Tuning The Performances Of Electrochemical Capacitors With Redox Active Polymers

In this thesis,redox active polymers have been applied to tune the performances of electrochemical capacitors(ECs).The main results are as follows:(1)The graphene/polyhydroquinone double-network composite electrodes were prepared by a two-step method.In comparison with the ECs employing the bare graphene electrodes,the specific capacitance and specific energy of the ECs employing the graphene/polyhydroquinone double-network electrodes are enhanced due to the additional contribution from the Faradaic capacitance of polyhydroquinone.By employing the conductive graphene as the first network and the redox active polyhydroquinone as the second network to prepare the double-network electrodes,the work presented here provides a universal way for the application of redox active polymers with low conductivities to improve the performances of ECs.(2)The composite electrodes were fabricated by complexing the negatively charged carboxylated multi-walled carbon nanotubes(cMWCNT)with the redox active units-containing positively charged random copolymers.Viologen and 2,2,6,6-Tetramethylpiperidinyl-N-oxyl are employed as model redox active units to exemplify the strategy of the concurrent increase of specific energy and suppression of self-discharge of a two-electrode device.The enhanced specific energy is mainly attributed to the increased electrolyte decomposition window induced by the faster redox reactions than those of the hydrogen and oxygen evolution reactions.The improved performance of self-discharge is due to the suppression of the cross-diffusion and redox shuttling of the redox couples induced by the complexation between the cMWCNT and the copolymers.By employing the redox active units-containing charged copolymers,this work provides a convenient and universal strategy to concurrently increase specific energy and suppress self-discharge of electrochemical capacitors with the carbon-based electrodes.