Unraveling the origin of electrochemical drift in membrane-based microfluidic electrochemical systems with gas-ionic liquid interface

Ionic liquid–integrated membrane contactors have been widely explored for applications in gas separation, CO₂ capture, and regeneration processes. Here, we investigate a previously unreported electrochemical signal instability/drift source in a gas-ionic liquid membrane contactor. The cassette comprises two microchannels separated by a hydrophobic polytetrafluoroethylene membrane: one channel confines the ionic liquid, while the other carries gas. The ionic liquid is in contact with gold interdigitated microelectrodes, facilitating real-time electrochemical measurements. A previously unexplored source of instability in these platforms was identified, manifesting as a progressive decrease in resistance during impedance measurements under no-gas-flow conditions (a 36 % decrease after 15 min for 1-ethyl-3-methylimidazolium acetate ionic liquid incorporated cassette). Systematic root-cause analysis revealed that this drift originates specifically in ionic liquid–based cassette, with no evidence of contributions from chemical interactions or membrane wetting, as confirmed through Raman/FTIR spectroscopy and contact angle measurements. Comparative studies across ionic liquids of varying properties showed that hydrophilic ionic liquids exhibited the most pronounced drift. Controlled-humidity experiments demonstrated that both the magnitude and rate of drift scale strongly with relative humidity, establishing that ambient water uptake, which causes a decrease in viscosity of ionic liquids, is the dominant driver for the drift observed in the impedance signal. Despite this humidity-induced interference, we demonstrate that the platform retains analyte-specific detection capabilities when using CO₂ as a model target analyte and CO₂-reactive ionic liquid 1-ethyl-3-methylimidazolium 2-cyanopyrrolide as the sensing liquid.