Response of electrochemical oxygen sensors to inert gas-air and carbon dioxide-air mixtures: measurements and mathematical modelling

Electrochemical oxygen gas sensors are widely used for monitoring the state of inertisation of flammable atmospheres and to warn of asphyxiation risks. It is well established but not widely known by users of such oxygen sensors that the response of the sensor is affected by the nature of the diluent gas responsible for the decrease in ambient oxygen concentration. The present work investigates the response of electrochemical sensors, with either acid or alkaline electrolytes, to gas mixtures comprising air with enhanced levels of nitrogen, carbon dioxide, argon or helium. The measurements indicate that both types of sensors over-read the oxygen concentrations when atmospheres contain high levels of helium. Sensors with alkaline electrolytes are also shown to underestimate the severity of the hazard in atmospheres containing high levels of carbon dioxide. This deviation is greater for alkaline electrolyte sensors compared to acid electrolyte sensors. A Computational Fluid Dynamics (CFD) model is developed to predict the response of an alkaline electrolyte, electrochemical gas sensor. Differences between predicted and measured sensor responses are less than 10% in relative terms for nearly all of the gas mixtures tested, and in many cases less than 5%. Extending the model to simulate responses of sensors with acid electrolytes would be straightforward.     

Inkjet printed electrode arrays for potential modulation of DNA self-assembled monolayers on gold

In this paper, we report a novel and cost-effective fabrication technique to produce electrode arrays that can be used for monitoring and electrical manipulation of the molecular orientation of DNA self-assembled monolayers (SAMs) on gold. The electrode arrays were prepared from gold coated glass sides or compact discs (CD-Rs) by using standard office inkjet printers without any hardware or software modifications. In this method, electrode arrays of varied shape and size (from submillimeter to centimeter) can be rapidly fabricated and are suitable for standard electrochemical measurements. We were able to use a dual-channel potentiostat to control the electrodes individually and a fluorescence (FL) scanner to image the electrode array simultaneously. With such an integrated modulation setup, the structural switching behavior (from "lying" to "standing" position) and the enhanced hybridization reactivity of thiolate DNA SAMs on gold under potential control have been successfully demonstrated.     

Ionic liquids as electrolytes for the development of a robust amperometric oxygen sensor

A simple Clark-type online electrochemical cell design, consisting of a platinum gauze working electrode and incorporating ionic liquids (IL) as electrolytes, has been successfully applied for the amperometric sensing of oxygen. Studying ILs comprising the bis(trifluoromethylsulfonyl)imide anion, the obtained analytical parameters were found to be strongly dependent on the choice of cation. Compared with a conventional Clark cell design based on an aqueous supporting electrolyte, the modified oxygen sensor achieves substantial improvements in performance and stability. A limit of detection for oxygen as low as 0.05 vol?%, linearity over an oxygen partial pressure between 0% and 20%, and a steady-state response time of 2 min was demonstrated, with a stable analytical response shown over the examined period of 90 days with no obvious fouling of the electrode surface. Based on the attractive physical attributes of ionic liquids (e.g., thermal stability beyond 150 °C), one can envision intriguing utility in nonstandard conditions and long-term online applications, as well as extension to the determination of other gases, such as methane and nitric oxide.     

A pulse amperometric sensor for the measurement of atmospheric hydrogen peroxide

Gaseous H(2)O(2) is sampled through a Nafion membrane diffusion scrubber while 1 mM HCl is maintained stationary in the scrubber. After a preselected preconcentration time (typically, 5-10 min), a valve is opened to allow the scrubber liquid to flow by gravity over an electrochemical H(2)O(2) sensor for a brief period. The miniature flow-over sensor consists of a Pt/Rh wire working electrode and a Pt wire counter electrode wound respectively on separate segments of a Nafion solid polymer electrolyte tubing supported on a Ag/AgCl wire reference electrode. A simple electronic interface and a personal computer are used to control and record the electrochemical measurement. The liquid phase detection limit for this sensor is ～30 nM H(2)O(2) in the anodic oxidation mode. For a 9 min gas sample preconcentration period, the LOD (S/N = 3 criterion) is 0.11 ppbv H(2)O(2)(g). Ambient H(2)O(2) data obtained with this instrument were in excellent agreement with those obtained by an established fluorometric technique in a blind intercomparison.     

(Ba(x)La(1-x)(2))In(2)O(5+x) (0.4 < or = x < or = 0.6) electrolyte-supported mixed-potential CO sensors

The dense (Ba(x)La(1-x)(2))In(2)O(5+x) electrolytes with different compositions (x = 0.4, 0.5, 0.6) were synthesized by Pechini method. The obtained sintered (Ba(x)La(1-x)(2))In(2)O(5+x) electrolytes showed a high relative density of approximately 98%, and the major phase of three electrolyte compositions was indexed as a cubic phase. The CO sensing properties of as-fabricated planar-type (Ba(x)La(1-x)(2))In(2)O(5+x)-based sensors coupled with ITO and Pt as the sensing electrode and reference electrode, respectively, were investigated. The effects of factors such as gas flow rate, chemical compositions, and density of the electrolytes on the sensing performance were investigated. The sensors showed good sensitivity to different concentrations of CO from approximately 100 to approximately 500 ppm and excellent selectivity over low concentrations of methane (<500 ppm). Linear relationships between emf of the sensors and CO gas concentrations from approximately 100 to approximately 400 ppm were observed. However, the sensors indicated more sluggish response compared with the sensors coupled with a corresponding porous electrolyte. The probable reason has been discussed. The long-term stability of the sensor for the detection of CO was also investigated, which indicated a reasonably stable sensor signal after an initial decline during the incubation period.     

The influence of the electrode size on the electrical response of a potentiometric gas sensor to the action of oxygen

As a part of our research on new gas sensors, an original potentiometric gas sensor was developed. This gas sensor is made of a solid electrolyte (beta alumina) associated with two different metallic electrodes (gold and platinum) located in the same gas mixture. Tests performed under oxygen pressure show that the potential difference read between the electrodes depends on the experimental conditions, oxygen pressure, and temperature, but also on the electrodes surface area ratio. Then, we studied the electrical responses of devices composed of electrodes of the same nature (gold or platinum) but of different size. These electrode size influences are analyzed in terms of different capacitive effects occurring at the electrode-solid electrolyte interface. If we consider that the adsorption of oxygen species is responsible for the electrostatic potential, the proposed model is able to account for the experimental results. It is then possible to explain and to better understand the importance of the electrodes on the electrical response of such a device.     

Electrochemical sensing of ethylene employing a thin ionic-liquid layer

We introduce an electrochemical ethylene sensor that employs a thin layer of ionic liquid as electrolyte. Ethylene is oxidized in a potential window starting ～600 mV before the onset of the gold working electrode oxidation, which inhibits the ethylene oxidation at high applied potential. The current amplitude and sensor response time depend on the ionic-liquid film thickness, relative humidity, and applied potential, in agreement with a theoretical model based on diffusion. A detection limit of 760 ppb and a linear response up to 10 ppm were achieved. As illustrated by the detection of ethylene, ionic liquids could serve as an alternative electrolyte for many electrochemical gas sensors that heretofore relied on a strongly acidic electrolyte.     

Electrochemical NO2 sensor using a NiFe1.9Al0.1O4 oxide spinel electrode

A novel solid-state electrochemical sensor using (Sc2O3)0.08(ZrO2)0.92 (ScSZ) electrolyte solid and a NiFe1.9Al0.1O4 oxide spinel electrode was tested for the detection of NO2 at temperatures greater than 700 degrees C for automobile applications. The sensor was found to respond rapidly, reproducibly, and selectively to NO2 at 703 and 740 degrees C. The response time of the sensor was approximately 8 s, and the recovery time was 10 s at both 703 and 741 degrees C. The response of the sensor was highly reproducible to the change in concentration of NO2 and also showed negligible cross-sensitivity to potentially interfering gases such as O2, CO, and CH4 in the gas stream.     

Sintering Caβ″/β/α-Al_2O_3 High Temperature Oxygen Sensor

An extended-life and ultra-low oxygen sensor has been fabricated by using polycrystalline Caβ″/β/α-Al2O3 as a solid electrolyte. Five reference electrodes CaO+O2, Caβ″/β/α-Al2O3 (powder)+O2,Cr+Cr2O3, Nb+NbO and Mo+MoO2 were tested in order to select a better reference electrode for this sensor. The limit of determining oxygen activity and the extended-life of the sensor were also tested in this study.     

Lithium-Ion Battery Separators for Ionic-Liquid Electrolytes: A Review

Ionic liquids (ILs) are widely studied as a safer alternative electrolyte for lithium-ion batteries. The properties of IL electrolytes compared to conventional electrolytes make them more thermally stable, but they also have poor wetting with commercial separators. In a lithium-ion battery, the electrolyte should completely wet out the separator and electrodes to reduce the cell internal resistance. Investigations of cell materials with IL electrolytes have shown that the wetting issues in IL–electrolyte cells are most likely due to poor separator compatibility, not electrode compatibility. A compatible separator must be developed before IL electrolytes can be used in commercial lithium-ion batteries. Herein, separators for IL electrolytes, including commercial and novel separators, are reviewed. Separators with different processing methods, polymers, additives, and different IL electrolytes are considered. Collated, the separator studies show a strong correlation between ionic conductivity and membrane porosity, even more than the electrolyte type. The challenge of a suitable separator for IL electrolytes is not solved yet. Herein, it is revealed that a separator for IL electrolytes will most likely require a combination of high thermal and mechanical stability polymer, ceramic additives, and an optimized manufacturing process.     

A carbon dioxide gas sensor by combination of multivalent cation and anion conductors with a water-insoluble oxycarbonate-based auxiliary electrode

A compact and inexpensive carbon dioxide gas sensor was successfully realized by the combination of a divalent magnesium ionic conductor of Mg0.7(Zr0.85Nb0.15)4P6O24 and a divalent oxide anion conducting ZrO2-Y2O3 solid electrolyte with the water-insoluble Li- and Ba-codoped Nd2O2CO3 solid solution as the auxiliary electrode. The sensor response was continuous and reproducible, and the present sensor also demonstrated a theoretical Nernst response in the atmosphere where water vapor, nitrogen oxides, ammonia, etc., coexist. The exposure of the present sensor to water dew and variation in oxygen concentration does not interfere with the sensor response, which will be a great advantage in applying the in situ practical CO2 detection in combustion exhaust gas atmospheres.     

In‐situ‐Sauerstoffmesszellen für den Einsatz im Vakuum. In‐situ oxygen sensors for the use in vacuum

The use of galvanic cells with oxide‐ion‐conducting solid electrolytes as sensors in vacuum allows to measure directly the oxygen partial pressure deciding for redox processes at the surface of workpieces during heat treatments. The oxygen exists either as a free molecular gaseous component or in the thermodynamic equilibrium with other gases. The bases of the known gas potentiometry are valid also in vacuum. Reducing gases are indicated in redoxquotients as Q_H = p(H₂O)/p(H₂). For the technique of measurements with solid electrolytes in vacuum special requirements arise. Probes with air reference electrode are already offered commercially. A solid reference electrode formed with Cu and Cu₂O was tested now in the range of pressure from 1 to 10^‐7 bar. It is usable at sensor temperatures between 400 and 650 centigrades. Important disturbances by oxygen permeability of the solid electrolyte were not observed in this temperature range. Changes of the composition of rest gases in vacuum, often arising as a result of wall reactions are indicated by alterations of p(O₂) or Q_H respectively. The accuracy of measurements is improved by consideration of temperature differences between the electrodes.     

喷墨打印制备电化学生物传感器的研究进展

喷墨印刷技术是一种非接触式、工艺简单、无版数字化的印刷技术,越来越多的研究者将该技术应用到制备电化学生物传感器中,以应对电化学生物传感器因向数字化、智能化等方向发展而对其制备技术提出的更高要求。因此,在对喷墨打印技术制备电化学生物传感器原理与优劣进行分析的基础上,依据其发展历程对近年来的研究进行了总结与分析,探讨了其在制作过程中存在的主要问题,即对油墨的要求较高。寻找合适的方法解决喷墨打印金属电极的电导率问题,研究导电聚合物的浓度、层数等对成膜质量和传感器响应程度的影响及利用喷墨打印技术制备整个传感器的研究将是今后本领域的研究重点。     

Tuning the Solid Electrolyte Interphase for Selective Li‐ and Na‐Ion Storage in Hard Carbon

Solid‐electrolyte interphase (SEI) films with controllable properties are highly desirable for improving battery performance. In this paper, a combined experimental and theoretical approach is used to study SEI films formed on hard carbon in Li‐ and Na‐ion batteries. It is shown that a stable SEI layer can be designed by precycling an electrode in a desired Li‐ or Na‐based electrolyte, and that ionic transport can be kinetically controlled. Selective Li‐ and Na‐based SEI membranes are produced using Li‐ or Na‐based electrolytes, respectively. The Na‐based SEI allows easy transport of Li ions, while the Li‐based SEI shuts off Na‐ion transport. Na‐ion storage can be manipulated by tuning the SEI layer with film‐forming electrolyte additives, or by preforming an SEI layer on the electrode surface. The Na specific capacity can be controlled to < 25 mAh g^?1; ≈ 1/10 of the normal capacity (250 mAh g^?1). Unusual selective/preferential transport of Li ions is demonstrated by preforming an SEI layer on the electrode surface and corroborated with a mixed electrolyte. This work may provide new guidance for preparing good ion‐selective conductors using electrochemical approaches.     

高温水蒸汽对CO2电化学传感器性能的影响

使用锂钡掺杂氧化碳酸盐作为敏感电极材料制备YSZCO₂电化学传感器,研究了高温水蒸汽对传感器性能的影响。结果表明,经300℃高温水蒸汽处理(24~120 h)后,传感器对CO₂浓度的变化(271~576802 μL/L)仍然表现出准确的响应特性,电子转移数接近理论值2;未经高温水蒸汽处理和经高温水蒸汽处理120 h的传感器,均表现出较低的氧含量依赖特性,在不同的氧含量条件下传感器对CO₂浓度突变的响应电动势相同。这种传感器不但能在含有一定比例水蒸汽的环境中长时间工作,而且在经过一定程度的高温水蒸汽累积作用后其性能没有明显的劣化。     

Influence of the cellulose substrate on the electrochemical properties of paper-based polypyrrole electrode materials

The influence of the cellulose substrate on the electrochemical performance of supercapacitor electrode materials made of polypyrrole (PPy) and cellulose is investigated. Composites were synthesized by chemical polymerization of pyrrole on dispersed fibers of cellulose from Cladophora algae and dispersed wood cellulose-based commercial filter papers, respectively, as well as on Cladophora cellulose and filter paper sheets. The resulting composites, which were characterized using scanning electron microscopy, cyclic voltammetry, and elemental analysis, were found to exhibit specific charge capacities proportional to the PPy content of the composites. The highest specific capacity (i.e., 171 C/g composite or 274 C/g PPy) was obtained for composites made from dispersed Cladophora cellulose fibers. The higher specific capacities for the Cladophora cellulose composites can be explained by the fact that the Cladophora cellulose fibers were significantly thinner than the wood cellulose fibers. While the PPy was mainly situated on the surface of the Cladophora cellulose fibers, a significant part of the PPy was found to be present within the wood fibers of the filter paper-based composites. The latter can be ascribed to a higher accessibility of the aqueous pyrrole solution to the wood-based fibers as compared to the highly crystalline algae based cellulose fibers. The present results clearly show that the choice of the cellulose substrate is important when designing electrode materials for inexpensive, flexible and environmentally friendly paper-based energy storage devices.     

Controlled growth of vertically oriented hematite/Pt composite nanorod arrays: use for photoelectrochemical water splitting

Highly ordered and vertically grown Pt-doped α-Fe(2)O(3) nanorod arrays on a gold substrate were successfully prepared by the electrochemical co-deposition method using an anodized aluminum oxide template. The effect of the Pt doping in α-Fe(2)O(3) nanorod arrays on their water splitting ability was investigated for the first time. The elemental maps obtained by energy dispersive spectroscopy showed that the Pt was uniformly dispersed in the α-Fe(2)O(3) nanorod arrays. The photoelectrochemical properties of the α-Fe(2)O(3)/Pt composite nanorod arrays as a function of the Pt content were studied by measuring their photocurrent-potential behavior in 1 M NaOH electrolyte under AM 1.5 100 mW cm(-2) illumination. The Pt-doped α-Fe(2)O(3) nanorod arrays show an improvement in solar-to-hydrogen conversion efficiency (～5%) for photoelectrochemical water splitting compared to undoped samples. To the best of our knowledge, it is the highest value yet obtained from α-Fe(2)O(3).     

SO x solid state gas sensors: A review

The performance of any solid state electrochemical gas sensor is always rated on its response time, thermodynamic stability, operating temperature, gas sensing ability, sensitivity and gas concentration range which is sensed. Here, we have reviewed the factors contributing towards a gradual development of electrochemical solid state SO _x sensor in terms of a continuous tailoring of its two basic components, i.e. solid electrolyte and reference electrode with high ionic and mixed (ionic + electronic) conductivities, respectively.     

Paper-based vapor detection of hydrogen peroxide: colorimetric sensing with tunable interface

Vapor detection of hydrogen peroxide still remains challenging for conventional sensing techniques, though such vapor detection implies important applications in various practical areas, including locating IEDs. We report herein a new colorimetric sensor system that can detect hydrogen peroxide vapor down to parts per billion level. The sensory materials are based on the cellulose microfibril network of paper towels, which provide a tunable interface for modification with Ti(IV) oxo complexes for binding and reacting with H(2)O(2). The Ti(IV)-peroxide bond thus formed turns the complex from colorless to bright yellow with an absorption maximum around 400 nm. Such complexation-induced color change is exclusively selective for hydrogen peroxide, with no color change observed in the presence of water, oxygen, common organic reagents or other chelating reagents. This paper-based sensor material is disposable and one-time use, representing a cheap, simple approach to detect peroxide vapors. The reported sensor system also proves the technical feasibility of developing enhanced colorimetric sensing using nanofibril materials that will provide plenty of room to enlarge the surface area (by shrinking the fiber size), so as to enhance the surface interaction with gas phase.     

Electrochemical studies on polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) membranes prepared by electrospinning and phase inversion—A comparative study

The synthesis, characterization and electrochemical properties of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-co-HFP)} prepared by electrospinning and phase inversion methods are reported. The morphologies of the membranes were studied by field emission scanning electron microscope and atomic force microscope. Thermal properties of the membranes were evaluated by differential scanning calorimetry. The resultant porous membranes are good absorbents of liquid electrolytes and exhibit high electrolyte retention capacity. The polymer electrolytes were prepared by soaking the membranes in liquid electrolyte. The temperature dependent ionic conductivity and electrochemical properties were evaluated. Li/LiFePO₄ cell with electrospun membrane delivers a discharge capacity of 145 mAh/g, which corresponds to 85% utilization of active material under the test conditions and shows lower capacity fade under continuous cycling.