# Electrode Kinetics of Ion Jelly and Ion Sol-Gel Redox Materials on Screen-Printed Electrodes
## 3 Results and Discussion
### Electrochemical Characterization of IJ and ISG
A larger baseline hysteresis was observed, which corresponded to high capacitive currents. The formal potentials of the reaction fell in between those observed in SPE and SPE-IJ, at +106 \(\pm\) 7 mV. Variation of peak separation with scan rate followed a profile similar to that of the unmodified SPE: at lower scan rates variation was small, but above 50 mV\(\cdot\)s\({}^{-1}\) it rose sharply, up to 542 mV. Unlike the other two cases, the I\({}_{\rm pc}\)/I\({}_{\rm pa}\) ratio in ion sol-gel oscillated between 0.4 at low scan rates and 1.3 at high scan rates. Irreversible behavior was initially considered based on this atypical behavior and high peak separations. Diffusion coefficients for each system were calculated from the slopes of peak current against the square root of the scan rate (Figure 4). The Randles-Sevcik equation was used to calculate D\({}_{\rm O}\) and D\({}_{\rm R}\) in unmodified SPE and in ion jelly-modified SPE, while the modified equation for irreversible processes [55] was used for ISG-modified electrodes. The results are summarized in Table 2. The value of \(\alpha\) used was obtained according to a reported method [56]; \(\alpha\) for the scan rates where kinetics were more irreversible, corresponding to the \(\Delta\)Ep \(\geq\) 300 mV (\(\
u\) = 50, 100 and 200 mV\(\cdot\)s\({}^{-1}\)) were used. Those charge transfer coefficients were averaged out, giving a mean \(\alpha\) = 0.56. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multicolumn{2}{c}{\(\
u\) (mV\(\cdot\)s\({}^{-1}\))} & \multicolumn{1}{c}{**2.5**} & \multicolumn{1}{c}{**5**} & \multicolumn{1}{c}{**10**} & \multicolumn{1}{c}{**50**} & \multicolumn{1}{c}{**100**} & \multicolumn{1}{c}{**200**} \\ \hline \multirow{4}{*}{SPE} & E\({}^{\circ}\) (mV) & 145 \(\pm\) 5 & 159 \(\pm\) 4 & 141 \(\pm\) 2 & 166 \(\pm\) 1 & 165 \(\pm\) 1 & 162 \(\pm\) 3 \\ \cline{2-7}  & \(\Delta\)Ep (mV) & 113 \(\pm\) 2 & 130 \(\pm\) 1 & 147 \(\pm\) 2 & 302 \(\pm\) 1 & 381 \(\pm\) 2 & 477 \(\pm\) 4 \\ \cline{2-7}  & I\({}_{\rm pc}\)/I\({}_{\rm pa}\) & 1.05 \(\pm\) 0.03 & 1.01 \(\pm\) 0.01 & 1.02 \(\pm\) 0.01 & 1.00 \(\pm\) 0.01 & 1.03 \(\pm\) 0.02 & 1.07 \(\pm\) 0.05 \\ \hline \multirow{4}{*}{SPE-IJ} & E\({}^{\circ}\) (mV) & & 24 \(\pm\) 2 & 28 \(\pm\) 1 & 26 \(\pm\) 1 & 25 \(\pm\) 1 & 23 \(\pm\) 2 \\ \cline{2-7}  & \(\Delta\)Ep (mV) & - & 90 \(\pm\) 1 & 95 \(\pm\) 3 & 120 \(\pm\) 1 & 129 \(\pm\) 1 & 155 \(\pm\) 1 \\ \cline{2-7}  & I\({}_{\rm pc}\)/I\({}_{\rm pa}\) & & 1.14 \(\pm\) 0.02 & 1.24 \(\pm\) 0.02 & 1.15 \(\pm\) 0.01 & 1.16 \(\pm\) 0.01 & 1.17 \(\pm\) 0.0 As expected, diffusion coefficients were lower when a layer of material covered the electrode, as it imposes a physical barrier to the diffusion of molecules to and from the electrode's surface. The diffusion coefficients were very close for Fe(CN)\({}_{6}\)\({}^{3-}\) and Fe(CN)\({}_{6}\)\({}^{4-}\), since both ions have approximately the same size, an octahedral structure, and behave similarly in solvated environments [46]. However, in the ion sol-gel matrix, diffusion of Fe(CN)\({}_{6}\)\({}^{4-}\) was significantly lower than that of its oxidized form. D\({}_{\text{O}}\) and D\({}_{\text{R}}\) were two orders of magnitude lower in IJ-modified electrode than in an unmodified SPE, resembling the diffusion coefficients of water obtained in the swelling experiments of ion jelly [24]. In ISG, D\({}_{\text{O}}\) and D\({}_{\text{R}}\) were a whole four to five orders of magnitude lower than in the SPEs, which is in agreement with the very low peak currents measured. However, considering that other silica-based ionogels have shown much greater responses by cyclic voltammetry [28], the cause for this hindered diffusion most likely lies in the methylation of the silica network that allows the retention of [omim][TFSI] during water immersion. A possible solution to this problem that at the same time avoids sacrificing water stability could lie in a different method of immobilizing an alkalimidazole TESI IL, which was investigated by [PERSON] and co-workers [57].