Defective Carbon Derived Using a Dissolution–Recrystallization Strategy for Oxygen Reduction Electrocatalysis

Dopant-free defective carbon electrocatalysts have been considered as promising alternatives to traditional precious metal electrocatalysts recently. Compared with precious metal catalysts and transition-metal catalysts, since there are no metals doped, electrochemical devices assembled with dopant-free defective carbons are free from environmental pollution and subsequent recovery problems. In order to obtain abundant carbon defects with high-intrinsic catalytic activity, the synthesis of dopant-free defective carbons requires complex and harsh preparation conditions. Therefore, the construction of active defects with efficient utilization, especially through a simple process, is still a great challenge for the development of dopant-free defective carbon electrocatalysts. Herein, dissolution-recrystallization strategy was employed to design Zn-MOF-74 precursors for the synthesis of dopant-free defective carbons, realizing the synchronous manipulation of high ratio of carbon defects and highly exposed mass transfer channels. One-dimensional porous defective carbon nanorods (d-CNRs), which exhibited excellent oxygen reduction reaction (ORR), electrocatalytic activity, and molecular selectivity, were synthesized by directly carbonizing rodlike Zn-MOF-74 precursors. Attributed to the dissolution-recrystallization strategy, with the activation of in situ-formed ZnO, the synthesized d-CNRs exhibited unique pore-crack nested porous structures, which carried abundant defects as activity sites for ORR and showed a surprisingly high specific surface area of 2459 m2/g with a high ratio of mesopores. d-CNRs also showed promising applications in Zn-air batteries with a stable long-term discharge of no obvious voltage drop after 60 h. The dissolution-recrystallization strategy provided a simple controllable pathway for the efficient construction of dopant-free defective carbon electrocatalysts.