Solvent Evaporation Rate as a Tool for Tuning the Performance of a Solid Polymer Electrolyte Gas Sensor

Solid polymer electrolytes show their potential to partially replace conventional electrolytes in electrochemical devices. The solvent evaporation rate represents one of many options for modifying the electrode-electrolyte interface by affecting the structural and electrical properties of polymer electrolytes used in batteries. This paper evaluates the effect of solvent evaporation during the preparation of solid polymer electrolytes on the overall performance of an amperometric gas sensor. A mixture of the polymer host, solvent and an ionic liquid was thermally treated under different evaporation rates to prepare four polymer electrolytes. A carbon nanotube-based working electrode deposited by spray-coating the polymer electrolyte layer allowed the preparation of the electrode-electrolyte interface with different morphologies, which were then investigated using scanning electron microscopy and Raman spectroscopy. All prepared sensors were exposed to nitrogen dioxide concentration of 0-10 ppm, and the current responses and their fluctuations were analyzed. Electrochemical impedance spectroscopy was used to describe the sensor with an equivalent electric circuit. Experimental results showed that a higher solvent evaporation rate leads to lower sensor sensitivity, affects associated parameters (such as the detection/quantification limit) and increases the limit of the maximum current flowing through the sensor, while the other properties (hysteresis, repeatability, response time, recovery time) change insignificantly

Effect of the Different Crystallinity of Ionic Liquid Based Solid Polymer Electrolyte on the Performance of Amperometric Gas Sensor

Solid polymer electrolytes (SPE) based on ionic liquid, poly-(vinylidene fluoride) and solvent N-methyl-pyrrolidone represent an effective component in electrochemical sensors. The advantage lies in their composition, which offers an opportunity to prepare SPE layers with a different porosity and microstructure. The study shows how the SPEs of different crystallinities affect the performance of an amperometric gas sensor from the point of view of current response (sensitivity), limit of detection and current fluctuations. The morphology of SPE has an impact not only on its conductivity but also on sensor sensitivity due to the morphology of the interface SPE/working electrode (WE)

Solvent Evaporation Rate as a Tool for Tuning the Performance of a Solid Polymer Electrolyte Gas Sensor

Solid polymer electrolytes show their potential to partially replace conventional electrolytes in electrochemical devices. The solvent evaporation rate represents one of many options for modifying the electrode-electrolyte interface by affecting the structural and electrical properties of polymer electrolytes used in batteries. This paper evaluates the effect of solvent evaporation during the preparation of solid polymer electrolytes on the overall performance of an amperometric gas sensor. A mixture of the polymer host, solvent and an ionic liquid was thermally treated under different evaporation rates to prepare four polymer electrolytes. A carbon nanotube-based working electrode deposited by spray-coating the polymer electrolyte layer allowed the preparation of the electrode-electrolyte interface with different morphologies, which were then investigated using scanning electron microscopy and Raman spectroscopy. All prepared sensors were exposed to nitrogen dioxide concentration of 0-10 ppm, and the current responses and their fluctuations were analyzed. Electrochemical impedance spectroscopy was used to describe the sensor with an equivalent electric circuit. Experimental results showed that a higher solvent evaporation rate leads to lower sensor sensitivity, affects associated parameters (such as the detection/quantification limit) and increases the limit of the maximum current flowing through the sensor, while the other properties (hysteresis, repeatability, response time, recovery time) change insignificantly

Electrochemical nitrogen dioxide sensor with solid polymer electrolyte based on ionic liquids

Tato disertační práce se zabývá perspektivními elektrochemickými senzory s polymerním elektrolytem založeným na organických materiálech pro detekci plynných látek. Úvodní část je věnována základním pojmům a vlastnostem senzorů pro detekci par a plynů. Následuje popis a zhodnocení současných principů detekce s ohledem na možnosti využití organických materiálů. Ve druhé části se práce podrobněji zaměřuje na perspektivní oblast elektrochemických senzorů. Pozornost je věnována základnímu rozdělení, elektrodovým topologiím, reakčním mechanismům a vyhodnocovacím obvodům. Teoretická část je zakončena charakterizací základních vlastností organických iontových kapalin nezbytných pro uplatnění v elektrochemických senzorových aplikacích. Experimentální část je věnována návrhu tříelektrodového ampérometrického senzoru s polymerním elektrolytem na bázi organické iontové kapaliny a popisu předpokládaných reakčních mechanismů. V této části jsou rovněž popsány technologické aspekty ovlivňující morfologii a strukturu jednotlivých senzorových vrstev. Hlavní část práce je zaměřena na studium vlivu geometrických parametrů pracovní elektrody na senzorovou odezvu. Výsledkem práce je návrh a realizace nového typu elektrochemického senzoru s polymerním elektrolytem pro detekci oxidu dusičitého.Katedra technologií a měřeníObhájenoThis thesis deals with the construction of electrochemical devices based on organic materials for the detection of gas phase substances. The introductory part is focused on the description of basic terms and sensor properties which are generally used in the field of gas sensors. Subsequently, basic detection principles are described with regard to the potential use of organic materials in particular types of sensors. The middle part is concentrated on my activities in the field of electrochemical sensors. The attention is paid to the description of basic sensor classification, electrode topologies, electronic evaluation circuits and reaction mechanisms. This part of the thesis also includes the description and characterization of properties of organic ionic liquids. The experimental part is dedicated to the design of three-electrode amperometric electrochemical sensor with a new type of polymeric electrolyte based on organic ionic liquid and to the description of reaction mechanisms occurring in the sensor. The main part is concentrated on the study of the influence of the geometry of a working electrode on the properties of the sensor response. Finally, the design and implementation of new type of the electrochemical sensor for nitrogen dioxide detection is presented

The Effect of the Orientation Towards Analyte Flow on Electrochemical Sensor Performance and Current Fluctuations

Analyte flow influences the performance of every gas sensor; thus, most of these sensors usually contain a diffusion barrier (layer, cover, inlet) that can prevent the negative impact of a sudden change of direction and/or the rate of analyte flow, as well as various unwanted impacts from the surrounding environment. However, several measurement techniques use the modulation of the flow rate to enhance sensor properties or to extract more information about the chemical processes that occur on a sensitive layer or a working electrode. The paper deals with the experimental study on how the analyte flow rate and the orientation of the electrochemical sensor towards the analyte flow direction influence sensor performance and current fluctuations. Experiments were carried out on a semi-planar, three-electrode topology that enabled a direct exposure of the working (sensing) electrode to the analyte without any artificial diffusion barrier. The sensor was tested within the flow rate range of 0.1–1 L/min and the orientation of the sensor towards the analyte flow direction was gradually set to the four angles 0°, 45°, 90° and 270° in the middle of the test chamber, while the sensor was also investigated in the standard position at the bottom of the chamber

Amperometric gas sensor in different orientation towards analyte flow at different flow rates and different concentrations

This dataset contains three sets of raw measurement data. The experiments were carried out on three−electrode sensor platform based on ceramic substrate with platinum counter and pseudoreference electrode. Solid polymer electrolyte (SPE) contained [C2mim][NTf2] ionic liquid, PVDF and NMP. Carbon working electrode (WE) was prepared by spray coating a mixture consisting of 300 mg glassy carbon spherical powder and 1 ml of ethanol. More information about the sensors can be found in Ref.[1-2]. All three sets contain the current responses of particular sensors in time domains at conditions specified below. Within the first set of experiments, sensors of three different working electrode areas (2.9, 8.5 and 22.4 mm2) were particularly exposed to the test profile that consisted of a stepwise increase in nitrogen dioxide concentration from 0 to 3 ppm (1 step equaled 1 ppm NO2) with subsequent three consecutive exposures to the same concentration of 3 ppm NO2 . The same test profile was applied to four different total flow rates of analyte (0.1, 0.5, 0.8 and 1 L/min) in order to observe the impact of the flow rate level on sensor parameters (sensitivity, response/recovery time, limit of detection, repeatability) for each size of the working electrode area. Each tested sensor was placed on the same position in the test chamber to be in the most identical conditions. The second set of experiments was carried out on the sensor with the largest WE surface area which was placed in the air and rotated for angles 0°, 45°, 90° and 270° in order to examine the effect of mutual orientation of the WE surface area and analyte flow direction on sensor parameters. The same test profiles of the first experimental sets were applied to a particular angle. The third set of experiments was provided under equilibrium conditions when the sensor with the largest WE surface area was being kept at the particular conditions (concentration and flow rate) for required amount of time to fulfil memorylessness of current fluctuations. These measurements of DC current and its fluctuation were done (i) for a range of concentration at the constant flow rate (1 L/min) and (ii) for a range of flow rates at a constant concentration (NO2 3 ppm). Firstly, a particular NO2 concentration (e.g. 1 ppm) was set with the particular total flow rate (e.g. 1 L/min). The DC current via sensor was monitored until it not changed its mean value for 100 seconds. After this (approximately 300 s from the beginning of the procedure), current fluctuations measurement (CH1) with DC current measurement (CH2) were carried out. Relative humidity and temperature were constant within all experiments (298 K and 40 %RH). The used measurement setups are described in detail in [2,3] as well as in manuscript "Effect of orientation to analyte flow on electrochemical sensor performance and current fluctuations" submitted to journal Sensors, where all evaluations are also described

Amperometric gas sensor in different orientation towards analyte flow at different flow rates and different concentrations

This dataset contains three sets of raw measurement data. The experiments were carried out on three−electrode sensor platform based on ceramic substrate with platinum counter and pseudoreference electrode. Solid polymer electrolyte (SPE) contained [C2mim][NTf2] ionic liquid, PVDF and NMP. Carbon working electrode (WE) was prepared by spray coating a mixture consisting of 300 mg glassy carbon spherical powder and 1 ml of ethanol. More information about the sensors can be found in Ref.[1-2]. All three sets contain the current responses of particular sensors in time domains at conditions specified below. Within the first set of experiments, sensors of three different working electrode areas (2.9, 8.5 and 22.4 mm2) were particularly exposed to the test profile that consisted of a stepwise increase in nitrogen dioxide concentration from 0 to 3 ppm (1 step equaled 1 ppm NO2) with subsequent three consecutive exposures to the same concentration of 3 ppm NO2 . The same test profile was applied to four different total flow rates of analyte (0.1, 0.5, 0.8 and 1 L/min) in order to observe the impact of the flow rate level on sensor parameters (sensitivity, response/recovery time, limit of detection, repeatability) for each size of the working electrode area. Each tested sensor was placed on the same position in the test chamber to be in the most identical conditions. The second set of experiments was carried out on the sensor with the largest WE surface area which was placed in the air and rotated for angles 0°, 45°, 90° and 270° in order to examine the effect of mutual orientation of the WE surface area and analyte flow direction on sensor parameters. The same test profiles of the first experimental sets were applied to a particular angle. The third set of experiments was provided under equilibrium conditions when the sensor with the largest WE surface area was being kept at the particular conditions (concentration and flow rate) for required amount of time to fulfil memorylessness of current fluctuations. These measurements of DC current and its fluctuation were done (i) for a range of concentration at the constant flow rate (1 L/min) and (ii) for a range of flow rates at a constant concentration (NO2 3 ppm). Firstly, a particular NO2 concentration (e.g. 1 ppm) was set with the particular total flow rate (e.g. 1 L/min). The DC current via sensor was monitored until it not changed its mean value for 100 seconds. After this (approximately 300 s from the beginning of the procedure), current fluctuations measurement (CH1) with DC current measurement (CH2) were carried out. Relative humidity and temperature were constant within all experiments (298 K and 40 %RH). The used measurement setups are described in detail in [2,3] as well as in manuscript "Effect of orientation to analyte flow on electrochemical sensor performance and current fluctuations" submitted to journal Sensors, where all evaluations are also described

The effect of the orientation towards analyte flow on electrochemical sensor performance and current fluctuations

Analyte flow influences the performance of every gas sensor; thus, most of these sensors usually contain a diffusion barrier (layer, cover, inlet) that can prevent the negative impact of a sudden change of direction and/or the rate of analyte flow, as well as various unwanted impacts from the surrounding environment. However, several measurement techniques use the modulation of the flow rate to enhance sensor properties or to extract more information about the chemical processes that occur on a sensitive layer or a working electrode. The paper deals with the experimental study on how the analyte flow rate and the orientation of the electrochemical sensor towards the analyte flow direction influence sensor performance and current fluctuations. Experiments were carried out on a semi-planar, three-electrode topology that enabled a direct exposure of the working (sensing) electrode to the analyte without any artificial diffusion barrier. The sensor was tested within the flow rate range of 0.1–1 L/min and the orientation of the sensor towards the analyte flow direction was gradually set to the four angles 0°, 45°, 90° and 270° in the middle of the test chamber, while the sensor was also investigated in the standard position at the bottom of the chamber

Effect of various flow rate on current fluctuations of amperometric gas sensors

The flow rate of analyte is a key parameter in the measurement system that influences response of gas sensors. The paper focuses on possibility of improved gas detection by modulation of analyte flow rate around amperometric sensors at equilibrium conditions by studying the direct current level and its fluctuations at selected concentration. To independently explore an impact of concentration and flow rate on spectral density of current fluctuations, all measurements were provided out under the same temperature, and each sample sensor was put to the same position at the test chamber to be under same fluidic condition. The experiments were carried out on the fully-printed amperometric NO2 sensor based on a semi-planar three electrode topology. The aims of this experimental study are two-fold: firstly, to show that spectral density of current fluctuations significantly changes in the level and the shape as flow rate increases at constant concentration of detected gas; and secondly, to demonstrate that evaluation of these fluctuations and DC component can be used to compensate the negative effect of flow rate on sensor responses. The spectral density of current fluctuations develops as several mechanisms related to fluctuation phenomena become dominant with increasing flow rate. Thus, signal-to-noise ratio of current response on detected gas decreases as flow rate increases, while the ratio is almost invariant to gas concentration