Dielectric relaxation and electrochemical studies on trihexyl tetradecyl phosphonium chloride [P14,6,6,6][Cl] ionic liquid

The conductivity relaxation, charge transport and electrochemical performance of trihexyl tetradecyl phosphonium chloride ([P14,6,6,6][Cl]) ionic liquid were studied by broadband dielectric spectroscopy and electrochemical workstation. Dielectric spectroscopy reviews polarity fluctuations due to the collective rotational dynamics of dipolar species and in electrically conductive systems an additional translational contribution due to charge transport was reported. The conductivity relaxation was fitted with Random barrier model by Dyre and secondary relaxation was fitted with Havriliak -Nigami function. The temperature dependence of the conductivity relaxation time can be described by Vogel - Fulcher - Tamman (VFT) equation. From the VFT fits the glass transition temperature was estimated as Tg = 195.03 K·The secondary relaxation was detected below the glass transition temperature and activation energy, Ea = 15 kJ/mol was estimated from the Arrhenius law. The electrochemical behaviour of [P14,6,6,6][Cl] was studied by fabricating an electrochemical supercapacitor and cyclic voltammetry, impedance spectroscopy and charge-discharge investigations were conducted to assess the performance of the supercapacitor. A very high specific capacitance of 370 F/g with high rate scalability (up to 1000 cycles) and increased operation voltage of 3.5 V were achieved to propose this electrolyte is a promising electrolyte for practical supercapacitor applications.