Electrode materials for potentiometric hydrogen sensors

Due to their relatively high sensitivity, improved long-term stability, possibilities for miniaturization and low cost products, mixed potential solid electrolyte sensors can be competitive for the in situ measurement of hydrogen trace concentrations in oxygen containing gases. Their response behavior in non-equilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. In this work the sensitivity of electrodes made of composites (Au/MeO) has been investigated in hydrogen containing gases in the concentration range φ(H₂) = 0…800 vol.-ppm using a two-chamber setup with Pt-air reference. Electrodes made of Au/Nb₂O₅ composites show the highest sensitivities of up to 20 mV/vol.-ppm at φ(H₂) = 10 vol.-ppm and the lowest catalytic activity for hydrogen oxidation. Selected composite materials were tested additionally in self-heated solid electrolyte sensors with both electrodes exposed to the same atmosphere (gas-symmetrical sensor).     

Influence of ceramic oxide materials on lithium based potentiometric CO2 sensors

In these potentiometric sensors, a mixed binary carbonate sensing material consisting of 90 mol% Li₂CO₃ and 10 mol% BaCO₃ was modified by adding ceramic oxide materials such as SiO₂, B₂O₃, La₂O₃, Bi₂O₃, CeO₂ and In₂O₃ in different mol% concentrations. Various sensors mixed with these external oxides have shown good performance at operating temperatures below 300 °C. Scanning electron microscopy reveals that a glassy sensing phase is formed in the sensing bi-carbonate by the addition of ceramic oxides and sintered at 600 °C for 1 h. The sensor mixed with SiO₂:B₂O₃:Bi₂O₃ in 1:2:1 mol% showed an excellent response and recovery characteristics and followed a fair Nernstian behavior with a ΔEMF/dec value of −48.18 at as low as 150 °C. The decrease in operating temperature is attributed to the enhanced lithium ion migration through the glassy sensing phase of the sensing electrode.     

Modeling and simulation of light-addressable potentiometric sensors

Results of modeling and theoretical simulation of the influence of intensity-modulated irradiation on the light-addressable potentiometric sensors based on the electrolyte-insulator-semiconductor and electrolyte-membrane-insulator-semiconductor structures are presented. A theoretical model for measuring a.c. photocurrent is developed based on the assumption that under modulated irradiation the conductivity of the semiconductor depletion layer is modulated. The electric equivalent a.c. schemes are presented and the measured a.c. components of photocurrents are calculated. Analytical expressions for photocurrent dependences on the parameters of the semiconductor and insulator, irradiation adsorption coefficient and intensity, gate voltage and pH concentration are presented. Numerical calculations were made for the p-Si/insulator/electrolyte and p-Si/insulator/membrane/electrolyte sensors. It is shown that only periodical excitation of any membrane brings to essential changes of the a.c. component of photocurrent.     

Diode-laser-based ultraviolet absorption sensor for nitric oxide

An all-solid-state continuous-wave laser system for ultraviolet absorption measurements of the nitric oxide (NO) molecule has been developed and demonstrated. The single-mode, tunable output of a 10-mW, 395-nm external-cavity diode laser (ECDL) is sum-frequency-mixed with the output of a 115-mW, frequency-doubled, diode-pumped Nd:YAG laser in a beta-barium-borate crystal to produce 40 nW of tunable radiation at 226.8 nm. The wavelength of the 395-nm ECDL is then scanned over NO absorption lines to produce fully resolved absorption spectra. Initial results from mixtures of NO in nitrogen in a room-temperature gas cell are discussed. The estimated NO detection limit of the system for a demonstrated absorption sensitivity of 2×10^-3 is 0.2 ppm per meter of path length for 300 K gas. The estimated accuracy of the measurements is ±10%. Received: 25 February 2002 / Revised version: 31 May 2002 / Published online: 8 August 2002     

Doped thin metal oxide films for catalytic gas sensors

TiO₂ and Pt doped TiO₂ thin films were grown by pulsed laser deposition on 〈0 0 1〉 SiO₂ substrates. The doped films were compared with undoped ones deposited in similar experimental conditions. An UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser was used for the irradiation of the TiO₂ or Pt doped TiO₂ targets. The substrate temperatures were fixed during the growth of the thin films at values within the 300-500 °C range. The films’ surface morphology was investigated by atomic force microscopy and their crystalline quality by X-ray diffractometry. The corresponding transmission spectra were recorded with the aid of a double beam spectrophotometer in the spectral range of 400-1100 nm. No contaminants or Pt segregation were detected in the synthesized anatase phase TiO₂ thin films composition. Titania crystallites growth inhibition was observed with the increase of the dopant concentration. The average optical transmittance in the visible-infrared spectral range of the films is higher than 85%, which makes them suitable for sensor applications.     

Carbon nanotube-cuprous oxide composite based pressure sensors

In this paper,we present the design,the fabrication,and the experimental results of carbon nanotube (CNT) and Cu 2 O composite based pressure sensors.The pressed tablets of the CNT-Cu 2 O composite are fabricated at a pressure of 353 MPa.The diameters of the multiwalled nanotubes (MWNTs) are between 10 nm and 30 nm.The sizes of the Cu 2 O micro particles are in the range of 3-4 μm.The average diameter and the average thickness of the pressed tablets are 10 mm and 4.0 mm,respectively.In order to make low resistance electric contacts,the two sides of the pressed tablet are covered by silver pastes.The direct current resistance of the pressure sensor decreases by 3.3 times as the pressure increases up to 37 kN/m 2.The simulation result of the resistance-pressure relationship is in good agreement with the experimental result within a variation of ±2%.     

NO气体的空间交叉CARS

采用具有高空间分辨率的空间交叉BOX CARS相位匹配方法,完成了对NO气休室温下、Q支(v=0→v=1)振转CARS谱的测量,研究了它与NO气体压强及激光线宽的关系.从CARS基本理论出发,考虑到激光线宽及不同线型,计算出理论曲线,与实验谱线进行了比较,洛伦兹线型的理论模拟和实验结果符合较好.     

Electrochemical sensors based on transition metal oxide bronzes

Tungsten and molybdenum oxide bronzes of the general formulas A_xMO₃ and A_xM₆O₁₇ (A=K, Li, Na; M=W, Mo) are well known as electrode materials with good response to pH changes. However, there is also a high cross sensitivity to other ions, e.g. Na⁺ or Li⁺. Currently, the synthesis of tailored materials for special applications is the priority task. Preparation routes such as fused salt electrolysis, solid state reactions in vacuum or hydrothermal synthesis were studied. New compounds of the general formula Li_xMo_1−yW_yO₃ and also A_xWO₃ (A = bi- or trivalent) have a high technological potential. Preliminary experiments have shown that some of these new materials possess properties of reference electrodes within a restricted pH range. To prepare electrodes, usually single crystals are required. This is adverse because of high operating expense of single crystal synthesis. In some cases it is also possible to use polycrystalline materials for the preparation. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

Carbon nanotubeben cuprous oxide composite based pressure sensors

In this paper, we present the design, the fabrication, and the experimental results of carbon nanotube (CNT) and Cu₂O composite based pressure sensors. The pressed tablets of the CNT-Cu₂O composite are fabricated at a pressure of 353 MPa. The diameters of the multiwalled nanotubes (MWNTs) are between 10 nm and 30 nm. The sizes of the Cu₂O micro particles are in the range of 3-4 μm. The average diameter and the average thickness of the pressed tablets are 10 mm and 4.0 mm, respectively. In order to make low resistance electric contacts, the two sides of the pressed tablet are covered by silver pastes. The direct current resistance of the pressure sensor decreases by 3.3 ×as the pressure increases up to 37 kN/m². The simulation result of the resistance-pressure relationship is in good agreement with the experimental result within a variation of ± 2%.     

Strain sensors based on carbon nanotubes-cuprous oxide composite

This paper presents the design, fabrication and experimental results of carbon nanotubes-cuprous oxide (CNTs-Cu₂O) composite based strain sensors. The press-tablets were fabricated from the blend of CNTs (25 wt%) and Cu₂O (75 wt%) at a pressure of 353 MPa. The diameter of multiwalled carbon nanotubes (MWCNTs) varied between 10 and 30 nm. The sizes of Cu₂O micro-particles were in the range of 3-4 μm. The thickness of the press-tablets was 1 mm. The samples were installed on the polymer elastic beam by glue. The electric contacts to the samples were made by silver paste. The inter-electrodes distance (length) and diameter of the surface-type samples were in the range of 6-8 mm and 10 mm, respectively. The DC resistance of the strain sensors increases under tension and decreases under compression, while the average strain sensitivities are in the range of 44-46 and 24-28 for tension and compression, respectively. The simulation is in good agreement with the experimental results.     

Zinc oxide nanostructures for applications as ethanol sensors and dye-sensitized solar cells

ZnO nanostructures were prepared by thermal oxidation technique for applying as ethanol sensors and dye-sensitized solar cells. To improve sensitivity of the sensor based on ZnO nanostructures, gold doping was performed in ZnO nanostructures. Gold-doped with 0%, 5%, and 10% by weight were investigated. The improvement of sensor sensitivity toward ethanol due to gold doping was observed at entire operating temperature and ethanol concentration. The sensitivity up to 145 was obtained for 10% Au-doped ZnO sensor. This can be explained by an increase of the quantity of oxygen ion due to catalytic effect of gold. Also, it was found that oxygen ion species at the surface of the Au-doped ZnO sensor remained O²⁻ as pure ZnO sensor. For dye-sensitized solar cell application, the dye-sensitized solar cell structure based on ZnO as a photoelectrode was FTO/ZnO/Eosin-Y/electrolyte/Pt counter electrode. ZnO with different morphologies of nanobelt, nano-tetrapod, and powder were investigated. It was found that DSSCs with ZnO powder showed higher photocurrent, photovoltage and overall energy conversion efficiencies than that of ZnO nanobelt and ZnO nano-tetrapod. The best results of DSSCs were the short circuit current (J_sc) of 1.25 mA/cm², the open circuit voltage (V_oc) of 0.45 V, the fill factor (FF) of 0.65 and the overall energy conversion efficiency (η) of 0.68%.     

Chemisorption of nitric oxide by nickel

The adsorption of nitric oxide on clean and pre-oxidized nickel has been investigated by X-ray photoelectron spectroscopy. Three distinct states of chemisorption have been recognised at room temperature; one is dissociative while two involve molecularly adsorbed NO. Pre-exposing the nickel surface to oxygen enabled the activity of the surface to be controlled such that adsorption was confined to only one of the molecular states. The two molecular states are suggested to arise from “bent” and “linear” forms of NO.     

Effect of palladium oxide electrode on potentiometric sensor response to carbon monoxide

Ionics - This study aims to explore the potential merits of palladium oxide sensing electrode. PdO is applied on a solid-state potentiometric sensor on an yttria-stabilized zirconia (YSZ)...     

Infrared diode laser spectroscopy of nitric oxide

The lineshapes of the rotational-vibrational lines $\text{R(}\text{17}\text{2}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{, R(}\text{19}\text{2}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, and $\text{R(}\text{19}\text{2}\text{)}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ of nitric oxide were measured using a PbS_0.61Se_0.39 diode laser. These lineshapes were measured for a NO/N₂ mixture and an NO/H₂O/N₂ mixture at atmospheric pressure. This is the first high resolution spectroscopic mearuement of the rotational-vibrational lineshape of NO broadened by H₂O. The effect of the H₂O is to broaden the lines, increasing the halfwidth by up to 30% for a 10% volume concentration of H₂O. For the case of NO broadened by N₂, the measured linestrengths for the $\text{R(}\text{19}\text{2}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{R(}\text{17}\text{2}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ lines are within 2% of previously published values.     

Ultrahigh-frame-rate nitric oxide planar laser-induced fluorescence imaging

We demonstrate the ability to generate ultrahigh frequency burst sequences of deep UV at 226 nm by mixing the optical parametric oscillator signal output at 622 nm with third harmonic at 355 nm from a pulse burst laser system. We obtained 226 nm burst sequences with uniform burst envelopes, and the average pulse energy is approximately 0.5 mJ. Nitric oxide planar laser-induced fluorescence image sequences at ultrahigh (100 kHz) frame rates have been obtained.     

An optical system for measuring nitric oxide using spectral separation techniques

An optical sensor based on differential absorption spectroscopy for real-time monitoring of industrial nitric oxide (NO) gas emission is described. The influence of gas absorption interference from sulfur dioxide (SO₂) in the environment was considered and a spectral separation technique was developed in order to eliminate this interference effect. The absorption spectrum of SO₂ around 226 nm was evaluated by the SO₂ concentration obtained using the experimentally recorded absorption spectrum around 300 nm. The absorption spectrum of NO around 226 nm was obtained by subtracting the absorption of SO₂ from the integral absorption spectrum of SO₂ and NO. The concentration measurements were performed at atmospheric pressure. The technique was found to have a lower detection limit of 0.8 ppm for NO per meter path length (SNR=2) and be immune from the influence from SO₂ on the NO measurement. The sensor based on this technique was successfully employed for in situ measurement of SO₂ and NO concentrations in the flue gas emitted from an industrial coal-fired boiler.     

Modified INOvent for delivery of inhaled nitric oxide during cardiac MRI

Background

The aim of this study was to assess the feasibility of delivering NO through a modified system to allow clearance of the magnetic field and thus compatibility with cardiac magnetic resonance (CMR). Nitric oxide (NO) is an inhalational, selective pulmonary vasodilator with a wide range of applications in a variety of disease states, including diseases that affect the right ventricle. Accurate assessment of dynamic changes in right ventricular function necessitates CMR; however, delivery of NO is only possible using equipment that is not magnetic resonance imaging (MRI) compatible (INOvent delivery system, Ohmeda, Inc., Madison, WI, USA).

Methods

The INOvent delivery system was modified by using 35 ft. of standard oxygen tubing to allow NO delivery through an electrical conduit and into the MRI suite. The concentrations of oxygen (O₂), nitrogen dioxide (a harmful byproduct, NO₂) and NO were measured in triplicate using the built-in electrochemical analyzer on the INOvent. After confirmation of safety, the system was used to administer drug to a patient x, and dynamic MRI measurements were performed.

Results

When the standard INOvent was set to administer 40 ppm of NO, the mean/standard deviation of gas delivered was as follows: NO: 42/0 ppm; NO₂: 0.3/0.1 ppm; and O₂: 93/0 ppm. In comparison, the gas delivery of the modified INOvent was follows: NO: 41/0 ppm; NO₂: 0.5/0 ppm; and O₂: 93.7/0.6 ppm. During administration to an index patient with severe pulmonic insufficiency (PI), a measurable reduction in PI was observed by CMR.

Conclusions

Nitric oxide can be administered through 35 ft. of standard oxygen tubing without significantly affecting dose delivery. This technique has potential application in patients with right-sided structural heart disease for determination of dynamic physiological changes.     

Reference electrode formation in potentiometric CO2 sensors with alkali ion conducting alumosilicate glasses as solid electrolytes

Potentiometric CO₂ gas sensors with Li conducting glasses/glass ceramics of the system Li₂O-Al₂O₃-SiO₂ (different nominal composition) as solid electrolytes have been investigated. Li₂CO₃ was used as CO₂ and O₂ sensitive auxiliary electrode. During the sensor test measurements, the CO₂ partial pressure was varied between 1×10⁻³ and 1×10⁻¹ bar at a constant O₂ partial pressure of 2.1×10⁻¹ bar whereas N₂ was used as carrier gas. Comparative measurements were accomplished with sensors comprising Na and K ion conducting glasses. A metastable reference electrode was formed at the contact zone between the Au metal electrode and the former Li glasses of definite nominal composition by crystallization processes taking place, which lead to stable, reproducible CO₂ dependent EMF signals for more than 90d. The thermodynamically expected EMF difference and the observed EMF difference agree quite well between 500 and 600 °C. At 600 °C, the drift of sensors with glasses as solid electrolytes and direct Au glass/glass ceramics contact as reference electrode amounts typically 0.32 mV/d (p(CO₂)=1×10⁻³ bar, p(O₂)=2.1×10⁻¹ bar at the measuring electrode), if a metastable multiphase equilibrium is formed. At identical partial pressures of CO₂ and O₂, the signal reproducibility of these sensors with different solid electrolyte glasses of the same nominal composition lies within 30 mV at 600 °C. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996