Significance of redistribution reactions detected by in situ atomic force microscopy during early stages of fast scan rate redox cycling experiments at a solid 7,7,8,8-tetracyanoquinodimethane-glassy carbon electrode-aqueous (electrolyte) interface |
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Authors: | Marco F Suárez Alan M Bond Richard G Compton |
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Institution: | (1) Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, UK e-mail: richard.compton@chemistry.oxford.ac.uk, Fax: +44-1865-275410, GB;(2) Department of Chemistry, Monash University, Clayton, Victoria 3168, Australia, AU |
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Abstract: | The reduction of solid 7,7,8,8-tetracyanoquinodimethane (TCNQ) at an electrode-TCNQ-aqueous (electrolyte) is complex, irrespective
of whether the solid on the electrode surface is attached by direct adherence or formed by electrochemical deposition. In
order to understand the origin of reaction pathways that accompany the TCNQ]0/− process, fast scan rate (0.1 V s−1) redox cycling and potential step experiments on TCNQ mechanically attached to a glassy carbon electrode placed in aqueous
solution containing 0.1 M electrolyte (KCl, CsCl, or Et4NCl) have been monitored by the technique of in situ atomic force microscopy (AFM). The shapes of cycling voltammograms are
consistent with the presence of a mixture of diffusion and surface processes in the initial cycles. AFM results show that,
during the early stage of the redox cycling experiments, electrochemical reduction of TCNQ to sparingly soluble TCNQ− is accompanied by a redistribution process. This rearrangement results in the transformation of arrays of almost amorphous
solid to a lower energy microcrystalline state which has a more thin film-type appearance. When CsCl is the electrolyte, long
needle-type crystals are detected by the AFM method after long periods of redox cycling. The identity of the cation in the
supporting electrolyte and the solubility of the reduced salt formed by reduction of TCNQ affect the nature of the voltammetry
observed during early stages of redox cycling. When the redistribution process is completed and the stable crystalline phase
is formed, the voltammetry of the TCNQ]0/− couple is predominantly controlled by a nucleation-growth mechanism.
Received: 8 March 1999 / Accepted: 12 April 1999 |
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Keywords: | 7 7 8 8-Tetracyanoquinodimethane Atomic force microscopy Redistribution reaction Redox cycling |
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