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Electrochemical sensor for measurement of volatile organic compounds in air

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Air pollution is one of the main problems of many urban areas all over the world. Volatile organic compounds (VOCs) belong to a group of the most hazardous pollutants emitted to the atmosphere. They are known as not only the precursors of photochemical oxidation, but also as the carcinogenic substances (benzene, 1,3-butadiene, styrene). Upon presence of nitrogen oxides the VOCs form ozone, which is the main component of a photochemical smog. Moreover, some VOCs contribute to a progress of the greenhouse effect (halide derivatives of hydrocarbons) and to a formation of the secondary organic aerosols (toluene, xylene, ethylbenzene) [1]. Volatile organic compounds originate from both the processes connected with anthropogenic activity as well as from the natural sources [2]. On a global scale the natural emission of the VOCs is of fundamental importance. Natural sources release over ten times more VOCs than the anthropogenic ones. The main source of the natural emission is vegetation. In more densely populated regions a contribution of the natural emission decreases, while the anthropogenic emission increases. In Europe the biogenic sources are responsible for only 57% of the total VOCs output. According to the EU directive [3], it is required to monitor the ozone precursors. The aim is to analyze the trends of changes of the precursor’s concentration in order to evaluate an effectiveness of the strategies oriented towards reduction of their emission, to supervise the consistence of emission record keeping and to classify the sources of emission. An additional goal is better understanding of the processes of ozone formation, ozone precursors transport and spreading as well as application of the photochemical models. The measurements employing sensors can be a valuable source of qualitative and quantitative information concerning pollution due to the VOCs. Chemical sensors can be an alternative to the expensive, sophistic[...]

The influence of electrocatalytic toxic gas sensor construction on its performance

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In recent years, a new and particularly interesting group of electrochemical gas sensors, which employ cyclic voltammetry technique to solid electrolytes, has been proposed and intensively developed [1-7]. Cyclic voltammetry is a method widely used in liquid electrochemistry for determination of chemical species concentration. The method is based on oxidation and reduction of chemical specie[...]

Zastosowanie metody różnic skończonych do symulacji czujników elektrokatalitycznych

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Czujniki elektrokatalityczne zbudowane na bazie elektrolitów stałych stanowią stosunkowo nowy typ czujników elektrochemicznych. Czujniki te pobudzane są okresowym sygnałem trójkątnym przy jednoczesnym pomiarze odpowiedzi prądowej czujnika (woltamperometria cykliczna). Jak pokazały nasze wcześniejsze badania [1, 2], w obecności NO2, So2 i Co2 w otoczeniu czujników zbudowanych na bazie wybrany[...]

Energia aktywacji i mechanizm przewodzenia w polimerowych czujnikach wilgotności z polietylenoiminy

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Oddziaływania pomiędzy cząsteczkami pary wodnej z filmem polimeru w dużym stopniu zależą od temperatury. Mechanizm procesów sorpcyjnych może być opisywany w oparciu o analizę wartości funkcji termodynamicznych. Zmiana entalpii adsorpcji H jest funkcją stopnia związania adsorbatu z polimerem, a zmiana energii swobodnej G określa tendencje systemu gaz/polimer do oddziaływań wzaje[...]

Electrocatalytic gas sensor with non-triangular excitation

  In recent years, solid state ion conducting materials have been intensively developed. These materials have a relatively high ionic conductivity based on a single predominantly conducting anion or cation species and have negligibly small electronic conductivity. Typically, useful solid electrolytes exhibit ionic conductivities from 10-1 to 10-5 S/cm at room temperature. Solid state electrolytes exhibit a potential for application in a variety of solid state electrochemical devices such as fuel cells, batteries, membranes, pumps and sensors [1]. Gas sensors are one of the most critical and rapidly growing areas in modern solid electrolyte technology. Solid state gas sensors are cost effective, small, rugged and reliable [2, 3]. Usually electrochemical solid state sensors operate in either potentiometric or amperometric mode [4, 5]. A lack of selectivity is sometimes a shortcoming of such sensors. It seems that improvements of selectivity can be obtained in case of the electrocatalytic sensors. Their working principle is based on acquisition of an electric current, while voltage ramp is applied to the sensor. The current-voltage response depends in a unique way on the type and concentration of ambient gas. In case of electrocatalytic gas sensors usually a linearly changing voltage excitation signal of symmetrical triangular shape in range from 5 to -5 V is applied to the sensors terminals [6]. The voltage sweep rate is adjusted to 50 mV/s. This, originated from liquid electrochemistry, method has some shortcomings. In typical conditions, one measuring cycle takes up to 7 min. Stable response is obtained most often after 2 or more cycles, thus extending measuring time even further. Long measuring time can limit application of electrocatalytic sensors in environments with fast gas concentration changes. In th[...]

Electrocatalytic sensor based on Nasicon with auxiliary layer

  In recent years electrochemical gas sensors based on solid state electrolytes have been intensively investigated. They are relatively easy to fabricate, simple in use and quite durable. Nasicon (Na Super Ionic Conductor) is one of the most promising materials, which have been used in construction of gas sensors. Sensors based on Nasicon are used for detecting of different gases including carbon oxides [1, 2], nitrogen oxides [3-6] and sulfur dioxide [7]. Most of these devices operate in potentiometric or amperometric mode. In case of some sensor constructions, besides electrolyte and metal electrodes, additional layers are applied. In some cases such phase is required to obtain sensitivity to specific gas or to shift operating temperature to more preferred one [7]. In other cases sensor properties such as selectivity or stability are improved. Auxiliary phase usually forms extra interface between measured gaseous compound and electrolyte or electrodes. For example, in case of amperometric sensors, it was noticed, that presence of auxiliary layer on surface of sensing electrode can increase the number of reaction sites thus improving sensor sensitivity [5]. Auxiliary layer may also be used to create a diffusion barrier. In case of the potentiometric or amperometric nitrogen oxides sensors based[...]

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