# Studies on the Electrochemical Behavior of Sulfite on Incoloy 800 in a Neutral Environment
## 3 Results
### Linear Voltammetry  
At higher sulfite concentrations (\(10^{-1}\), \(5\times 10^{-1}\); and \(1\) mol L\({}^{-1}\)), a significant depolarization of the anodic branches of the voltammetric plots occurs, which shows that sulfite is oxidized through an electronation process that occurs directly on the electrode. Given that multiple voltammetric plots are not recorded, it can be appreciated that the process takes place in a single monoelectronic step with the intermediate formation of dithionate (reactions (3) and (4)), in agreement with the mechanisms proposed by other authors [29]. Moreover, in potential ranges where current densities are not limited by the diffusion of sulfite ions on the anode surface, the kinetics of the oxidation process is controlled by the charge transfer step. Therefore, the kinetic parameters that characterize the electrode process can be determined: the anodic transfer coefficient \(\alpha\) and the exchange current density \(i_{\rm o}\). For this purpose, linear polarization plots were recorded at a lower polarization scan rate (\(1\) mV s\({}^{-1}\)), which would ensure pseudo-potentiostatic conditions for the electrode processes to occur. The linear voltammograms plotted on Incoloy 800 in a base solution of \(1\) mol L\({}^{-1}\) Na\({}_{2}\)SO\({}_{4}\), with \(10^{-1}\), \(5\times 10^{-1}\), and \(1\) mol L\({}^{-1}\) Na\({}_{2}\)SO\({}_{3}\), respectively, are shown in Figure 2.  
Figure 2 reveals that, as expected, the presence of sulfite in the base solution produces a significant depolarization of the anodic process proportional to its concentration. The kinetic parameters \(\alpha\) and \(i_{\rm o}\) were determined using the Tafel slope method, graphically representing the anodic process overpotential \(\eta\) (charge transfer overpotential) as a function of the decimal logarithm of the current density \(i\) (Figure 3). Figure 2: Linear voltammograms recorded on the Incoloy 800 electrode in \(1\) mol L\({}^{-1}\) Na\({}_{2}\)SO\({}_{4}\) with different concentrations of Na\({}_{2}\)SO\({}_{3}\), scanning rate \(1\) mV s\({}^{-1}\). For anodic processes, the dependence of the charge transfer overpotential \(\eta\) on the net current density \(i\) crossing the electrode is given by the relation (6). \[\eta=\text{a}+\text{ b}\lg i \tag{6}\]  
The ordinate at the origin a and the slope b in Tafel relationship are given by the relations (7) and (8), respectively. \[a=-\frac{2.303 RT}{\mathbf{a}zF}\lg i_{\text{o}} \tag{7}\]  
\[b=\frac{2.303 RT}{\mathbf{a}zF} \tag{8}\]  
where R is universal gas constant (8.314 J K\({}^{-1}\) mol\({}^{-1}\)), T is the thermodynamic temperature (K), z is the stoichiometric number of electrons, and F is the Faraday number (96,484.56 C mol\({}^{-1}\)). Table 2 shows the values obtained for the kinetic parameters at the standard temperature (298 K) at which the voltammetric measurements were performed. The values obtained for the anodic transfer coefficient \(\alpha\) on the Incoloy 800 electrode are lower than those reported in the literature for the Pt electrode, which reaches 0.36-0.48 A m\({}^{-2}\) under the same conditions. Partly, this effect of decreasing catalytic activity is compensated by the increase in the exchange current \(i_{\text{o}}\), which on Incoloy 800 (2.6-3.4 A m\({}^{-2}\)) [41] is significantly higher than on Pt. It should be noted that higher values of the transfer coefficient \(\alpha\) were obtained on graphite (0.31-0.35), but the exchange currents \(i_{\text{o}}\) are much lower (0.21-0.80 A m\({}^{-2}\)) than on Incoloy 800, in neutral solutions of 1 mol L\({}^{-1}\) Na\({}_{2}\)SO\({}_{4}\)[39]. Functionalization of the