## 3 Results and Discussion  
### Membrane Surface Characterization  
Surface chemical changes associated to ILs doping of Nafion112 membrane was studied by XPS analysis, which allows the determination of the atomic concentration percentage (A.C.%) of the elements present on the membranes surfaces. Table 1 presents the atomic concentration percentages (A.C.%) of the characteristic elements (C \(1s\), O \(1s\), F \(1s\), S \(2p\) and N \(1s\)) found on the surfaces of the studied membranes, which were obtained from high resolution spectra of the main photoelectron peaks, as well as the Nafion theoretical values according to its formulae [2]. Small percentages (\(<\)0.5%) of other elements such (chlorine, silicon, _etc._) also found are not indicated since they are associated to surface contamination. As it can be observed in Table 1, the comparison of theoretical and experimental values for the Nafion membrane only shows slight differences, which are attributed to surface contamination, particularly to the presence of adventitious carbon. The reduction of fluorine concentration (Nafion \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **C\%** & **O\%** & **F\%** & **S\%** & **N\%** \\ \hline Nafion (theoretical) & 30.8 & 7.7 & 60.0 & 1.5 & - \\ Nafion112 & 39.0 & 6.6 & 53.4 & 1.0 & 0.2 \\ Nafion112/TMPA\({}^{+}\) & 45.6 & 7.0 & 44.2 & 1.0 & 1.3 \\ Nafion112/BMIM\({}^{+}\) & 47.9 & 4.8 & 42.3 & 0.9 & 3.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Atomic concentration percentages of the characteristic elements found on the membrane surfaces. characteristic element) in Nafion112/TMPA\({}^{+}\) (17%) and Nafion112/BMIM\({}^{+}\) (21%) doped membranes is an indication of membrane surface coverage by the ILs, which is also supported by the increase in the nitrogen A.C.%. The lower the fluorine concentration, the lower is the hydrophobic character. This means that according to these values, the Nafion112/BMIM\({}^{+}\) sample must show the lower hydrophobic character. This point can be discriminated by considering the XPS spectra, which provide information on the chemical interactions among the different elements on the solid surface. As expected, the N atomic concentration% was higher for sample Nafion112/BMIM\({}^{+}\) that presents two nitrogen atoms per formula. Figure 1 shows the C 1\(s\) core level normalized spectra of Nafion112, Nafion112/BMIM\({}^{+}\) and Nafion112/TMPA\({}^{+}\) doped membranes. The higher relative intensity of the contributions at low binding energy (284.0-288 eV) observed in samples Nafion112/BMIM\({}^{+}\) and Nafion112/TMPA\({}^{+}\) are due to the presence of phenyl and alkyl groups of the IL cations. Table 2 lists the decomposition of the C 1\(s\) spectra of the studied membranes in five contributions that are assigned as follows: C1 to adventitious carbon and phenyl moiety in the case of TMPA\({}^{+}\) and the alkyl chain in the case of BMIM\({}^{+}\); C2 to carbons linked to nitrogen; C3, C4 and C5 are assigned to carbons bonded to fluorine of the Nafion membranes. It is clear that upon the incorporation of the IL cations, the sum of C1 and C2 are 52.43% and 42.03% for Nafion112/TMPA\({}^{+}\) and Nafion112/BMIM\({}^{+}\), respectively, while this sum is only 11.68% for Nafion112. This surface analysis supports the surface incorporation of the ILs cations and the correspondent decrease of the percentages of the contributions C4 and C5. This incorporation suggests a decrease in hydrophobic character. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **C1** & **C2** & **C3** & **C4** & **C5** \\ \hline Nafion112 & 8.05 & 3.63 & 8.37 & 69.70 & 10.20 \\ Nafion112/TMPA\({}^{+}\) & 36.92 & 15.51 & 8.29 & 36.30 & 2.97 \\ Nafion112/BMIM\({}^{+}\) & 14.01 & 28.05 & 22.96 & 31.56 & 3.42 \\ \hline \end{tabular}
\end{table} 
Table 2: Decomposition of the C 1\(s\) spectra (in %) for Nafion112, Nafion112/BMIM\({}^{+}\) and Nafion112/TMPA\({}^{+}\) doped membranes.