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Organic room temperature phosphorescent (ORTP) materials provide an exciting research direction for phosphorescent oxygen (O2) sensors due to their high sensitivity and rapid response to O2. However, most pure ORTP materials are tightly-packed aromatic compound crystals in a face-to-face manner, which largely prohibits effective O2 diffusion for sensing. Thus, how to solve this contradiction still faces huge challenges. Here, the use of organic phosphorescent indicator carbon dots (CDs), inorganic matrix layered double hydroxides (LDHs) and polymers (PVA) successfully prepared an ultra-long RTP composite film whose phosphorescence decay intensity is linearly related to O2 concentration. More importantly, the use of the abundant O2 defects (Vo) on the surface of the inorganic matrix LDHs to adsorb O2, which further accelerates the phosphorescence quenching of the thin film and improves the O2 response. This strategy will provide the possibility to develop high-sensitivity phosphorescent O2 sensors from a new perspective.

High-temperature solid-state electrolyte is a key component of several important electrochemical devices, such as oxygen sensors for automobile exhaust control, solid oxide fuel cells (SOFCs) for power generation, and solid oxide electrolysis cells for H2 production from water electrolysis or CO2 electrochemical reduction to value-added chemicals. In particular, internal diffusion of protons or oxygen ions is a fundamental and crucial issue in the research of SOFCs, hypothetically based on either oxygen-ion-conducting electrolytes or proton-conducting electrolytes. Up to now, some electrolyte materials based on fluorite or perovskite structure were found to show certain degree of dual-ion transportation capability, while in available electrolyte database, particularly in the field of SOFCs, such dual-ion conductivity was seriously overlooked. Actually, few concerns arising to the simultaneous proton and oxygen-ion conductivities in electrolyte of SOFCs inevitably induce various inadequate and confusing results in literature. Understanding dual-ion transportation behavior in electrolyte is indisputably of great importance to explain some unusual fuel cell performance as reported in literature and enrich the knowledge of solid state ionics. On the other hand, exploration of novel dual-ion conducting electrolytes will benefit the development of SOFCs. In this review, we provide a comprehensive summary of the understanding of dual-ion transportation in solid electrolyte and recent advances of dual-ion conducting SOFCs. The oxygen ion and proton conduction mechanisms at elevated temperature inside oxide-based electrolyte materials are first introduced, and then (mixed) oxygen ion and proton conduction behaviors of fluorite and perovskite-type oxides are discussed. Following on, recent advances in the development of dual-ion conducting SOFCs based on fluorite and perovskite-type single-phase or composite electrolytes, are reviewed. Finally, the challenges in the development of dual-ion conducting SOFCs are discussed and future prospects are proposed.

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.

Detection of oxygen plays an important role in food industry, medicine and controlling automotive exhaust. Here, we have developed a Co3O4 nanoparticle-based oxygen gas sensor. Effect of Gadolinium (Gd) doping on oxygen sensing is investigated using the variation in electrical resistance method which clearly reveals improvement in the sensitivity with the increase in Gadolinium doping in Co3O4. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) studies were systematically performed, to understand the effect of the morphology and crystallographic phase on the level of sensitivity with Gadolinium doping. XRD studies reveal a distortion in the Co3O4 lattice as the lattice parameters increase with increasing Gd doping. SEM and TEM show a change in particle shape and size with Gd doping. Presence of both Co+2 and Co+3 oxidation states were confirmed by XPS. Gd doping, up to 6%, improved the gas sensing response of Co3O4 nanoparticles which is attributed to the decrease in particle size and an increase in oxygen adsorption with Gd doping. Minimum response time of 4 s, 6 s, 10 s and 14 s were observed for pure Co3O4 in 1%, 2%, 3% and 4% oxygen environment respectively. Pure Co3O4 nanoparticles also showed minimum recovery time which was 6 s, 7 s, 9 s and 11 s in 1%, 2%, 3% and 4% oxygen environment respectively. All the prepared compositions were selective to oxygen at 240 °C.

Nanopowders and thin films of (СeO2)1-x(Y2O3)x composition (x = 0.10, 0.15 and 0.20) were obtained by the sol-gel process, using hydrolytically active complexes of the metal alkoxoacetylacetonate class [M(C5H7O2)3-y(C5H11Oi)y] (M = Ce3+ and Y3+) as precursors. The impact of the chemical composition and crystallization conditions on the microstructure, electrophysical and chemosensory characteristics of the obtained planar-type solid electrolytes was studied. The prospects of the thin-film nanostructures obtained as receptor components of resistive oxygen sensors, as well as of electrolytes of planar-type intermediate-temperature solid oxide fuel cells (SOFC) have been shown. It has been found that (CeO2)0.90(Y2O3)0.10 thin films demonstrate the maximum values of electrical conductivity (550 °C) and the highest sensory response when detecting oxygen (concentration range 1–20%, operating temperature range 300–450 °C).

A comprehensive overview is provided about the role of bulk conductivity contributions in compounds of the composition YbxCa1-xMnO3 (0–10 at. % Yb-dopant concentration). For this purpose, in-situ impedance spectroscopy was successfully employed at different temperatures (−100 up to 300 °C) and frequencies (1 Hz–1 MHz). These experiments reveal the main role of grain boundaries as well as electronic and ionic contributions in conductivity. The contribution of different resistance components in electric transport properties were proposed on the base of a double-Schottky-barrier model. Migration of oxygen vacancies and their participation in conductivity were studied and the results are confirmed by observing oxygen released using a ZrO2 oxygen sensor during dilatometry measurements in a wide range of temperatures.

Ce0.8Gd0.2−xCaxO2−δ (0 ≤ x ≤ 0.20) and LaNi0.6Fe0.4O3–δ (LNF64) powders were synthesized using a sol-gel method, and their phase structures were characterized by X-ray diffraction (XRD). The influence of the temperature and oxygen concentration on the electrical conductivity of Ce0.8Gd0.2−xCaxO2−δ solid electrolyte was examined by AC impedance spectroscopy. The XRD results show that calcium has a solid solubility limit in the Ce0.8Gd0.2−xCaxO2−δ series with the cubic fluorite structure, and LNF64 had the rhombohedral perovskite structure. The electrical conductivity of the Ce0.8Gd0.2−xCaxO2−δ electrolyte varied with the concentration of the Ca2+ dopant. The composition in which x = 0.05 exhibited the highest electrical conductivity and was thus more suitable as the electrolyte of a limiting-current oxygen sensor. A novel limiting-current oxygen sensor was prepared using Ce0.8Gd0.15Ca0.05O2−δ as an oxygen pump layer and LNF64 as a dense diffusion barrier layer. The electrochemical properties (current–voltage [I V] and current–time [I–t] curves) of the oxygen sensor were investigated within the oxygen concentration range of 0.9–4.0% at 750–810 °C. The sensor exhibited a stable limiting-current plateau within a low operating voltage range. At all the studied temperatures, the sensor exhibited a strong linear relationship between the limiting current and the oxygen concentration. The response and recovery times of the oxygen sensor were about 25–35 s and 40–50 s, respectively. Furthermore, the temperature had little influence on the response time.

We present a sensor system to monitor the uptake of oxygen by mammalian cells as a direct indicator for the metabolism under consideration of the requirements for the usage in biolabs. That includes reliable oxygen sensing as well as a small footprint of the setup without sophisticated external equipment, the usage of compatible materials and the suitability for a high degree of integration and automation. These requirements are fulfilled by a system that consists of a microfluidic chip with an integrated oxygen-sensitive phosphorescent film, heater and temperature sensor, external optical read-out and 3D-printed holders and housing. The chip with the closed microfluidic chamber is made by clean-room technologies out of silicon and glass. An excitation LED and a small and low-cost Raspberry Pi camera are used to measure the phosphorescent signal. With this system, the concentration of dissolved oxygen can be determined with an accuracy of ±0.8% (air) for oxygen concentrations between 0 and 26% (air) and at any temperature between 23 and 41 °C. To demonstrate the capabilities, the oxygen consumption rates of HaCaT-cells (human keratinocyte cell line) are determined at different temperatures.

In this work, the functionalization degree of siloxane crosslinkers by allyldiphenylphosphine oxide (adppo) and its effect on the performance of a lanthanide-based optical oxygen sensor were evaluated. Linear poly(dimethyl-co-hydromethylsiloxane) (PMS) and cyclic tetramethylcyclotetrasiloxane (D4i) crosslinkers were functionalized with different concentrations of adppo to chemically bond the [Tb(dcba)3]·1/2H2O (dcba = dichlorobenzoate) complex. Mechanically stable luminescent silicone membranes were obtained after the curing of the poly(dimethylsiloxane)-vinyl terminated siloxane backbone with the pre-functionalized crosslinkers. Sensing materials exhibit green emission upon 350 nm excitation, and their luminescent properties are dependent of functionalization degree of the crosslinkers. The luminescent sensor materials show fully reversible response and non-linear Stern-Volmer plots, which are fitted by two quenching parameter model, with highest KSV of 0.08930%−1 when using functionalized D4i as crosslinker and complex concentration of 0.75%.

(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.

Research in wearable electronics has paved the way for next-generation technology, sought to create point-of-care biosensors that combine chemical sensing on a biocompatible platform with a broad range of applications in human health monitoring. Despite significant progress, the microspatial mechanical mismatch and fluid-impermeable interface presented between skin and the electronics create adscititious problems in device lamination, conformality, and long-term monitoring. Herein, we engineered a skin-inspired, deterministically patterned, electrochemical biosensor that can be fully integrated with the curvilinear surface of the human body, while mechanically adapting to the natural stresses applied to the skin and allowing the mass transfer of gas and fluids. In particular, we developed mechanically-compliant lattice-structured biosensors for the continuous evaluation of lactate and oxygen. Systematic studies of the sensor performance were evaluated with variations in polymeric membranes and its ability to withstand commonplace harsh, multiaxial stresses.

The development of novel single molecular probe based optical ratiometric oxygen sensor with simple fabrication, high sensitivity, and linear response is highly desirable. Herein, benzo[ghi]perylene (BzP) and coronene (Cron) were explored as dual-emissive ratiometric oxygen nano-sensors that displayed linear plots at a low probe concentration (6 μM). The sensor fabrication was simple, and the probes exhibited efficient fluorescence quenching of monomer emission by molecular oxygen. However, the excimer emission of probe remained unaffected. Thus a ratiometric method is developed based on the dual emitting luminophore. The method can be used to estimate dissolved oxygen in liquids and 5–100% of oxygen concentration in gaseous mixtures.

A comprehensive study was performed in order to find the effect of different calcination and sintering conditions on the physical properties of calcium manganite ceramics in dependence of temperature T and partial pressure of oxygen p(O2). The eventual formation of oxygen vacancies during sintering was investigated and the results were confirmed by monitoring the release of oxygen using a ZrO2 oxygen sensor. The phase transition behavior was studied using thermogravimetric analysis (TGA) in a wide range of p(O2) ≈ 10−1 MPa down to 10-19 MPa at high temperatures accompanied by dilatometry- and XRD-measurements. Furthermore, the present study reveals for the first time a way for reducing and preventing crack formation that may occur during sintering. The present systematic research provides essential fundamental information before performing electrical measurements necessary in order to understand important factors about charge carriers and electrical transport mechanism.

CexZr1-xO2 (x = 0.25, 0.5 and 0.75) was synthesized by solid phase chemical reaction synthesis and characterized by X-ray diffraction (XRD), thermal expansion, Hebb-Wagner method and DC van der Pauw method. ZrO2 has a high melting point and CeO2 has a variable valence state, which can make the CexZr1-xO2 material have mixed ionic-electronic conductivity and stability. The synthesis method has the advantages of having a lower synthesis temperature and no waste liquid discharge, which is beneficial to energy conservation and environmental protection. A limiting current oxygen sensor was prepared with Ce0.75Zr0.25O2 dense diffusion barrier and ZrO2 stabilized by 9 mol% Y2O3 (9YSZ) solid electrolyte by Pt sintered-paste method. Limiting current plateau of the oxygen sensor was obtained and the effects of operate temperature (T), oxygen concentration (x(O2)) and water vapor pressure (p(H2O)) on the limiting current was studied, respectively. The results show that the Ce0.75Zr0.25O2 material has maximum electronic and total conductivity at 800 oC and is the most suitable ceramic material to be a dense diffusion barrier of limiting current oxygen sensor. The oxygen sensor exhibits good sensing characteristics under different research conditions, including different T, x(O2) and p(H2O). The limiting current is related to various research factors, for example, log(IL·T) depends linearly on 1000/T, IL depends linearly on x(O2) and IL is not influenced obviously by p(H2O). The experiment supplements the application of mixed conductor material CexZr1-xO2 (x = 0.25, 0.5 and 0.75) as a dense diffusion barrier in limiting current oxygen sensor.

New oxygen and pressure sensitive paints (PSPs) with four-arm polymeric structures were prepared by using a kind of controlled living polymerizations – atom transfer radical polymerization (ATRP). The polymers composing of poly(isobutyl methacrylate)-co-poly(trifluoroethyl methacrylate)s (PolyIBMA-co-PolyTFEM)s act as the matrices for the platinum porphyrin-based phosphorescence probes, which were copolymerized in the matrices. The polymers were characterized by using 1H NMR, 19F NMR, and GPC to demonstrate their successful preparation. The influence of polymer structures on sensing activity including the sensitivity and response time to oxygen and/or pressure was investigated. Results showed that copolymers with suitable compositions (herein P3) can have highest sensitivity. Polymer structure’s influence on response time to oxygen was also investigated. For increasing the polymer’s surface area for further improving sensing sensitivity, electrospinning method was used for preparing films with micro-spherical or fibrous structures. The morphologies of electrospinning coated films were observed by SEM. Results showed that electrospinning coated films can respond much better to oxygen and pressure than their corresponding sprayed plates. This is the first time to apply the controlled living polymerization approach to prepare PSPs with multi-arm structures, which will broaden the PSP functional materials’ design strategy.

Polymeric microfibers, particularly the fluorinated copolymers’ fibers, are promising functional materials for photoelectric devices, sensing, and energy storage due to their various surface characteristics. However, to obtain the high fluorine content copolymer-based fibers with considerable uniformity is likely to be especially challenging, which seriously debilitates their applications in sensor devices. Herein, for the first time, we presented a high fluorine content platinum porphyrin-grafted poly(isobutyl methacrylate-co-dodecafluoroheptyl methacrylate) copolymers (PtTFPP-p(IBM-co-DFHMA)) microfibrous thin-films used as optical oxygen sensors. The porous thin-film frameworks were formed of uniform microfibers, which afforded an exceptional improvement in sensitivity and exhibited 584% higher sensitivity than the solid sensing film owing to the large specific surface area, porous structures and oxygen diffusion enhancement by fluorine elements. Additionally, the remarkable emission intensity-changing characteristic of the microfiber sensing film under various air pressures facilitates convenient visualization of pressure distributions on film surface. The characteristics are particularly important for the computational fluid dynamics simulations in various sensing fields such as unsteady flow visualization and unsteady pressure measurements, etc. Owing to its attractive advantages and versatile performance, fluorine-containing copolymers fibers are expected to provide a new strategy for the rational design of high performance gas sensor devices.

We present a solution-processed flexible organic photodiode (f-OPD) with a bulk heterojunction (BHJ) structure based on a blend of poly (3-hexylthiophene-2,5-diyl) and 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (P3HT:PCBM). We used Cs2CO3-doped polyethyleneimine ethoxylated (d-PEIE) as the electron transport layer (ETL) material, which significantly improved the electron injection properties of the f-OPD. Compared with f-OPDs with conventional ETL materials such as Cs2CO3, the external quantum efficiency (EQE) of the d-PEIE-based f-OPD was highly improved. Analytical results showed that the d-PEIE reduced the work function of the cathode, thereby facilitating the efficiency of electron injection from the active layer (AL) to the cathode of the f-OPD. In addition, after 10,000 cycles of tensile bending at a bending radius of 5 mm, the normalized ID variation (ID/ID0) in the d-PEIE-based f-OPD remained above 90%, indicating an excellent device bending stability. Finally, f-OPD-based luminescent oxygen (O2) sensors were successfully fabricated consisting of a photoluminescent O2 sensing film, a light source, and an f-OPD. The O2 sensors based on d-PEIE-based f-OPDs showed the highest photocurrent and O2 sensitivity in relation to the O2 concentration compared with O2 sensors based on f-OPDs with conventional ETL materials.

La9.67Si6-xCuxO26.5-x (LSC, x = 0, 0.1, 0.3 and 0.5) are synthesized by a citric-nitrate method. Substitution Si with Cu promotes the densification process of silicate apatite. Unit cell parameters and volume increase linearly with Cu content. The Rietveld refinement reveals a much more distorted (Si,Cu)O4 tetrahedra in the oxygen stoichiometric La9.67Si5.5Cu0.5O26 sample. The structural observation from high temperature XRD implies a second-order phase transition in La9.67Si5.5Cu0.5O26. Cu-doping decreases the activation energy of oxygen ion conduction and increases the conductivity of LSC materials in the temperature range of 550–800 °C. La9.67Si5.5Cu0.5O26 shows the conductivity values of 29.3 and 12.3 mS cm−1 at 800 °C and 650 °C, respectively. The oxygen ion transference number of La9.67Si5.5Cu0.5O26 is higher than 0.99. These attractive properties make the La9.67Si5.5Cu0.5O26 a promising oxygen ion conducting electrolyte for applications of solid oxide fuel cells, oxygen sensors, oxygen separation membranes, etc.

Automotive industry targets such as complying with emission legislations and increasing fuel economy, require the improvement of air-fuel ratio control systems. Oxygen sensors are a crucial part of these control systems and regulations oblige monitoring of their performance and detecting sensor-related faults. The primary purpose of this paper is to develop a methodology for precise and accurate monitoring and diagnosis of oxygen sensors to meet legislations and performance targets while the required calibration effort is reduced. Input parameters with the highest correlation factors were selected to be utilized in different system identification methodologies to statistically determine the most fitting model. In the end, a NARX model with two hidden layers and eight neurons in each hidden layer with standard deviation and mean threshold values was determined to be the optimum design to detect if the oxygen sensor was functioning or faulty.

The technical state of the internal combustion engine systems influences the level of pollutant emissions. Depending on the fault, these are recognized by the OBD system. Often, the car is functional and in good conditions to drive even when some defects are diagnosed. The study refers to the test on the dynamometer stand of four cars equipped with the same type of engine, Renault K7M. Controlled engine defects were induced. The intended devices are decommissioned by disconnecting the electrical connection. That is considered a defective. The concentrations of pollutant emissions were measured in several test regimes both in good operating condition and in defective conditions. The defects were related to the air pressure transducer in the intake manifold, the oxygen sensor in the exhaust manifold, and to one of the four injectors. Results shown how the induced engine defects influence the concentrations of pollutant emissions. It is found that, if an injector does not work, the emission level increases significantly, more than if the oxygen sensor does not work. The air pressure sensor failure in the intake manifold had a lesser influence on pollutant emissions. Intake manifold air pressure sensor malfunction had a lesser influence on pollutant emissions.

Optical oxygen sensors based on indicators immobilized into porous and nonporous matrix materials were investigated in regard to their sensing behaviour under high hydrostatic pressure. The sensors were subjected to step-wise pressure increase up to approximately 200 bar in multiple cycles using a custom-made chamber. The investigated materials are based on oxygen indicators (a platinum(II) benzoporphyrin dye and ruthenium(II) polypyridyl complexes) immobilized in microparticles: silica gels of different porosities, controlled pore glass, poly(phenylsilsesquioxane), crosslinked polystyrene, the metal-organic frameworks ZIF-8 and UiO-66. The microparticles are in turn dispersed in highly oxygen-permeable silicone and Hyflon AD matrices. Homogeneous films of dye doped polystyrene and polyurethane hydrogels as well as non-porous polystyrene nanospheres directly dispersed in water were used for comparison purposes. All the porous materials were found to be stable under elevated hydrostatic pressure. Although the actual oxygen concentration remained unchanged upon increasing pressure, the sensors demonstrated an apparent decrease of calculated oxygen concentration (between −0.02 and −0.45 mg O2 L-1 H2O per 100 bar), which was fully reversible. Furthermore, the kinetics of the pressure response of the sensors was determined in experiments with high temporal resolution. Spikes attributed to pressure-induced oxygen diffusion between sensor components were observed within the first seconds after pressurization/depressurization.

There are the imperious demands for novel oxygen (O2) sensors in cutting-edge biochemical technologies and industrial hygiene. Here, we develop a colorimetric O2 sensor based on a spherical nano-sized reduced TiO2 (TiO2 – x) catalyst, which resolves the critical bottlenecks of conventional systems. The sensing mechanism of our O2 sensors relies on two characteristics which are proven by simulations based on density functional theory (DFT) calculations. First, nano-TiO2–x, in the partially reduced form, shows a rapid, reversible O2 uptake at room temperature. Second, the partially reduced form of nano-TiO2–x, called black TiO2, shows a change in the lightness of color. Owing to these characteristics, the developed sensor it is well-suited for use at ambient temperature/pressure in the absence of a reference gas, in contrast with the conventional system. Also, it allows long-term operations and it can withstand degradation because the former comprises solid-state inorganic compounds.

This paper presents a new hepatic culture device, in which oxygen concentration gradient formed by cellular respiration can be visualized as a two-dimensional optical image. An oxygen sensor layer containing Pt (II) octaethylporphyrin (PtOEP) was embedded at the bottom of the device, allowing visualization of oxygen concentration distribution over the cell culture area. Oxygen concentration was determined by analyzing the modulation of fluorescence intensity emitted by the sensor, which is negatively correlated to the concentration. The results in HepG2 cell culture showed that the oxygen gradient and local oxygen partial pressure could be regulated by controlling the perfusion flow rate in the device. The local and physiological oxygen gradient comparable to the in vivo liver lobules can successfully be reproduced in the device. Therefore, periportal and perivenous hepatic like-zones were successfully realized in vitro. The present device would be helpful in the development of novel in vitro methods recapitulating the liver physiology for investigation of hepatic zonation and drug screening system recapitulating the liver physiology.

Mono-dispersed polystyrene-based microspheres with diameters about 1 μm encapsulating rhodamine moieties as oxygen insensitive internal reference probes and platinum octaethylporphyrin units as oxygen sensitive probes were synthesized as new ratiometric oxygen sensors (Rhod-PtOEP-PS). The dual luminophors of rhodamines and platinum porphyrin moieties exhibited emissions maxima at 585 nm and 644 nm, respectively. The microspheres showed good oxygen sensing properties in different oxygen partial pressures (pO2) and dissolved oxygen (DO) concentrations. It was found the oxygen probes and reference probes in microspheres showed higher photo-stability than their corresponding free fluorophores in solution. The microspheres also showed good sensitivity for air-pressure and cellular oxygen in cell culture medium. These microspheres were used to detect DOs in a few kinds of liquids including some daily drinks and it was found the measured errors were within positive/negative 11% as compared with the measured results using traditional oxygen electrodes.

An amphiphilic graft copolymer (P3) composed of poly(oligo (ethylene glycol) methacrylate) (POEGMA) as a hydrophilic segment and a polystyrene (PS) as a hydrophobic chain was prepared. P3 was used to incorporate a highly efficient hydrophobic oxygen probe platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP) in its micelles to enable the application of PtTFPP in aqueous solution for biosensing. For achieving ratiometric oxygen sensing, a hydrophobic conjugated polymer (CP) was used as a fluorescence resonance energy transfer (FRET) donor for PtTFPP - the FRET acceptor. Results showed that diameters of these nano-oxygen sensors ranging from 50 to 60 nm and FRET efficiency as high as 98% could be achieved. Further, FRET contributed to the brightness of PtTFPP in micelles. High quantum yields of PtTFPP in non-FRET micelles and FRET micelles under nitrogen were achieved to be 0.109 and 0.231, respectively. The sensors were found to be able to measure oxygen concentrations from 0.082 to 40.9 mg/L at room temperature with linear Stern-Volmer constants. These sensors were also demonstrated to be suitable for monitoring extracellular oxygen consumption of E. Coli and HeLa cells. This study illustrated a feasible approach to achieve highly efficient ratiometric oxygen sensors without specific structure modification of the efficient PtTFPP probe, however using an amphiphilic graft copolymer approach.

Perovskite nanocrystals (PNCs) have emerged as advanced materials for various applications. Herein, we developed oxygen insensitive PNCs in polymer matrices and applied them as internal reference to achieve ratiometric sensing for oxygen. Significant emission color changes from orange under nitrogen to green under oxygen were observed. Further micro-patterned sensors were prepared by micro/nano-imprint technology. Results showed that all these micro-structures increased sensors’ sensitivity, however, affected sensors response time significantly. The film with pinholes slowed down the response times; the films with pillars shorted the response time. Therefore, for the first time we prepared new PNCs-based ratiometric gaseous oxygen sensing films and further prepared micro-structured sensors. This study may broaden the applications of perovskite materials and also oxygen sensors.

Summary Recent works on potentiometric volatile organic compound (VOC) detection based on oxygen sensor with yttria-stabilized zirconia (YSZ) and modified Pt electrodes is reviewed. Sub-ppm or lower level of VOC contamination in air is now detectable using YSZ based oxygen concentration cell. The VOC contamination fluctuates the concentration of adsorbed oxygen on the Pt sensing electrode, leading to a substantial deviation from the electromotive force (EMF) value predicted by the Nernst equation, E = (RT/4F)ln{P1(O2)/P2(O2)}. Sensitivity of the Pt electrode is tunable by the coating of the Pt electrode with some ceramic layers tunes, which may vary the concentration of the adsorbed oxygen and even the reaction electron number of oxygen.

TiO2 is one of the most popular materials used as air/fuel ratio (A/F) oxygen lambda sensor for automobiles, because of its excellent gas sensing properties. As is well known, the composition of gasoline is very complex and trace amounts of phosphorus-containing additives are present in many kinds of gasoline. Many studies have shown that a large amount of phosphorus containing particles is loaded on the surface of the failed oxygen sensor. However, few studies have focused on the effects of phosphorus on the TiO2 sensing film. In this work, pure TiO2 and P2O5 contaminated TiO2 oxygen lambda sensor were prepared to discuss the effects of phosphorus on TiO2 sensing film. The results showed that the transient response of the sensor is significantly affected when TiO2 is poisoned by P2O5. XRD, SEM, EDS and XPS were used to analyze the phase structure, morphology and surface chemistry state of TiO2 sensing film poisoned by P2O5. It is found that the TiO2 surface was coated by phosphate radical, resulting in a barrier layer on the grain surface which blocks the transfer of electrons to O2 molecule.

We present a phosphorescence lifetime imaging (PLIM) based oxygen sensor to monitor the local O2 level in conventional petri dish-based or microfluidic in vitro cell culture. The sensor film is fabricated by dissolving Pt(II) meso-tetrakis(pentafluorophenyl) porphine (PtTFPP) into a thermal curable poly(perfluoroether) (PFPE). The lifetime response of the sensor to O2 follows a linear Stern-Volmer relationship. Compared with PDMS as polymer matrix, the use of PFPE as the polymer matrix for PtTFPP mitigates both the dye induced cytotoxicity and the biomolecule adsorption problems of polydimethylsiloxane (PDMS), while maintaining cell compatibility. By using the sensor film with PFPE as the polymer matrix, the O2 tension during cell proliferation can be monitored in real time, and the resulting value can be used to calculate the per-cell O2 consumption. We tested the application of the sensor for monitoring the O2 tension during long term cell culture of HeLa cells and MDA-MB-231 cells, and calculated the O2 consumption per cell for MDA-MB-231 cells. Our study demonstrates that the PtTFPP/PFPE sensor can be employed as a general noninvasive lifetime imaging platform for studying the di-oxygen in in vitro tissue models at the cellular level as a function of space and time.

Amperometric NOx sensors are increasingly used in automotive industry to meet the stringent emission measurement regulations. These sensors measure O2 and NOx concentration using two different sensing cells. In this work, a physics-based model was developed and then employed to predict the sensor output for oxygen as a function of sensor temperature and oxygen concentration. A temperature perturbation method was also developed based on the model to calibrate the sensor output with respect to oxygen concentration. The model accurately matched the experimental results for steady state and transient conditions. A two step sensor diagnostics procedure based on the sensor temperature perturbation method was then proposed. The first diagnostics step evaluates the sensor output to check if it is within the acceptable range. The second diagnosis step checks the plausibility of the sensor output based on the physics based model and temperature perturbation. A self-calibration procedure was also implemented inside the diagnostics procedure using temperature perturbation at engine-off. This self-recalibration only requires an external relative humidity measurement.

(M = Fe, Cr and Co) doped CaZrO3, CaZr0.7M0.3O3 (M = Fe, Cr and Co), was synthesized by solid state reaction method. Crystalline structure, microstructures, electronic conductivity, total conductivity and sensing performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Hebb-Wagner, DC van der Pauw and voltammetry method, respectively. XRD measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples belong to an orthorhombic perovskite structure. SEM measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples have fine grains with average grain size of 0.5–2 μm. Electrical property measurements show that the CaZr0.7Fe0.3O3 and CaZr0.7Cr0.3O3 samples have the highest electronic conductivity and total conductivity in air, respectively. Sensing performance measurements show that limiting current-type oxygen sensors with 9YSZ solid electrolyte and CaZr0.7M0.3O3 dense diffusion barrier exhibit good limiting current (IL) plateau. Log IL depends linearly on 1000/T. IL depends linearly on oxygen partial pressure.

In this study, a reliable and novel testing methodology is presented for the burst test of heat pipes developed for space applications. The test set up enables heat pipe to be tested at flight configuration. The target internal pressure of the heat pipe is achieved by increasing the temperature of the heat pipe and consequently the ammonia inside. The setup uses microphones, oxygen sensors and thermocouples for the accurate determination of the burst instant and temperature. Burst temperature and specific volume are then used in conjunction for the determination of the burst pressure via thermodynamic data for ammonia.

Mn-containing additives, such as methylcyclopentadienyl manganese tricarbonyl (MMT), are usually used to improve the octane value of unleaded gasoline. Several studies have reported the adverse effects of MMT on oxygen sensors. However, the failure mechanisms of the oxygen sensor are seldom discussed. TiO2 has been widely used as oxygen lambda sensor to control the air-to-fuel ratio (A/F) in vehicles. In this work, TiO2 based lambda sensors were fabricated by thick film technology and then were directly poisoned by MMT. Their dynamic response characteristics were studied in comparison with pure TiO2 sensors. The results showed that the dynamic response properties of TiO2 lambda sensor were deteriorated sharply by MMT. XRD, SEM, EDS and XPS were used to analyze the phase structure, morphology and surface chemistry state of TiO2 sensing film poisoned by MMT. Finally, a barrier model and a resistance model were proposed to discuss the deterioration mechanisms.

A temperature-sensing method immune to oxygen interference is established based on phosphorescent metalloporphyrins on regenerated cellulose (RC). A series of metalloporphyrins (hematoporphyrin monomethyl ether coordinated to Pd, Gd, and Lu ions: Pd-, Gd-, and Lu-HMME) are designed to be embedded in RC. The phosphorescence emissions of these metalloporphyrins are effectively enhanced on RC, affording phosphorescence quantum yields of 1.8%, 3.3%, and 2.2%, respectively. The phosphorescence emissions of these metalloporphyrins on RC (metalloporphyrins/RC) are independent of oxygen concentration because RC provides an oxygen-impermeable microenvironment. Meanwhile, the phosphorescence emissions are effectively quenched with increasing temperature. The phosphorescence lifetimes also decrease with temperature, indicating an increase in non-radiative relaxation, which weakens phosphorescence emission. The oxygen-independence and temperature-dependence of these metalloporphyrins/RC reveal that they could serve as promising anti-oxygen-interference temperature indicators. Temperature-response plots are obtained in the range from −75 to 50 °C. The temperature sensitivities of Pd-, Gd-, and Lu-HMME on RC are evaluated to be 0.50, 0.28, and 0.36%/°C based on the temperature-response plots. The temperature resolution values of Pd-, Gd-, and Lu-HMME on RC are 0.5, 1.3, and 1.2 °C. These temperature indicators have high photostability under extended irradiation, making them suitable for practical use. The method offers attractive new insights into phosphorescent temperature-sensing materials and the development of oxygen sensors with temperature compensation.

In this work, we presented the robust and magnetically recoverable dual sensor particles that are capable of real-time monitoring of dissolved oxygen (DO) and glucose concentrations in aqueous solutions. The dual sensor consists of glucose oxidase-functionalized polyethylenimine-coated Fe3O4 particles (Fe3O4@PEI-GOD) and sub-micro-sized Fe3O4-modified poly(Platinum porphyrin-co-Styrene) ((PtTFPPMA-PS)@Fe3O4) fluorescent spheres. The dual sensing functions originate from the cascade catalysis amplification driven by the recyclable Fe3O4@PEI-GOD particles and glucose oxidase consumption of oxygen in the process of glucose oxidation. Consequently, the (PtTFPPMA-PS)@Fe3O4 fluorescent spheres exhibited higher fluorescence intensity due to the effective alleviation of fluorescence quenching effect raised from the decrease of DO. The remarkable fluorescence intensity-changing characteristics of the solutions facilitate convenient identification of oxygen concentrations and glucose concentrations even with naked eyes. Thanks to the magnetically recoverable superiority, the recycle study proved that the multifunctional particles could be repeatedly utilized without significant catalytic activity loss after 10 cycles. Interestingly, the sensing film comprising the (PtTFPPMA-PS)@Fe3O4 fluorescent spheres can also be applied to the unsteady pressure measurement and unsteady air flow visualization due to its remarkable light intensity-changing features.

(La0.4Ce0.6O2-δ)1-x(FeO1.5)x (x = 0, 0.03, 0.04, 0.10, and 0.20) was synthesized by co-precipitation method. Crystalline structure, microstructure, electronic and ionic conductivities were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Hebb-Wagner method, and AC impedance method, respectively. The effects of FeO1.5 dopant on the properties of samples were investigated. A limiting current oxygen sensor based on (La0.4Ce0.6O2-δ)0.96(FeO1.5)0.04 as dense diffusion barrier and 8YSZ as solid electrolyte was prepared by Pt paste bonding method. The effects of temperature and oxygen concentration on sensing performance were investigated. The XRD measurements showed that the solid solubility of FeO1.5 in La0.4Ce0.6O2-δ (LDC) was between 3 mol% and 4 mol%. The electrical conductivity analysis showed that (La0.4Ce0.6O2-δ)0.96(FeO1.5)0.04 had the highest electronic and ionic conductivities. The sensor had a good performance and the limiting current depended linearly on the oxygen concentration, and exponentially on 1/T.

1 A luminescent film comprising Eu (Ш)-doped yttrium oxide nanosheets was fabricated by electrophoretic deposition, modified by 2-thenoyltrifluoroacetonate, and coated with polystyrene to obtain a novel oxygen sensor capable of detecting both dissolved (DO) and gaseous (GO) oxygen based on luminescence intensity quenching. Based on the results of luminscence lifetime, the mechanism of molecular oxygen–induced luminescence quenching was discussed in detail. The above film exhibited high sensitivity and a well-linear response, with its high photostability making it a promising material for DO and GO sensing.

The Seebeck-coefficient (aka thermopower) is a less wide-spread parameter to determine constants for defect chemical models of semiconductor oxides. It is a measure for the charge carrier concentration. In contrast to the often investigated electrical conductivity, it has the benefit of being independent of the material geometry. BaFe0.7Ta0.3O3‐δ is known as a temperature-independent conductometric oxygen sensor material with perovskite crystal structure. The present work considers the Seebeck-coefficient as well as the electrical conductivity of bulk and thick-film BaFe0.89Al0.01Ta0.1O3‐ δ (BFAT10). Seebeck-coefficient and electrical conductivity were measured simultaneously between 600 and 950 °C under varying oxygen partial pressures from 10− 24 to 1 bar. BFAT10 thick films have been successfully deposited by the novel Aerosol Deposition Method (ADM) at room temperature on a special transducer. The electrical conductivity of thick-film sensors shows almost no temperature dependency but depends strongly on the oxygen partial pressure in the temperature range from 600 to 800 °C. An n-to-p-type transition was observed in the investigated oxygen partial pressure and temperature range. The defect parameters were derived from the experimental results and an initial defect model for BFAT10 is discussed. A hopping-type conduction mechanism is assumed due to the very low charge carrier mobility.

We report a novel, simple and cheap generator–collector electrode system, employing platinum leaves, with micron-sized pores and typically 100–300 nm thickness, sandwiched with a porous track etch membrane spacer with typically 30 nm diameter pores. The electrode assembly is sealed into a polymer lamination pouch with one side 2 mm diameter exposed to electrolyte solution. The generator electrode with sweeping potential (top or bottom electrode) shows transient current with high capacitive current component. The collector electrode with fixed potential shows well-defined steady state current response at low potential sweep rates. The fabricated device shows good performance in monitoring both 1,1′-ferrocenedimethanol oxidation and proton reduction redox processes. Oxygen sensor signals are assigned to a lowering of the steady state proton reduction current.

Alumina is widely used as substrate material for oxygen lambda sensors. It has been reported that response properties of sensors are highly dependent on surface state of substrates. In this work, Al 2 O 3 -x%SiO 2 (x = 2–30) substrates were specially prepared for TiO 2 based lambda sensors for high temperature operation. Structure and surface state of prepared substrates were characterized by XRD, SEM and XPS. TiO 2 sensing film was prepared by screen printing method. Results indicated that sensors fabricated on Al 2 O 3 -10%SiO 2 substrate exhibited the best sensing properties. Moreover, final steady-state voltages of all sensors were limited to less than 100 mV at 600–800 ℃.

Using a thermogravimetric analyzer and an oxygen sensor, relative oxygen potentials of mixed oxide (MOX) fuels with Pu contents of 45% and 68% were measured at 1473 K – 1873 K; the relative oxygen potentials provide the relation among the equilibrium oxygen-to-metal (O/M) ratio, temperature, and oxygen partial pressure of the flowing gas. To evaluate the effect of the Pu content on the relative oxygen potential of MOX and related defect formation energy, this work aims to bridge the gap in the results available in existing reports, where Pu contents of 0%-46% and 100% have been studied [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] . The measured data indicate that the trend of increasing relative oxygen potential with increasing Pu content, which can occur as a consequence of more Pu cations changing from being tetravalent to trivalent, reaches a saturation at a Pu content of 68%, in particular in the region of O/M

A series of (8YSZ)1-x(CeO2)x (0 ≤ x ≤ 0.3) materials are synthesized by co-precipitation. Both crystalline structure and electrical conductivity of material are detected. (8YSZ)1-x(CeO2)x (0 ≤ x ≤ 0.3) belongs to cubic phase and (8YSZ)0.9(CeO2)0.1 is provided with the highest electrical conductivity. Select 8YSZ as solid electrolyte and (8YSZ)0.9(CeO2)0.1 as dense diffusion barrier to prepare an oxygen sensor by Pt paste bonding method. Limiting current plateau of the sensor is observable at 2% oxygen concentration and at 720–900 °C, and logarithm of the limiting current (log IL) plays a linear relationship to 1000/T. Limiting current of the sensor is observable at 850 °C and 2–14% oxygen concentration, which is linearly related to the oxygen concentration. The limiting current of the sensor does not vary significantly in the range of water vapor pressure (p(H2O)) 280.66–2268.63 Pa and in the range of carbon dioxide concentration 0–90%, respectively. The limiting current of the sensor does not decay in the oxygen concentration of 2% at 850 °C during the detection time of 120 h.

t-ZrO2 is a promising structural and functional semiconductor material, which is widely used in the fields of oxygen sensors, solid fuel cells and coating materials. However, the effect on the structural stability mechanism and property of yttrium stabilized tetragonal zirconia is still unclear. In particular, for the Y-Vo-Y trimer structure of yttrium stabilized tetragonal zirconia, the influence of the interaction between Y atoms and Vo on the electronic and mechanical properties is not well understood. The results show that the Y11(Vo)-2NN(1) trimer structure is the most stable. In the other models, due to the effects of the Zr-4 d state and the O-2 p state, changes occur near the Fermi level, which improves the electronic transition between the valence band and the conduction band, and improves the electronic performance. As for mechanical properties, Y-doped and Vo compensation weaken the volume deformation resistance, shear deformation resistance and elastic stiffness of t-ZrO2. The hardness of doped with compensation structure increases slightly, while that of non-compensated structure decreases obviously, which is consistent with the change of B / G . Therefore, the interaction between double Y and Vo is through chemical bonding and charge balance to achieve the stability of the structure and electronic properties, while reducing the material's resistance to deformation.

Based on a 1.0 L turbocharged GDI engine and product-level ion current detection system, the potential of using ion sensing technology for transient EGR control is studied. Firstly, ion sensing performance under steady-state EGR condition is studied. The result shows that the correlation coefficient between mean value of Imax, Isum and IMEP is over 0.96 under steady-state condition, but the cyclic variation of ion current signal is too high for control. Thus, the moving average method is used to effectively reduce the cyclic variation of ion current signal to the same level as cylinder pressure signal. Based on that, ion sensing and UEGO sensor performance under transient EGR condition is compared. The weighted moving average method is proposed optimized from the moving average method to shorten the response delay of ion current signal. The response delay could be reduced by 30% in the case study. Finally, the applicability of ion current signal under different operating conditions is studied. The result shows that ion current signal could be used for transient EGR control. However, if the variation of ion current signal is within the cyclic variation range of ion current signal, the variation of EGR is hard to be distinguished.

The high consumption rates of fossil fuel and unburned hydrocarbons pollution in exhaust gases are considered to be the main problems that face the world today. The use of Brown’s gas (HHO gas i.e. mixture of hydrogen and oxygen) as a new source of energy, reducing the amount of injected fuel and ensuring complete combustion of the mixture are gaining an increasing interest worldwide. There are two different types of HHO cells; HHO wet cell and HHO dry cell. In this paper, the HHO dry cell was used because it has several advantages, such as its small size and ease to install in engines. The HHO dry cell uses the electrolysis process in order to produce the HHO gas from water, which is ionized by adding NaOH as the electrolyte. Three types of HHO dry cell were used, namely alpha, beta and omega cells. Many measured data were done to choose the best one of the HHO dry cells. Oxygen sensor, MAP sensor, and MAF sensor were used to control the fuel injection. From the recorded measured experimental data, the beta cell has shown a good performance for the engine. The amount of HHO gas needed to be supplied to a 1500 CC engine is 0.375 LPM. The results also showed that there is a 17% reduction in fuel consumption and a 17% reduction in CO, a 27% reduction in HC, a 15% increase in O2 and a 1% increase in CO2.

In recent years, room temperature ionic liquids (RTILs) have been highly utilized in electrochemical fields. Specifically, ionic liquids (ILs) as electrolytes augur promising potential for the next generation of advanced and miniaturized electrochemical gas sensors. In this paper, 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM][PF6]), 1-propyl-3-methylimidazolium hexafluorophosphate ([PMIM][PF6]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) were synthesized through a facile one-pot method. We found that [EMIM][PF6] and [PMIM][PF6] exist in the solid state at room temperature. Hence, these ILs can effectively avoid the leakage of electrolytes. However, [BMIM][PF6] can be present in liquid state at room temperature as the melting point decreases, due to the increasing of alkyl chain (Cn, n < 6) for the ILs. Compared to solid electrolyte gas sensors, sensors based on liquid electrolytes offer a reliable response and achieve sufficient ion mobility to sense oxygen. Our work provides an incentive to enhance the properties of a liquid electrolyte by mixing it with Pt-modified ordered mesoporous carbons (Pt-OMCs), which not only prevents the aggregation of OMCs but also provides a large number of active sites for oxygen reduction. The limit of detection (LOD) in oxygen sensors based on Pt/CMK-3-COOH-[BMIM][PF6] is relatively low (1.10% O2). Our results indicate that the synergistic combination of ILs and Pt-OMCs markedly promotes the performance of electrochemical oxygen sensors.