The X-ray photoelectron spectroscopy (XPS) measurements were performed using a K-alpha spectrometer (Thermo Fisher Scientific, East Grinstead, UK), applying a micro-focused, monochromatized Al Kα X-ray source (hν = 1486.6 eV) with 400 µm spot size. The metal electrodes (supported by the spacer) were placed on a sample holder using copper tape and transferred without exposure to air or moisture to an Ar-filled glovebox connected to the spectrometer. In case of localized surface charging, the binding energy shifts were minimized using the K-Alpha charge compensation system during analysis, using a electron flood gun as charge compensation with low energy-electrons of 8 eV kinetic energy and Ar ions with low energy. Data acquisition and processing was carried out using the Thermo Avantage software (Version 5.9922, Thermo Scientific). All spectra were referenced to the hydrocarbon C 1s peak (C-C, C-H) at 285.0 eV while the overall binding energy scale was controlled by means of the well-known photoelectron peaks of metallic Cu, Ag, and Au, respectively.