Quartz crystal microbalance studies of deposition and dissolution mechanisms of electrochromic films of diheptylviologen bromide

The quartz crystal microbalance (QCM) technique is used in conjunction with cyclic voltammetric and potential step measurements to study the deposition and dissolution mechanisms of thin films of diheptylviologen bromide. Deposition of a uniform, compact film with little incorporation of supporting electrolyte is indicated for potential steps well past the first reduction wave of the viologen. Films with considerable surface roughness are deposited when using potential sweep methods, depending on conditions. Methods are presented which provide the apparent molar mass of the depositing species from appropriate combination of the QCM and electrochemical data. The use of microgravimetric Anson plots together with conventional Anson plots provides a particularly useful approach to such determinations. Due to the potentially detrimental influence of non-uniform current density on the QCM measurements, an ancillary study of copper deposition was carried out using the same concentrations and ionic strengths as those in the viologen experiments. This demonstrated the uniformity of the current density in the viologen experiments and verified the use of QCM measurements under such conditions.