Nitrogen-Doped Carbon/Graphitic Cqds Composites with 98.8% Microporosity as a Highly Stable Metal-Free Catalyst for Oxygen Reduction

Abstract

Designing micropore-rich carbon materials with large specific surface area (SSA) as a metal-free oxygen reduction reaction (ORR) electrocatalyst is still frontier but remains challenging in catalysis of zinc-air batteries. Here we propose a new strategy for synthesis of nitrogen atoms co-doped carbon sheets and carbon quantum dots (N-C@CQDs) with an SSA of 1485.3 m2 g-1 and 98.8% micro-porosity from α-cellulose via using a complex salt (ZnCl2-NH4Cl) with low eutectic point (179 °C) as a pore regulator and K2FeO4 as a graphitization catalyst, which can serve as an active and stable metal-free ORR electrocatalyst. The role of K2FeO4 not only promotes graphitization but also oxidizes the large-sized graphitic carbon particles into a huge amount of uniformly distributed CQDs. This catalyst has exhibited a comparable ORR activity and superior stability to the Pt/C, but a Zn-air battery assembled with the former has delivered a higher peak power density (214 mW cm-2) and a larger gravimetric energy density (ED) of (959 Wh [[EQUATION]]), especially in which it also displays an outstanding catalytic durability with 98.7% ED retention during a ~110 h continuous discharge. This work provides a new pathway for design of high-performance metal-free carbon ORR catalysts in various energy devices.

Keywords: Nitrogen-doped carbon, Carbon quantum dots, electrocatalysis, Oxygen reduction