Electrochemical Reaction in a High Gravity Field Vertical to an Electrode Surface-Analysis of Diffusion Process with a Gravity Electrode

Abstract

With a new type of electrode system that utilizes the radial component of the centrifugal force instead of the real gravity force, the effect of the promoted gravity field on the diffusion process of ions was examined. First, the diffusion equation was derived in the case when the gravity field is imposed vertically onto an electrode surface. Then, it was theoretically clarified that numerous minute convection cells with sizes of the order of the diffusion layer thickness appear through a self-organization process from a top-heavy distribution of fluid density arising from the electrode reactions. The equation predicted that the diffusion current density is proportional to the 1/3rd order of the gravity acceleration and the 1st order of the difference between the bulk and surface concentrations. Then, we attempted to confirm this prediction by using the redox reaction of a ferricyanide–ferrocyanide system, and found that all of the experimental results exhibits good agreement with the predictions. Finally, the dependences of the diffusion coefficients of ferrocyanide and ferricyanide ions on the enhanced gravity fields were measured. However, for the gravity fields up to 650g, it was concluded that no remarkable dependence of the diffusion coefficient on the gravity is observed.