Evolution of Crystallinity During the Electrodeposition of Body-centered Cubic Thallium (III) Oxide onto Glassy Carbon


The electrochemical nucleation and growth of crystalline Tl2O3 onto glassy carbon was studied by analyzing current-time transients resulting from potential steps. Stripping voltammetry, x-ray diffraction, and ex situ atomic force microscopy (AFM) were further used to characterize the deposit. The initial layers of Tl2O3 deposited as amorphous material up to a driving-force-dependent critical thickness. The critical thickness was 77 nm at zero driving force, and decreased exponentially as the overpotential was increased. When the critical thickness was exceeded at times greater than the induction time, faceted islands of crystalline material were observed. At the induction time, crystalline islands with an average diameter of 1200 nm were observed by AFM. The increase in current after the induction time is attributed to an increase in the rate of deposition, rather than a simple increase in geometric area. The exchange current densities for amorphous and crystalline Tl2O3 were measured to be 7 × 10-6 and 3 × 10-5 A/cm2, respectively. Crystalline development may proceed by a cooperative process between material depositing from solution and reorganization of amorphous material previously deposited on the surface. Open-circuit measurements showed a 72 mV driving force for this reorganization process.



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