Considerations of Thermodynamics and Kinetics for the Effects of Relative Humidity on the Electrolyte in Electrochemical Toxic Gas Sensors

Abstract

In this paper, the physical chemistry of the absorption and desorption of water vapor for electrochemical gas sensors with commonly used sulfuric acid as the electrolyte is investigated. Electrochemical gas sensors are being increasingly used for monitoring toxic gases in the environment, and they are, in principle, simple devices, but in practice, their operation is complex. In particular, changes in atmospheric humidity and temperature can have significant effects on the sensor output. A model has been developed for the calculation of sensor weight changes as humidity varies, which are in good agreement with the analysis of experimental results. This then allows for the calculation of the rather more important electrolyte volume variations. Changes in acid molarity and physical characteristics of the electrolyte have also been determined. The effects on working electrode (WE) electrocatalytic activity are discussed, and potential problems with sensors for environmental monitoring are highlighted. In particular, changes in the electroactive area of the WE and, consequently, of the sensor output, and flooding of the WE catalyst aggregates which can lead to problems with electrolyte leakage from sensors are considered.

Laboratory Performance Evaluation of a Low-Cost Electrochemical Formaldehyde Sensor

“…Second, most of the studies focused on formaldehyde concentration ranges that were higher than typical indoor (~17 ppb) [31] or ambient (~3 ppb) [32] levels in the United States. In addition, previous studies have reported the influence of temperature and RH on the performance of electrochemical sensors [25,[33][34][35][36]. However, some studies report contradictory results regarding the effect of RH [37], and many studies only report qualitative results [30,[38][39][40].…”

An Improved Humidity Sensor with GO-Mn-Doped ZnO Nanocomposite and Dimensional Orchestration of Comb Electrode for Effective Bulk Manufacturing

“…In general, two-dimensional (2D) materials are recognized as promising sensors with advantages such as high surface area and surface functionality. Ultra-thin materials such as palladium nanosheets (PdNS) and MXene (2D transition metal carbides, nitrides, and carbon nitride family) are trending nanocomposite materials for many types of gas and humidity sensing [ 15 , 16 , 17 ]. However, there are limitations to the mass production of nanomaterials with high surface area as well as uniform quality.…”

“…By reducing the humidity, the distance between layers is reduced and the resistance is restored. Thus, the main mechanism in Mxene is the change of layer spacing [ 17 ]. Hence, maintaining the layer-by-layer spacing in Mxene without water intercalation at high humidity levels is a major limitation.…”

Detection of PPB-Level H2S Concentrations in Exhaled Breath Using Au Nanosheet Sensors with Small Variability, High Selectivity, and Long-Term Stability

“…18,19 Electrochemical sensors are also commercialized, but they are less sensitive than MOS gas sensors and susceptible to temperature and humidity changes. 20,21 Other types of H 2 S sensors have been proposed, such as colorimetric sensors, 22 surface acoustic wave gas sensors, 23 and sensors made using conductive materials (e.g., graphenes and polymers). 24,25 However, these sensors are hindered by challenges related to selectivity or ppb-level detection.…”

“…Various types of H 2 S sensors have been proposed and used to address these requirements. , The most common H 2 S sensors are based on semiconducting metal oxides; they have low costs and are operated rapidly and easily. − However, metal oxide semiconductor (MOS) gas sensors typically have poor selectivity because they react to all reducing or oxidizing gases. , Electrochemical sensors are also commercialized, but they are less sensitive than MOS gas sensors and susceptible to temperature and humidity changes. , Other types of H 2 S sensors have been proposed, such as colorimetric sensors, surface acoustic wave gas sensors, and sensors made using conductive materials (e.g., graphenes and polymers). , However, these sensors are hindered by challenges related to selectivity or ppb-level detection. Decorating conducting materials, such as MOS, , graphenes, and carbon nanotubes (CNTs), with metal and MOS nanoparticles (NPs) has recently been used to achieve sensor selectivity and ppb-level detection.…”