Degradation of bifunctional α-MnO2/NiO@Ni gas-diffusion electrodes for Zn-air batteries: Space-resolved Ni chemical-state evolution mapped by soft X-ray spectral ptychography

The degradation of Mn-based gas diffusion electrodes (GDEs) limits the durability of rechargeable Zn–air batteries. In our previous study [ 1 ], scanning transmission X-ray microscopy (STXM) at the Mn l -edge revealed pathways of Mn reduction and dissolution, but could not resolve Ni, whose nanometric dispersion and weak absorption made it undetectable. Here, we apply soft X-ray ptychography at the Ni l -edge to the same electrodes. The higher spatial resolution of ptychography allowed detection of Ni distributions that were inaccessible by STXM, while Kramers–Kronig (KK) reconstruction of phase spectra provided absorption-equivalent information in regions where the magnitude signal was unusable. The workflow was validated by direct comparison of KK-converted and magnitude spectra, and by reconstructing hybrid datasets combining both channels. Applied to three bifunctional samples, this approach revealed distinct Ni–Mn correlations: localized oxidized Ni overlapping with Mn(II) in the low-Ni sample, more homogeneous Ni distribution stabilizing Mn redox activity at higher Ni loading, and unexpected Ni–Mn(II) co-localization under zincate cycling, consistent with dissolution–reprecipitation processes. These results demonstrate that ptychography, combined with KK-based spectral reconstruction, extends nanoscale spectromicroscopy beyond the limits of absorption contrast and provides new insights into the cooperative behavior of Ni and Mn in bifunctional electrocatalysts. The spectromicroscopy findings are accompanied by the detailed electrochemical analysis of GCD ageing followed by chronopotentiometric and electrochemical impedance measurements, which consistently identify the optimized Ni loading as the most stable electrode architecture.