Electrochemical Liquid-Liquid-Solid Deposition of Ge at Hg Microdroplet Ultramicroelectrodes

Abstract

Individual Hg microdroplet electrodes were used to perform Ge electrochemical liquid-liquid-solid (ec-LLS) crystal growth in aqueous solutions containing dissolved GeO2. The Hg microdroplets were prepared by electrodeposition of Hg onto pre-existing Pt ultramicroelectrodes (r < 10 μm). These Hg microdroplet ultramicroelectrode platforms were then used for analyses of Ge ec-LLS by both voltammetry and amperometry. Voltammetric responses indicated that Ge was neither immediately nor quantitatively dissolved into Hg upon electroreduction of aqueous solutions of GeO2. Separately, chronoamperometry performed at large overpotentials for reduction of dissolved GeO2 yielded crystalline Ge but with notable differences as compared to ec-LLS at a bulk Hg pool electrode. One set of experiments featured the surface of the Hg microdroplets possessing a complete Ge shell. The data suggested this shell formed within the first 1000 s and essentially passivated the electrode against further heterogeneous GeO2 reduction but allowed limited H+ reduction. The other set of experiments exhibited a similar shell but with fissures or cracks that exposed fresh Hg to the electrolyte and allowed Ge electrodeposition to persist much longer. In these experiments, hollow, spiral crystalline Ge tubes were extruded from the interior of the Hg microdroplets.