## 3 Results
### Xps  
The chemical composition of all samples was determined by XPS using the overview spectra data (Figure S3); the results are summarized in Table 2. This method of analysis is surface-sensitive and makes it possible to analyze thin (up to 5 nm) layers of material. An analysis of overview PE spectra showed that the surface layers of MWCNTs samples and composites do not contain any foreign impurities, except for a trace amount of potassium in the composition of the Mn-0 composite. The intensity of the potassium 2p lines in the overview spectrum of this sample barely exceeded the noise level. Low-intensity K2p peaks were also observed in the high-energy region of the C 1s PE spectrum, measured at lower analyzer pass energy and with higher accumulation statistics (see Figure S4). According to our estimates, the concentration of this element on the surface of the composite was less than 0.05 at.% and was not taken into account in quantitative calculations. The concentration of manganese and rhenium in the composites is approximately 3.3 and 1.5 at.%, respectively. Figure 2: XRD patterns for MWCNTs and composites based on them. In this case, the high value of the oxygen concentration for the composites indicates the presence of metals in the oxidized state. Figure 3a shows the C1s PE spectra for all samples. It can be seen that the position of the maximum of the C1s line practically does not change from sample to sample and is about 284.6 eV (which corresponds to C=C bonds (sp\({}^{2}\)) [49]), and the FWHM of the lines has a close value of 0.7 eV (Table 2). This result indicates that after the deposition of manganese oxide, heat treatments, and the addition of rhenium, the structure of the nanotubes is not disturbed. For Mn-580 + Re and Mn-700 + Re samples, a slight decrease in the FWHM value is even observed, which may indicate an improvement in the crystal structure of nanotubes due to double heat treatment at the stages of manganese and then rhenium oxide deposition. This leads to the annealing of structural defects and the removal of functional oxygen-containing groups formed as a result of the pretreatment of MWCNTs in nitric acid. \begin{table}
\begin{tabular}{c c c c} \hline
**Peak Name** & **Peak Position, eV** & **FWHM, eV** & **Atomic \%** \\ \hline \multicolumn{4}{c}{MWCNTs} \\ \hline C1s & 284.63 & 0.71 & 95.38 \\ O1s & 533.12 & 1.95 & 4.62 \\ \hline \multicolumn{4}{c}{Mn-0} \\ \hline C1s & 284.60 & 0.75 & 74.94 \\ O1s & 532.14 & 2.40 & 18.49 \\ Mn2p & 642.08 & 2.93 & 6.57 \\ \hline \multicolumn{4}{c}{Mn-580} \\ \hline C1s & 284.66 & 0.73 & 83.35 \\ O1s & 530.02 & 1.13 & 13.05 \\ Mn2p & 641.57 & 2.74 & 3.60 \\ \hline \multicolumn{4}{c}{Re-360} \\ \hline C1s & 284.63 & 0.73 & 90.28 \\ O1s & 532.69 & 2.59 & 9.40 \\ Re4f & 46.49 & 1.57 & 0.32 \\ \hline \multicolumn{4}{c}{Mn-580 + Re} \\ \hline C1s & 284.63 & 0.68 & 84.47 \\ O1s & 532.40 & 2.56 & 11.90 \\ Mn2p & 641.78 & 3.06 & 2.80 \\ Re4f & 48.86 & 1.68 & 0.83 \\ \hline \multicolumn{4}{c}{Mn-700 + Re} \\ \hline C1s & 284.62 & 0.68 & 85.73 \\ O1s & 532.36 & 2.82 & 11.07 \\ Mn2p & 641.85 & 2.99 & 2.43 \\ Re4f & 48.86 & 1.56 & 0.77 \\ \hline \end{tabular}
\end{table} 
Table 2: Chemical analysis of samples by XPS. Figure 3b shows the O1s PE spectra for the systems under study. As can be seen, in all Mn-0, Mn-580, Mn-580 + Re and Mn-700 + Re composites, two peaks are distinguished, which belong to different oxygen-containing bonds. So, manganese oxide (Mn-O bond) is located at 529.5-530.5 eV, whereas C=O bond and water (H-O-H) is at 531.8-532.2 and 532-534 eV, respectively [50; 51]. In the case of the Re-360 composite, oxygen is present as a single broad peak. This is due to the fact that oxygen, in bonding with rhenium, is located at 531-532 eV and is masked under the oxygen peak in C=O and water (H-O-H) [50]. Figure 4 shows the Mn2p PE spectra of Mn-0, Mn-580, Mn-580 + Re and Mn-700 + Re composites. The analysis of the chemical state was carried out using the most intense Mn2p3/2 doublet line (binding energy of about 642 eV).