MOF-Based Metal-Doping-Induced Synthesis of Hierarchical Porous Cu-N/C Oxygen Reduction Electrocatalysts for Zn-Air Batteries

A transition-metal-nitrogen/carbon (TM-N/C, TM = Fe, Co, Ni, etc.) system is a popular, nonprecious-metal oxygen reduction reaction (ORR) electrocatalyst for fuel cell and metal-air battery applications. However, there remains a lack of comprehensive understanding about the ORR electrocatalytic mechanism on these catalysts, especially the roles of different forms of metal species on electrocatalytic performance. Here, a novel Cu-N/C ORR electrocatalyst with a hybrid Cu coordination site is successfully fabricated with a simple but efficient metal-organic-framework-based, metal-doping-induced synthesis strategy. By directly pyrolyzing Cu-doped zeolitic-imidazolate-framework-8 polyhedrons, the obtained Cu-N/C catalyst can achieve a high specific surface area of 1182 m(2) g(-1) with a refined hierarchical porous structure and a high surface N content of 11.05 at%. Moreover, regulating the Cu loading can efficiently tune the states of Cu(II) and Cu-0, resulting in the successful construction of a highly active hybrid coordination site of N. Cu(II). Cu-0 in derived Cu-N/C catalysts. As a result, the optimized 25% Cu-N/C catalyst possesses a high ORR activity and stability in 0.1 m KOH solution, as well as excellent performance and stability in a Zn-air battery.