Size-confined Co nanoparticles embedded in ultrathin carbon nanosheets for enhanced oxygen electrocatalysis in Zn-air batteries

Abstract

The carbonization of metal-organic frameworks (MOFs) has been recognized as a universal method to construct metal-based electrocatalysts for Zn-air batteries (ZABs). The key challenge in enhancing the activity of electrocatalysts is to improve the utilization efficiency of active sites. Herein, we demonstrate a facile strategy to modulate the composition and morphology of MOF precursor, wherein cobalt(II) phthalocyanine complexes (Co-Pc) are in situ synthesized and immobilized in the grids of Zn-MOF, while the bulk MOF is exfoliated into ultrathin nanosheets. Owing to the small size and large density of Co nanoparticles loaded on carbon nanosheets with high surface area, the obtained Co-N-C bifunctional catalyst (Co@N-CNSs) possesses elevated utilization efficiency of active sites, showing high ORR half wave potential (0.89 V), and low OER overpotential (ƞ = 0.39 V). The assembled rechargeable ZABs also exhibit a high specific capacity of 775 mA h gZn-1, a maximum peak power density of 227 mW cm-2, and significant stable rechargeability (voltage gap remains 0.51 V after continuous charge-discharge for more than 350 hours), which indicates that Co@N-CNSs has great capacity as dual-function air electrode catalyst.