INFLUENCE OF SENSING MATERIAL CHARACTERISTICS ON GAS SENSOR PROPERTIES

There has been a constant development of semiconductor metal oxides that led to improvement in their sensing properties for gas detection. Semiconductor metal oxides are widely used in gas sensors due to their excellent sensing properties, abundance and ease of manufacturing. The best example of these sensing materials is TiO2 offering a wide bandgap and an unique set of functional properties, the most of which are electrical conductivity and high surface reactivity. There are two important material specific aspects that strongly affect the gas sensing properties and can be controlled by synthesis method: These are morphology/nano-structuring and dopants to vary crystallographic structure of metal oxide sensing material. Moreover, sensor designs such as these including p-n junctions, chemo- and memristor enhance sensor signal significantly. This plenary talk presents the recent advances in gas sensor material development and their influences on sensor's response and performances

MXene Heterostructures as Perspective Materials for Gas Sensing Applications

This paper provides a summary of the recent developments with promising 2D MXene-related materials and gives an outlook for further research on gas sensor applications. The current synthesis routes that are provided in the literature are summarized, and the main properties of MXene compounds have been highlighted. Particular attention has been paid to safe and non-hazardous synthesis approaches for MXene production as 2D materials. The work so far on sensing properties of pure MXenes and MXene-based heterostructures has been considered. Significant improvement of the MXenes sensing performances not only relies on 2D production but also on the formation of MXene heterostructures with other 2D materials, such as graphene, and with metal oxides layers. Despite the limited number of research papers published in this area, recommendations on new strategies to advance MXene heterostructures and composites for gas sensing applications can be driven

Laser-Induced Interdigital Structured Graphene Electrodes Based Flexible Micro-Supercapacitor for Efficient Peak Energy Storage

The rapidly developing demand for lightweight portable electronics has accelerated advanced research on self-powered microsystems (SPMs) for peak power energy storage (ESs). In recent years, there has been, in this regard, a huge research interest in micro-supercapacitors for microelectronics application over micro-batteries due to their advantages of fast charge–discharge rate, high power density and long cycle-life. In this work, the optimization and fabrication of micro-supercapacitors (MSCs) by means of laser-induced interdigital structured graphene electrodes (LIG) has been reported. The flexible and scalable MSCs are fabricated by CO2 -laser structuring of polyimide-based Kapton ® HN foils at ambient temperature yielding interdigital LIG-electrodes and using polymer gel electrolyte (PGE) produced by polypropylene carbonate (PPC) embedded ionic liquid of 1-ethyl-3-methyl-imidazolium-trifluoromethansulphonate [EMIM][OTf]. This MSC exhibits a wide stable potential window up to 2.0 V, offering an areal capacitance of 1.75 mF/cm2 at a scan rate of 5.0 mV/s resulting in an energy density (Ea) of 0.256 µWh/cm2 @ 0.03 mA/cm2 and power density (Pa) of 0.11 mW/cm2 @0.1 mA/cm2 . Overall electrochemical performance of this LIG/PGE-MSC is rounded with a good cyclic stability up to 10,000 cycles demonstrating its potential in terms of peak energy storage ability compared to the current thin film micro-supercapacitors

Metal Oxide-Based Sensors for Ecological Monitoring: Progress and Perspectives

This paper aims to provide a large coverage of recent developments regarding environmental monitoring using metal oxide-based sensors. Particular attention is given to the detection of gases such as H2, COx, SOx, NOx, and CH4. The developments and analyses of the design of sensors and types of metal oxide sensing materials are emphasized. The sensing mechanisms and peculiarities of metal oxides used in chemoresistive sensors are provided. The main parameters that affect the sensitivity and selectivity of metal oxide sensors are indicated and their significance to the sensor signal is analyzed. Modern data processing algorithms, employed to optimize the measurement process and processing of the sensor signal, are considered. The existing sensor arrays/e-nose systems for environmental monitoring are summarized, and future prospects and challenges encountered with metal oxide-based sensor arrays are highlighted

Processing of Rh-doped perovskite protective filters for selective gas sensing

Owing to its excellent properties, BaTiO3 is used for manufacturing of thermistors and dielectric ceramic capacitors, photocatalysis, and in gas sensing. The incorporation of precious metals into the perovskite structure enables the stabilization of BaTiO3 catalysts due to the self-healing mechanisms: the formation of well-dispersed metal nanoparticles under reducing conditions and re-incorporation of metal nanoparticles into the crystal lattice under oxidizing environments. This concept is successfully proven for gas sensing/monitoring of reformate products (CO and H2 ) and during hydrogen separation and purification. Significant decomposition of traditional SnO2 sensors under such reducing conditions necessitates the use of protective coatings to improve the performance as well as avoidance of sensing layer degradation. In this sense, the perovskite group of materials display several advantages such as: ease removal of oxygen, oxygen vacancies, electron mobility, and valence control that could improve gas sensing. This work reports on the synthesis of Rh-incorporated BaTiO3 by oxalate-assisted co-precipitation method and processing into microgranules for better application of protective filters on to gas sensors. The synthesis process was performed in two steps: (1) preparation of precursor solutions with following mixing; (2) co-precipitation by pouring an oxalic acid ethanol solution in the cationic precursor solution with subsequent precipitate filtration, drying and calcination. The micro-granulation process is carried out in a laboratory spray-dryer. Soluble organic polymers are added as processing-aids as well as sacrificial pore-formers that lead to a structural porosity that enhances gas diffusion within the Rh-incorporated BaTiO3 granulates

High-temperature NO sensing performance of WO3 deposited by spray coating

This work reports the fabrication of sensors by a facile deposition of water-based ink blended commercial WO3 powders via spray coating on sensor platforms fitted with Au-interdigitated electrodes (IDEs) and the characterization of their sensing performances under hot NO-containing air at temperatures exceeding 500 °C. After deposition and heat treatment of the sensing material on the substrate fitted with Au-IDE at 700 °C, the composition and morphology of the active material were analyzed and the presence of a single phase, fine particulates of WO3, has been confirmed by XRD and SEM, respectively. The investigation of the sensing properties revealed that, contrary to the previous reports, this WO3 sensor can detect NO with a good sensitivity (∼22% for 200 ppm NO) and selectivity at 700 °C under humidity

Synthesis and evaluation of core/shell structured NMC cathode material

Cathode materials are the main elements of the Li-ion batteries and determine their key performing characteristics, including power and energy density values, cell voltage, capacity and cycle life. Up to date, Lithium-Nickel-Manganese-Cobalt-Oxide (so-called NMC) remains the most successful formulas for cathode powder, delivering strong overall performance and excellent specific energy. Within these compositions, Nickel provides high energy density and increased storage capacity at lower cost and contributes to the circular economy due to the durability, recyclability and possible second life. Therefore, Ni-rich composition, NMC 811, is more preferentially used in high performance batteries. However, the formation of the Ni2+ phase during the successive charge/discharge cycles resulting in Ni-oxidation causes chemical and structural degradation and thus, deteriorates the cyclic performance. On the other hand, Manganese in NMC composition acts not only as a stabilizer, but also, prevents Nickel-oxidation and thus, reduces the risk of capacity fading. Regarding these facts, development of core/shell structured NMC morphologies deserved a special attention. This morphology provides surface stabilization of Ni-rich NMC by keeping the energy storage capabilities at higher level and prevents degradation of cathode. In this work, we describe an oxalate-assisted co-precipitation route for synthesis of core/shell structured NMC cathode particles. For achievement of core and shell in different compositions, two-staged wet-chemical synthesis approach was applied. It is well known that morphology is affected strongly by synthesis parameters, therefore the influence of solvent type, co-precipitation temperature, stirring speed, reaction time and sintering parameters was studied in accordance with electrochemical performance testing. Li incorporation was carried by two approaches; top-down and bottom-up methods. Identification of the compositional and structural relations within the core/shell particles, SEM, TEM, FIB and XRD techniques were used. Electrochemical characterization indicated that Li infiltration process and parameters of heat treatment play a significant role in achievement of good cathode performance