## 2 Materials and Methods
### Characterization Techniques  
We confirmed the crystal structure and phase purity for \(\alpha\)-MnO\({}_{2}\) with powder X-ray diffraction patterns using a PANalytical X'Pert Pro powder diffractometer with a Cu K\(\alpha\) radiation (\(\lambda\) = 0.15406 nm) operating at 45 kV and 30 mA. Infrared spectra (FT-IR) were recorded on an FT-IR spectrometer Vertex 70 (Bruker, Munich, Germany) using the KBr pellet method in the wavenumber range of 400-4000 cm\({}^{-1}\), 128 scans, and a resolution of 8 cm\({}^{-1}\) to study the chemical structures. Raman spectra were obtained using a multi-probe imaging MultiView 1000 TM system (Nanoics Imaging, Jerusalem, Israel), and ultraviolet-visible spectroscopy was performed using \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Electrode** & \(\alpha\)**-MnO\({}_{2}\)** & **Vulcan (mg)** & **Nafion Solution (\(\upmu\)L)** & **Ethanol (\(\upmu\)L)** & **DMF (\(\upmu\)L)** \\ \hline G & - & - & - & - & - \\ \hline G\({}_{\text{V-EOH}}\) & - & 2 & - & 500 & - \\ \hline G\({}_{\text{N-EOH}}\) & - & - & 10 & 500 & - \\ \hline G\({}_{\text{V-N-EOH}}\) & - & 2 & 10 & 500 & - \\ \hline G\({}_{\text{MnO2-EOH}}\) & 3 & - & - & 500 & - \\ \hline G\({}_{\text{MnO2-V-EOH}}\) & 3 & 2 & - & 500 & - \\ \hline G\({}_{\text{MnO2-N-EOH}}\) & 3 & - & 10 & 500 & - \\ \hline G\({}_{\text{MnO2-V-EOH}}\) & 3 & 2 & 10 & 500 & - \\ \hline G\({}_{\text{V-DMF}}\) & - & 2 & - & - & 500 \\ \hline G\({}_{\text{N-DMF}}\) & - & - & 10 & - & 500 \\ \hline G\({}_{\text{V-N-DMF}}\) & - & 2 & 10 & - & 500 \\ \hline G\({}_{\text{MnO2-DMF}}\) & 3 & - & - & - & 500 \\ \hline G\({}_{\text{MnO2-V-DMF}}\) & 3 & 2 & - & - & 500 \\ \hline G\({}_{\text{MnO2-N-DMF}}\) & 3 & - & 10 & - & 500 \\ \hline G\({}_{\text{MnO2-V-N-DMF}}\) & 3 & 2 & 10 & - & 500 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The codes used to identify the bare electrode and each modified electrode, with the compositions of the suspensions employed in the modification process. UV-Vis-NIR Spectrophotometer Perkin Elmer type Lambda 950 (PerkinElmer, Waltham, MA, USA) with an integrating sphere module in the 300-1000 nm range. The morphological characterization of the samples was performed by recording scanning electron microscopy images (SEM, JEOL-6700F from FEI, Eindhoven, The Netherlands). The phase transformations were studied by thermogravimetric analysis (TGA) in an argon atmosphere in the 50 to 1000 \({}^{\circ}\)C range, with a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\). Electrochemical measurements were performed using a VoltaLab PGZ 402 potentiostat (Radiometer Analytical, Lyon, France) together with a three-electrode conventional glass cell. A Pt plate (S\({}_{\text{geom}}\) = 0.8 cm\({}^{2}\)) and the Ag/AgCl (sat. KCl) electrode were the auxiliary and reference electrodes, respectively. The working electrode was the graphite support (S\({}_{\text{geom}}\) = 0.28 cm\({}^{2}\)), either bare or modified with the compositions specified in Table 2. The double-layer capacitance investigations at the electrode/electrolyte solution interface were carried out by recording cyclic voltammograms in 0.1 mol L\({}^{-1}\) KCl electrolyte solution at different scan rates (\(v\) = 0.1, 0.15, 0.2, 0.25, and 0.3 V s\({}^{-1}\)) and in a potential range where no Faradic currents were present. All electrochemical experiments were performed at room temperature and all potentials are represented vs. the Ag/AgCl (sat. KCl) electrode. Catalytic degradation of RhB from aqueous solution over \(\alpha\)-MnO\({}_{2}\) was studied to appreciate the catalytic properties of the MnO\({}_{2}\) in the dark and under solar irradiation. The effect of solar light irradiation was investigated for the catalytic degradation reaction of dye in an aqueous solution using 30 mL RhB (initial concentration of 1.5 mg L\({}^{-1}\)) and 10 mg of brown \(\alpha\)-MnO\({}_{2}\) continuously mixed with a magnetic stirrer at 300 rpm in comparison with the absence of irradiation.