γ-Graphyne nanotubes as defect-free catalysts of the oxygen reduction reaction: a DFT investigation.

Graphyne materials are potential candidates to fabricate low-cost but efficient metal-free oxygen reduction reaction (ORR) electrocatalysts. However, due to the coexistence of sp and sp2 carbon atoms in graphyne, some factors playing important roles in determining the ORR activity have received little attention. In the present paper, we carried out thorough density functional theory (DFT) calculations to study the curvature effect on the ORR activity of γ-graphyne. Our results suggest that the (5, 0)-γGyNT would be an excellent metal-free ORR catalyst. Its limiting potential was computed to be 0.80 V and the corresponding active sites occupy up to 16.7% in content, much better than previously reported CACs. Moreover, it is revealed that the curvature can tune the degree of exposure of p electrons of active sites, thus tuning the ORR activity. Our findings are beneficial for further understanding catalytic behavior on graphyne related materials and we suggest a new strategy to design high performance metal-free ORR catalysts.