NEW SOLID MEDIUM FOR ELECTROCHEMISTRY AND ITS APPLICATION TO DYE-SENSITIZED SOLAR CELLS - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 115

and κ-carrageenan solids. The plot on the vertical line in figure 9 shows the R ct (32.6Ω) in the
aqueous solution containing 10 mM Fe(CN) 6 3- . The R ct in the κ-carrageenan solid is of the
same order of magnitude as in an aqueous solution and even lower in the 4 wt% κ-
carrageenan. In figure 8 it was shown thatκ-carrageenan anionic groups improve the charge
transfer between the electrode and the redox compound in the solid. A high concentration of
the -SO 3 - groups would facilitate charge transfer between the electrode and the redox
compound. It is surprising that the R ct decreased with increasing polysaccharide concentration
in the solids. The reason is not clear yet, but one reason might be a technical problem; since a
higher polysaccharide concentration causes a higher viscosity of the polysaccharide solution
when it is warm, the insertion of the electrodes into this solution could give a better and more
stable contact between the electrodes and the medium. In the next chapter 4 it will be shown
that the ionic conductivity also increases with the polysaccharide concentration (later in figure
11). This fact and the results of figure 9 for the R ct indicate that the increase of the
polysaccharide concentration does not increase the resistance for molecular/ionic diffusion
probably because the increase of the polysaccharide concentration induces the growth of the
chain aggregation rather than increasing the crosslinked structures that can be a resistance for
molecular/ionic diffusion.
Figure 8. Concentration dependence of (a) the charge transfer resistance ( R ct ) and (b) the double layer
capacitance ( C dl ) of Fe(CN) 6 3- in 2 wt% agarose (squares), 2 wt% κ-carrageenan (triangles) and aqueous
solution (diamonds) containing 0.5 M KCl at the rest potential [3].