Electrochemical quartz crystal microbalance study of redox transformations of TCNQ microcrystals in concentrated LiCl solutions

Microcrystals of 7,7,8,8-tetracyanoquinodimethane (TCNQ) immobilized on gold surface have been investigated by combined cyclic voltammetry/chronoamperometry and piezoelectric nanogravimetry at an electrochemical quartz crystal microbalance (EQCM) in dilute and concentrated LiCl solutions. It is proved that TCNQ microcrystals even when TCNQ is reduced to its highly soluble Li+TCNQ− salt can be studied in aqueous solutions when the water activity is decreased to a low level. At high electrolyte concentrations the voltammetric and chronoamperometric responses obtained for TCNQ microcrystals show the theoretically predicted pattern characteristic to the solid–solid phase transformation under the control of the nucleation and growth kinetics. The utilization of the idea presented in this work, i.e., using electrolyte of high concentrations (or decreasing the water activity by adding an indifferent component to the liquid phase in high concentration) can open up new vistas in the study of redox transformations of immobilized microcrystals which are soluble in water.