Zeolitic Imidazolate Frameworks Derived Co₉S₈/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 Co 9 S 8 nanoparticles embedded in nitrogen-doped hierarchically porous hollow carbon spheres (Co 9 S 8 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 Co 9 S 8 NPs/NHCS-0.5 electro-catalyst exhibits decent performance for ORR (E 1/2 = 0.85 V) and OER (E 10 = 1.55 V). A rechargeable ZAB assembled using the Co 9 S 8 NPs/NHCS-0.5 as air cathode delivers a maximum power density of 116 mW cm À 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 Co 9 S 8 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-RuO 2 .

Fe, N-Doped Hollow Porous Carbon Spheres Decorated with Ultrasmall Co NPs as Efficient Bifunctional Electrocatalysts for Rechargeable Zinc–Air Batteries

“…In addition, the disappearance of characteristic signals of metallic Zn confirmed the complete evaporation of Zn species under high temperatures, which benefits the generation of micro/ mesopores and enhancement of specific surface area. 23 Two characteristic peaks at 1344.2 and 1582.4 cm −1 occurred in the Raman spectra, attributed to the D and G signals, respectively. 24 The relative intensity ratio of the D and G peaks (I D /I G ) values can determine the density of defects and the degree of graphitization for carbonaceous materials.…”

“…Notably, the Fe-based crystal phases were not detected, which may be attributed to the ultrafine dispersion (Figures i and S1k) and low contents of Fe in the Co/Fe-NC (1.12 wt %) and Fe-NC (1.88 wt %). In addition, the disappearance of characteristic signals of metallic Zn confirmed the complete evaporation of Zn species under high temperatures, which benefits the generation of micro/mesopores and enhancement of specific surface area …”