## 3 Results and Discussion
### Chemical Surface Characterization of the RC/IL Films
Figure 2a,b show the fluorine and phosphorous core level signals for the RC/BMIMPF\({}_{6}\) film, while the chlorine spectra for the RC/AliquatCl film is shown in Figure 2c, where that obtained for the AliquatCl IL is also indicated; the oxygen core level signal for both RC/IL films and the RC-support is drawn in Figure 2d, showing the three samples a symmetrical peak at the same B.E., which confirms the adsorption to the RC-support of the oxygen content determined for both RC/IL films. Table 1 shows the A.C. % of the different elements founded on the surfaces of the studied RC/IL films and, for comparison reasons, the A.C. % of the chemical elements  
Figure 2: (**a**) Fluorine and (**b**) phosphorous core level signals for the RC/BMIMPF\({}_{6}\) film. (**c**) Comparison of chlorine signals for the RC/AliquatCl film (blue solid line) and the AliquatCl IL (blue dashed–dot line. (**d**) Oxygen core level signals for the RC/BMIMPF\({}_{6}\) film (red solid line), the RC/AliquatCl film (blue solid line) and the RC-support (black dashed line). determined for the AliquatCl IL and the BMIMPF\({}_{6}\) ILs as well as for the RC-support are given as Supplementary Information in Table S1. On the other hand, as was indicated above, two non-characteristic ILs elements such as oxygen and silicon, associated with the RC-support, were also detected on the surface of the RC/IL samples, which is an indication of support surface partial coverage. It should be pointed out that organic compounds with silicon are sometimes purposefully added to polymeric films to improve its plasticity (or an impurity from the monomers purifying columns) [40]. The analysis of the ARXPS spectra allows us to obtain in-deep chemical information of both RC/IL films, and Figure 3 shows the variation with the take-off angle of the atomic concentration % of the elements detected on each RC/IL film; for comparison reasons, the A.C. % of oxygen and silicon obtained for the RC support are also included in Figure 3d,e. These results seem to indicate more homogeneous coverage for the RC/AliquatCl film, taking into account the constancy of the carbon percentage (84 \(\pm\) 1%) for depths ranging between 2.3 nm and 9.5 nm (see Figure 4a), as well as the lower percentages for oxygen and silicon (support elements) exhibited by this film. \begin{table}
\begin{tabular}{l c c c c c c} \hline
**RC/IL Film** & **C (\%)** & **N (\%)** & **F (\%)** & **P (\%)** & **Cl (\%)** & **O (\%)** & **Si (\%)** \\ \hline RC/AliquatCl & 83.2 & 2.7 & — & — & 0.6 & 12.6 & 0.3 \\ RC/BMIMPF\({}_{6}\) & 68.4 & 1.4 & 5.1 & 1.0 & — & 21. 21.5 & 1.4 \\ \hline \end{tabular}
\end{table} 
Table 1: Concentration atomic percentages determined at 45\({}^{\circ}\) take-off angle for the different elements observed on the surfaces of the RC/AliquatCl and the RC/BMIMPF\({}_{6}\) films. Figure 3: Variation with the take-off angle of A.C. % for: (**a**) carbon; (**b**) nitrogen; (**c**) fluorine or chlorine; (**d**) oxygen; and (**e**) silicon. RC/AliquatCl (blue solid points), RC/BMIMPF\({}_{6}\) film (red solid points). Black open points in (**d,e**) correspond to the RC support.