC models.

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