New insight to the role of edges and heteroatoms in nanocarbons for oxygen reduction reaction

Abstract

Oxygen reduction reaction (ORR) is the cornerstone for clean and sustainable energy conversion/storage technologies, depending on effective and robust catalysts. In the rational design of efficient and renewable carbon-based ORR electrocatalysts, the effect of intrinsic carbon edge sites on ORR remains elusive. In this study, nano-cutting is applied to multi-walled carbon nanotubes (MWCNTs) to synthesize a series of edge-engineered nanoribbon/nanotube hybrids with variable edge contents to probe the role of carbon edges. The previously overlooked but certainly emerged difference in conductivity in the edge creation process among the dopant-free carbocatalysts is taken into account towards the ORR activity, aiming to distinguish the function of edges. The carbocatalyst with a higher edge content is proven to be more reactive for ORR, with the premise of catalyst conductivity higher than ~70 S m−1. Further, with heteroatoms (N and S) introduced into the carbocatalysts, a positive correlation between the accommodated heteroatom content and the edging degree is revealed, indicating that edge sites afford anchoring sites for heteroatoms into the carbon framework, which further accelerates the ORR kinetics. This study provides new insights to the intrinsic role of the edge sites in nanocarbons as well as the synergy with heteroatom doping for promoted activity of carbocatalysts in ORR.