Electrochemical studies of heterogeneous reduction of tetracyanoquinodimethane in poly(ethylene oxide) electrolytes using ac impedance and cyclic voltammetry at an ultramicroelectrode

Electrochemical studies of the TCNQ(0)/TCNQ(-) couple have been carried out using ac impedance spectroscopy and cyclic voltammetry at platinum ultrami croelectrodes (UME). Liquid poly(ethylene oxide) (PEO) CH3-O-(CH2-CH2-O)(4) -CH3 has been used as the solvent with different concentrations of the TCNQ (0)/TCNQ(-) couple and LiClO4 as the supporting electrolyte. On the basis o f the ac impedance results at the UME it has been found that the double lay er capacitance and standard heterogeneous rate constant are independent of the presence of electroactive species and supporting electrolyte concentrat ions, indicating that adsorption of electroactive species onto the electrod e is not significant. The standard heterogeneous rate constant k(s) was fou nd to be 0.109 +/-0.005 cm s(-1). A similar value of k(s)=0.094 cm s(-1) wa s obtained for the second reduction step TCNQ(-)/TCNQ(2-). Diffusion coeffi cients of both TCNQ and TCNQ(-) are equal, D=1.0x10(-6) cm(2) s(-1) for a 0 .5 M LiClO4 solution. Higher diffusion coefficients are obtained in less co ncentrated supporting electrolyte. Comparison is made between these results and those reported previously for PEO-400 HO-(CH3CH2O)(8)-OH.(1) The diffe rent end groups significantly influence the viscosity and hence k(s).