Metal-organic framework-derived porous carbon for the advanced aqueous zinc-ion hybrid capacitor

Aqueous zinc ion hybrid capacitors (ZIHCs) are considered one of the most promising electrochemical energy storage systems due to their high safety, environmental friendliness, low cost, and high power density. However, the low energy density and the lack of sustainable design strategies for the cathodes hinder the practical application of ZIHCs. Herein, we design the N and O co-doped porous carbon cathode by annealing metal-organic framework (ZIF-8). ZIF-8 retains the original dodecahedral structure with a high specific surface (2814.67 m²/g) and I_G/I_D ratio of 1.0 during carbonization and achieves self-doping of N and O heteroatoms. Abundant defect sites are introduced into the porous carbon to provide additional active sites for ion adsorption after the activation of carbonized ZIF-8 by KOH treatment. The ZIHCs assembled with modified ZIF-8 as the cathode and commercial zinc foil as the anode show an energy density of 125 W · h/kg and a power density of 79 W/kg. In addition, this ZIHCs device achieves capacity retention of 77.8% after 9000 electrochemical cycles, which is attributed to the diverse pore structure and plentiful defect sites of ZIF-8-800(KOH). The proposed strategy may be useful in developing high-performance metal-ion hybrid capacitors for large-scale energy storage.