Bifunctional ligand Co metal-organic framework derived heterostructured Co-based nanocomposites as oxygen electrocatalysts toward rechargeable zinc-air batteries

Rational construction of efficient and robust bifunctional oxygen electrocatalysts is key but challenging for the widespread application of rechargeable zinc-air batteries (ZABs). Herein, bifunctional ligand Co metal-organic frameworks were first explored to fabricate a hybrid of heterostructured CoOx/Co nanoparticles anchored on a carbon substrate rich in CoNx sites (CoOx/Co@CoNC) via a one-step pyrolysis method. Such a unique heterostructure provides abundant CoNx and CoOx/Co active sites to drive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. Besides, their positive synergies facilitate electron transfer and optimize charge/mass transportation. Consequently, the obtained CoOx/Co@CoNC exhibits a superior ORR activity with a higher half-wave potential of 0.88 V than Pt/C (0.83 V vs. RHE), and a comparable OER performance with an overpotential of 346 mV at 10 mA cm-2 to the commercial RuO2. The assembled ZAB using CoOx/Co@CoNC as a cathode catalyst displays a maximum power density of 168.4 mW cm-2, and excellent charge-discharge cyclability over 250 h at 5 mA cm-2. This work highlights the great potential of heterostructures in oxygen electrocatalysis and provides a new pathway for designing efficient bifunctional oxygen catalysts toward rechargeable ZABs.

Recent Advances on MOF Derivatives for Non-Noble Metal Oxygen Electrocatalysts in Zinc-Air Batteries

Oxygen electrocatalysts are of great importance for the air electrode in zinc-air batteries (ZABs). Owing to the high specific surface area, controllable pore size and unsaturated metal active sites, metal-organic frameworks (MOFs) derivatives have been widely studied as oxygen electrocatalysts in ZABs. To date, many strategies have been developed to generate efficient oxygen electrocatalysts from MOFs for improving the performance of ZABs. In this review, the latest progress of the MOF-derived non-noble metal-oxygen electrocatalysts in ZABs is reviewed. The performance of these MOF-derived catalysts toward oxygen reduction, and oxygen evolution reactions is discussed based on the categories of metal-free carbon materials, single-atom catalysts, metal cluster/carbon composites and metal compound/carbon composites. Moreover, we provide a comprehensive overview on the design strategies of various MOF-derived non-noble metal-oxygen electrocatalysts and their structure-performance relationship. Finally, the challenges and perspectives are provided for further advancing the MOF-derived oxygen electrocatalysts in ZABs.

N-doped defective carbon with trace Co for efficient rechargeable liquid electrolyte-/all-solid-state Zn-air batteries

Simple synthesis of multifunctional electrocatalysts with plentiful active sites from earth-abundant materials is especially fascinating. Here, N-doped defective carbon with trace Co (1.5 wt%) was prepared via a scalable one pot solid pyrolysis process. The sample exhibits efficient bifunctional OER/ORR activity in alkaline, mainly ascribed to the unique micro-mesoporous structure (1-3 nm), high population of graphitic-N doping (up to 49.0%), abundant defects and the encapsulated Co nanoparticles with graphitized carbon. The according rechargeable liquid Zn-air batteries showed excellent performance (maximum power density of 154.0 mW cm^-2; energy density of 773 Wh kg^-1 at 5 mA cm^-2 and charging-discharging cycling stability over 100 cycles). As a proof-of-concept, the flexible, rechargeable all-solid-state Zn-air batteries were constructed, and displayed a maximum power density as high as 45.9 mW cm^-2, among the top level of those reported previously.