Impact of mass transport on meniscus electrochemistry determined by time-resolved operando X-ray photoelectron spectroscopy†

Ambient pressure X-ray photoelectron spectroscopy (APXPS) combined with the dip-and-pull method can be used for operando studies of electrochemical systems. A complete coupling between the spectroscopic and the electrochemical measurements is generally challenging due to an inherent difference between the meniscus and the bulk electrolyte – the mass transport. This work investigates meniscus mass transport and its effect on the meniscus electrochemical processes by simultaneously conducting time-resolved APXPS and chronoamperometry for two types of electrochemical processes: capacitive and faradaic. Additionally, experiments are complemented with simulations based on a purposefully constructed transmission line model. In the investigated system, based on a gold electrode and carbonate electrolyte, the meniscus resistance is shown to be over 1000 times larger than the bulk electrolyte resistance. Consequently, during faradaic processes, considerable iR drop in the meniscus results in two to three orders of magnitude slower rate of charge transfer in the meniscus than in the bulk electrolyte. Using the acquired understanding of the meniscus mass transport, we suggest an experimental practice to quantify the iR drop and propose possible remedies for experiments where any impact of the iR drop must be avoided.