Direct Probing the Electrical Double Layer at Graphite/Nafion Interface via Depth Profiling APXPS

Understanding the electrical double layer (EDL) is fundamental for enhancing the efficiency, capacity, and stability of electrochemical systems. The EDL at the electrode/polyelectrolyte interface exhibits significantly different properties with a more complex structure compared to liquid electrolyte systems. Characterizing this intricate interface experimentally remains a major challenge. In this study, we directly observed the potential distribution at the electrode–polyelectrolyte interface using a delicate in situ electrochemical cell coupled with ambient pressure X-ray photoelectron spectroscopy (APXPS) at various probing depths. The electrode/polyelectrolyte (graphite/Nafion) interface was successfully constructed, and the APXPS measurements were performed under nonpolarizing conditions. The binding energy shift of the F 1s photoelectron with applied bias provided the information on potential distribution. Experimental results, simulated by the typical exponential and linear potential distribution models, indicate the formation of a 1–3 nm EDL at the electrode/polyelectrolyte interface. This work provides methodological guidance for in situ X-ray photoelectron spectroscopic studies and offers valuable fundamental data for electrochemical research.