Current Oxygen Sensor Research Articles

Effects of oxygen volume fraction, temperature and diffusion layer thickness on the sensing characteristics of limiting current oxygen sensor

Oxygen sensors are prepared by Pt paddle bonding method with dense diffusion barrier of short-circuited yttria-stabilized zirconia (YSZ) solid electrolyte. Different from the previous normal diffusion and Knudsen diffusion mechanisms, the limiting current equation of this type oxygen sensor is derived based on the diffusion of oxygen ions in the dense diffusion barrier. The effects of oxygen volume fraction, temperature and diffusion layer thickness on the limiting current density are investigated. The relationship between the physical quantities in the experiment is consistent with the derived equation.

Ti-Doped AgNbO3 as Novel Dense Diffusion Barriers of Limiting Current Oxygen Sensors

Ti-Doped AgNbO₃ as Novel Dense Diffusion Barriers of Limiting Current Oxygen Sensors

Personal safety monitoring system of electric power construction site based on AIoT Technology

For the purpose of real-time monitoring the hazard information on the electric power construction site, a personal safety monitoring system based on Artificial intelligence internet of things (AIoT) technology is designed. After the system sensing layer collects the gas information of the construction site through the gas sensor, limit current oxygen sensor and DS1820B temperature sensor, the edge computing device of the edge layer directly stores its calculation in the database of the platform layer through the data gateway. The Artificial Intelligence (AI) analysis module of this layer invokes the monitoring data of the power construction site of the database, and uses the personal safety identification method of the power construction site based on artificial intelligence technology, to complete the abnormal identification of monitoring data and realize personal safety monitoring. In addition, the system is also equipped with a power-fail detection module, which can collect the working voltage through the voltage transformer and compare it with the mains power standard to judge whether there is a power-fail risk, so as to prevent the problem of threatening personal safety due to the power-fail of the energized equipment. After testing, the system can monitor the operation status of the construction site in real time to protect personal safety.

Low temperature preparation of YSZ-based thin-film limiting current type oxygen sensor

Oxygen sensors based on YSZ solid electrolyte thin films have great application prospects due to their advantages in miniaturization and integration. Here, we report the gas sensing performance of Pt/YSZ/Pt oxygen gas sensors with low preparing temperatures. YSZ thin films with (200) preferred orientation have been prepared by room temperature RF magnetron sputtering combined with annealing at a temperature of 650 °C. The 700 nm-thick YSZ films exhibit an obvious limiting current platform, and the limiting current IL shows a linear dependence on oxygen concentration X(O2) (in the range of 6%–21%). Moreover, the devices with 700 nm-thick YSZ films worked well at the temperature range from 500 to 650 °C, and a linear relationship between logIL and 1000/T has been observed. These results demonstrate that YSZ thin films prepared by low temperature magnetron sputtering combined with the annealing process can reduce the working temperature.

Research on limiting current oxygen sensor based on La2MoWO9

In this paper, an oxygen sensor with La2MoWO9 as the base material and La0.6Sr0.4Fe0.8Co0.2O3 mixed conductor material as the diffusion barrier layer was made by solid state synthesis method. The sensor has the characteristics of low price, low working temperature, simple preparation process, and has a good application prospect. However, there is also the problem of poor stability, which needs to be further studied.

Effect of Co concentration on the Y0.1Ca0.9Zr1-xCoxO3-δ limiting current dense diffusion barrier oxygen sensor

Y0.1Ca0.9Zr1-xCoxO3-δ (x = 0, 0.1, 0.3, and 0.5) was synthesized by a solid-state reaction. Y0.1Ca0.9Zr1-xCoxO3-δ is orthorhombic perovskite structure. The electronic conductivity and total conductivity increase with increasing Co concentration and temperature. The activation energy of electronic conductivity and total conductivity is lowest when the Co concentration is x = 0.5. A lower activation energy is conducive to the migration of oxygen ions. Using Y0.1Ca0.9Zr0.7Co0.3O3-δ and Y0.1Ca0.9Zr0.5Co0.5O3-δ as dense diffusion barrier and 8YSZ (8 mol% yttria-stabilized zirconia) as a solid electrolyte, the limiting current oxygen sensor was fabricated by the Pt sintered-paste method, and its sensing performance was studied. The oxygen sensor exhibits a limiting current plateau at 760–850 °C. The oxygen measurement range increases with increasing Co concentration. The limiting current is directly proportional to the oxygen concentration, indicating that it shows excellent sensing characteristics at different temperatures. When the test time is more than 75 h, the oxygen sensor has good stability, and the stable limiting current is approximately 4.23 mA. The voltage range of the limiting current plateau has no effect on the increase of the detection time, and its voltage range is 0.75–1.75 V.

LSGMCF dense diffusion barrier preparation and electrical characteristics for limiting current oxygen sensor

La0.8Sr0.2(Ga0.8Mg0.2)1-x(Cr0.4Fe0.6)xO3-δ(LSGMCF, x = 0.1, 0.3, 0.5, 0.7 and 0.9) and La0.8Sr0.2Ga0.8Mg0.2(LSGM) were synthesized by solid-state reaction with La2O3, SrCO3, Ga2O3, MgO, Cr2O3 and Fe2O3 as raw materials. By characterizing the phase analysis and micro-structure of LSGMCF, it was found that Cr and Fe dissolved in the main crystalline phase LSGM in a wide range. The effects of Cr and Fe concentrations on the electronic and total conductivity of LSGMCF were analyzed by Hebb-Wagner and Linear Sweep Voltammetry methods. The results show that when x = 0.9, it has better electronic conductivity and the highest total conductivity. LSGMCF(x = 0.9) and LSGM were prepared into limiting current oxygen sensor by co-pressing and co-sintering technique, and its sensing characteristics were studied. The oxygen sensor exhibits a limiting current in the range of 0–7% oxygen concentration at 730–790 °C. The limiting current is directly proportional to the oxygen concentration, indicating that it shows good sensing characteristics at different temperatures. In addition, its sensing performance has excellent stability between 0 -42h.

Sensing property of limiting current oxygen sensor with (8YSZ)0.4(CeO2)0.6 dense diffusion barrier based on 8YSZ solid electrolyte

In this manuscript, (8YSZ)1-x(CeO2)x (0 ≤ x ≤ 0.6), belonging to the cubic fluorite structure, was prepared by a co-precipitation method. We highlighted the effect of a dense diffusion barrier conductivity on the sensing performance by choosing the lowest conductivity of (8YSZ)0.4(CeO2)0.6 as a dense diffusion barrier compared with the highest conductivity of (8YSZ)0.9(CeO2)0.1 published. A sensor was fabricated using bonding Pt paste. Limiting current (IL) platforms were obtained at different oxygen concentrations x(O2) in a temperature range of 720–900 °C. The oxygen sensor had a smaller oxygen measurement range of 0–10% at 850 °C compared to (8YSZ)0.9(CeO2)0.1 as a diffusion layer. These results showed that the higher oxide ion conductivity of the diffusion layer can achieve a wider oxygen measurement range, which can guide the search for new mixed conductor with higher oxide ion conductivity. The sensing performance of the oxygen sensor was not influenced by p(H2O) and x(CO2), which showed the sensor had a strong selectivity towards oxygen. Furthermore, the limiting current of the sensor remained stable during 144 h of detection.

Thermal behavior, crystal structure and electrical conductivity of {(ZrO2)0.92(Y2O3)0.08}1-x(Cr2O3)x (x = 0, 0.05, 0.10, 0.15) solid solution

{(ZrO2)0.92(Y2O3)0.08}1-x(Cr2O3)x solid solution is composed by co-precipitation method and the effects of Cr2O3 content on thermal analysis, crystal structure, microstructure and electrical conductivity are researched. The results discuss the potential for application as a diffusion barrier material at temperatures between 600 and 850 °C to the limiting current oxygen sensors. TG and DSC results show that the main weight loss and heat absorption processes occur below 600 °C and the {(ZrO2)0.92(Y2O3)0.08}1-x(Cr2O3)x solid solution is obtained above 600 °C. XRD analysis shows that the solid solution is fluorite type cubic phase and the solubility of Cr2O3 in (ZrO2)0.92(Y2O3)0.08 is less than 0.10. The SEM-EDS results show that the grain size of the sintered body decreases with increasing Cr2O3 content and distribution of each element is uniform. The conductivity of solid solution decreases first and then increases as Cr2O3 doping content, reaches the maximum value of 4.33 × 10−3 S cm−1 at 850 °C. The doping of Cr2O3 is beneficial to improve the conductivity of the solid solution at low temperature.

Crystal structure and electrical conductivity of {(ZrO2)0.92(Y2O3)0.08}1-x(CuO)x (x=0, 0.1, 0.2 and 0.3)

{(ZrO2)0.92(Y2O3)0.08}1-x(CuO)x (ZYC) synthesized by the co-precipitation method with different stoichiometry (x=0, 0.1, 0.2 and 0.3) are evaluated through thermogravimetric-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD) and electrical conductivity using an electrochemical workstation and the effects of CuO doping content on the above properties are researched, respectively. The results are discussed in terms of the potential as diffusion barrier material to be applied in diffusion barrier limiting current oxygen sensors application at temperatures from 500 to 850 °C. Results derived from TG-DSC shows that the weight loss of the sample is mainly due to the decomposition of the precursor, forming ZYC above ~600 °C. XRD analysis shows that the ZYC sample is a cubic phase and the CuO doping is benefit to the crystallinity of ZYC. The electrical conductivity results indicate that the total conductivity decreases for ZYC1 but then increases with the increase of CuO doping content and reaches the maximum total conductivity of 2.02 × 10−1 S cm−1 at 850 °C and the activation energy (Ea) is 0.93 eV for ZYC3.

Limiting current oxygen sensor based on Y, In co-doped SrTiO3 as a dense diffusion barrier layer

A novel dense diffusion barrier material (YxSr1−xTi0.9In0.1O3−δ (x = 0.03, 0.05, 0.07)) was prepared by using a sol-gel method. The crystal structure, microstructures, electrical conductivity and ionic conductivity of barrier material were characterized. The results show that the samples exhibit the formation of cubic perovskite structure phase. The increase of Y-doping amount on A-site improved electrical conductivity and sinterability of materials. A limiting current oxygen sensor based on Y0.07Sr0.97Ti0.9In0.1O3−δ as a dense diffusion barrier shows excellent sensing performance. The linear relationship between limiting current logIL and 1000/T can described logIL = 4.6038 − 3.8475·1000/T. At 750 °C, 0.25% ≤ x(O2) ≤ 5.0%, the linear relationship between limiting current (IL) and oxygen amount (x(O2)) can described as IL = 7.0476 + 3.8751 x(O2).

Mixed conductivities of A-site deficient Y, Cr-doubly doped SrTiO3 as novel dense diffusion barrier and temperature-independent limiting current oxygen sensors

A-site-deficient Y, Cr doubly doped SrTiO3 ((Y0.08Sr0.92)1-xTi0.8Cr0.2O3−δ (x = 0.01, 0.03, 0.05)) powders were synthesized via sol–gel method, followed by sintering at 1450 °C at ambient condition. The phase composition, mixed conductivities, and sensing performance are characterized to identify the influence of A-site deficiency on the Y- and Cr-doubly doped SrTiO3. The ionic conductivity and total conductivity of (Y0.08Sr0.92)1-xTi0.8Cr0.2O3−δ clearly increase and decrease upon an increase in the A-site deficiency, respectively. The enlarged saddle point and decreased relaxation time are responsible for the augmentation of ionic conductivity. The oxygen sensor with (Y0.08Sr0.92)1-xTi0.8Cr0.2O3−δ dense diffusion layer show superior sensing performance with A-site deficiency level increasing. The relationship between logIL and 1000/T is obtained and the charge compensation mechanism is systematically discussed. The obtained results demonstrated that limiting current is nearly independent of temperature at high operating temperature. This paper provides a chemical strategy to enhance the mixed conductivity of oxygen sensors through Y- and Cr-double doping and via a simple, low cost, and traditional sol–gel technique.

Mixed conductivity evaluation and sensing characteristics of limiting current oxygen sensors

Strontium titanate based materials are promising candidates for fabrication of oxygen sensors. As a dense diffusion barrier layer of limiting current oxygen sensor, strontium titanate based materials should be able to control the diffusion rate of oxygen ions or accelerate the formation of limiting current. Based on this key question, indium oxide was introduced to strontium titanate based materials and then Y0.08Sr0.92Ti0.6Fe0.4-xO3-δ/x/2 In2O3 (x = 0.04, 0.06, 0.08) composites were prepared. To understand the efficacy of doping indium oxide on the physical and sensing properties of the strontium titanate, the ionic and electronic conductivity were intently investigated. The obtained results demonstrated that the ionic and total conductivity simultaneously increased upon increasing the concentration of indium oxide dopant. Increasing the content of In2O3 accelerates the occurrence of limiting current of the sensor at lower voltages and then elevate the working life of the sensor.

Diffusion kinetics mechanism of oxygen ion in dense diffusion barrier limiting current oxygen sensors

Limiting current oxygen sensors based on strontium titanate composites have been prepared and their physical properties were investigated in details. B-site deficient yttrium and iron co-doped strontium titanate was prepared to scrutinize the contribution of electronic and ionic features on the electrical conductivity and investigate oxygen ions diffusion in the barrier layer. The mixed conductivity and sensing properties of the aforementioned materials were attentively studied in order to identify the impact of B-site deficiency on the SrTiO3-based dense diffusion barrier and therefore performance of the fabricated limiting current oxygen sensors. The obtained results demonstrated that the total conductivity conspicuously increased and the ionic conductivity decreased upon an augmentation in the content of B-site deficiency. The increase of B-site deficiency can accelerate the occurrence of limiting current of the sensors at lower voltages and then elevate the service life of the sensor and promote an independence relationship between limiting current and temperature. Y-doping affects interatomic force in the crystal structure of Y0·08Sr0·92(Ti0·6Fe0.4)0.97O3-δ and therefore, reduces the diffusion rate of oxygen vacancy which is favorable for development of limiting current oxygen sensor.

Y-doped CaZrO3/Co3O4 as novel dense diffusion barrier materials for a limiting current oxygen sensor.

Herein, we illustrate a feasible strategy to strengthen the gas sensing of Y-doped CaZrO3 (YxCa1-xZr0.7O3-δ (x = 0.05, 0.06, and 0.07))/0.1Co3O4 used as sensing materials. This compound was prepared via a solid-state reaction technique. The structural, morphological, electrical, and sensing features such as phase identification, microstructure, ionic conductivity, total conductivity and sensitivity of the fabricated sensors were evaluated via X-ray diffraction, scanning electron microscopy, electron-blocking method, electrochemical impedance spectroscopy and cyclic voltammetry. In addition, the influence of the Y-dopant on the properties of YxCa1-xZr0.7O3-δ/Co3O4 was thoroughly studied. XRD results revealed the formation of the orthorhombic perovskite phase of YxCa1-xZr0.7O3-δ. Moreover, the obtained results from the electrical properties elucidated high electronic and low ionic conductivities, and small polaron conduction of YxCa1-xZr0.7O3-δ/Co3O4. Furthermore, the results confirmed an excellent limiting current plateau for the fabricated oxygen sensor based on YxCa1-xZr0.7O3-δ/Co3O4. In particular, experimental observation indicates that Y-doping at the Ca site and/or Zr site might be difficult.

Conductivity and mixed conductivity of a novel dense diffusion barrier and the sensing properties of limiting current oxygen sensors.

First-principles calculations were used to explore the effect of various Y-doping levels on the electrical conductivity of SrTiO3. Herein, we prepared ((Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ)/x/3Co3O4 (x = 0.1, 0.2, 0.3)) composites using a solid state reaction method. The properties of these sensing materials and the fabricated sensors including crystal phase composition, microstructures, oxygen ionic conductivity, total conductivity and sensor performance were investigated in detail. XRD demonstrates the formation of a highly cubic perovskite structure. The introduction of Co3O4 promotes remarkably the electronic conductivity of the Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ/x/3Co3O4 composites due to the formation of n-type CoO and p-type Co2O3. A limiting current oxygen sensor based on (Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ)/x/3Co3O4 as a dense diffusion barrier shows excellent sensing performance. The recovery time is less than the response time, indicating that Co2O3 promotes the gas desorption reaction which results in a shorter recovery time. The obtained results demonstrate a direct relationship between limiting current (IL) and oxygen content.

A dense diffusion barrier limiting current oxygen sensor for detecting full concentration range

Although the limiting current-type oxygen sensors based on dense diffusion barriers have been developed for detecting oxygen concentration in harsh exhaust environments, their oxygen concentration measuring range is far below that of the sensors based on porous diffusion barriers, which can be improved through using electrochemically stable mixed oxide-ion/electron conductor. Here, we prepared a new family of mixed oxide-ion/electron conductor by partial substitution of Ta for Nb at B-site in perovskite AgNbO3 under hydrothermal conditions. Among the investigated compositions, AgTa0.5Nb0.5O2.52 (ATN) exhibits oxide-ion conductivities of 6.7 × 10−5 (450 °C) to 1.1 × 10-3 S cm-1 (850 °C) with activation energy of 0.59 eV and good electrochemical stability. Using it as dense diffusion barrier and 8YSZ (yttria-stabilized zirconia) as solid electrolyte, we demonstrate a novel dense diffusion barrier limiting current oxygen sensor that exhibited a linear relationship between the limiting current and oxygen concentration in range of 1.3−100 mol% at 800 °C at a low operating voltage. Furthermore, the sensor also shows good anti-interference ability for interfering CO2 gas and water vapor, acceptable long-term stability and poisoning robustness.

A limiting Current Oxygen Sensor Constituted of(CeO2)0.95(Y2O3)0.05 as Solid Electrolyte Layer and(CeO2)0.75(ZrO2)0.25 as Dense Diffusion Barrier Layer.

Using the co-precipitation method to synthesize (CeO2)0.95(Y2O3)0.05 (YDC) and solid reaction method to synthesize (CeO2)0.75(ZrO2)0.25 (ZDC), and the crystal structure, micro-structure, total conductivity and electronic conductivity of the two materials was measured with X-ray diffraction (XRD), scanning electron microscope (SEM), DC van der Pauw and Hebb-Wagner methods. A limiting current oxygen sensor was prepared with YDC solid electrolyte and a ZDC dense diffusion barrier layer by employing platinum pasting bonding. Sensing characteristics of the sensor were obtained at different conditions, including temperature (T), oxygen concentration (x(O2)) and water vapor pressure (p(H2O)), and the influence of various conditions on sensing performance was studied. The long-term stability of the sensor was measured in an oxygen concentration of 1.2% and at a temperature of 800 °C for 120 h. XRD results show that the phase structure of both YDC and ZDC belongs to the cubic phase. SEM results show that both YDC and ZDC layers are dense layers, which are then qualified to be the composition materials of the sensor. The limiting current (IL) of the sensor is obtained and the sensor exhibits good sensing characteristics to satisfy the Knudsen model. Log(IL·T) depends linearly on 1000/T with a squared correlation coefficient (R2) of 0.9904; IL depends linearly on x(O2) with an R2 of 0.9726; and sensing characteristics are not affected by p(H2O). It was found that the oxygen sensor has good long-term stability.

An application of (4YSZ)0.93(Fe2O3)0.07 in limiting current oxygen sensor

(4YSZ)0.93(Fe2O3)0.07 and 9 mol% Y2O3 stabilized ZrO2 (9YSZ) were synthesized by co-precipitation method and their crystalline structure, microstructure, electronic conductivity, total conductivity were characterized. A limiting current oxygen sensor was assembled with (4YSZ)0.93(Fe2O3)0.07 dense diffusion barrier and 9YSZ solid electrolyte by Pt sintered-paste method. Influences of temperature (T), oxygen concentration (x(O2)) and water vapor pressure (p(H2O)) on sensing characteristics of the limiting current oxygen sensor were investigated. The crystalline structure of (4YSZ)0.93(Fe2O3)0.07 and 9YSZ belong to cubic structure with {bf{Fm}}overline{{bf{3}}}{bf{m}}. The total conductivity of (4YSZ)0.93(Fe2O3)0.07 is higher than that of 9YSZ and the electronic and total conductivities of the samples meet the linear relationship with 1000/T. The limiting current oxygen sensor exhibits excellent sensing characteristics under test conditions. The effects of T, x(O2) and p(H2O) are as follows: Log(IL·T) depends linearly on 1000/T, IL depends linearly on x(O2) and IL is not significantly dependent on p(H2O).

A limiting current oxygen sensor based on (La0.4Ce0.6O2-δ)0.96(FeO1.5)0.04 as dense diffusion barrier

(La0.4Ce0.6O2-δ)0.96(FeO1.5)0.04 ((LCO)0.96(FeO1.5)0.04) and Y0.08Zr0.92O2 (8YSZ) powders were prepared by co-precipitation and used as dense diffusion barrier and solid electrolyte materials of a limiting oxygen sensor fabricated by a co-pressing and co-sintering method, respectively. The crystalline structure, conductivity, fracture characteristics, distribution of elements, and sensing performance of the prepared sample were characterized. The results show that the electronic and ionic conductivities of (LCO)0.96(FeO1.5)0.04 are 2.86 × 10−4 and 2.16 × 10−2 S cm−1 at 850 °C, respectively, satisfying the requirement of dense diffusion barrier. The SEM-EDS analysis shows an excellent bonding property between solid electrolyte and dense diffusion barrier, and a homogeneous distribution of elements without evident diffusion. The oxygen sensor exhibits a stable sensing performance. The limiting current shows a linear relation with the oxygen concentration, and an exponential relation with the inverse temperature.