Search

In the mixed-potential gas sensor, the electrode type, particle size, microstructural morphology, as well as the interface state between the oxide-sensitive electrode and the solid electrolyte, are the key factors for determining the magnitude of the mixed potential. NiO-based material with the addition of Y 2 O 3 -stabilized ZrO 2 (YSZ) particles is considered as one of the promising sensitive electrode materials for preparing the mixed-potential NO x sensors due to its excellent gas sensitivity. In this paper, the preparation technology of NiO-sensitive electrodes is developed and optimized for improving NO x (NO and NO 2) gas-sensitivity properties of the NO x sensors. The experimental results show that the addition of YSZ can effectively improve the agglomeration morphology of NiO particles in the NO x -YSZ-based electrode material during high temperature sintering (i.e. 1200 °C) and enhance the bonding strength with the solid electrolyte. The sensor which was prepared by using the developed NO x -YSZ-based electrode material with the YSZ addition of 20 wt% has the most sensitive response characteristic to NO gas, and its response potential value increases with NO gas concentration. Elevating electrode sintering temperature can increase the size of NiO particles and shorten the length of the three-phase boundary (TPB) in the sensitive electrode. The average length of TPB is the longest in the sensitive electrode sintered at 1000 °C which corresponds to the best sensitive response to NO gas. The sensitive electrode's thickness also affects the NO response sensitivity, and the sensor with an electrode thickness of 14 μm has the most NO response sensitivity. In addition, the NO/NO 2 gas mixture test results indicate that the current developed sensor is more sensitive to NO 2 gas than that of NO gas. [ABSTRACT FROM AUTHOR]

A vehicle-mounted measurement system (SEMS) which included sensors such as NOx sensor and NH3 sensor directly inserted into the exhaust pipe was installed on a heavy-duty diesel vehicle that complies with the 2016 exhaust gas regulations. Then, we acquired the data in the transportation business driving. Based on these data, the NOx purification rate, space velocity, etc. were analyzed as the parameters to investigate the NOx purification performance of the Cu-based zeolite SCR catalyst. As an example, during DPF regeneration, the purification rate gradually decreased to about 40% due to the oxidation of NH3 in the process of temperature rise. [ABSTRACT FROM AUTHOR]

Modern diesel engines are commonly equipped with NOx sensors for precise and efficient selective catalytic reduction (SCR) reductant injection control, but due to the limitations of operating characteristics and environmental conditions, the output signal of NOx sensors may show abnormalities such as drift, deviation, or even distortion. Therefore, the evaluation and adjustment of the NOx sensor signal is essential to achieve intelligent control of the engine SCR system. In this study, an engine NOx calculation model is designed using deep neural network (DNN) to predict the upstream NOx emission concentration of engine SCR and provide reference values for sensor fault diagnosis, evaluate the sensor fault status by calculating the relative integration error index (IE), and reconstruct the sensor signal using the model prediction signal after the fault is confirmed. In addition, this paper uses the firefly algorithm (FA) to find the appropriate diagnostic threshold (IEthre) and integration period (T) to meet the requirements of diagnosis response speed. Finally, based on the data collected from World Harmonized Transient Cycle (WHTC) bench test of a commercial high-pressure common rail diesel engine, the IEthre = 12.76% and the T = 7.57 s. The root mean square error (RSME) of the NOx concentration signal predicted by the engine NOx calculation model was 37.35 ppm, and the normalized cumulative NOx emission was 98% of the actual signal. The performance of the designed algorithm was tested using the synthesized bias fault and drift fault signals. The sensor signal RSME was reduced from 108.46 to 29.66 ppm for the bias fault, and from 106.92 to 31.30 ppm for the drift fault. [ABSTRACT FROM AUTHOR]

Electrochemical NOx sensors based on yttria-stabilized zirconia (YSZ) provide a reliable onboard way to control NOx emissions from glass-melting furnaces. The main limitation is the poisoning of this sensor by sulfur oxides (SOx) contained in the stream. To overcome this drawback, an "SO2 trap" with high SOx storage capacity and low affinity to NOx is required. Two CuO/BaO/SBA-15 traps with the same CuO loading (6.5 wt.%) and different BaO loadings (5 and 24.5 wt.%, respectively) were synthetized, thoroughly characterized and evaluated as SO2 traps. The results show that the 6.5%CuO/5%BaO/SBA-15 trap displays the highest SO2 adsorption capacity and can fully adsorb SO2 for a specific period of time, while additionally displaying a very low NO adsorption capacity. A suitable quantity of this material located upstream of the sensor could provide total protection of the NOx sensor against sulfur poisoning in glass-furnace exhausts. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO2) sensors utilising graft copolymers bearing poly(3-hexylthiophene) chains have been developed and investigated in terms of their operation parameters using different carrier gases (N2 or air) and in either dark conditions or with ultraviolet (UV) irradiation. Interestingly, sensor performance improved upon transition from N2 to air, with the inverse being true for most NO2 sensors. UV irradiation both improved sensor dynamics and stabilised the sensor electrical baseline, allowing sensors based on SilPEG to fulfil the requirements of sensing solutions used in industry (below 10% baseline drift after sensors reach saturation) and making them promising candidates for further development and applications. Based on conducted multi-variate experiments, an initial mechanism underlying the interplay of exposure to oxygen (present in air) and UV irradiation was postulated. [ABSTRACT FROM AUTHOR]

Electrochemical NOx sensors based on yttria-stabilized zirconia (YSZ) provide a reliable onboard way to control NOx emissions from glass-melting furnaces. The main limitation is the poisoning of this sensor by sulfur oxides (SOx) contained in the stream. To overcome this drawback, an “SO2 trap” with high SOx storage capacity and low affinity to NOx is required. Two CuO/BaO/SBA-15 traps with the same CuO loading (6.5 wt.%) and different BaO loadings (5 and 24.5 wt.%, respectively) were synthetized, thoroughly characterized and evaluated as SO2 traps. The results show that the 6.5%CuO/5%BaO/SBA-15 trap displays the highest SO2 adsorption capacity and can fully adsorb SO2 for a specific period of time, while additionally displaying a very low NO adsorption capacity. A suitable quantity of this material located upstream of the sensor could provide total protection of the NOx sensor against sulfur poisoning in glass-furnace exhausts.

Composites of functionalized single walled carbon nanotubes (SWCNTs) and gold nanoparticles (Au NPs) of ≈15 nm diameter were drop-cast on a printed circuit board (PCB) substrate equipped with interdigitated electrodes to make a hybrid thin film. Addition of Au NPs decorated the surface of SWCNTs networked films and acted as catalysts which resulted into an enhanced sensitivity and low ppb concentration detection limit. The compositions of the film were characterized by scanning electron microscope (SEM). SWCNTs clusters were loaded with various amount of Au NPs ranging from 1–10% (by weight) and their effect on Nitric oxide (NO) sensitivity was studied and optimized. Further, the optimized composite films were tested in both air and nitrogen environments and as well as over a wide relative humidity range (0–97%). Sensors were also tested for the selectivity by exposing to various gases such as nitrous oxide, ammonia, carbon monoxide, sulfur dioxide and acetone. Sensitivity to NO was found much higher than the other tested gases. The advantage of this sensor is that it is sensitive to NO at low ppb level (10 ppb) with estimated response time within 10 s and recovery time around 1 min, and has excellent reproducibility from sensor to sensor and works within the wide range of relative humidity (0–97%). [ABSTRACT FROM AUTHOR]

[Display omitted] Herein, we adopted a new paradigm for developing a high-performance gas sensor by leveraging the mixed spinel ZnFe 2 O 4 structure (mZFO) to enhance the adsorption of NO x molecules. Material characterization reveals the formation of the mZFO due to the cation inversion in lattice sites. The estimated value of the inversion degree is observed to shift from 0.78 to 0.39 with an increase in the calcination temperature. The mZFO nanoparticles calcined at 500 °C show exceptional sensing performance due to their suitable grain size (∼2 times Debye length), neck diameter, and surface area. The sensing studies conducted at various NO x concentrations indicate that the sensor can detect ppb level of NO x with a detection limit of about 9 ppb at room temperature. The detailed sensing mechanism is elucidated based on the density functional theory calculations (DFT) and Bader charge analysis. The outstanding sensor performance is attributed to the formation of a mixed spinel structure, wherein the adsorption energy of NO x (∼-0.6 eV) in the presence of surface adsorbed oxygen is higher than that of the normal spinel structure (∼-0.1 eV). Furthermore, the sensor exhibited a fast response and recovery times (7 and 92 s at 800 ppb NO 2), excellent stability, and selectivity. The practical suitability of the mZFO sensor was studied by analyzing the vehicle exhaust emissions. We strongly believe this work would pave a novel approach to developing a high-potential gas sensor by modifying the cation distributions in the spinel ferrites. [ABSTRACT FROM AUTHOR]

The (Pt/YSZ)/YSZ sensor unit is the basic component of the NOx sensor, which can detect the emission of nitrogen oxides in exhaust fumes and optimize the fuel combustion process. In this work, the effect of sintering temperature on adhesion property and electrochemical activity of Pt/YSZ electrode was investigated. Pt/YSZ electrodes were prepared at different sintering temperatures. The microstructure of the Pt/YSZ electrodes, as well as the interface between Pt/YSZ electrode and YSZ electrolyte, were observed by SEM. Chronoamperometry, linear scan voltammetry, and AC impedance were tested by the electrochemical workstation. The results show that increasing the sintering temperature (≤1500 °C) helped to improve adhesion property and electrochemical activity of the Pt/YSZ electrode, which benefited from the formation of the porous structure of the Pt/YSZ electrode. For the (Pt/YSZ) electrode/YSZ electrolyte system, O2− in YSZ is converted into chemisorbed O2 on Pt/YSZ, which is desorbed into the gas phase in the form of molecular oxygen; this process could be the rate-controlling step of the anodic reaction. Increasing the sintering temperature (≤1500 °C) could reduce the reaction activation energy of the Pt/YSZ electrode. The activation energy reaches the minimum value (1.02 eV) when the sintering temperature is 1500 °C. [ABSTRACT FROM AUTHOR]

Illegal manipulation (i.e., tampering) of vehicles is a severe problem because vehicle emissions increase orders of magnitude and significantly impact the environment and human health. This study measured the emissions before and after representative approaches of tampering of two Euro 6 Diesel light-duty passenger cars, two Euro VI Diesel heavy-duty trucks, and a Stage IV Diesel non-road mobile machinery (NRMM) agricultural tractor. With tampering of the selective catalytic reduction (SCR) for NOx, the NOx emissions increased by more than one order of magnitude exceeding 1000 mg/km (or mg/kWh) for all vehicles, reaching older Euro or even pre-Euro levels. The tampering of the NOx sensor resulted in relatively low NOx increases, but significant ammonia (NH3) slip. The particle number emissions increased three to four orders of magnitude, reaching 6–10 × 1012 #/km for the passenger car (one order of magnitude higher than the current regulation limit). The tampered passenger car's NOx and particle number emissions were one order of magnitude higher even compared to the emissions during a regeneration event. This study confirmed that (i) tampering with the help of an expert technician is still possible, even for vehicles complying with the current Euro standards, although this is not allowed by the regulation; (ii) tampering results in extreme increases in emissions. [ABSTRACT FROM AUTHOR]

The zirconia solid electrolyte SOFC (solid oxide fuel cell) has the characteristics of oxygen ion conduction function, high-temperature resistance, thermoelectric coupling effect, etc. A NOx sensor based on zirconia solid electrolyte has common characteristics and problems with the SOFC in principle and application. The research objective of this paper is to solve the application problems of smart NOx sensors in diesel vehicles or gasoline vehicles. Improvements in the application performance of the NOx sensor can help the NOx emissions of gasoline vehicles or diesel vehicles better meet the requirements of emission regulations. The smart NOx sensor is a regulatory sensor required by vehicles for China's Phase VI Vehicle Exhaust Emission Regulations or Euro Phase VI Vehicle Exhaust Emission Regulations. The smart NOx sensor is a key sensor device for improving fuel efficiency and reducing pollution. Moreover, its measurement performance includes dynamic immunity to interference, response speed, and measurement accuracy, which are key factors affecting vehicle emissions. This paper focuses on the impact of the physical structure, electrode characteristics, and control strategies of the sensor on its performance during the application. An excellent sensor structure, electrode structure, and control strategy are given based on application analysis and experimental testing. The results show that the application performance of this smart NOx sensor meets the requirements of exhaust aftertreatment systems. [ABSTRACT FROM AUTHOR]

The aim of this study is to eliminate the impact of inconsistency in probe production through artificial neural network model, to reduce the defect rate in the production process of NOx sensors. Different from existing research, the voltage and current signals inside the sensor probe were the inputs of the artificial neural network model. The parameters of the artificial neural network model were optimized through the data obtained under transient engine operation conditions, so as to ensure that the model works in real time and with high accuracy within the NOx sensor controller. It was found that the current of the main pump and the current of the measuring pump had high impact on the NOx signal, with a contribution rate of more than 80%. The voltage of the auxiliary pump in the sensor probe had the lowest influence on the NOx signal, with a contribution rate of less than 2.36%. Experimentally, the results showed that the artificial neural network model can eliminate the adverse effects caused by hardware differences of the NOx probes. The accuracy of the probes was improved from 0.7048 to 0.9748. An increase of 38.3% on average in dynamic conditions. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO2) sensors utilising graft copolymers bearing poly(3-hexylthiophene) chains have been developed and investigated in terms of their operation parameters using different carrier gases (N2 or air) and in either dark conditions or with ultraviolet (UV) irradiation. Interestingly, sensor performance improved upon transition from N2 to air, with the inverse being true for most NO2 sensors. UV irradiation both improved sensor dynamics and stabilised the sensor electrical baseline, allowing sensors based on SilPEG to fulfil the requirements of sensing solutions used in industry (below 10% baseline drift after sensors reach saturation) and making them promising candidates for further development and applications. Based on conducted multi-variate experiments, an initial mechanism underlying the interplay of exposure to oxygen (present in air) and UV irradiation was postulated.

Composites of functionalized single walled carbon nanotubes (SWCNTs) and gold nanoparticles (Au NPs) of ≈15 nm diameter were drop-cast on a printed circuit board (PCB) substrate equipped with interdigitated electrodes to make a hybrid thin film. Addition of Au NPs decorated the surface of SWCNTs networked films and acted as catalysts which resulted into an enhanced sensitivity and low ppb concentration detection limit. The compositions of the film were characterized by scanning electron microscope (SEM). SWCNTs clusters were loaded with various amount of Au NPs ranging from 1–10% (by weight) and their effect on Nitric oxide (NO) sensitivity was studied and optimized. Further, the optimized composite films were tested in both air and nitrogen environments and as well as over a wide relative humidity range (0–97%). Sensors were also tested for the selectivity by exposing to various gases such as nitrous oxide, ammonia, carbon monoxide, sulfur dioxide and acetone. Sensitivity to NO was found much higher than the other tested gases. The advantage of this sensor is that it is sensitive to NO at low ppb level (10 ppb) with estimated response time within 10 s and recovery time around 1 min, and has excellent reproducibility from sensor to sensor and works within the wide range of relative humidity (0–97%).

The (Pt/YSZ)/YSZ sensor unit is the basic component of the NOx sensor, which can detect the emission of nitrogen oxides in exhaust fumes and optimize the fuel combustion process. In this work, the effect of sintering temperature on adhesion property and electrochemical activity of Pt/YSZ electrode was investigated. Pt/YSZ electrodes were prepared at different sintering temperatures. The microstructure of the Pt/YSZ electrodes, as well as the interface between Pt/YSZ electrode and YSZ electrolyte, were observed by SEM. Chronoamperometry, linear scan voltammetry, and AC impedance were tested by the electrochemical workstation. The results show that increasing the sintering temperature (≤1500 °C) helped to improve adhesion property and electrochemical activity of the Pt/YSZ electrode, which benefited from the formation of the porous structure of the Pt/YSZ electrode. For the (Pt/YSZ) electrode/YSZ electrolyte system, O2− in YSZ is converted into chemisorbed O2 on Pt/YSZ, which is desorbed into the gas phase in the form of molecular oxygen; this process could be the rate-controlling step of the anodic reaction. Increasing the sintering temperature (≤1500 °C) could reduce the reaction activation energy of the Pt/YSZ electrode. The activation energy reaches the minimum value (1.02 eV) when the sintering temperature is 1500 °C.

The zirconia solid electrolyte SOFC (solid oxide fuel cell) has the characteristics of oxygen ion conduction function, high-temperature resistance, thermoelectric coupling effect, etc. A NOx sensor based on zirconia solid electrolyte has common characteristics and problems with the SOFC in principle and application. The research objective of this paper is to solve the application problems of smart NOx sensors in diesel vehicles or gasoline vehicles. Improvements in the application performance of the NOx sensor can help the NOx emissions of gasoline vehicles or diesel vehicles better meet the requirements of emission regulations. The smart NOx sensor is a regulatory sensor required by vehicles for China’s Phase VI Vehicle Exhaust Emission Regulations or Euro Phase VI Vehicle Exhaust Emission Regulations. The smart NOx sensor is a key sensor device for improving fuel efficiency and reducing pollution. Moreover, its measurement performance includes dynamic immunity to interference, response speed, and measurement accuracy, which are key factors affecting vehicle emissions. This paper focuses on the impact of the physical structure, electrode characteristics, and control strategies of the sensor on its performance during the application. An excellent sensor structure, electrode structure, and control strategy are given based on application analysis and experimental testing. The results show that the application performance of this smart NOx sensor meets the requirements of exhaust aftertreatment systems.

Composite NOx sensors were fabricated by combining partially and fully stabilized yttria-doped zirconia with alumina forming a composite electrolyte, Y2O3-ZrO2-Al2O3, and strontium-doped lanthanum manganese oxide mixed with gold to form the composite sensing electrode, La0.8 Sr0.2MnO3-Au. A surface chemistry analysis of the composite sensor was conducted to interpret defects and the structural phases present at the Y2O3-ZrO2-Al2O3 electrolyte, as well as the charge conduction mechanism at the LaSrMnO3-Au electrode surface. Based on the surface chemistry analysis, ionic and electronic transport properties, and microstructural features of sensor components, the working principle was described for NOx sensing at the composite sensor. The role of the composite materials on the NOx sensing response, cross-sensitivity to O2, H2O, CO, CO2, and CH4, and the response/recovery rates relative to sensor accuracy were characterized by operating the composite NOx sensors via the impedimetric method. The composite sensors were operated at temperatures ranging from 575 to 675 °C in dry and humidified gas environments with NO and NO2 concentrations varying from 0 to 100 ppm, where the balance gas was N2. It was found that the microstructure of the composite NOx sensor electrolyte and sensing electrode had a significant effect on interfacial reactions at the triple phase boundary, as well as the density of active sites for oxygen reactions. Overall, the composite NOx sensor microstructure enabled a high NOx sensing response, along with low cross-sensitivity to O2, CO, CO2, and CH4, and promoted NO detection down to 2 ppm.

Based on a heavy-duty stoichiometric natural gas engine which can meet the requirement of China-VI regulations, steady-state and transient cycles were carried out to measure the exhaust NOx concentration out of TWC by a NOx sensor and a gaseous emission analyzer simultaneously. The results show that the measurement results of NOx sensor are relatively higher when the NOx emission concentrations are lower than 50 ppm, and the accuracy is not high enough. Due to the obviously smaller proportion of lower NOx concentrations, especially for the concentrations below 10ppm, the average concentration measured by the NOx sensor was 24.3% higher than the average concentration measured by the emission analyzer during the whole testing process. When the NOx concentrations are higher than 50ppm, the frequency distributions of NOx concentration measured by NOx sensor and emission analyzer are almost the same, and the deviations of average NOx concentrations between these two measurement methods can be within ±4.5%, which represent a significantly high reliability of NOx sensor.

This paper reports on the synthesis of mesoporous ZnO microspheres via hydrothermal production of zinc hydroxide carbonate (ZHC) and subsequent calcination of the ZHC precursor at 500 °C and their application to NO X gas sensors. Materials characterization using various analytical techniques reveals that the ambient (air or vacuum) of the calcination process has a profound impact on the microstructure, morphology, and defect states of the resultant ZnO microspheres. The sample calcined under vacuum displays a microstructure of much smaller nanoparticles (<10 nm), a morphology of higher porosity and larger surface area, and a higher oxygen vacancy concentration compared to the air-calcined sample. The vacuum sample also has much better sensor performance (gas response: 19.8 to a low NO X concentration of 0.1 ppm at 100 °C), with a high selectivity toward NO X , than the air sample. We further discuss the sensing mechanism, suggesting that the differences in particle size, morphology, and oxygen vacancy concentration are responsible for the disparity in sensing performance. [ABSTRACT FROM AUTHOR]

The control of selective catalytic reduction (SCR) systems, via NH $_{\text{3}}$ injection, requires from a precise estimation of the SCR load in order to ensure NOx reduction by minimizing ammonia slip. This article aims to resolve the cross-sensitivity of current NOx sensors at the outlet of the SCR, by providing the control unit with an estimation of NOx and ammonia slip. The problem of discerning between NOx and ammonia slip is solved by identifying an intermediate variable representing the SCR load. The SCR load is estimated by combining the mass conservation principle between the inlet and the outlet of the SCR and a NOx reduction model, via an extended Kalman filter. Current models and observers have several limitations to represent the real behavior of the SCR along all the operating conditions; on one hand, when relying on the mass conservation, small errors at models are integrated, leading to important bias on the SCR load and on the other hand, the dynamics at the SCR must be precisely modelled for an adequate adaptation of the model. The main focus of the developed algorithm is to use a simplified model which might be used for ammonia slip estimation, being aware of current limitations of SCR models in real operation. Experimental results in a EURO 6 compression ignited (CI) engine show the potential of such observation in transient conditions and an adequate correlation with external ammonia measurements provided by additional sensors available on the test bench. [ABSTRACT FROM AUTHOR]

Planar potentiometric NO2 sensors based on 8YSZ (8 mol% Y2O3-doped ZrO2) were prepared with WO3 sensing electrode material. The various electrode microstructures prepared by different sintering temperatures were characterized by field emission scanning electron microscopy (SEM), and the microstructure influences on the sensors' performances were investigated. The sensor sintered at 800°C, with the most reaction sites, moderate adsorption sites and appropriate electrode thickness, exhibits the highest NO2 voltage response. While the sensor sintered at 750°C exhibits the lowest NO2 sensitivity because of the strongest gas-phase catalytic consumption in the WO3 sensing electrode. Based on the results of SEM characterization and electrochemical impedance spectroscopy tests, the difference in NO2-sensing performance was attributed to different amounts of electrochemical reaction sites at three-phase boundary, adsorption sites and different degrees of gas-phase catalysis.

The low-power sensing platform proposed by the Convergence project is foreseen as a wireless, low-power and multifunctional wearable system empowered by energy-efficient technologies. This will allow meeting the strict demands of life-style and healthcare applications in terms of autonomy for quasi-continuous collection of data for early-detection strategies. The system is compatible with different kinds of sensors, able to monitor not only health indicators of individual person (physical activity, core body temperature and biomarkers) but also the environment with chemical composition of the ambient air (NOx, COx, NHx particles) returning meaningful information on his/her exposure to dangerous (safety) or pollutant agents. In this article, we introduce the specifications and the design of the low-power sensing platform and the different sensors developed in the project, with a particular focus on pollutant sensing capabilities and specifically on NO2 sensor based on graphene and CO sensor based on polyaniline ink.

A new type solid-electrolyte impedancemetric sensor using a zeolite as a receptor and a Li 1.5 Al 0.5 Ti 1.5 (PO 4 ) 3 (LATP) disc as a transducer, respectively, was designed and its sensing properties were investigated for detection of NO and NO 2 in the range of 100–500 ppm at 300–500 °C. It was revealed that the impedance responses of the sensor device attached with a zeolite receptor changed with depending on NO x concentration. Cation-exchange in zeolites gave good improvement of the sensor responses. Among the ion-exchanged zeolites, K + -doped Y-type zeolite-based sensor showed the highest sensitivity and selectivity to NO 2 . [ABSTRACT FROM AUTHOR]

The catalytic activity of an oxygen-pumping electrode is very important to the performance of amperometric NO x (NO and NO 2) sensors. To enhance the stability of electrochemical NO x sensors based on Pt electrodes, we fabricated sensitive electrodes of Pt-based materials doped with small and different Au contents on 8% mol Y 2 O 3 -stabilized ZrO 2 (8YSZ) solid electrolyte substrates by screen printing and high-temperature co-firing. The effects of Au on the porous Pt electrode's catalytic activity and long-term stability were investigated, and the results are as follows. First, the catalytic capacity of the Pt–Au alloy electrode decreases with increasing Au content due to the inhibition of the oxygen adsorption on Au, which decreases the amount of oxygen participating in the reaction at triple-phase boundaries (TPBs). Second, the catalytic ability of the alloy electrode decreases exponentially with aging time due to the reduction in the length of TPBs caused by the significant reduction in the number of holes in the electrode, and the oxidation of Pt. In addition, the conductivity decay rate of the electrode decreases with increasing Au doping. This indicates that Pt-based electrodes doped with varying Au contents, long-term, and high-temperature aging have notably regular effects on the catalytic activity of oxygen-pumping electrodes, for which we have developed a model of Au passivation and the synergistic effect of aging time on the activity of Pt-based oxygen-pumping electrodes. [Display omitted] • DFT and EIS experiments were combined to elucidate the role of Au passivation. • The aging mechanism of electrodes was illustrated by long-term aging tests. • Synergistic effect of Au passivation and aging on catalytic activity was modeled. [ABSTRACT FROM AUTHOR]

Electrochemical NOx sensors based on yttria-stabilized zirconia (YSZ) are commercialized to detect overall NOx concentrations in Diesel exhausts without distinction between NO and NO 2 . To overcome this inconvenient, a high-sensitive sensor based on selective electrochemical reduction of NO 2 is proposed. An electrochemical cell consisting of three metallic electrodes on solid-state electrolyte (YSZ) operating under electric polarization between a gold working electrode and a platinum counter electrode allows selective NO 2 detection at 400-550 °C with high sensitivity, and without any significant interferences to other gases like hydrocarbons, carbon monoxide and also ammonia and nitrogen monoxide. A mechanism based on cathodic overpotential is proposed. [ABSTRACT FROM AUTHOR]

The pulsed polarization measurement technique using conventional thimble type lambda probes is suitable for low ppm NOx detection in exhaust gas applications. To evaluate the underlying sensor mechanism, the unknown influence of the reference atmosphere on the NO sensing behavior is investigated in this study. Besides answering questions with respect to the underlying principle, this investigation can resolve the main question of whether a simplified sensor element without reference may be also suitable for NO sensing using the pulsed polarization measurement technique. With an adequate sensor setup, the reference atmosphere of the thimble type lambda probe is changed completely after a certain diffusion time. Thus, the sensor response regarding NO is compared with and without different gas atmospheres on both electrodes. It is shown that there is still a very good NO sensitivity even without reference air, although the NO response is reduced due to non-existing overlying mixed potential type voltage, which is otherwise caused by different atmospheres on both electrodes. Considering these results, we see an opportunity to simplify the standard NOx sensor design by omitting the reference electrode.

To improve the performance of the NOx sensor, a combined model based on the electrochemical model and the diffusion model is developed for the NOx pumping cell of the NOx sensor. Considering that a small amount of oxygen enters the third chamber and part of NO is decomposed in the second chamber, the reactions of both NO and oxygen at cathode are taken into account in the electrochemical model, and the diffusion model additionally takes the diffusion of oxygen and the decomposition of NO into consideration. To validate the model at different gas concentrations, the sensor is mounted on the designed test rig. Then, the simulation results are compared with experimental data from the test rig and good agreement is obtained. In addition, three key parameters in the model of the NOx pumping cell are analyzed. The values and changing trends of these three parameters are given in the paper. • A combined model is developed based on the electrochemical model and the diffusion model. • Oxygen disturbance and NO premature decomposition are considered in the model. • The model results are in good agreement with the experiments. • The values and changing trends of three key parameters of the model are given. [ABSTRACT FROM AUTHOR]

The fuel injectors in a heavy-duty diesel engine with a selective catalytic reduction (SCR) system operate in harsh conditions that cause them to deteriorate, resulting in changes in the fuel injection quantity. In this study, a method for determining the injection quantity of fuel injected using the output of a NOx sensor in a heavy-duty diesel engine equipped with a SCR system is developed. A mathematical model was derived to calculate the fuel injection quantity based on the oxygen concentration in the exhaust gases. Bench tests were conducted at various engine operating conditions. The results indicate that at high engine loads, the absolute error between the oxygen concentration measured by the NOx sensor and that measured by a gas analyser was less than 2%, which is acceptable, and the reactions in the SCR reactor consumed no more than 1% of the oxygen in the exhaust gases, which is negligible. An analysis of the model demonstrates that the calculated value of the injection quantity based on the oxygen concentration in the exhaust is more accurate for lower oxygen concentrations (i.e., at greater engine loads). The test data reveal that the error in the fuel injection quantity obtained from the model was less than 2% at high engine loads. This research demonstrates that the on-board calculation of the fuel injection quantity based on the oxygen concentration signals from the NOx sensor is possible at high engine loads. [ABSTRACT FROM AUTHOR]

The pulsed polarization measurement technique using conventional thimble type lambda probes is suitable for low ppm NOx detection in exhaust gas applications. To evaluate the underlying sensor mechanism, the unknown influence of the reference atmosphere on the NO sensing behavior is investigated in this study. Besides answering questions with respect to the underlying principle, this investigation can resolve the main question of whether a simplified sensor element without reference may be also suitable for NO sensing using the pulsed polarization measurement technique. With an adequate sensor setup, the reference atmosphere of the thimble type lambda probe is changed completely after a certain diffusion time. Thus, the sensor response regarding NO is compared with and without different gas atmospheres on both electrodes. It is shown that there is still a very good NO sensitivity even without reference air, although the NO response is reduced due to non-existing overlying mixed potential type voltage, which is otherwise caused by different atmospheres on both electrodes. Considering these results, we see an opportunity to simplify the standard NO x sensor design by omitting the reference electrode. [ABSTRACT FROM AUTHOR]

To improve the performance of the NOx sensor, a combined model based on the electrochemical model and the diffusion model is developed for the main oxygen pumping cell of the NOx sensor. One important feature of this combined model is that the model eliminates the intermediate variable and only shows the relationship between the pumping voltage and the pumping current. To validate the model at different gas concentrations, the sensor is mounted on the designed test rig. Then, the simulation results are compared with experimental data from the test rig and good agreement is obtained. Comparing the cathode and anode overpotential, it is found that the anode concentration overpotential can be ignored. In addition, since the activation overpotentials of the cathode and anode are relatively small, they can all be regarded as linear changes with the pumping current. The subsequent characteristic analysis determines the changes of the internal characteristics of the sensor during operation, which will provide guidance for the design and control of the sensor. • A combined model is developed based on the electrochemical model and the diffusion model. • A method of estimating activation polarization parameters is provided. • The model results closely match the experiments with the maximum 7.1% error. • The characteristic analysis will provide guidance for the design and control of the sensor. [ABSTRACT FROM AUTHOR]

Abstract: Extensive emissions and fuel economy directives are stimulating the development of every more sophisticated sensors, catalyst systems and emissions traps with improved performance and self-evaluation capabilities. For the development of such systems, deeper insights are required to understand the often complex interplay between the chemical state of the material and its electrical, optical, thermal and mechanical properties. Three examples, illustrating how information gained about the defect, electronic and transport structure of oxide materials can be used to optimize sensor and catalyst properties, are presented. Also discussed are means for in situ monitoring of the status of exhaust catalysts and traps. [Copyright &y& Elsevier]

Abstract: Solid-electrolyte impedancemetric NOx (NOx; NO, NO2) sensor devices were designed by using metal oxides (Fe2O3, Co3O4, NiO, CuO, ZnO) as a receptor material and an 8mol%-yttria-stabilized zirconia (YSZ) plate as a solid electrolyte transducer material. The sensing signal could be simply detected as the impedance change of the transducer. The sensing performance of the impedancemetric NOx sensor for the detection of NOx in the range 10–150ppm at 300–500°C was investigated using impedance analyzer. Among the sensor device tested NiO/YSZ sensor showed good sensing properties for NO and NO2 at 400°C on 100kHz. Moreover, the sensing response properties showed good selectivity and stability to NO2. [Copyright &y& Elsevier]

Selective catalytic reduction by ethanol on silver-based catalysts was proved to be very effective to abate the nitrogen oxides emitted at the exhaust of an automotive engine. Moreover, the selectivity to ammonia of this reaction may be exploited to further enhance the NOx reduction using a dedicated transition metal exchanged zeolite catalyst. This coupling between HC- and NH-SCR is called Dual SCR. In order to control the silver-based catalyst efficiency via ethanol injection, a NOx sensor is located downstream of it, as usually done for urea-SCR on series vehicles. Furthermore, based on the cross-sensitivity of this NOx sensor, large amounts of ammonia were estimated that would help to reduce the remaining NOx on the zeolite based catalyst. However, when measured by FTIR technique, the concentrations of ammonia produced by the HC-SCR catalyst were surprisingly not as high as expected, while large amounts of acetaldehyde were detected and, in a lesser extent, formaldehyde and hydrogen cyanide. NOx were partly reduced over the iron-exchanged zeolite catalyst, improving the overall deNOx efficiency by up to 15 points, while acetaldehyde to formaldehyde ratio reversed and ammonia concentration remains unchanged. The cross-sensitivity of the NOx sensor was further investigated on synthetic gas bench. If its partial dependence on the ammonia concentration is rather well known, the influence of aldehydes and hydrogen cyanide in presence of ammonia had not yet been investigated. The NOx sensor's signal remains unchanged whatever the aldehydes concentration and a strong sensitivity to the hydrogen cyanide was highlighted. [ABSTRACT FROM AUTHOR]