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Carbon fragments as highly active metal-free catalysts for the oxygen reduction reaction: a mechanistic study

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Abstract

In metal-free carbon-fullerene-based or defective graphene-based electrocatalysts, pentagon rings are known to play a key role in boosting catalytic activities for the oxygen reduction reaction (ORR). However, the fundamental chemical mechanism underlying the remarkable catalytic effect of the pentagon rings towards the ORR is still not fully understood. Herein, we perform a comprehensive computational study of the catalytic activities of various carbon fullerenes and fullerene fragment species, all containing pentagon rings, by using the density functional theory (DFT) and computational hydrogen electrode (CHE) methods. We find that more active sites on carbon are associated with more neighbouring pentagon rings and stronger adsorption of the key intermediates of O*, OH* and OOH* for the ORR. Importantly, two C60-based fragments, namely, C60-frag1 and C60-frag2l, show a very high activity towards the ORR, as both yield overpotentials as low as 0.389 and 0.407 V, and entail suitable adsorption free energy of OH* and OOH* species. These desirable chemical properties of fullerene fragments can be attributed to the high-energy HOMO orbitals, induced by the low-symmetry fullerene-fragment structures. Both the number of neighbouring pentagon rings and the degree of overall symmetry of the fragment appear to be the two important factors that can be adjusted for the design of optimal metal-free carbon electrocatalysts towards high ORR activities.

Graphical abstract: Carbon fragments as highly active metal-free catalysts for the oxygen reduction reaction: a mechanistic study

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Publication details

The article was received on 24 Jun 2019, accepted on 29 Jul 2019 and first published on 29 Jul 2019


Article type: Paper
DOI: 10.1039/C9NR05338G
Nanoscale, 2019, Advance Article

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    Carbon fragments as highly active metal-free catalysts for the oxygen reduction reaction: a mechanistic study

    K. Mao, W. Zhang, J. Dai and X. C. Zeng, Nanoscale, 2019, Advance Article , DOI: 10.1039/C9NR05338G

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