Search

Electrochemical sensors have widespread application in the automotive and energy industries-two major users of fossil fuels. The combustion of fossil fuels is a major source of air pollution and has been under increasing scrutiny by public and government organizations. This article discusses the current state-of-the-art solid-state sensor technology that is used in the automotive and energy industries for combustion control and details several promising technologies that are potentially useful to these two industries. This article discusses the various types of oxygen sensors that are currently in use and then describe the other electrochemical sensors that are being used to sense the presence of various combustible and/or toxic gases in the atmosphere.

Monitoring of methane leaks from natural gas (NG) sources during production and transport is vital to combating the threat of greenhouse gases to the global climate. An additive manufacturing route was developed for the printing of a CTE matched, low reactivity and low ionic conductivity magnesia stabilized zirconia (MSZ) substrate for production of a four-electrode (indium tin oxide, lanthanum strontium chromite, and Au sensing electrodes measured against a Pt negative electrode) same-side planar mixed potential electrochemical sensor (MPES) with porous 3 mol% YSZ as electrolyte. The MSZ substrate based MPES achieves a 40 ppm limit of detection for methane in a simulated natural gas mix. Additionally, a 20 times enhanced response in the ITO vs. Pt signal over sensors using yttria-stabilized zirconia (YSZ) substrates at 100 ppm CH 4 in simulated natural gas is observed. This research illustrates the importance of a CTE matched, low reactivity, low conductivity substrate for optimal performance of same-side planar MPES devices for NG leak detection while allowing for application of high temperature co-fired ceramic technologies. • Natural gas emissions account for 21 % of anthropogenic methane emissions. • Cheap and robust natural gas sensors are needed for continuous monitoring of the oil and gas infrastructure. • Sensitivity of a same-side planar mixed potential sensor is enhanced through the use of a low-ionic conductivity substrate. • Limit of detection for well-head natural gas of the sensor is 40 ppm of methane equivalent. [ABSTRACT FROM AUTHOR]

The development of on-board sensors for emissions monitoring is necessary for continuous monitoring of the performance of catalytic systems in automobiles. We have fabricated mixed potential electrochemical gas sensing devices with Pt, La 0.8 Sr 0.2 CrO 3 (LSCO), and Au/Pd alloy electrodes and a porous yttria-stabilized zirconia electrolyte. The three-electrode design takes advantage of the preferential selectivity of the Pt + Au/Pd and Pt + LSCO pairs towards different species of gases and has additional tunable selectivity achieved by applying a current bias to the latter pair. Voltages were recorded in single, binary, and ternary gas streams of NO, NO 2 , C 3 H 8 , and CO. We have trained artificial neural networks to examine the voltage output from sensors in biased and unbiased modes to both identify which single test gas or binary mixture of two test gases is present in a gas stream as well as extract concentration values. We are able to identify single and binary mixtures of these gases with accuracy of at least 98%. For determining concentration, the peak in the error distribution for binary mixtures was 5% and 80% of test data fell under <12% error. The sensor stability was also evaluated over the course of over 100 days and the ability to retrain ANNs with a small dataset was demonstrated. [ABSTRACT FROM AUTHOR]

Zirconia-based electrochemical sensors have revolutionized oxygen monitoring and combustion control. These robust, solid-state devices are found in virtually every internal combustion engine today providing feedback information for tight air to fuel ratio control thus minimizing unwanted emissions and improving engine efficiency. Variations on the sensor design and operational mode enable the measurement of nitrogen oxides to part per million levels, providing control information for exhaust after-treatment systems. Emerging designs include the development of "gas analyzers on a chip" capable of monitoring oxygen, carbon monoxide, nitrogen oxides, ammonia and hydrocarbons. • Zirconia based electrochemical gas sensors can detect wide variety of pollutants. • Potentiometric, amperometric, impedance-based, and pulsed polarization methods are reviewed. • Modeling of sensor behavior can predict sensor response. • Machine learning techniques can be applied for sensor signal decoding. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mixed-potential electrochemical sensors are used to analyze diesel engine exhaust. [•] These sensors exhibit cross-interference between ammonia and hydrocarbons. [•] An array of sensors is created by varying bias currents applied to a single device. [•] Bayesian modeling is employed to infer ammonia concentrations in mixtures with propylene. [•] Minimal data acquisition requirements are investigated. [ABSTRACT FROM AUTHOR]

Abstract: In this investigation, an electrochemical mixed potential type gas sensor was characterized using impedance spectroscopy. Specifically, the effect of operating temperature (435–610°C) on sensor response and response time was studied. Propylene was used as the analyte to test the ‘La0.8Sr0.2CrO3/YSZ/Pt’ sensor configuration. Two-electrode AC impedance measurement was performed with a frequency sweep from 13MHz down to 10mHz and excitation voltage of 10mV. For a fixed propylene concentration, the bulk and interfacial resistances was seen to decrease with increase in the sensor operating temperature. An Arrhenius behavior of the bulk and interfacial resistance was observed. The activation energy for O2 ion conduction and charge transfer was found to be 0.94eV and 1.54eV respectively. For a 150°C rise in operating temperature from 485 to 585°C, a 26-fold improvement in response rise time was observed while an 82% reduction in sensor response was recorded. It is postulated that the increase in operating temperature results in faster reaction kinetics, faster oxygen reduction and greater heterogeneous catalysis. [Copyright &y& Elsevier]

We have demonstrated a mixed potential, zirconia electrolyte-based sensor that utilizes dense, thin films of LaMnO3 and Y0.16Tb0.30Zr0.54O2⋅− as electrodes to generate an EMF that is proportional to the oxidizable gas species (CO, C3H6, and C3H8) concentration in a gas stream containing oxygen. The devices reported in this work were tested at 600 and 700 °C and in gas mixtures with O2 concentrations between 0.86 and 1.75%. An Au/LaMnO3/YSZ/Y0.16Tb0.30Zr0.54O2⋅−/Au device was tested for a total of 3000 h at 600 and 700 °C and was subject to periodic excursions to 10−10 atm PO2 to simulate reducing conditions. SEM analysis indicated that the aging effects measured in the device response over the course of this experiment may be linked to the sintering of the Au pad used for current collection on the metal oxide electrode. Three-terminal devices were fabricated so that the magnitude of the mixed potential generated from CO and C3H6 exposure on the Au/Y0.16Tb0.30Zr0.54O2⋅−, Pt/Y0.16Tb0.30Zr0.54O2⋅−, Au/LaMnO3, and Pt/LaMnO3 metal/metal oxide electrode combinations could be studied at 600 °C and in 1% O2. It was found that the catalytic properties of the Au or Pt used for current collection played a significant role in the generation of the mixed potential for both metal oxides tested. The combination of Pt on LaMnO3 gave an equilibrium response whereas a significant mixed potential was generated on both Au/Y0.16Tb0.30Zr0.54O2⋅− and Au/LaMnO3 electrodes at 600 °C. [Copyright &y& Elsevier]