# 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  
In order to compare the electrochemical properties of each material, the redox couple ferricanide/ferrocyanide was chosen for being one of the most well-studied reversible single-step electron transfer processes, providing well-defined peaks, thus being a good redox model for diffusion studies [44]. Voltammogram characteristics of Fe(CN)\({}_{6}\)\({}^{3-}\)/Fe(CN)\({}_{6}\)\({}^{4-}\) redox behavior on a clean SPE, a modified SPE covered with an IJ  
Figure 2: Real part of conductivity for ISG with [omim][TFSI], and IJ made with [emim][EtSO4], at 20 \({}^{\circ}\)C.  
film (SPE-IJ), and a modified SPE with an ISG film (SPE-ISG) are represented in Figure 3. The formal potentials, peak separations and peak symmetries are shown in Table 1.  
The peak separations of Fe(CN)63\({}^{-}\)/Fe(CN)64\({}^{-}\) pair on clean SPEs were affected by the scan rate used, with large values of \(\Delta\)Ep being observed at scan rates above 50 mV\(\cdot\)s\({}^{-1}\), which is in agreement with the less reversible behavior at higher scan rates. The formal potential of the process was on average +157 \(\pm\) 10 mV. Anodic and cathodic peak symmetry (ratio J\({}_{\text{PC}}\)/I\({}_{\text{Pa}}\)) were also not affected by the scan rate, as expected for a reversible process, with values close to 1 on all tested scan rates. \(\mid\) Ep-Ep/2\(\mid\) was approximately constant at 80 mV for scan rates up to 10 mV\(\cdot\)s\({}^{-1}\), rising up to 185 mV at higher scan rates. Observation of the typical reversible behavior of the ferricyanide redox pair process is often dependent on pretreatment of the electrode surfaces [45]. At high scan rates, large peak separations are commonly observed on many surfaces, falling into quasi-reversible behavior [46, 52]. A difference of 56 mV in \(\mid\)Ep-Ep/2\(\mid\), as well as a \(\Delta\)Ep of 57 mV, which are characteristic of ideal reversible processes, are rarely found in experimental conditions. This potential difference is due to several factors, such as solution resistance [53] and also incomplete removal/depletion of reduced or oxidized species at the switching potentials. Faradaic current would have to decay completely to zero before the reverse scan was initiated  
Figure 3: Representative 3 rd cycles of the cyclic voltammograms attained with 10 \(\times\) 10\({}^{-3}\) mol\(\cdot\)dm\({}^{-3}\) Fe(CN)63\({}^{-}\)/Fe(CN)64\({}^{-}\) in 1 mol\(\cdot\)dm\({}^{-3}\) KNO3 at various scan rates for SPE, SPE-IJ and SPE-ISG (inset is a magnification of the lower scan rates, in mV\(\cdot\)s\({}^{-1}\)), respectively. in order to minimize this factor, which is not very practical, as it involves stopping the measurement and holding it at very negative potentials [54]. Therefore, even experimental \(\Delta\)Ep values for one-electron reversible systems with fast kinetics are usually 70 mV or greater [55]. Taking all of this into consideration, the behavior of ferrocyanide in carbon SPEs appeared to be reversible in the low scan rate region but exhibited a quasi-reversible behavior in the high scan rate region. Due to the changes ion jelly undergoes when it comes in contact with aqueous solutions, scan rates that involve a long running time (2.5 mV\(\cdot\)s\({}^{-1}\)) were not performed, and CV assays were performed for only two cycles in order to minimize the experimental time. The formal potential of Fe(CN)\({}_{6}\)\({}^{3-}\)/Fe(CN)\({}_{6}\)\({}^{4-}\) in SPE-IJ electrodes was on average +26 \(\pm\) 1 mV, a shift of about 130 mV in the negative direction when compared with the unmodified electrodes (Figure 3). Maximum peak currents were considerably inferior in the presence of IJ, which was expected since having a gel matrix on top of an electrode hinders molecule diffusion. Peak symmetry was lower, with an average I\({}_{\rm pc}\)/I\({}_{\rm pa}\) of 1.17. Peak intensity in the ion sol-gel (ISG) system was markedly lower, which was indicative of severely hindered diffusion (Figure 3).