Amperometric Gas Sensors Research Articles

Hydrogen Gas Sensing Properties of Calcium Metaphosphate Glass-derived Hydrogels

Abstract A calcium metaphosphate glass-derived hydrogel shows high electrical conductivities of about 1 mS/cm around room temperature. Potentiometric hydrogen gas sensors using the hydrogel showed good Nernstian response to hydrogen gas concentration difference generated between detective and reference electrodes. The proton transport number of the hydrogel was estimated to be almost 1; no contribution of Ca2+ and OH− ions in the hydrogel was shown. The evaluation of amperometric hydrogen gas sensors showed that limiting currents vary with hydrogen gas flow rates.

Amperometric Acetone Gas Sensor for Non-Invasive Diabetic Diagnosis

not Available.

Impedance Investigations of Amperometric Gas Sensor Containing Aprotic Solvent

AbstractThe authors designed an amperometric gas sensor employing a three‐electrode system, with gold working electrode vacuum sublimation deposited directly on Nafion membrane. The paper presents the results of investigations on static characteristics of a sulfur dioxide sensor with the internal electrolytes containing various dimethylsulfoxide/water ratio. Impedance data were analyzed using an electrical equivalent circuit in order to evaluate its particular elements.

The Direct Electrochemical Oxidation of Ammonia in Propylene Carbonate: A Generic Approach to Amperometric Gas Sensors

AbstractThe direct electrochemical oxidation of ammonia in propylene carbonate is reported for the first time. The voltammetric responses at glassy carbon, boron‐doped diamond, edge and basal plane pyrolytic graphite electrodes are explored and compared with the outcome indicating that the optimum electrode substrate for analytical purposes in this solvent is glassy carbon. Proof‐of‐concept is shown for the amperometric detection of ammonia using basal plane pyrolytic graphite electrodes abrasively modified with glassy carbon spheres. Given the significantly lower vapor pressure of propylene carbonate in comparison to water the implications for extending the life‐time of practical sensors are evident. Propylene carbonate shows a wide potential window with glassy carbon electrodes permitting this approach to be used for a potential diversity of gaseous analytes.

A New Solid State Amperometric Gas Sensor for Detection of Hydrogen Sulfide in Industrial Hygiene Applications.

not Available.

Mass transfer in amperometric gas sensors

The mass transfer in amperometric gas sensors intended for atmosphere monitoring is studied theoretically and experimentally. External and internal constituents of the diffusion resistance (DR) of the sensors are determined. The external constituent is defined by conditions of convective diffusion of air under analysis relative to the sensor. The internal constituents are defined by parameters of construction of sensor elements, and electrolyte film, as well as the structure of the indicator electrode, and solubility of the gas under analysis in the electrolyte. Testing a chlorine sensor shows that the DR of the internal constituents is independent of the conditions of convective diffusion of the environment under analysis near the sensor. The similarity criterion of sensors of different types is shown to be the relative share of DRs of individual constituents in the overall DR of the sensor. The results obtained can be used for the development and design of sensors with required range and resolution.

Direct Detection of S-Nitrosothiols Using Planar Amperometric Nitric Oxide Sensor Modified with Polymeric Films Containing Catalytic Copper Species

The direct amperometric detection of S-nitrosothiol species (RSNOs) is realized by modifying a previously reported amperometric nitric oxide gas sensor with thin hydrophilic polyurethane films containing catalytic Cu(II)/(I) sites. Catalytic Cu(II)/(I)-mediated decomposition of S-nitrosothiols generates NO(g) in the thin polymeric film at the distal tip of the NO sensor. Three different species are examined to create the catalytic layer: (1) a lipophilic Cu(II)-ligand complex; (2) Cu(II)-phosphate salt; and (3) small (3-microm) metallic Cu(0) particles. All three catalytic layers yield reversible amperometric response in proportion to the concentration of S-nitrosothiols (e.g., nitrosocysteine, nitrosoglutathione, S-nitroso-N-acetylcysteine, S-nitrosoalbumin) present in the aqueous test solution. Sensitivity toward the different RSNO species is dependent on the respective catalytic rates of decomposition of the RSNO species by reactive Cu(I), accessibility of the species into the polyurethane layer containing the catalyst, the level of reducing agents (ascorbate) used in solution to help generate reactive Cu(I) species, and the concentration of metal ion complexing agents present in the test solution (e.g., EDTA). Under optimized conditions, all RSNO species can be detected at < or =1 microM levels, with sensor lifetimes of at least 10 days for the sensors based on Cu(II)-phosphate and Cu0 particles. It is further shown that the new RSNO sensors can be used to assess the "NO-generating" ability of fresh blood samples by effectively detecting the total level of reactive RSNO species present in such samples.

A kinetic study for electrooxidation of NO gas at a Pt/membrane electrode-application to amperometric NO sensor

The electrochemical oxidation of nitric oxide (NO) gas at a Pt/membrane electrode has been studied. The Pt/Nafion ® electrode was prepared by the impregnation–reduction (I–R) chemical plating method and was tested over the NO concentration range from 0 to 500 ppm. It is assumed that the electrooxidation of NO gas at the electrode can be considered as an irreversible process, from which a transcendental equation describing the I– E relationship can be derived. The derived I– E relationship fits the experimental data reasonably well. Several electrochemical parameters for the reaction, including the half-wave potential ( E 1/2), the standard apparent rate constant ( rak 0), the transfer coefficient ( α), and the exchange current density ( i 0) can be extracted from the experimental data. Under the kinetic controlled regime, with the potential in the range of 0.7–0.9 V (versus Ag/AgCl/sat. KCl), the kinetic model predicts the electrooxidative behavior of NO at a Pt/Nafion ® electrode over a wide concentration range of 100–500 ppm. An amperometric NO gas sensor based on a Pt/Nafion ® electrode has been fabricated and tested over the NO concentration range from 0 to 500 ppm at 1.15 V (versus Ag/AgCl/sat. KCl) and a flow rate of 200 ml per min.

Electrochemical investigations on multi-metallic electrodes for amperometric NO gas sensors

The activities of Pt/YSZ, PtAu/YSZ and RhPtAu/YSZ thick film electrodes in O 2, N 2 and NO, N 2 gas mixtures at high temperatures were investigated by electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). As compared with the Pt/YSZ electrode the cathodic O 2 reduction at both multi-metallic electrodes is strongly inhibited, which is confirmed by charge transfer resistance for cathodic O 2 reduction as follows: R ct(Pt/YSZ) < R ct(PtAu/YSZ) < R ct(RhPtAu/YSZ). In contrast to that the cathodic NO reduction is accelerated only by the RhPtAu/YSZ electrode, indicating that the RhPtAu mixture is a suitable working electrode material for amperometric NO sensors based on the solid electrolyte (YSZ). A new amperometric NO sensor with only one working electrode made of RhPtAu mixture was tested in simulated gas mixtures containing NO, O 2, N 2, resulting in a linear response to the NO concentration, which is nearly independent of the O 2 concentration.

Enhanced sensing performance of the amperometric gas sensor by laser-patterning of the polymer membrane electrode

Ultraviolet laser patterning has been employed for enhancing the sensing performance of the electrochemical gas sensors. Two kinds of catalyst layers (platinum for CO and gold for SO 2) coated on the polytetrafluoloethylene film have been selectively removed by KrF laser irradiation. The laser fluence, repetition rate and number of shots were carefully controlled to avoid the damage of the membrane substrate. The threshold fluences for complete removal of gold film and PTFE-bonded platinum layer are about 60 and 500 mJ/cm 2, respectively. The sensors (especially the SO 2 sensors) with patterned catalyst electrodes exhibit excellent sensing capabilities in sensitivity as well as the response and recovery times. The sensitivity of the SO 2 sensor with patterned sensing electrode is about 0.63 μA/ppm, 14 times improved as compared with the unpatterned sensor. The response and recovery times are shortened from 11 and 17 s to 6 and 9 s, respectively. The signal-to-noise ratio is improved by two times. Due to the original good porous microstructure of the PTFE-bonded platinum layer, the improvement of the patterned CO sensor is not as much as that of the patterned SO 2 sensor. However, the sensitivity is doubled. The great enhancement in the sensing performance is attributed to the increase of the electrochemically active surface area and the higher diffusion efficiency.

Improvement of electrochemical NO 2 sensor by use of carbon–fluorocarbon gas permeable electrode

An amperometric gas sensor for the detection of nitrogen dioxide (NO 2) was developed by use of a novel gas diffusion electrode. The sensor using two types of gas permeable membranes was made to compare the sensitivity and selectivity for NO 2 detection. The sensor using carbon–fluorocarbon (C–F) membrane showed higher sensitivity for NO 2 and selectivity of NO 2 against ozone than that using conventional expanded PTFE membrane. The superior characteristic of the C–F sensor could be due to the high gas permeability and a catalytic nature of the C–F membrane. The sensor will be useful for monitoring of NO 2 in the atmosphere.

The electrochemical oxidation of ammonia at boron-doped diamond electrodes exhibits analytically useful signals in aqueous solutions

Boron-doped diamond electrodes are shown to exhibit well-defined analytically useful voltammetric signals for the electrochemical oxidation of ammonia in aqueous solutions in comparison to commonly used carbon based electrode substrates. Proof-of-concept is shown for the construction of a miniature amperometric ammonia gas sensor utilising conductive boron-doped diamond.

Chemical Sensors for Electronic Nose Systems

Chemical sensors have been widely used for the analysis of volatile organic compounds. Employing chemical sensors in an array format with pattern recognition provides a higher degree of selectivity and reversibility leading to an extensive range of applications. When such systems are used for odour analysis they are termed ‘electronic noses’. Application of electronic noses ranges from the food industry, medical industry to environmental monitoring and process control. Many types of different gas sensors have been employed in the array. These include conducting polymers, metal oxide semiconductors, piezoelectric, optical fluorescence and amperometric gas sensors The transducer principle of these sensors is varied and is discussed in detail within this review. Examples of the current trends in sensor array technology as well as the applications to which the sensor-based noses have been applied are also discussed.

Amperometric sensor for selective and stable hydrogen measurement

Amperometric gas sensors in a three-electrode configuration were investigated for hydrogen measurements in atmospheres containing carbon monoxide. The hydrogen-sensing working electrode was based on a platinum black electrode deposited on a porous Teflon ® substrate. To achieve selectivity, an FEP membrane was mounted at the gas inlet of the sensor. Hydrogen readily diffused through the FEP membrane and was detected on the Pt working electrode. The cross-sensitivity to gases such as carbon monoxide, ammonia and hydrogen sulfide was eliminated with nearly 100% efficiency in the short term. In addition, the poisoning effect of the carbon monoxide was virtually eliminated. Sensor stability to high levels of hydrogen was improved by the development of a hydrogen-insensitive reference electrode.

Amperometric nitrogen dioxide gas sensor based on PAn/Au/NafionS prepared by constant current and cyclic voltammetry methods

Polyaniline (PAn) was electro-deposited on Au/Nafion® by the cyclic voltammetry (CV) and constant current (CC) methods, respectively. The electrochemical properties and surface morphologies of PAn/Au/Nafion® were characterized by SEM, cyclic voltammetry, and ac impedance, respectively. The maximum BET surface area was found to be 10.36 m2 g−1 for PAn/Au/Nafion® prepared by CV method with cycle number of 25 in 1.0 M HClO4 aqueous solution. Using PAn/Au/Nafion® prepared by CV method in 1.0 M HClO4, 1.0 M HCl, and 0.5 M H2SO4 aqueous solutions as working electrodes, the sensitivities of NO2 gas sensors with a gas flow rate of 300 ml min−1 were evaluated to be 3.04, 2.68, and 2.54 μA ppm−1, respectively. Using PAn/Au/Nafion® prepared with CC method to fabricate NO2 gas sensor, the sensitivity decreased from 2.35 to 1.41 μA ppm−1 when the current density for preparing PAn/Au/Nafion® increased from 1 to 10 mA cm−2.

Amperometric nitrogen dioxide gas sensor based on PAn/Au/Nafion® prepared by constant current and cyclic voltammetry methods

Polyaniline (PAn) was electro-deposited on Au/Nafion® by the cyclic voltammetry (CV) and constant current (CC) methods, respectively. The electrochemical properties and surface morphologies of PAn/Au/Nafion® were characterized by SEM, cyclic voltammetry, and ac impedance, respectively. The maximum BET surface area was found to be 10.36m2g−1 for PAn/Au/Nafion® prepared by CV method with cycle number of 25 in 1.0M HClO4 aqueous solution. Using PAn/Au/Nafion® prepared by CV method in 1.0M HClO4, 1.0M HCl, and 0.5M H2SO4 aqueous solutions as working electrodes, the sensitivities of NO2 gas sensors with a gas flow rate of 300mlmin−1 were evaluated to be 3.04, 2.68, and 2.54μAppm−1, respectively. Using PAn/Au/Nafion® prepared with CC method to fabricate NO2 gas sensor, the sensitivity decreased from 2.35 to 1.41μAppm−1 when the current density for preparing PAn/Au/Nafion® increased from 1 to 10mAcm−2.

Amperometric Solid-State Gas Sensor Using LaGaO3 Based Perovskite Oxide Electrolyte for Detecting Hydrocarbon in Exhaust Gas: II. Improvement of Inactive Electrode Performance

(LSGM) based solid electrolyte coupled with suitable electrodes was demonstrated to be a highly sensitive hydrocarbon sensor in the temperature range of 523-673 K. Sensors were studied in the amperometric mode. Keeping Pt as the active electrode, the various inactive electrode materials were studied. It was seen that (LSC 55) gave the best sensitivity among the studied catalysts. Furthermore, it was found that the performance of the sensor with (LSM 55) showed the highest sensitivity (≈600 μA/decade at 623 K) among all the investigated perovskite oxides for an inactive electrode. The sensitivity of all the sensors was fast, reversible, and the current linearly increased with increasing concentration. Over a broad range of oxygen concentration, the sensitivity was found unaltered. The thickness of the electrolyte played an important role for increasing the sensitivity. The measured value of the open circuit potential in the potentiometric mode was very small; but it confirmed the development of mixed potential between the two electrodes which palyed the key role for changing current in the present amperometric sensor. © 2004 The Electrochemical Society. All rights reserved.

Amperometric Sensing of NOx with Cyclic Voltammetry.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Novel Amperometric O2 Gas Sensor Based on Supported Room‐Temperature Ionic Liquid Porous Polyethylene Membrane‐Coated Electrodes

AbstractA novel solid‐state amperometric O2 gas sensor based on the supported 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIBF4) porous polyethylene membrane‐coated electrodes has been proposed with its characterization. By electrochemical impedance technique, the ionic conductivity of the supported EMIBF4 membrane was estimated to be ca. 0.6 S m−1, indicating that the supported EMIBF4 membrane (the thickness: 50 μm) can be used as a solid state ionic conductor at room temperature. The cyclic voltammograms obtained for the one‐electron redox reaction of O2/O2−.(O2−.: superoxide ion) couple at high scan rates (&gt;100 mV s−1) showed a couple of usual redox peaks, while at low scan rates (&lt;30 mV s−1) S‐shaped steady‐state voltammograms similar to those obtained by rotating disk voltammetry were obtained. These results were explained on the basis of the mass transport of O2 at the supported EMIBF4 membrane‐coated electrode system. The transient and steady‐state reduction currents for the reduction of O2 to O2−.as well as the transient oxidation current for the reoxidation of O2−.to O2, which were obtained by potential‐step chronoamperometry, could be used to measure the change of O2 concentration in O2‐N2 mixed gas stream. The present O2 gas sensor demonstrated a wide detection range, a high sensitivity and an excellent reproducibility.

O2 Gas Sensor Using Supported Hydrophobic Room-temperature Ionic Liquid Membrane-coated electrode

Abstract A solid-state amperometric O2 gas sensor was successfully fabricated by using supported 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) porous polyethylene membrane as a solid-state electrolyte. The present O2 gas sensor, which is capable of being operated at room temperature, shows a wide detection range and a high stability.