High Rate Performance of Flexible Pseudocapacitors fabricated using Ionic-Liquid-Based Proton Conducting Polymer Electrolyte with Poly(3, 4-ethylenedioxythiophene):Poly(styrene sulfonate) and Its Hydrous Ruthenium Oxide Composite Electrodes

We report the studies on all-solid-state flexible pseudocapacitors based on poly (3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT-PSS) and PEDOT-PSS/hydrous ruthenium oxide composite electrodes separated by nonaqueous proton conducting polymer electrolyte. Structural, thermal and electrochemical properties including high ionic conductivity (6.2 × 10(-2) S cm(-1) at 20 °C) of the polymer electrolyte, comprising ionic liquid 1-ethyl 3-methyl imidazolium hydrogen sulfate (EMIHSO4) immobilized in the blend of poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP), demonstrate its excellent suitability in supercapacitor fabrication. A substantial improvement in the specific capacitance (hence the specific energy) has been obtained when the PEDOT-PSS electrodes in the symmetrical pseudocapacitor are replaced by the composite electrodes PEDOT-PSS/RuO2·xH2O. High rate capability of the capacitor cell (with PEDOT-PSS electrodes) has been observed, as evidenced from the high knee frequency (∼966 Hz), low response time (∼70 ms) and high pulse power (∼10.2 kW kg(-1)), observed by impedance analysis. Almost rectangular (capacitive) cyclic voltammetric patterns for high scan rates (up to 15 V s(-1)) confirm the high rate performance of the pseudocapacitor. The PEDOT-PSS/RuO2·xH2O composite electrodes show the lower rate capability (knee frequency ∼312 Hz, response time ∼1 s, pulse power ∼3.2 kW kg(-1) and capacitive CV response up to 500 mV s(-1)) because of slow exchange of charges at the interfaces via RuO2·xH2O. However, the pseudocapacitor with composite electrodes shows higher rate performance relative to many reported RuO2·xH2O systems. About 15% improvement is noticed in the capacitance value when the capacitor with composite electrodes is initially charged and discharged up to ∼200 cycles. Thereafter, the cell shows almost constant value of specific capacitance (∼70 F g(-1)) for 1000 cycles.