Liquid-liquid ion transport junctions based on paired gold electrodes in generator-collector mode.

Simultaneous electrochemically driven double anion transfer across liquid-liquid interfaces is demonstrated at a gold-gold junction electrode. In the presence of two closely spaced electrodes (generator and collector), anion uptake into the organic phase (oxidation) and anion expulsion into the aqueous phase (reduction) can be combined to result in a generator-collector anion transport system across the liquid-liquid interface. In this report we are employing a paired gold junction grown by electro-deposition to ca. 5 microm gap size with the N,N-diethyl-N',N'-didodecyl-phenylene-diamine water immiscible redox liquid immobilized into the gap to demonstrate simultaneous perchlorate anion uptake and expulsion. The effects of redox liquid volume and scan rate on the magnitude of currents and two mechanistic pathways for ion transport are discussed in the context of micro-electrophoretic processes.

Microwave-enhanced electroanalytical processes: generator-collector voltammetry at paired gold electrode junctions.

Generator-collector electrode systems allow redox processes and reaction intermediates from multi-step electrode reactions to be monitored. Analytically, collector electrode current responses are insightful and highly sensitive due to (i) the absence of capacitive current components and (ii) an enhanced current response due to 'feedback' between generator and collector electrode. Here, a symmetric gold-gold junction grown by controlled electro-deposition is employed for generator-collector voltammetry in conjunction with microwave activation. Three redox systems are investigated in aqueous 0.1 M KOH: (i) the reduction of Fe(CN)(6)(3)(-), (ii) the reduction of chloramphenicol, and (iii) the reduction of oxygen. Microwave radiation, when focused into the electrode-solution interfacial zone, causes locally enhanced temperatures with electrode surface temperatures reaching up to typically 380 K (estimated from the shift in the Fe(CN)(6)(3)(-/4)(-) equilibrium potential, at both gold electrodes). The resulting increase in the rate of diffusion and the onset of convection result in non-linear Arrhenius limiting current characteristics and in an increase in collection efficiency with microwave power. The gold electrode junction geometry allows diffusion effects (which increase the feedback current within the gap) to dominate over convection effects (which suppress the feedback current).