Synthesis and electrochemical capacitive performance of thieno[3,4-b]pyrazine-based Donor-Acceptor type copolymers used as supercapacitor electrode material

Two novel donor-acceptor-donor type monomers were synthesized by using thieno[3,4-b]pyrazine (TPZ) as the acceptor units (A) and 3-methylthiophene or 3-methoxythiophene as the donor units (D). The as-prepared D-A-D monomers were named as MOTP and MTP, respectively. These two monomers could be facilely polymerized on the glass carbon electrode (GCE) via a potentiostatic method, and the resultant D-A-D alternative conjugated polymers were referred as PMOTP and PMTP. The obtained conjugated polymers were routinely characterized by FT-IR, SEM and TGA at first. Then, as supercapacitor electrode materials, they were further investigated in detail by cyclic voltammetry (CV), constant galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) methods The GCD results showed that the polymer-modified GCEs had high specific capacitances of 678.2 and 319.1   F/g, for PMOTP and PMTP, respectively, at a current density of 1   A/g. Excellent switching stabilities were also observed for both polymer-modified GCEs, with the high retention rates of 77.3% and 53.4% for PMOTP and PMTP, respectively, after 1000 times of charge-discharge cycling at a current density of 10   A/g. Notably, the maximum energy densities of 22.4   Wh/kg and 7.94   Wh/kg were attained at the power density of 0.55   kW/kg for the symmetric supercapacitor based on PMOTP and PMTP, respectively. The excellent performances of these two D-A-D type conjugated polymers make them to be the promising electrode materials for energy-storage and conversion applications.