Rational Design of\nHierarchical Structure Electrodes\nto Suppress Shuttle Diffusion in Redox-Enhanced Supercapacitors

In carbon-based supercapacitors, redox couples can effectively\nimprove the energy density of supercapacitors; however, most redox\ncouples still suffer from serious shuttle diffusion. Currently, there\nis no universal strategy to effectively constrain their shuttle diffusion.\nTherefore, developing a simple, effective, and universal method to\nsuppress shuttle diffusion remains a great challenge. Herein, we designed\nand prepared a hierarchical structure electrode composed of three\nfunctional layers (inner conductive layer, intermediate storage layer,\nand outer confinement layer) for redox-enhanced supercapacitors. The\nhierarchical electrode can be fabricated on a large scale in three\nsimple steps based on commercial carbon felt. The rationally designed\nthree functional layers endow the hierarchical structure electrode\nwith excellent conductivity, adsorption capacity, and confinement\nability. Long-term charge–discharge cycle results prove that\nthe hierarchical structure electrode exhibits an outstanding restriction\neffectiveness on three redox media with different molecular sizes\n(anthraquinone (AQ), naphthoquinone (NQ), and p-benzoquinone (PQ)).\nSpecifically, for AQ, NQ, and PQ, the hierarchical structure electrodes\nshowed CV peak current attenuation rates of only 5.64%, 3.54%, and\n10.34% after 5,000 cycles of charge–discharge, while common\nelectrodes exhibited attenuation rates of 10.44%, 15.02%, and 20.20%,\nrespectively. Moreover, the soft-pack supercapacitors composed of\nhierarchical electrodes still had a capacitance retention of 86.6%\nafter 5,000 cycles of charge–discharge. All the results demonstrate\nthat the structure design is reasonable and the hierarchical structure\nelectrode has a great potential to be the universal electrode for\nsuppressing the shuttle diffusion of redox media in supercapacitors\nand other energy storage devices.