Zeolitic Imidazolate Frameworks Derived Co9 S8 /Nitrogen-Doped Hollow Porous Carbon Spheres as Efficient Bifunctional Electrocatalysts for Rechargeable Zinc-Air Batteries.

Abstract

The development of nonprecious metal-based electrocatalysts with remarkable catalytic activity and long-cycling lifespan toward oxygen reduction reaction (ORR) and evolution reaction (OER) is especially important for rechargeable zinc-air batteries (ZABs). Herein, monodispersed Co9 S8 nanoparticles embedded in nitrogen-doped hierarchically porous hollow carbon spheres (Co9 S8 NPs/NHCS) are synthesized through a template-assisted strategy followed by a co-assembly, thermal annealing, and sulfurization process. Benefiting from larger specific surface area, hierarchically porous hollow structure, and carbon nanotubes self-growth, the obtained Co9 S8 NPs/NHCS-0.5 electrocatalyst exhibits decent performance for ORR (E1/2 =0.85 V) and OER (E10 =1.55 V). A rechargeable ZAB assembled using the Co9 S8 NPs/NHCS-0.5 as air cathode delivers a maximum power density of 116 mW cm-2 , high open circuit voltage of 1.47 V, and good durability (no obvious voltage decay after 1200 cycles (200 hours)). Such a hierarchically porous hollow structure of Co9 S8 NPs/NHCS-0.5 provides a confined space shell and an interconnected hollow core to achieve outstanding bifunctional catalytic activity and cycling stability, which surpass the benchmark Pt/C-RuO2 .