## 3 Results and Discussion
It can be noticed that the XANES spectrum coincides with the one of the references Mn\({}_{3}\)O\({}_{4}\), thus indicating that, when the access of oxygen to the electrocatalyst is restricted, the \(\alpha\)-MnO\({}_{2}\) can be fully transformed into Mn\({}_{3}\)O\({}_{4}\). These findings are in agreement with the work of [PERSON] et al. [12]and [PERSON] et al. [3], who demonstrated the formation of the Mn\({}_{3}\)O\({}_{4}\) from \(\beta\)-MnO\({}_{2}\) and electrodeposited manganese oxides, respectively, at high ORR overpotentials. The local structural evolution of the \(\alpha\)-MnO\({}_{2}\) material during the O\({}_{2}\) starvation process is investigated in detail by operando Mn K-edge EXAFS analysis. Figure 3b illustrates the corresponding amplitude of the Fourier transform (FT) of the k\({}^{3}\)-weighted Mn K-edge EXAFS oscillations of the GDEs and reference samples shown in Figure 3a. The description of the EXAFS spectrum of \(\alpha\)-MnO\({}_{2}\) is partially documented in the literature, but still allows the assignment of characteristic spectral features (see below). Out attribution assignment of EXAFS spectra to cryptomelane, on the one hand, is fully supported by the available literature and, on the other hand, is validated by XRD and Raman measurements of the same samples (dedicated paper in preparation). The typical  
Figure 3: Comparison of **(a)** Mn K-edge XANES and corresponding **(b)** FT amplitudes collected on the GDE before (solid blue and red lines), after partial (dashed blue and red lines), and after complete O\({}_{2}\) starvation (solid black line); the data were not corrected for phase shift. The figure also includes the reference XANES of Mn\({}_{3}\)O\({}_{4}\) (lime green) and pyrolusite-type MnO\({}_{2}\) (cyan) powder. **(c)** Same data of Panel **(b)**, reported vs. wavenumber in the full measured range. Figure 2: Chronovoltammetry test under ORR condition at j = \(-\)10 mA\(\cdot\)cm\({}^{-2}\) before and after application of the Kapton foil in front of the GDE window. FT features of the \(\alpha\)-MnO\({}_{2}\) phase are clearly visible for the GDE before O\({}_{2}\) starvation. These include three main peaks: the first peak is related to the Mn-O bonds, the second to the edge-shared Mn-Mn bonds, and the third to the corner-shared Mn-Mn bonds (see Figure 3a). It can be noticed that the FT signal remained relatively unchanged when comparing the ORR and the OER processes, where only the second peak (Mn-Mn\({}_{\text{edge}}\)) shows a small increase under the OER process. Such a weak rise in intensity of the FT peak may be attributed to the formation of additional bonds in the defective manganese oxide lattice [3] or to the depression of local structural disorder [13]. According to [PERSON] et al. [13], FT peak enhancement during the OER process can be regarded as clear evidence of the improved collinear alignment of the MnO\({}_{6}\) octahedra array. The shape and intensity of the FT peaks change drastically after the partial O\({}_{2}\) starvation process. A small shoulder emerges before the main Mn-O FT peak at a radial distance of around 1.1 A (indicated by a red asterisk in Figure 3b). Furthermore, the FT peak associated with the Mn-Mn\({}_{\text{corner}}\) interaction vanishes, thus indicating a more severe restructuring of the manganese oxide material. The shape and intensity of the FT peaks following complete O\({}_{2}\) starvation match those of Mn\({}_{3}\)O\({}_{4}\), confirming the complete transformation of \(\alpha\)-MnO\({}_{2}\) into Mn\({}_{3}\)O\({}_{4}\). For the Mn K-edge, variations in the XANES spectrum can be evidently resolved under electrochemical polarization before and after the partial O\({}_{2}\) starvation process. This clearly shows that, when the GDE is reduced in the absence of oxygen, the MnO\({}_{2}\) component undergoes major structural/chemical changes.