Shift in core level binding energy in double-layer species on potentiostatically emersed electrodes

Abstract

The initiation of this preliminary study reflected an interest in determining the chemical and compositional properties of the electrochemical double layer in its ex situ state using surface analytical techniques. Specifically, X-ray photoelectron spectroscopy was used to investigate the surfaces of electrodes that had been removed from aqueous electrolyte. Two parameters were monitored: the core level binding energy and the surface concentration of emersed species.Photoelectron spectra, taken from gold film electrodes emersed at various potentials from aqueous cesium sulfate electrolyte, revealed a shift in cesium core level binding energy with electrochemically imposed potential. The shift arises as a consequence of the presence of the double layer (ions and dipoles) at the surface which is stable to removal from the electrochemical environment, transfer and ultrahigh vacuum conditions. The electrochemical potential applied before emersion of the electrodes caused a systematic shift in the Cs3d52 binding energy over a range of about 0.8 V commensurate with the imposed change in emersion potential; this shift may be called an “electrochemically induced binding energy shift”. No systematic shift was observed in the substrate spectra over the potential range studied.Splitting of the 3d5232 photopeaks (of about 1.5 eV) was observed when electrodes were cycled electrochemically to 1.8 V and emersed at potentials lower than 0.5 V. A potential-induced shift was observed for the lower binding energy component peak. The binding energy of the other photopeak remained unchanged over the potential range. Data and results are discussed within the framework of physical and chemical aspects of the electrolyte-electrode interface.