## 3 Results and Discussion
### Electrical Characterization of Nafion112/IL-Cations Doped Membranes  
Electrical changes associated to IL-cation doping on Nafion-112 membrane were determined from impedance spectroscopy measurements performed with dry samples (Nafion112/TMPA\({}^{+}\) and Nafion112/BMIM\({}^{+}\)). Figure 4 shows a comparison of the Nyquist plot (\(-Z_{\text{imag}}\)_vs._\(Z_{\text{real}}\)) obtained for both doped samples, where significant differences can be observed. In both cases, the electrical response is a depressed semicircle, and the associate equivalent circuit corresponds to a parallel association of a resistance (R\({}_{\text{m}}\)) and a constant phase element or non-ideal capacitor (Q\({}_{\text{m}}\)) [15]. Figure 5 shows a comparison of Bode diagrams (\(Z_{\text{real}}\)_vs._ frequency, Figure 5a and \(-Z_{\text{imag}}\)_vs._ frequency, Figure 5b) for both ILs-cation doped membranes, Nafion112/TMPA\({}^{+}\) and Nafion112/BMIM\({}^{+}\), as well as the original Nafion-112 sample. As can be observed, significantly lower values for the real part of the impedance (directly related to electrical resistance) were obtained for the original Nafion-112 membrane in comparison with both IL-cations doped samples (almost 20 times higher for Nafion112/BMIM\({}^{+}\), but several orders of magnitude for Nafion112/TMPA\({}^{+}\)). Another significant point is the shift to lower frequency value (\(\sim\)400 Hz) of the maximum relaxation frequency obtained for the Nafion112/TMPA\({}^{+}\) membrane with respect to both Nafion-112 and Nafion112/BMIM\({}^{+}\) membranes, which use to be associated to more compact membrane structure [18]. Figure 4: Nyquist plot (\(-Z_{\text{imag}}\)_vs._\(Z_{\text{real}}\)) for Nafion112-TMPA\({}^{+}\) (\(\blacksquare\)) and Nafion112-BMIN\({}^{+}\) (\(\blacksquare\)) dry samples. Figure 3: TG profiles for Nafion112, Nafion112/BMIM\({}^{+}\) and Nafion112/TMPA\({}^{+}\) doped membranes. Due to the very similar molar volume of both cations, differences in electrical behaviour could be associated with the different shapes of both cations, sphere-like for TMPA\({}^{+}\) and lineal for BMIM\({}^{+}\) (see Scheme 1), which might facilitate the inclusion of the latter into the pinholes observed in the structure of the Nafion-112 membrane [25,26], but causing partial blockage when quasi-spherical TMPA\({}^{+}\) cation is used for membrane doping. In this context, it should also be mentioned the significant reduction (around two orders of magnitude) in methanol cross-over reported for both Nafion112/TMPA\({}^{+}\) and Nafion112/BMIM\({}^{+}\) membranes when compared with the original Nafion-112 sample [11], which can be of great interest for membranes' application in direct methanol fuel cells. Taking into account the more similar electrical response obtained for dry Nafion112/BMIM\({}^{+}\) doped membrane and the original Nafion-112 one, electrochemical characterization by determining counter-ions' transport through both samples in wet conditions (contact with HCl-aqueous solutions) was performed with these two samples [27]. Membrane potential, \(\Delta\Phi_{\text{memb}}\), is the electrical potential difference between both sides of a membrane separating two solutions of the same electrolyte but different concentrations (\(c_{1}\) and \(c_{2}\)) [28]. Figure 6 shows the variation of membrane potentials with the logarithm of the solution concentrations ratio for Nafion-112 and Nafion112/BMIM\({}^{+}\) membranes, where a practically linear relationship can be observed. Figure 6: Membrane potentials _versus_ HCl solutions concentrations ratio for Nafion-112 (o) and Nafion112/BMIM\({}^{+}\) (\(\blacksquare\)) membranes. Figure 5: Bode plots: (**a**) \(Z_{\text{real}}\)_vs._ frequency and (**b**) \(-Z_{\text{img}}\)_vs._ frequency, for dry Nafion-112 (o), Nafion112-TMPA\({}^{+}\) (\(\blacksquare\)) and Nafion112-BMIM\({}^{+}\) (\(\blacktriangle\)) membranes.