Edge Defect Engineering of Nitrogen-Doped Carbon for Oxygen Electrocatalysts in Zn–Air Batteries

Abstract

Metal-free bifunctional oxygen electrocatalysts are extremely critical to the advanced energy conversion devices, such as high energy metal–air batteries. Effective tuning of edge defects and electronic density on carbon materials via simple methods is especially attractive. In this work, a facile alkali activation method has been proposed to prepare carbon with large specific surface area and optimized porosity. In addition, subsequent nitrogen-doping leads to high pyridinic-N and graphitic-N contents and abundant edge defects, further enhancing electrochemical activities. Theoretical modeling via first-principles calculations has been conducted to correlate the electrocatalytic activities with their fundamental chemical structure of N doping and edge defect engineering. The metal-free product (NKCNPs-900) shows a high half-wave potential of 0.79 V (ORR). Furthermore, the assembled Zn–air batteries display excellent performance among carbon-based metal-free oxygen electrocatalysts, such as large peak power density up to 131.4 mW cm–2, energy density as high as 889.0 W h kg–1 at 4.5 mA cm–2, and remarkable discharge–charge cycles up to 575 times. Preliminarily, the rechargeable nonaqueous Li–air batteries were also investigated. Therefore, our work provides a low-cost, metal-free, and high-performance bifunctional carbon-based electrocatalyst for metal–air batteries.