This replication data set provides the raw data for the publication: https:/doi.org/10.1021/acs.chemmater.5c02979 It contains the microscopic four-point probe (PS4 four-micro-electrode Prober Shuttle, Kleindiek, Germany with CSPTSA025- CR200 electrodes, Mesoscope, Taiwan) experiments on pristine and operated membrane electrode assembly (MEA) anodes. The electrodes were arranged linearly on the sample and each sample measured in three separate positions for each region of interest. The microscope of a Hysitron TI 980 Nanoindenter (Bruker, USA) was used to locate the measurement positions. Further, it contains the scanning electron microscopy (SEM) images (FEI Quanta, Thermo Fisher Scientific, USA) of mechanically polished cross-sections of a pristine and an operated MEA. These images were used with an in-house developed, threshold-based segmentation algorithm to determine the anode thickness. It contains the Raman spectra (Alpha 300R Raman microscope, WITec/Oxford Instruments, Germany/UK and W Plan-Apochromat 63x / 1.0 M27, Zeiss, Germany) recorded at pristine and operated MEA anodes. Six spectra were recorded for each region of interest and averaged. Additionally, it contains the impedance data from alternating current scanning electrochemical microscopy (AC-SECM) mapping scans (M470, BioLogic, France) of a pristine and an operated MEA anode recorded with a 10 µm Pt UME in 100 mM sulfuric acid with a 10 mV, 1 MHz AC signal at open circuit voltage. Folder contents: - Fig2_Microscopic4PP: Microscopic four-point probe data. Read the respective _README.txt file within this folder for more information. - Fig3_CrossSection: SEM cross-section images. Read the respective _README.txt file within this folder for more information. - Fig4_Raman: Microscopic Raman spectroscopy data. Read the respective _README.txt file within this folder for more information. - Fig6_AC-SECM: Raw and normalized impedance data from AC-SECM. Read the respective _README.txt file within this folder for more information. (2026-03-16)