Rational Design of Hierarchical Structure Electrodes to Suppress Shuttle Diffusion in Redox-Enhanced Supercapacitors

In carbon-based supercapacitors, redox couples can effectively improve the energy density of supercapacitors; however, most redox couples still suffer from serious shuttle diffusion. Currently, there is no universal strategy to effectively constrain their shuttle diffusion. Therefore, developing a simple, effective, and universal method to suppress shuttle diffusion remains a great challenge. Herein, we designed and prepared a hierarchical structure electrode composed of three functional layers (inner conductive layer, intermediate storage layer, and outer confinement layer) for redox-enhanced supercapacitors. The hierarchical electrode can be fabricated on a large scale in three simple steps based on commercial carbon felt. The rationally designed three functional layers endow the hierarchical structure electrode with excellent conductivity, adsorption capacity, and confinement ability. Long-term charge–discharge cycle results prove that the hierarchical structure electrode exhibits an outstanding restriction effectiveness on three redox media with different molecular sizes (anthraquinone (AQ), naphthoquinone (NQ), and p-benzoquinone (PQ)). Specifically, for AQ, NQ, and PQ, the hierarchical structure electrodes showed CV peak current attenuation rates of only 5.64%, 3.54%, and 10.34% after 5,000 cycles of charge–discharge, while common electrodes exhibited attenuation rates of 10.44%, 15.02%, and 20.20%, respectively. Moreover, the soft-pack supercapacitors composed of hierarchical electrodes still had a capacitance retention of 86.6% after 5,000 cycles of charge–discharge. All the results demonstrate that the structure design is reasonable and the hierarchical structure electrode has a great potential to be the universal electrode for suppressing the shuttle diffusion of redox media in supercapacitors and other energy storage devices.