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 a 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 a high surface area, the obtained Co–N–C bifunctional catalyst (Co@N-CNSs) possesses elevated utilization efficiency of active sites, showing a high ORR half wave potential (0.89 V) and a low OER overpotential (η = 0.39 V). The assembled rechargeable ZABs also exhibit a high specific capacity of 775 mA h g_Zn⁻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 a dual-function air electrode catalyst.