Characterization of the Ionic Liquid/Electrode Interfacial Relaxation Processes Under Potential Polarization for Ionic Liquid Amperometric Gas Sensor Method Development

Abstract

Electrochemical amperometric sensors require a constant or varying potential at the working electrode that drives redox reactions of the analyte for detection. The interfacial redox reaction(s) can result in the formation of new chemical products that could change the initial condition of the electrode/electrolyte interface. If the products are not inert and/or cannot be removed from the system such that the initial condition of the electrode/electrolyte interface cannot be restored, the sensor signal baseline would consequently drift, which is problematic for the continuous and real-time sensors. By setting the electrode potential with the periodical ON-OFF mode, electrolysis can be forestalled during the off mode which can minimize the sensor signal baseline drift and reduce the power consumption of the sensor. However, it is known that the relaxation of the structure in the electrical double layer at the ionic liquid/electrode interface to the steps of the electrode potential is slow. This work characterized the electrode/electrolyte interfacial relaxation process of an ionic liquid based electrochemical gas (IL-EG) sensor by performing multiple potential step experiments in which the potential is stepped from an open circuit potential (OCP) to the amperometric sensing potential at various frequencies with different time periods. Our results showed that by shortening the sensing period as well as extending the idle period (i.e., enlarge the ratio of idle period versus sensing period) of the potential step experiments, the electrode/electrolyte interface is prone to relax to its original state, and thus reduces the baseline drift. Additionally, the high viscosity of the ionic liquids is beneficial for electrochemical regeneration via the implementation of a conditioning step at zero volts at the electrode/electrolyte. By setting the working electrode at zero volts instead of OCP, our results showed that it could further minimize the baseline drift, enhance the sensing signal stability, and extend the functioning lifetime of a continuous IL-EG oxygen sensor.

Electrical Double Layer Structure in Ionic Liquids and Its Importance for Supercapacitor, Battery, Sensing, and Lubrication Applications

“…Lin et al characterized the IL/electrode interfacial relaxation processes in the context of amperometric gas sensors for oxygen detection. 80 Because of the potential dependency of the interfacial EDL structure, variations in interfacial capacitance were found to occur, and these resulted in difficulties for analyte adsorption at the electrode. Different concentrations of the analyte in the EDL give a change in the response signal.…”

“…The authors suggested establishing a conditioning potential of 0 V before each measurement for oxygen detection to ensure a consistent and stable IL/electrode interface. 80 Zhan et al showed that the more densely packed EDL of [C 2 mim][TFSI] in an electric field shows a higher capacitance compared to the less densely packed EDL of [C 4 mpyrr][TFSI]. 81 They showed that changes in temperature can alter the behavior of the EDL in the presence of an analyte, such as carbon dioxide (CO 2 ).…”

Molecular Imaging of Viologen Adlayers and In Situ Monitoring Structural Transformations at Electrode–Electrolyte Interfaces

“…Design and control of functional molecular assembly on a surface into an ordered two-dimensional (2D) supramolecular architecture are essential because the ordered molecular layers, or adlayers, form the basis of molecular devices, − metal–organic frameworks (MOFs), sensors, − surface templates, and liquid crystal materials . Organic adlayers are generally generated via molecular self-assembly on well-defined surfaces such as a single crystal substrate, − highly oriented pyrolytic graphite (HOPG), , mica, − and atomically flat metal films. , The interplay of molecule–substrate and molecule–molecule interactions allows the creation of a variety of nanoscale architectures.…”

The Influence of Hydrogen on the Indications of the Electrochemical Carbon Monoxide Sensors

“…It was ascertained that in the cases of measurements for tests carried out at higher concentrations of H 2 in relation to CO, a sensor with an additional electrode is significantly better (more accurate) than a sensor without such an electrode. Differences at the significance level p = 0.01 for measurements made in the CO:H 2 mixture at a ratio of 1:3 were ascertained.Sustainability 2020, 12, 14 2 of 11 membranes [2,9,10]. The electrodes can be made of various materials.…”

“…Sustainability 2020, 12, 14 2 of 11 membranes [2,9,10]. The electrodes can be made of various materials.…”