## 1 Introduction  
In order to apply strategies for the rational design of bi-functional oxygen reduction reaction (ORR--discharge mode) and oxygen evolution reaction (OER--charge mode) catalysts for metal-air batteries, it is important to improve our understanding of the chemical and structural characteristics of the active material under reaction conditions. In this field, in recent years, X-ray absorption spectroscopy (XAS) is becoming increasingly popular because it can be combined with electrochemistry to elucidate the properties of catalytic materials in situ and operando. XAS can be separated into X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS). The former provides information on the electronic structure of the catalyst, while the latter assesses the interatomic distances and coordination numbers of the atoms (i.e., the chemical environments) that constitute the catalysts. XAS studies have been formerly applied in situ to a number of ORR and OER catalyst systems. Manganese-based oxides (Mn-oxides) are among the most active electrocatalysts for the ORR and the most studied using XAS-based methods for alkaline metal-air batteries. Mn oxides exist in a large variety of structures, where the Mn ions can have a wide range of valence states, typically from 2+ to 4+ [1], exhibiting different catalytic activities for the ORR and OER kinetics. Ex situ and in situ XAS at the Mn K-edge (hard XAS) and the Mn L\({}_{3,2}\)-edges (soft XAS) have been used in a number of investigations to correlate Mn valence with OER and ORR activity, and [PERSON] et al. [1] have provided a comprehensive overview of these studies. It is worth noting that, in most of the cases reported in the literature, owing to cell and time constraints, in situ and operando XAS measurements (for a distinction of the two approaches, see [2]) were carried out under experimental conditions that are far from realistic. Typical measured current densities are two to three orders of magnitude smaller than those used in actual metal-air battery applications [1; 3; 4] (e.g., jORR = \(-\)0.01 mA\(\cdot\)cm\({}^{-2}\) vs. \(-\)10 mA\(\cdot\)cm\({}^{-2}\)). Furthermore, the majority of operando XAS studies worked under potentiostatic conditions, while real batteries generally function in a galvanostatic mode.  
In the present investigation, we conducted in situ XAS measurements of a newly developed O\({}_{2}\) bi-functional gas diffusion electrode (GDE) made of \(\alpha\)-MnO\({}_{2}\) nanowires (NWs), obtained from a facile synthesis method, combined with commercially available carbon black. Both the architecture and composition of the electrode, as well as the configuration of the electrochemical setup, have been designed to achieve optimal edge-jumps and signal-to-noise ratio in the absorption spectra for the XAS Mn K-edge, without sacrificing the current densities applied during testing (electrode performance). In this way, we could perform high-quality operando XAS spectroscopy under practical GDE operating conditions. We compared the chemical changes that occur on the MnO\({}_{2}\) component when the GDE is tested under normal operating conditions, on the background of more critical conditions that simulate oxygen starvation in a flooded electrode, where the consumption of oxygen is faster than the rate at which oxygen is transported from the gas phase to the catalyst surface.