Engineering Pore Nanostructure of Carbon Cathodes for Zinc Ion Hybrid Supercapacitors

Zinc ion hybrid supercapacitors (ZIHCs) with both high power density and high energy density have tremendous potential for energy storage applications such as hybrid electric vehicles and renewable energy storage. However, the large radius of hydrated Zn2+ ions hampers their efficient storage in micropores with limited pore sizes, resulting in the limited gravimetric specific capacitance and inferior rate capability of ZIHCs. Therefore, it is critically important to understand to what extent pore size influences the storage of hydrated Zn2+ ions in the pores with limited sizes. Herein, porous carbon nanosheets with different pore architectures are prepared using an ammonium chloride molten salt carbonization strategy. The influence of pore size on hydrated Zn2+ ion storage in nanostructured carbon with divergent pore architectures is analyzed by electrochemical methods and molecular dynamic simulation. Micropores smaller than 6.0 angstrom obstruct the diffusion of hydrated Zn2+ ions, while micropores larger than 7.5 angstrom exhibit a low diffusion energy barrier for the hydrated Zn2+ ions. Mesopores improve capacitance and rate capability by exposing the electrochemically active sites and enhancing the diffusion of the hydrated Zn2+ ions.