Stabilization of sensing performance for mixed-potential-type zirconia-based hydrocarbon sensor

The recently reported sensing characteristics of the mixed-potential-type yttria-stabilized zirconia (YSZ)-based hydrocarbon (HC) sensor attached with ZnCr₂O₄-sensing electrode (SE) were found to be changed after the 10-day operation at 550 °C under the wet condition (5 vol.% water vapor). To improve the stability of the present sensor, the several modifications of the SE material by adding YSZ powder were examined. As a result, the sensor using the laminated (ZnCr₂O₄/YSZ)-SE gave the stable electromotive force (emf) response against 100 ppm C₃H₆ at 550 °C for about one month examined. Based on the scanning electron microscopy (SEM) observation and the AC complex-impedance measurements, it was concluded that the stable behavior of the sensor using the laminated (ZnCr₂O₄/YSZ)-SE was provided by the stabilization of the interface between ZnCr₂O₄ grains and YSZ particles. The fabricated sensor exhibited the linear dependence of sensitivity on the logarithm of either C₃H₆ concentration (in the range of 20-800 ppm) or mixtures of various hydrocarbons (HCs) (in the range of 90-2600 ppmC). In addition, the emf response was not altered by the change of O₂ (2-20 vol.%), H₂O (0-10.8 vol.%) and CO₂ (0-20 vol.%) concentrations, and no interference of other gases (CO, NO, NO₂, H₂, and CH₄) was observed.     

Potentiometric NOx sensor based on stabilized zirconia and NiCr2O4 sensing electrode operating at high temperatures

The two types of electrochemical sensors using stabilized zirconia and the oxide sensing electrode (SE) were developed for NO_x detection at high temperatures. For the mixed-potential-type sensor, NiCr₂O₄ was found to give fairly excellent NO_x sensing characteristics in air among several spinel-type oxides tested. This NO_x sensor provided a linear correlation between EMF and the logarithm of NO or NO₂ concentration in the range 25–436 ppm and in the temperature range 550–650°C. With fixed bias voltage being applied between the SE (oxide) and the counter (Pt) electrode (CE), the EMF between SE and the reference (Pt) electrode (RE) was measured as a sensing signal. The NiCr₂O₄-attached tubular device was found to provide selective response to NO over NO₂ if SE was polarized at +175 mV versus RE. It was also found that this device gave selective response to NO₂ over NO, if SE was polarized at −250 mV versus CE. The new design of the planar device was proposed to avoid the cross-sensitivities to the others gases usually coexisting in car exhausts.     

纳米结构CuO为敏感电极的阻抗谱型NO2传感器

以浸渍技术制备的纳米CuO颗粒作敏感电极,以YSZ作为固体电解质制备了阻抗谱型NO2传感器。采用XRD、SEM对NO2传感器敏感材料的相组成和微观形貌进行了表征,应用电化学工作站测试了传感器的敏感性能。结果表明:浸渍法制得的CuO颗粒均匀分布在电解质的多孔层内,粒径在200 nm左右。在450～550℃,传感器对NO2有良好的敏感性,在0.1 Hz总阻抗|Z|=(Z′2+Z″2)～(1/2)姨与NO2浓度(0～200 mL.m-3)呈良好的线性关系。传感器的固有响应时间为50 s,共存的O2和CO2气体对传感器敏感性能几乎没有影响。     

Selective CO Detection Using YSZ-based Sensor with a Combination of CuCrFeO4 and CoCrFeO4 Electrodes

A solid-state potentiometric sensor using yttria-stabilized zirconia (YSZ) as a solid electrolyte and oxide electrodes has been developed for selective CO detection. At 450^oC, the YSZ-based sensor using CuCrFeO₄ sensing-electrode (SE) was found to have similar gas sensing characteristic with the sensor using CoCrFeO₄-SE, except toward CO. When both SEs was paired on a YSZ tube, the responses to various gases except for CO could be cancelled out for the resulting combined-SEs sensor. Thus, this sensor could generate a sensitive and selective response to CO at 450^oC even under humid conditions.     

Gas sensing with nano-indium oxides (In2O3) prepared via continuous hydrothermal flow synthesis

A rapid, clean, and continuous hydrothermal route to the synthesis of ca. 14 nm indium oxide (In(2)O(3)) nanoparticles using a superheated water flow at 400 °C and 24.1 MPa as a crystallizing medium and reagent is described. Powder X-ray diffraction (XRD) of the particles revealed that they were highly crystalline despite their very short time under hydrothermal flow conditions. Gas sensing substrates were prepared from an In(2)O(3) suspension via drop-coating, and their gas sensing properties were tested for response to butane, ethanol, CO, ammonia, and NO(2) gases. The sensors showed excellent selectivity toward ethanol, giving a response of 18-20 ppm.     

Microwave-assisted hydrothermal synthesis of Pt/SnO2 gas sensor for CO detection

In this paper, the Pt/SnO₂ nanostructures were prepared via a facile one-step microwave assisted hydrothermal route. The structure of the introduced Pt/SnO₂ and its gas-sensing properties toward CO were investigated. The results from the TEM test reveal that Pt grows on the SnO₂ nanostructure, which was not found for bulk in this situ method, constructing Pt/SnO₂. The results indicated that the sensor using 3.0 wt% Pt/SnO₂ to 100 ppm carbon monoxide performed a superior sensing properties compared to 1.5 wt% and 4.5 wt% Pt/SnO₂ at 225 °C. The response time of 3.0 wt% sensor is 16 s to 100 ppm CO at 225 °C. Such enhanced gas sensing performances could be attributed to the chemical and electrical factors. In view of chemical factors, the presence of Pt facilitates the surface reaction, which will improve the gas sensing properties. With respect to the electrical factors, the Pt/SnO₂ plays roles in increasing the sensor’s response due to its characteristic configuration. In addition, the one-step in situ microwave assisted process provides a promising and versatile choice for the preparation of gas sensing materials.     

Sensing characteristics of aged zirconia-based hydrogen sensor utilizing Zn–Ta-based oxide sensing-electrode

We report here the enhanced sensing characteristics to H₂ for a potentiometric sensor using an yttria-stabilized zirconia (YSZ) solid electrolyte and a ZnO(+ 84 wt.% Ta₂O₅) sensing electrode (SE) after aging at 500 °C. The emf response toward 400 ppm H₂ was found to gradually increase up to − 800 mV after 40 days operation (aging) and was stabilized at this value until the 90th day. The aged and stabilized sensor exhibited highly sensitive response to H₂, with minor responses toward other examined gases such as NOx and HCs. The 90% response time toward 100 ppm H₂ was approximately 70 s. The H₂ sensitivity of the stabilized sensor was hardly affected by changes in water vapor as well as O₂ concentration, with repeatable and reproducible responses to H₂.     

Homogeneous Platinum‐Deposited Screen‐Printed Edge Band Ultramicroelectrodes for Amperometric Sensing of Carbon Monoxide

We report here the fabrication and application of an electrochemical carbon monoxide (CO) gas sensor based on the deposition of Pt nanoparticles on a screen‐printed edge band ultramicroelectrode (SPUME) with Nafion as the solid polymer electrolyte. Homogeneous size and distribution of Pt nanoparticles is stably deposited on the SPUME without either protective or capped agents. The edge diffusion effect at the SPUME, to even out the generation rate of hydrogen and to speed up the mass transfer of Pt solution, is believed to play a key role in achieving the deposition result. The obvious advantage of the proposed ultramicroelectrode system is that no supporting electrolyte (i.e., internal electrolyte) is required in the sensor scheme. The current–time curve recorded under conditions of +0.45 V vs. pseudo Ag reference electrode and various CO concentrations suggests that current response depends linearly on CO concentration up to 1000 ppm (correlation coefficient=0.994) with a sensitivity of 3.76 nA/(ppm?cm²). This report demonstrates potential application of the disposable CO gas sensor.     

Preparation of porous α-Fe2O3-supported Pt and its sensing performance to volatile organic compounds

Porous α-Fe2O3 was synthesized by a simple hydrothermal treatment of FeCl3 aqueous solution followed by a calcination process. In the synthesis of porous α-Fe2O3, no templates or pore-directing agents were used. The as-prepared porous α-Fe2O3 was further employed as a support for loading Pt nanoparticles. The gas sensing performance of the obtained porous α-Fe2O3-supported Pt to VOCs was investigated. The sensor presented a high response and fast response-recovery characteristic to several VOCs including acetone, ether, methanol, ethanol, butanol and hexanol. Meanwhile, it exhibited a much higher response than the pure α-Fe2O3 at the operating temperature of 260°C. The enhanced sensing properties may be related to the unique porous structure of the α-Fe2O3 support and the promoting effect of active Pt nanoparticles for the sensing reactions.     

A sensitive enzymeless hydrogen-peroxide sensor based on epitaxially-grown Fe3O4 thin film

A novel and facile approach has been developed to synthesize thin films of magnetite (Fe(3)O(4)) with epitaxial needle-like columnar grains on titanium nitride (TiN) buffered substrate using DC magnetron reactive sputtering. TiN buffer layer was first sputtered onto a substrate at 550 °C as a preferable substrate for growth following sputtering of epitaxial crystalline Fe(3)O(4) at 300 °C. The as-synthesized epitaxial Fe(3)O(4) was extensively characterized. The electrocatalytic activity of the epitaxial Fe(3)O(4) thin-film sensor against hydrogen peroxide (H(2)O(2)) reduction was rapid with a response time less than 5 s. The sensor also exhibited an acceptable stability, a satisfying sensitivity of 432.2 μA mM(-1) cm(-2), good specificity to the substrate, a dynamic working range of up to 0.7 mM and a low detection limit of 1.0 μM. The sensor performance correlated well (R(2)=0.996) with results obtained using a commercial HPLC-UV device. The sensor performance was robust and accurate in measuring H(2)O(2) in some complex matrices. The advantages of relative simplicity and ease of mass production make the epitaxial Fe(3)O(4) thin film promising candidate for use in sensing applications.     

Effect of Bimetallic Pd/Pt Clusters on the Sensing Properties of Nanocrystalline SnO<Subscript>2</Subscript> in the Detection of CO

Nanocrystalline tin dioxide modified by Pd and Pt clusters or by bimetallic PdPt nanoparticles was synthesized. Distribution of the modifers on the SnO₂ surface was studied by high-resolution transmission electron microscopy and energy dispersive X-ray microanalysis with element distribution mapping. It was shown that the Pd/Pt ratio in bimetallic particles varies over a broad range and does not depend on the particle diameter. The effect of platinum metals on the reducibility of nanocrystalline SnO₂ by hydrogen was determined. The sensing properties of the resulting materials towards 6.7 ppm CO in air were estimated in situ by electrical conductivity measurements. The sensor response of SnO₂ modified with bimetallic PdPt particles was a superposition of the signals of samples with Pt and Pd clusters.     

Study of an Au colloid self-assembled electrode and its application to the determination of carbon monoxide

A novel electrochemical sensor has been developed for the detection of carbon monoxide. The chemically modified electrode, prepared by reaction of cysteine and then an Au colloid of size approximately 15 nm with a platinum microelectrode, has excellent catalytic activity toward carbon monoxide, with an oxidation potential of +600 mV relative to the Ag/AgCl electrode. The CO gas sensor is based on an Au colloid self-assembled modified electrode as working electrode, an Ag/AgCl electrode as reference electrode, a Pt electrode as counter electrode, and a porous film which is in direct contact with the gas-containing atmosphere. The effects on the determination of CO of different internal electrolyte solutions of perchloric acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphate buffer of different concentrations were also studied. The sensor is characterized by a short response time and highly reproducible detection of CO. This sensor can be used in the field of environmental monitoring and control.     

Study of an Au colloid self-assembled electrode and its application to the determination of carbon monoxide

A novel electrochemical sensor has been developed for the detection of carbon monoxide. The chemically modified electrode, prepared by reaction of cysteine and then an Au colloid of size approximately 15 nm with a platinum microelectrode, has excellent catalytic activity toward carbon monoxide, with an oxidation potential of +600 mV relative to the Ag/AgCl electrode. The CO gas sensor is based on an Au colloid self-assembled modified electrode as working electrode, an Ag/AgCl electrode as reference electrode, a Pt electrode as counter electrode, and a porous film which is in direct contact with the gas-containing atmosphere. The effects on the determination of CO of different internal electrolyte solutions of perchloric acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphate buffer of different concentrations were also studied. The sensor is characterized by a short response time and highly reproducible detection of CO. This sensor can be used in the field of environmental monitoring and control.     

Mixed-potential-type propylene sensor based on stabilized zirconia and oxide electrode

By using an oxide sensing electrode, a stabilized zirconia-based sensor was developed for the selective detection of hydrocarbons at high temperature. Among the 14 kinds of oxides tested, CdO was found to be best suited for the sensing electrode of a tubular device, giving selective and quick response to propylene (C₃H₆) in air at 600°C. The emf value of the device was almost linear to the logarithm of C₃H₆ concentration in the range 50–800 ppm. The cross-sensitivities to other gases, such as CH₄, C₂H₄, C₂H₆, C₃H₈, H₂, CO, NO and NO₂, were small or insignificant. Furthermore, a compact planar device, which required no reference gas, was also fabricated. The C₃H₆ sensitivity of the planar device was found to be hardly influenced by a change in oxygen concentration in the sample gas in the range 2–21 vol.%. A sensing mechanism involving mixed potential was confirmed based on the measurements of polarization curves.     

Fabrication of multiwalled carbon nanotubes/polyaniline modified Au electrode for ascorbic acid determination

An ascorbate oxidase (AsOx) (E.C.1.10.3.3) purified from Lagenaria siceraria fruit was immobilized covalently onto a carboxylated multiwalled carbon nanotubes and polyaniline (c-MWCNT/PANI) layer electrochemically deposited on the surface of an Au electrode. The diffusion coefficient of ascorbic acid was determined as 3.05 × 10(-4) cm(2) s(-1). The behavior of different electrolytes on electro-deposition was also studied. An ascorbate biosensor was fabricated using a AsOx/c-MWCNT/PANI/Au electrode as a working electrode, Ag/AgCl (3 M/saturated KCl) as standard and Pt wire as an auxiliary electrode connected through a potentiostat. Linear range, response time and detection limit were 2-206 μM, 2 s and 0.9 μM respectively. The biosensor showed optimum response at pH 5.8 and in a broader temperature range (30-45 °C), when polarized at +0.6 V. The biosensor was employed for determination of ascorbic acid level in sera, fruit juices and vitamin C tablets. The sensor was evaluated with 91% recovery of added ascorbic acid in sera and 6.5% and 11.4% within and between batch coefficients of variation respectively for five serum samples. There was a good correlation (r = 0.98) between fruit juice ascorbic acid values by the standard 2,6-dichlorophenolindophenol (DCPIP) method and the present method. The enzyme electrode was used 200 times over a period of two months, when stored at 4 °C. The biosensor has advantages over earlier enzyme sensors in that it has no leakage of enzyme, due to the covalent coupling of enzyme with the support, lower response time, wider working range, higher storage stability and no interference by serum substances.     

Zirconia-based amperometric sensor using ZnO sensing-electrode for selective detection of propene

The sensing characteristics to propene (C₃H₆) were examined at 600 °C under wet condition for the amperometric sensor using a yttria-stabilized zirconia (YSZ) tube and ZnO (+8.5 wt%Pt) sensing-electrode (SE). In order to improve the sensitivity to C₃H₆, the “pulsed-potential method” was adopted here. It was found that the current response varied almost linearly with C₃H₆ concentration in the range of 0–200 ppm when SE was polarized at +1.0 V (vs. Pt/air reference electrode) for a period of 0.3 s. By using the present “pulsed-potential method”, the sensitivity to 100 ppm C₃H₆ was increased about 1000 times, compared with the normal “constant-potential method”. The excellent selectivity to C₃H₆ was also obtained for the present sensor without influence of other hydrocarbons, NO_x, CO, H₂, etc.     

纳米Pt/巯基丁二酰胺铜修饰电极的制备及其电催化活性

利用电沉积法将纳米Pt固定在巯基丁二酰胺铜(II)自组装金电极(Au/CuL)表面, 制备了一种纳米催化电极(Au/CuL/nano Pt). 分别以扫描电子显微镜(SEM)、原子力显微镜(AFM)、光电子能谱(XPS), 表面红外光谱(FT-IR)及电化学交流阻抗(EIS)对电极表面形貌进行了表征, 并采用循环伏安法(CV)研究了它的电化学性质. 结果表明, CuL具有良好的电化学活性并对H2O2的还原具有电催化作用, 纳米Pt可以显著增强这种催化性能. 在30 ℃、0.02 mol·L-1 PBS缓冲液(pH=6.0)中检测H2O2, 在0.00125-0.16 mmol·L-1浓度范围呈现线性响应, 相关系数为0.9960(信噪比为3), 检测极限为0.3 μmol·L-1. 该电极对H2O2电流响应灵敏度高(0.312 mA·cm-2·mmol-1·L)、检测迅速(4.3 s)、稳定性好(对46 μmol·L-1和2.8 mmol·L-1的H2O2连续测10 次, 变异系数分别为3.1%和3.9%; 保存70 d后对10 μmol·L-1 H2O2的响应为初始响应的95%).     

基于Pt/Au双金属修饰针灸针的非酶葡萄糖传感器

通过在不锈钢针灸针（AN）表面依次电沉积金（Au）纳米颗粒和铂（Pt）纳米颗粒,基于它们在AN表面的协同作用,实现了一种用于非酶葡萄糖检测的电化学生物传感器。首先,通过扫描电子显微镜对其功能界面（Pt/Au/AN）进行表征,结果显示类似卷心菜的纳米材料均匀致密地分布在AN表面。然后,通过循环伏安法和电化学阻抗法对Pt/Au/AN电极的电化学特性进行了研究。结果表明,与Au/AN或Pt/AN电极相比,Pt/Au/AN电极对葡萄糖氧化表现出优越的电催化活性。这表明双金属Pt/Au的接触界面是葡萄糖氧化的重要电催化位点。在pH7.4的模拟生理介质中,制得传感器的线性范围为0.1~35 mmol·L^-1,检测限为0.0763 mmol·L^-1,对葡萄糖的检测表现出较高的灵敏度和良好的抗干扰性能、稳定性。此外,该传感器已成功用于人体血清葡萄糖的检测。     

Binary clusters AuPt and Au6Pt: structure and reactivity within density functional theory

Within density functional theory with the general gradient approximation for the exchange and correlation, the bimetallic clusters AuPt and Au(6)Pt have been studied for their structure and reactivity. The bond strength of AuPt lies between those of Au(2) and Pt(2), and it is closer to that of Au(2). The Pt atom is the reactive center in both AuPt and AuPt(+) according to electronic structure analysis. AuPt(+) is more stable than AuPt. Au(6)Pt prefers electronic states with low multiplicity. The most stable conformation of Au(6)Pt is a singlet and has quasi-planar hexagonal frame with Pt lying at the hexagonal center. The doping of Pt in Au cluster enhances the chemical regioselectivity of the Au cluster. The Pt atom essentially serves as electron donor and the Au atoms bonded to the Pt atom acts as electron acceptor in Au(6)Pt. The lowest triplet of edge-capped rhombus Au(6)Pt clusters is readily accessible with very small singlet-triplet energy gap (0.32 eV). O(2) prefers to adsorb on Au and CO prefers to adsorb on Pt. O(2) and CO have stronger adsorption on AuPt than they do on Au(6)Pt. CO has a much stronger adsorption on AuPt bimetallic cluster than O(2) does. The adsorption of CO on Pt modifies the geometry of AuPt bimetallic clusters.     

NASICON-based H2 Sensor Using CoCrMnO4 Insensitive Reference Electrode and Buried Au Sensing Electrode

This work focuses on the H2 sensing performance of the sensor with buried Au sensing electrode and spi- nel-type oxide CoCrMnO4 insensitive reference electrode within sodium super ionic conductor（NASICON） film. The sensor showed the highest response to H2 gas on the insensitive material sintering at 800 ~C. Compared with those of the traditional structure device, the sensitivity and selectivity of the sensor using buried sensing electrode were greatly improved, giving a response of-177 mV in 9x10 5 g/L H2, which was about 3.5 times higher than that of sensors with traditional structure. Moreover, the AV value of the sensing device exhibited linear relationship to the logarithm of H2 concentration and the sensitivity（slope） was -135 mV/decade. A sensing mechanism related to the mixed potential was proposed for the present sensor.