Single-Use Impedimetric Carbon Dioxide Sensor Using a Room-Temperature Ionic-Liquid-Based Gel Electrolyte

This study presents a concept for a facilely fabricated single-use electrochemical carbon dioxide (CO2) sensor. The sensor is based on a room-temperature ionic-liquid (RTIL)–polymer gel electrolyte in contact with indium tin oxide (ITO) electrodes on a glass substrate. Based on the impedance changes in the sensor when it interacts with CO2, it is shown that CO2 can be detected in air in the relevant concentration range of 500–2000 ppmv. Importantly, sensor evaluation was performed in humid air and ambient oxygen concentrations to closely approximate application-relevant operating conditions. It is demonstrated that the ITO electrodes are suitable for use in humidified gas mixtures containing oxygen. The combination with ionic liquid ensures that the ITO electrodes can be used continuously at the bias voltage of 2.7 V applied for CO2 detection. Moreover, it is determined that using impedance spectroscopy, sensitivity to CO2 can be distinguished from cross-sensitivity to humidity. A possible sensing mechanism explaining the changes in the electrical double layer (EDL) and charge transfer at the interface between the ionic-liquid electrolyte and ITO electrodes is proposed. It is envisioned that this sensor, with its small form factor, potential for low-cost fabrication, and possibility to integrate with low-power microelectronics, may be applied in single-use bioreactors (SUBs) and biomedical devices.