Alkyl functionalized bithiophene end-capped with 3,4-ethylenedioxythiophene units: synthesis, electropolymerization and the capacitive properties of their polymers

• Three new EDOT bis-substituted bithiophene containing long alkyl side chain group comonomers were synthesized.
• The corresponding polymers as an active electrode material for supercapacitor were systematically investigated.
• The polymers had high thermal stability, good cycle ability, and favorable electrocapacitive performance.
• The three materials achieved a maximum specific capacitance of 132.5 F/g, 135.4 F/g, and 129.3 F/g at 1 A g−1, respectively.

ABSTRACTHere, three new 3,4-ethylenedioxythiophene bis-substituted bithiophene containing alkyl side chain groups (alkyl = hexyl, octyl, and dodecyl) comonomers, 5,5′-(4,4′-dihexyl-[2,2′-bithiophene]-5,5′-diyl) bis(2,3-dihydrothieno[3,4-b][1,4]dioxine (BEDOT-BT-BH), 5,5′-(4,4′-dioctyl-[2,2′-bithiophene]-5,5′-diyl) bis(2,3-dihydrothieno[3,4-b][1,4]dioxine (BEDOT-BT-BO), and 5,5′-(4,4′-di dodecyl -[2,2′-bithiophene]-5,5′-diyl) bis(2,3-dihydrothieno[3,4-b][1,4]dioxine (BEDOT-BT-BD) were synthesized, and the three comonomers were facilely formed into PBEDOT-BT-BH, PBEDOT-BT-BO, and PBEDOT-BT-BD polymers on platinum electrode by direct anodic oxidation, respectively. The structure and morphology of the polymers were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermal analysis. Electrochemical performances of the polymers were also studied by galvanostatic charge–discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical results showed that three polymers showed good cycle ability and favorable capacitive performance, namely, for PBEDOT-BT-BH, PBEDOT-BT-BO, and PBEDOT-BT-BD, the specific capacitance was 132.5 F/g, 135.4 F/g, and 129.3 F/g (three electrode configurations) at 1 A/g, respectively, the capacitance retention was nearly 50.1%, 84.6% and 77.1% after 1000 cycles. The energy density of the symmetric full cell based on two PBEDOT-BT-BO electrodes was 9.5 Wh/kg−1 at a power density of 13.8 kW/kg−1. These results implied that the three conducting polymers will be a kind of promising electrode material for supercapacitors.