Solid medium for conventional electrochemical measurements

Transport of neutral and ionic solutes: the gel/electrode and gel/electrolyte interfaces

Transport through a polysaccharide gel phase has been investigated voltammetrically using both redox voltammetry at a gel covered electrode and ion transfer voltammetry across the gel/liquid interface (Gel/L). The apparent diffusion coefficients, D(app), of a range of neutral and ionic electroactive species have been determined in both uncharged and anionic polysaccharide media, agar, and kappa-carrageenan, respectively. It is shown that the diffusion of electroactive species in agar gel occurs at a rate similar to that of diffusion in aqueous solution for a range of redox couples. In the kappa-carrageenan medium, by contrast, the diffusion coefficient obtained for cationic solutes was found to be approximately an order of magnitude lower than the value in aqueous solution. The difference in D(app) is attributed to two independent processes: electrostatic interactions between the charge of the sulfonate groups of the kappa-carrageenan gel and the charge of the solute, as well a change in hydration of the solute molecules.

Nanostructured Manganese Dioxide Thin Films prepared by a Novel Self-Assembly Process

We have reported herein a novel self-assembly horizontal submersion process for the deposition ofnanostructured manganese dioxide thin films on metalized plastic supporting substrates at ambient temperatureand pressure. Uniform manganese dioxide thin films were deposited directly onto metallized plastic supportingsubstrate via the spontaneous assembly of preformed manganese dioxide nanoparticles in the form of stablecolloidal suspension. This process affords a facile approach for the deposition of manganese dioxide thin filmsby simply repeating the submersion process after the prior deposited layer had been air-dried completely. Thinfilmdeposition process initially occurred through the spontaneous adsorption of manganese dioxidenanoparticles onto specific surface sites of the metalized substrate. Subsequent events of particle growth,clusters formation, and aggregation or self-organization of particle clusters eventually led to the deposition ofnanostructured thin films which were nanoparticulate and highly porous in nature. The surface morphologicalcharacteristics of deposited thin films were observed to be significantly affected by the duration of submersionand the post-deposition calcination temperature. By modulating and optimizing these parameters, thin films oftailored microstructure could therefore be prepared. Optimized manganese dioxide thin films were observed toexhibit excellent capacitive behavior as evidenced by the almost perfectly rectangular shape of cyclicvoltamograms within the potential range of 0.0 to 1.0 V (versus SCE) in mild aqueous Na2SO4 electrolyte. Thecycling stability and reversibility of these films were evaluated by prolonged charge-discharge cycling and nosubstantial deterioration of performance in terms of charge capacity and capacitive behaviors were observedafter 1000 cycles. We speculate that the high capacitance value exhibited by self-assembled manganese dioxidethin films in mild aqueous electrolyte could be attributed to reversible and homogenous intercalation anddeintercalation of protons during the charge and discharge cycling. The potential utility of self-assembledmanganese dioxide thin films for the fabrication of electrochemical devices, in particular thin-filmelectrochemical capacitors is therefore envisaged.