Spectroelectrochemical investigation of an electrogenerated graphitic oxide solid-electrolyte interphase

This study investigates electrogenerated graphitic oxides (EGO) on the surface of carbon optically transparent electrodes (C-OTEs) using a combined UV-vis spectroelectrochemical approach. By monitoring the π-π* aromatic carbon transition for reduced GO (270 nm) and GO (230 nm), we observe the growth of GO in KCl upon applying oxidizing potentials. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) are used to confirm sample composition and location of salt ions within the electrode. Formation of EGO stable enough to be observed by UV-vis is found to be unique to alkali chloride supporting electrolytes due to formation of a solid-electrolyte interphase (SEI) which incorporates the alkali cation to stabilize the negatively charged oxygen functional groups while the presence of chloride anion acts as a passivation agent that protects the electrode surface from dissolution. The spectroelectrochemical approach highlights the detection and study of EGO that cannot be detected by electrochemical measurements. Specifically, the amount of EGO observed by UV-vis scales with increasing cation size (Li(+), Na(+), K(+)) despite all the cations showing identical electrochemical response.