School of Energy and Environment Science, Anhui University of Technology, Maanshan, Anhui 243032, China and Department of Chemistry, University of Nebraska, Lincoln, NE 68588, USA.
Department of Chemistry, University of Nebraska, Lincoln, NE 68588, USA.
Nanoscale. 2019 Nov 7;11(41):19422-19428. doi: 10.1039/c9nr05338g. Epub 2019 Aug 8.
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 C-based fragments, namely, C-frag1 and C-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.
在无金属的碳富勒烯基或有缺陷的石墨烯基电催化剂中，五元环被认为在提高氧还原反应（ORR）的催化活性方面起着关键作用。然而，五元环对 ORR 具有显著催化作用的基本化学机制仍未完全理解。在此，我们通过使用密度泛函理论（DFT）和计算氢电极（CHE）方法，对各种含五元环的碳富勒烯和富勒烯片段物种的催化活性进行了全面的计算研究。我们发现，与更多的相邻五元环和 ORR 的关键中间体 O*、OH和 OOH的更强吸附相关联的是更多的碳活性位点。重要的是，两个基于 C 的片段，即 C-frag1 和 C-frag2l，对 ORR 表现出非常高的活性，因为它们的过电势均低至 0.389 和 0.407 V，并且涉及 OH和 OOH物种的合适吸附自由能。富勒烯片段的这些理想化学性质可以归因于低对称富勒烯片段结构诱导的高能 HOMO 轨道。相邻五元环的数量和片段的整体对称性的程度似乎是可以调整的两个重要因素，以设计具有高 ORR 活性的最佳无金属碳电催化剂。
