Fast Responding Amperometric CO2 Microsensor with Ionic Liquid-Aprotic Solvent Electrolytes

Knowledge about the microscale distribution of CO2 is essential in many environmental and technical settings, and electrochemical CO2 sensing may be optimized to yield such information. The performance of a Clark-type CO2 sensor was greatly improved by adding 20% dimethylformamide (DMF) to the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide (EMIM-DCA) previously used as an electrolyte. The addition of DMF resulted in a much faster response to increasing (95% response of about 100 s) or decreasing CO2 concentration, a negligible interference from low concentrations of N2O, and a signal temperature dependence similar to that of O-2 microsensors. The use of 80% EMIM-DCA/20% DMF as an electrolyte leads to CO2 reduction at -0.72 V (vs standard hydrogen electrode), reducing the overpotential by 0.2 V as compared to the use of 100% EMIM-DCA. The CO2 microsensor has a calculated limit of detection of 0.5 Pa CO2, and sensors optimized for high sensitivity exhibited a linear response within the range of 0-4.6 kPa (0-1.7 mM) CO2. A set of four sensors exhibited no noticeable change of zero current and CO2 sensitivity during 4 months of continuous polarization.