Investigation of a nanostructured polysaccharide solid medium for electrochemistry

The fundamental electrochemical characteristics of tight and elastic polysaccharide solids involving a nanostructured network and excess water were investigated. The diffusion of redox molecules, charge transfer resistance at the electrode|solid interface, and double layer capacitance on the electrode surface were studied. The cyclic voltammograms in the agarose and the κ-carrageenan solids show very similar features as in liquid water including the redox potential and peak currents, but with a slightly larger peak separation for the solid systems. The electrochemical impedance spectrum (EIS) was measured in the polysaccharide solid. The apparent diffusion coefficient (Dapp) of Fe(CN)63− in the solids is almost the same as in an aqueous solution. The charge transfer resistance (Rct) on the electrode surface in a κ-carrageenan solid was even smaller in a κ-carrageenan solid than that in an aqueous solution, although it was larger in an agarose solid. The Rct tends to decrease with the polysaccharide concentration in the solid. The double layer capacitance (Cdl) on the electrode surface in a Fe(CN)63− aqueous solution tends to increase with the Fe(CN)63− concentration, but for the solid systems Cdl values are only weakly dependent on the Fe(CN)63− concentration, and similar to that in an aqueous solution at 5 mM Fe(CN)63− concentration. It was elucidated that the polysaccharide solid can work well as a new solid medium for conventional electrochemical measurements and electrochemistry.