Heteroepitaxial metal-organic frameworks derived cobalt and nitrogen codoped carbon nanosheets to boost oxygen reduction

The rational design and facile construction of hybrid metal–organic framework (MOF) with hierarchical nanostructures can motivate novel and multifunctional platforms to attain desirable performance. In this work, a new series of MOF-on-MOF heterostructures, including ZIF-8/Zinc(II)-hexamethylenetetramine (ZIF-8/Zn-HMT) and ZIF-8 + ZIF-67/Zn-HMT-X (ZIF/Zn-HMT-X), can be conveniently synthesized by heteroepitaxial growth. The as-obtained carbon nanosheets of CoZnNC-X are calcined from a CoZn MOF-on-MOF precursor, and they have abundant N-doping, dispersive Co particles, conductive network and large specific surface area, exhibiting efficient oxygen reduction reaction (ORR) as well as Zn-air battery (ZAB) performance. Among them, the most optimal CoZnNC-2 shows an onset potential of 0.95 V, high diffusion-limited current density of 5.41 mA cm−2, small Tafel slope of 59.1 mV dec−1 and excellent stability. Furthermore, the as-assembled ZAB based on CoZnNC-2 reveals a large power density of 113 mW cm−2 and a high specific capacity of 713.5 mAh g−1. Hence, the demonstrated work paves a brand-new route to rationally regulate MOF-derived carbon nanomaterials as efficient electrocatalysts for energy conversion and storage applications.