Electrochemically controlled solid liquid interfaces probed with lab-based X-ray photoelectron spectroscopy

A micro-electrochemical cell is sealed with 2–5 layers of graphene to monitor the changing oxidation state of Cu nanoparticles (NPs) with X-ray photoelectron spectroscopy (XPS) in a mildly alkaline aqueous solution under electrochemical control. The main role of graphene is to ensure an abrupt change between the liquid and vacuum environments, where the latter is required for conducting XPS experiments. Decent transparency to the generated photoelectrons with a kinetic energy of few hundred eV is another requirement that graphene fulfils for performing such experiments. Graphene also acts as an electrically conducting support material for Cu NPs, ensuring that a bias can be applied to them. The proof-of-concept measurements presented in this work show that relatively lower flux X-ray sources, such as those with Al-Kα emission that are commonly used in laboratories, are sufficient for probing the solid–liquid interfaces with this approach.