## 3 Results and Discussion
Quantitative fitting analysis of the EXAFS at the Mn K-edge was used to investigate the evolution of the local chemical environment of the \(\alpha\)-MnO\({}_{2}\) during the O\({}_{2}\) starvation process. To perform the fitting analysis on the EXAFS oscillations, we constructed a model starting from the crystal structure of cryptomelane K\({}_{1.33}\)Mn\({}_{8}\)O\({}_{16}\). The model includes four adsorber-scatterer interactions (also denoted scattering paths), each corresponding to a distinct interatomic distance: two Mn-O interactions and two Mn-Mn interactions. The first scattering path relates to the distance between the Mn ion and the oxygen in the lattice that forms the characteristic MnO\({}_{6}\) octahedra (Mn-O\({}_{\text{lattice}}\)). The second Mn-O interaction (Mn-O\({}_{\text{ads}}\)) considers possible adsorbed oxygen-containing species (for instance, intercalated water molecules) [14], as well as hydroxide end groups on the catalyst surface [15]. The last two interactions are associated with the interatomic distances Mn-Mn\({}_{\text{edge}}\) and Mn-Mn\({}_{\text{corner}}\)[13, 16]. Systematic variation of the choice and combination of scattering path showed that neglecting one of the Mn-Mn or Mn-O paths leads to a degradation of the fit quality; in particular, subtle, but diagnostic details of the crypomelane structure cannot be followed. To perform the fit of the EXAFS oscillations, the amplitude reduction factor \(S_{0}^{2}\) was set to a constant value of 0.8, following the report of [PERSON] [17]. The edge energy E\({}_{0}\), the mean squared relative displacements \(\sigma\), the coordination numbers CN, and interatomic distances R were initially set as free variables. Eventually, a second refinement was done to improve the fit quality by constraining those parameters that showed a nearly constant value (to their average value; see quantities in boldface in Table 1). Fitting was carried out in the same R- and k-ranges of 1.25-3.25 A and 3-15 A\({}^{-1}\), respectively. Figure 4a shows the structural model representing the \(\alpha\)-MnO\({}_{2}\) that was used to match the EXAFS data (see Experimental Section for more information). Figure 4b shows the comparison of experimental data with the fitted model in R space for the GDE before and after partial O\({}_{2}\) starvation process. Table 1 lists all fitted parameters as a result of the refining method. The fit for both the ORR and OER processes over the analyzed R-range, as shown in Figure 4b, fits well with the experimental results for the GDE before O\({}_{2}\) starvation. Although the quality of the fit for the peak corresponding to the Mn-Mn\({}_{\text{corner}}\) interaction is rather poor after partial O\({}_{2}\) starvation, the peaks corresponding to the Mn-O and Mn-Mn\({}_{\text{edge}}\) interactions still show good agreement between the experimental data and the fit. It is worth noting that the relatively large value of the confidence interval for the Mn-O\({}_{\text{ads}}\) distances--corresponding to intercalation/surface species--with respect to the distances characteristic of the crystal bulk, is due to the multiplicity of oxygen adsorption sites and adsorbed oxygen-containing species. Instead, the confidence intervals of the other distances considered in our model are in line. An interesting result obtained from the fit is the parameter that corresponds to the coordination number for Mn-O\({}_{\text{lattice}}\) CN(Mn-O\({}_{\text{lattice}}\)). This is illustrated in Figure 4c. The value of CN(Mn-O\({}_{\text{lattice}}\)) changes considerably according to the condition applied (ORR vs. OER), where it increases during ORR and decreases during OER, respectively. More importantly, when comparing the data before and after O\({}_{2}\) starvation, the value of CN(Mn-O\({}_{\text{lattice}}\)) is decreased. This is consistent with a lowering of the average Mn oxidation due to the lack of oxygen supply from ambient air.