Designing quinone-dopamine-based conjugates as six electron system for high-performance hybrid electrode

Abstract

The development of electrode materials for supercapacitors is a necessary research and development work to address the present-day energy crises. The improvement of productive pseudo-capacitors requires quick and reversible kinetics of redox-molecules. In the development of pseudo-capacitors, quinone/hydroquinone redox couples are one of the promising molecules. Graphite sheet, along with quinone molecules with an increased number of carbonyl groups, is expected to give higher performance hybrid supercapacitors. In this direction, a simple one-step reaction of p-benzoquinone and dopamine hydrochloride to 2,5-bis((3,4-dihydroxyphenethyl)amino)cyclohexa-2,5-diene-1,4-dione molecule (BQ-DP) is carried and confirmed the formation from Fourier-transform infrared, high-resolution mass, proton and carbon nuclear magnetic resonance spectra. This molecule is used as a redox system along with a graphite sheet as active electrode material for supercapacitor, wherein a redox system consists of three quinone groups with six electrons transfer reaction. Cyclic voltammetry and charge-discharge graphs, and two constant phase elements obtained from EIS measurement clearly show the contribution of both electrochemical double layer and pseudo-capacitor components. Both benzoquinone and dopamine groups are involved in the redox reaction. The values of specific capacitance for this electrode are 910 F g−1 at 5 mV s−1 and 1180 F g−1 at 9.5 A g−1, respectively. This cell is subjected to 10,000 charge-discharge cycles, which underwent decay in specific capacitance from 416 to 209 F g−1 up to 1000 cycles and then remains constant up to 7000 cycles. In the case of a negligible contribution of EDLC, the supercapacitor cell could be treated as a battery cell. The battery gives an initial specific capacity of 115–58 mAh g−1 at 1000 cycles. This quinone molecule showed higher electrochemical performance compared to the earlier reports on quinone molecules for supercapacitors. An alternative strategy to increase the performance of the quinone-graphite electrode is made by making holes on graphite sheet and accommodated more amount of electro-active quinone molecule and used as an electrode in symmetric cell configuration in coin cell and subjected for 5000 cycles in the voltage range from 0 to 1 V at 9.5 F g−1. The value of specific capacitance for the symmetric cell obtained from charge-discharge measurement for the electrode (419 F g−1) is found to be higher than that of the electrode without holes (324 F g−1).