Amperometric NO Research Articles

Amperometric type NO2 sensor based on La0.75Sr0.25Cr0.5Fe0.5O3-δ-Bi2O3 sensing electrode prepared by self-demixing

Bi2O3 modified La0.75Sr0.25Cr0.5Fe0.5O3-δ (LSCF) composites have been successfully prepared by self-demixing and used as the sensing electrode (SE) of an amperometric NO2 sensor with yttria stabilized-zirconia (YSZ) electrolyte. The Bi2O3 modified LSCF composites were formed from precursor La0.75Sr0.25BixCr0.5Fe0.5O3+δ (x = 0, 5%, 10%, 20%, 30% and 40%) after calcining at 1200 °C. The particle size of LSCF was increased with the Bi2O3 content increasing. The YSZ porous framework structures were fabricated on YSZ to prolong TPB and the LSCF-xBi2O3-SE with porous structure was prepared on the porous YSZ backbone after calcining at 1000 °C. It is found that the sensors attached with LSCF-xBi2O3-SE are more sensitive to different concentrations of NO2 (25–300 ppm) than the LSCF-based sensor. Among them, LSCF-20% Bi2O3 based sensor exhibits the highest sensitivity (0.301 μA /ppm at 550 °C). The relationship between ΔIs and NO2 concentrations of the sensor varies linearly at a given temperature. Meanwhile, the sensor shows well anti-interference capability for co-existent gases.

Enhanced sensing performance of the amperometric NO2 sensor by use of a mixed conductive porous layer

A novel amperometric NO2 sensor was fabricated using a nanostructured La0.8Sr0.2MnO3-δ (nano-LSM) sensing electrode (SE) and a Ce0.8Gd0.2O1.9 (CGO) electrolyte. The focus of this study was to extend the electrochemical active site at the three-phase boundary (TPB) and reduce the interfacial resistance by introducing a hybrid ion/electron conducting porous layer (CGO +LSM) between the SE and the electrolyte. By adjusting the amount of LSM, the effects of the LSM/CGO ratio on the microstructure and sensitivity of the sensor were investigated. The results showed that the addition of LSM did not change the porous structure of the CGO porous skeleton, but the number of pores decreased with the increase of LSM addition, while the size of pores increased with increasing the amount of LSM added. The nano-LSM was prepared in-situ into the porous skeleton by the impregnation technology, which was highly dispersed in the porous skeleton, having reached the bottom of the porous layer with a particle size of less than 100 nm. The sensor with a mixed conductor as the porous layer effectively improved the sensitivity of the sensor. Analysis by electrochemical impedance spectroscopy (EIS) and the distribution of relaxation techniques (DRT) demonstrated that the addition of the electronic conductor LSM into the CGO porous layer significantly reduced the diffusion resistance of the sensor and enhanced the oxygen exchange performance, thus improving the response performance of the sensor. The sensor with 30wt% LSM/CGO porous layer had good reproducibility and excellent stability. The sensor had good anti-interference performance against co-existing CH4, CO2, H2, NO, and NH3, with good linearity between sensor response values and NO2 concentrations over different O2 concentrations and relative humidity (RH).

Sensing properties of amperometric ppb-level NO2 sensor based on sodium ion conductor with sensing electrodes comprising different WO3 nanostructures

In this study, amperometric NO2 sensors based on Na+ superionic conductor electrolyte and sensing electrodes with different WO3 nanostructures (WO3 nanoparticles, WO3 nanosheets, and mesoporous WO3) have been fabricated and compared. Sensing properties, such as optimum test temperature, sensitivity, repeatability, and selectivity have been determined and compared. Compared with the literatures, the sensors, prepared using three different WO3 nanostructures, all showed improved sensing properties to 100–1000 ppb NO2 at low work temperatures of 100–150 °C. Among above sensors, the sensor equipped with mesoporous WO3 sensing electrode exhibited the best amperometric sensitivity characteristics and the minimum test temperature. The relationship between the sensing properties and the mesoporous structure has also been discussed. What’s more, the sensor can test ppb-level NO2 in low temperature, which makes it possible to monitor low concentrations of NO2 in the air.

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.

Application of TiO2 to amperometric NOx sensors based on NASICON

The work focused on improvement of the current response to NO and the reduction of response time of both NO and NO2. By adding a layer of TiO2 catalyst layer, the shortcoming of NO insensitivity of traditional NASICON based amperometric NO2 sensor was solved. TiO2 was known as an n-type semiconductor and a high-performance NO oxidation catalyst. We separately applied different types of TiO2 (rutile and Degussa P25) on the device and compared the test results with the traditional type without a catalyst layer. The results showed that the TiO2 attached device exhibited a significant improvement to NO response, and P25 was better than rutile TiO2 on account of the higher activity of anatase TiO2. In addition, TiO2 also played a role of a semiconductor electrode, resulting in the increase of response to NO2. The response time of NO and NO2 was separately shrunk from 153s, 70s to 77s, 43s owing to the P25 layer. The current responses were found to be barely affected by the coexistence of CO2.

Amperometric NOxSensor Based on Oxygen Reduction

A novel ceria-based amperometric NO x and NH3 sensor was investigated. The sensor consisted of gadolinium-doped ceria electrolyte membrane with (La0.60Sr0.40) (Co0.20Fe0.80) $\text{O}_{3-\delta }$ (LSCF) electrodes applied to opposite sides. The assembly operated in combustion exhaust streams with higher sensitivity to both NO x and NH3, less dependence on oxygen partial pressure, and faster response than previously reported. The sensor had an operational temperature range of 200 °C–550 °C and was resistant to common exhaust gas contaminants, such as steam, CO2, and sulfur oxides. Electrochemical testing and in-situ DRIFTS studies showed NO x adsorption on the sensor causing accelerated kinetics for oxygen reduction reaction (ORR) whereby adsorbed NO x species acted as a catalyst for an alternative ORR pathway, thus enabling an amperometric sensing mechanism.

Ionic Liquid based polymer electrolytes for electrochemical sensors

Amperometric NO2 printed sensor with a new type of solid polymer electrolyte and a carbon working electrode has been developed. The electrolytes based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][N(Tf)2], 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][CF3SO3] and 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4] ionic liquids were immobilized in poly(vinylidene fluoride) matrix [PVDF]. The analyte, gaseous nitrogen dioxide, was detected by reduction at -500 mV vs. platinum pseudoreference electrode. The sensors showed a linear behavior in the whole tested range, i.e., 0 - 5 ppm and their sensitivities were in order of 0.3 x∙10-6 A/ppm. The sensor sensitivity was influenced by the electric conductivity of printing formulation; the higher the conductivity, the higher the sensor sensitivity. The rise/recovery times were in order of tens of seconds. The use of screen printing technology and platinum pseudoreference electrode simplify the sensor fabrication and it does not have any negative effect on the sensor stability.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7371

Quantitative fluctuation-enhanced sensing in amperometric NO2 sensors

Nitrogen dioxide represents threat to human health even at low concentrations. A new amperometric sensor with three-electrode topology (platinum/solid polymer electrolytes/carbon) was developed to overcome limitations of standard solid NO2 sensors based on inorganic materials. The paper aims to the study of fluctuation phenomena in amperometric sensor and presents preparation technology. The sensor has been exposed to NO2 concentration from 0 to 3ppm. Experimental results show that thermal noise is only apparent for zero concentration. For higher NO2 concentrations, adsorption–desorption (A–D) noise and diffusion noise become main components of current fluctuations, and the noise spectra exhibit Lorentzian-like shape. The spectral density of current noise at frequency 0.2Hz depends linearly on NO2 concentration. This linear behavior can be described by adsorption–desorption model for the interaction for two reservoirs. Thus, considering adsorption–desorption noise as a dominant noise source, the noise model is introduced based on Langmuir theory.

The Study of NO<sub>2</sub> Gas Sensor Based on NASICON

NASICON materials can be used as the solid electrolyte component in the sensor system, because they have excellent Na+ conductivity. This study prepares NASICON materials by solid state reaction method, and their phase, microstructure and electrical property will be characterized by XRD, SEM and EIS. Then an amperometric NO2 sensor is fabricated to detect NO2 gas in the level of ppb. The sensor current signal will be studied by changing different NO2 concentrations, employing different materials on the counter electrode and using different applied voltages when the working temperature is 150°C.

Effective improvement of sensing performance of amperometric NO2 sensor by Ag-modified nano-structured CuO sensing electrode

An amperometric-type NO2 gas sensor using La10Si5AlO26.5 (LSAO) with the configuration of dense electrolyte| porous electrolyte, Ag-modified nano-structured CuO sensing electrode was investigated. The composition and microstructure of the sensor sample were characterized by SEM and XRD and the performance of the sensor was examined. The prepared Ag-modified nano-structured CuO particles sensing electrode by impregnation technique are homogeneously dispersed in LSAO porous backbone. The sensor displays good response to NO2 and the response currents are almost linear to NO2 concentrations in the range of 0–500ppm at 550–700°C. Ag addition to the CuO sensing electrode can remarkably increase sensor sensitivity, showing that the performance of the sensor is effectively improved by introducing Ag. The best performance is observed at molar ratio of 1:0.5 for CuO:Ag. The cross-sensitivities of the sensor to co-existant gases (H2, CH4, CO2, NH3 and toluene) are rather small.

High temperature amperometric NO2 sensor based on nano-structured Gd0.2Sr0.8FeO3−δ prepared by impregnating method

Based on an YSZ electrolyte and a nano-structured Gd 0.2 Sr 0.8 FeO 3− δ sensing-electrode prepared by impregnating method, a new-type amperometric sensor is fabricated and tested. The fabricated sensor for detection of NO 2 can be operated at high temperatures (500–800 °C). When the bias potential of −400 mV is applied to sensor the response currents of the sensor are almost linear to NO 2 concentrations from 25 to 500 ppm at a fixed temperature. The sensor shows good sensitivity, response and stability to NO 2 . The sensitivity of the sensor reached up to 2.60 μA ppm −1 and the 90% response time is about 150 s for 500 ppm NO 2 at 800 °C. • A amperometric NO 2 sensor is proposed with Gd 0.2 Sr 0.8 FeO 3−δ sensing-electrode. • The Gd 0.2 Sr 0.8 FeO 3−δ nano-particles are prepared by impregnating method. • The sensor had good responses to NO 2 at high temperature. Aimed at automobile exhaust monitoring of NO x , a new-type amperometric sensor was fabricated by using yttria-stabilized zirconia (YSZ) as electrolyte and a nano-structured perovskite-type oxide Gd 0.2 Sr 0.8 FeO 3− δ (GSF) as sensing-electrode (SE) prepared by impregnating method. The fabricated sensor was examined for detection of NO 2 at high operating temperatures (500–800 °C) in N 2 carrier gas. It was found that the response current of the sensor was almost linear to NO 2 concentration from 25 to 500 ppm at 500–800 °C when SE was polarized at −400 mV. The sensitivity of the sensor reached 2.61 μA ppm −1 at 800 °C. The sensor showed good selectivity, response, reproducibility and stability to NO 2 .

An amperometric NO2 sensor based on La10Si5NbO27.5 electrolyte and nano-structured CuO sensing electrode

A novel amperometric-type NO2 sensor based on La10Si5NbO27.5 (LSNO) electrolyte and nano-structured CuO sensing electrode was fabricated and tested. A bilayer LSNO electrolyte including both a dense layer and a porous layer was prepared by conventional solid state reaction method and screen-printing technology. The nano-structured CuO sensing electrode was in situ fabricated in LSNO porous layer by impregnating method. The composition and microstructure of the sample were characterized by XRD and SEM, respectively. The results showed that the CuO particles with diameters range of 200–500nm were homogeneously dispersed on the LSNO backbone in porous layer. The sensor exhibited well sensing characteristics to NO2. The response current was almost linear to NO2 concentration in the range of 25–500ppm at 600–800°C. With increase of operating temperature, the sensitivity increased and reached 297nA/ppm at 800°C. The response currents toward NO2 were slightly affected by coexistent O2 (0–21vol%) and CO2 (0–5vol%).

Effect of the geometry of a working electrode on the behavior of a planar amperometric NO2 sensor based on solid polymer electrolyte

An amperometric NO2 sensor with a new type of solid polymer electrolyte (SPE) and a glassy carbon working electrode is presented. The electrolyte is based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim][NTf2] ionic liquid immobilized in poly(vinylidene fluoride) matrix [PVDF]. The analyte, gaseous nitrogen dioxide, was detected by reduction at −500mV vs. a platinum pseudoreference electrode. The sensor exhibited a linear behavior in the whole tested range, i.e., 0–10ppm, and its sensitivity was 0.66×10−6A/ppm. The rise/recovery times were of the order of tens of seconds. In addition, the influence of the geometry (area and thickness) of the carbon working electrode on sensor response during short-term and long-term exposure to nitrogen dioxide was investigated. The area of the working electrode strongly influenced the stability and noise of the sensor: the smaller the electrode area, the better the stability of the sensor and the lower the noise level. The response times were influenced by the thickness of the carbon working electrode: the thicker the electrode, the longer the response time. It was also demonstrated that glassy carbon is a good candidate for the preparation of the working electrode. The use of a platinum pseudoreference electrode simplifies sensor fabrication and does not have any negative effect on sensor stability.

A novel amperometric NO2 sensor based on nano-structured La0.75Sr0.25Cr0.5Mn0.5O3−δ–Ag composite sensing electrode prepared by impregnating method

An amperometric NO2 sensor using nano-structured La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM)–Ag composite sensing electrode with Ce0.9Gd0.1O1.95 (CGO) electrolyte was fabricated. The LSCM–Ag particles in the range of 100–200nm were prepared in the porous CGO layer by impregnating method. The NO2 sensing characteristics were examined. The sensor showed high response to NO2 and the response current was almost linear to NO2 concentration at 400–600°C. With the Ag loading level increased, the sensitivity of the sensor increased remarkably and the best performance was observed at the LSCM/Ag molar ratio of 1:0.5. The response current was slightly affected by changing O2 concentrations in the range of 0–10vol%.

An amperometric NO2 sensor based on nano-structured La0.75Sr0.25Cr0.5Mn0.5O3−δ prepared by impregnating method

An amperometric NO2 sensor using nano-structured perovskite-type oxide La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) as sensing electrode with Ce0.9Gd0.1O1.95 (CGO)electrolyte was fabricated. The LSCM particles were prepared in the porous CGO layer by impregnating method. The composition and microstructure of the sample were characterized by XRD and SEM, respectively. The properties of the sensor for monitoring NO2 were studied. The results showed that the LSCM particles in the range of 50–150nm were homogeneously dispersed in the porous CGO layer. The response current was almost linear to NO2 concentration in the range between 20 and 300ppm. With the temperatures increasing, the sensitivity increased and reached 111.36nAppm−1 at 500°C. The sensor showed good response, recovery, reproducibility and stability. Although the response current was slightly affected by changing O2 concentrations in the range of 0–10vol%, the influence was negligibly small.

Measurements of Location-Dependent Nitric Oxide Levels on Skin Surface in relation to Acupuncture Point.

Location-dependent skin surface's partial nitric oxide pressure (pNO) is studied using highly sensitive amperometric NO microsensor with a small sensing area (diameter = 76 μm). The pNO level of LI4 (Hegu) acupuncture point is measured and compared with the pNO level of nonacupuncture point. In addition, the mapping of pNO is carried out over the left wrist skin area one- as well as two-dimensionally. Statistically higher pNO levels near the position of acupuncture points than non-acupuncture points are observed consistently, implying tight relationship between the level of NO release of skin and acupuncture points. The amperometric planar NO microsensor successfully monitors the heterogeneity of skin pNO distribution in high spatial resolution due to its advantageous features such as high sensitivity and small sensing dimension. The current study suggests the direct connection between NO and acupuncture points and possibly provides beneficial information to understand physiological roles and basis of the acupuncture points.

Glassy carbon electrodes modified with hemin-carbon nanomaterial films for amperometric H2O2 and NO2− detection

In this work a new chemical sensor for the H2O2 and nitrite amperometric detection was assembled, using a glassy carbon (GC) bare electrode modified by two different nanocomposite materials. The nanocomposite films were prepared by casting a functionalised carbon nanofiber (CNF-COOH) and single-walled carbon nanotubes (SWCNT-OH, for comparison) on the glassy carbon electrode surface; then an iron(III) protoporphyrin IX (Fe(III)P) was adsorbed on these modified surfaces. A morphological investigation of the nanocomposite layers was also carried out, using the Scanning Electron Microscopy (SEM). The electrochemical characterization, performed optimising several electro-analytical parameters (such as different medium, pH, temperature, scan rate, and potential window), demonstrated that the direct electrochemistry of the Fe(III)P/Fe(II)P redox couple involves 1e−/1H+ process. A kinetic evaluation of the electron-transfer reaction mechanism was also carried out, demonstrating that the heterogeneous electron transfer rate constant resulted higher at CNF/hemin/GC biosensor than that evaluated at SWCNT/hemin/GC modified electrode. Finally, the electrocatalytic activity toward the H2O2 reduction was also demonstrated for both sensors but better results were observed working at CNF/hemin/GC modified electrode, especially in terms of an extended linearity (ranging from 50 to 1000μM), a lower detection limit (L.O.D.=3σ) of 2.0×10−6M, a higher sensitivity of 2.2×10−3AM−1cm−2, a fast response time (9s), a good reproducibility (RSD%<1, n=3) and operational stability. In addition, a nitrite electrocatalytic effect was also demonstrated only at CNF/hemin/GC modified electrode, showing an extended linearity (ranging from 5.0×10−3 to 2.5×10−1M), a lower detection limit (L.O.D.=3σ) of 3.18×10−4M, a higher sensitivity of 1.2×10−2AM−1cm−2, a fast response time of 10s, a good reproducibility (RSD% <1, n=3) and finally a good operational stability.

Sensing behavior of YSZ-based amperometric NO2 sensors consisting of Mn-based reference-electrode and In2O3 sensing-electrode

Yttria-stabilized zirconia (YSZ)-based amperometric NO2 sensors comprised of an In2O3 sensing-electrode (SE), a Pt counter-electrode (CE) and a Mn2O3 reference-electrode (RE) in both tubular and rod geometries were fabricated and their sensing characteristics were examined. For comparative purposes, the performance of the In2O3-SE and Pt-CE were also examined against an internal Pt/air-RE. Experimental observations of tubular YSZ-based gas sensors revealed that a three-electrode system exhibited better electrical signal stability, when compared with a two-electrode system. Additionally, replacing the internal Pt/air-RE with an external Mn2O3-RE (exposed to the sample gas), was found to have a negligible effect on the gas sensing characteristics of the tubular sensor. This gas sensing equivalence indicates that Mn2O3-RE can successfully replace the Pt/air-RE in an amperometric gas sensor. Similarly, rod-type sensors utilizing an In2O3-SE and a Mn2O3-RE were observed to have almost identical NO2 sensing characteristics to that of the tubular sensor. Furthermore, both sensors (tubular or rod geometry) exhibited a linear response to increasing NO2 concentration in the range of 20–200ppm at 550°C.

Simple Fabrication of Amperometric Nitric Oxide Microsensors Based on Electropolymerized Membrane Films

AbstractDemand for highly sensitive, selective, and practically reliable sensors which could be easily fabricated is increasing for various applications in biological and biomedical systems. Thus, here we present a novel and simple amperometric NO microsensor based on electropolymerized polymeric films. The sensor consists of a platinized Pt disk anode (25‐μm diameter) which surface is modified with electropolymerized polymer films and a Ag/AgCl wire cathode coiled around the anode. Three different electropolymerized films prepared from m‐phenylenediamine (m‐PD), 2,3‐diaminonaphthalene (2,3‐DAN), and 5‐amino‐1‐naphthol (5A1N) are compared in terms of their permselectivity for NO over major biological interferents such as anionic nitrite, ascorbic acid, uric acid; neutral acetaminophen; and cationic dopamine. Poly‐5A1N film layer among the three different polymers shows the best anti‐interference characteristics for all the electroactive interferents examined. Indeed, single polymer film of electropolymerized 5A1N without any additional modification as a NO selective membrane is confirmed to be sufficient to reject anionic, neutral, as well as cationic interferents while allowing relatively high permeation of NO through it. Other analytical performance of the NO microsensor fabricated with poly‐5A1N is evaluated: reliable linear dynamic range (a few tens nM to μM); sensitivity of 122.0±2.5 pA/μM; detection limit of &lt;5.8 nM (S/N=3); response time, t90%&lt;5 s, which are excellent when considering the small sensor size. Another sensor design which has both an anode (poly‐5A1N modified platinized Pt) and a cathode (Ag/AgCl disk) embedded in a single sensor body is also presented.

Amperometric S-nitrosothiol sensor with enhanced sensitivity based on organoselenium catalysts

A new S-nitrosothiol (RSNO) detection strategy based on an electrochemical sensor is described for rapidly estimating levels of total RSNOs in blood and other biological samples. The sensor employs a cellulose dialysis membrane covalently modified with an organoselenium catalyst that converts RSNOs to NO at the distal tip of an amperometric NO sensor. The sensor is characterized by very low detection limits (<20nM), good long-term stability, and can be employed for the rapid detection of total low-molecular-weight (LMW) RSNO levels in whole blood samples using a simple standard addition method. A strategy for detecting macromolecular RSNOs is also demonstrated via use of a transnitrosation reaction with added LMW thiols allowing the estimation of total RSNO levels in blood. The sensor is shown to exhibit high selectivity over nitrosamines and nitrite. Such RSNO detection is potentially useful to reveal correlation between blood RSNO levels and endothelial cell dysfunction, which often is associated with cardiovascular diseases.