Environmental monitoring of CO2 concentration flows with novel fast Li-Garnet based electrochemical sensor

Global energy production and consumption growth sets new environmental and energy challenges that require innovative solutions to store, track, transfer and monitor CO2 flows. To date, the most common solution to monitor CO2 involves either the use of expensive and energy-consuming near infrared gas sensors, or semiconducting metal oxide gas sensors in which adsorbed gases modify their resistivity. Both meet requirements in terms of response time and accuracy, however their limited working temperature ranges and power consumption give way for other types of sensors. Here, electrochemical sensors based on the Taguchi principle seem to be a suitable alternative, due to their simplicity, scalability and tracking sensibly changes in CO2 concentrations with respect to their electromotive force pf the cell. Despite number of reports on the carbon dioxide sensing performance of devices based on sodium and lithium conductors such as NASICON and LISICON, the need of well performing, stable and power efficient devices is still not yet fully satisfied. Therefore new engineered electrolyte materials, such as doped lithium lanthanum zirconates, attract considerable attention for improving long-term chemical stability and faster kinetics. In this work, we report on a new class of Taguchi-type carbon dioxide sensors, based on Li-ions conducting solid state electrolytes with fast conducting Li-garnet structures as an alternative to state-of-the-art NASICON based structures. Ceramic processing of the sensor unit based on a dense ceramic pellet electrolyte of Li6.75La3Zr1.75Ta0.25O12 and thick film porous sensing electrodes based on Li2CO3-containing pastes are discussed. We elaborate on the ceramic fabrication routes for the pellet based sensor structures and structural stabilities investigated in terms of Raman Spectroscopy and X-Ray Diffraction showing the intended electrolyte and electrode crystal structures. The electrochemical performance of the system and electrode-electrolyte interface behavior is discussed in terms of electrochemical impedance spectroscopy. The sensing performance of the device is tested in steady gas flows at elevated temperatures in a range of 250-450oC. The sensing performance results show stable response to carbon dioxide concentration change in a range of 0-8000ppm CO2 with the 90% response time below 1min. Pellet based device exhibit high stability over cycling. The sensing resolution of the sensor is as large as 35mV per decade. V shows close to theoretical linear behavior over the measured range for the discussed device. Given this, pellet based sensor show potential application value in the detection of CO2 gas for environmental monitoring with low energy requirements

Design of LTCC-based Ceramic Structure for Chemical Microreactor

The design of ceramic chemical microreactor for the production of hydrogen needed in portable polymer-electrolyte membrane (PEM) fuel cells is presented. The microreactor was developed for the steam reforming of liquid fuels with water into hydrogen. The complex three-dimensional ceramic structure of the microreactor includes evaporator(s), mixer(s), reformer and combustor. Low-temperature co-fired ceramic (LTCC) technology was used to fabricate the ceramic structures with buried cavities and channels, and thick-film technology was used to make electrical heaters, temperature sensors and pressure sensors. The final 3D ceramic structure consists of 45 LTCC tapes. The dimensions of the structure are 75 × 41 × 9 mm3 and the weight is about 73 g

Carbon Dioxide Gas Sensors and Method of Manufacturing and Using Same

A gas sensor includes a substrate and a pair of interdigitated metal electrodes selected from the group consisting of Pt, Pd, Au, Ir, Ag, Ru, Rh, In, and Os. The electrodes each include an upper surface. A first solid electrolyte resides between the interdigitated electrodes and partially engages the upper surfaces of the electrodes. The first solid electrolyte is selected from the group consisting of NASICON, LISICON, KSICON, and .beta.''-Alumina (beta prime-prime alumina in which when prepared as an electrolyte is complexed with a mobile ion selected from the group consisting of Na.sup.+, K.sup.+, Li.sup.+, Ag.sup.+, H.sup.+, Pb.sup.2+, Sr.sup.2+ or Ba.sup.2+). A second electrolyte partially engages the upper surfaces of the electrodes and engages the first solid electrolyte in at least one point. The second electrolyte is selected from the group of compounds consisting of Na.sup.+, K.sup.+, Li.sup.+, Ag.sup.+, H.sup.+, Pb.sup.2+, Sr.sup.2+ or Ba.sup.2+ ions or combinations thereof

Contribution Towards Ideal Solid Contact Ion-Selective Electrodes: Mechanistic Studies, Optimization, and Characterization

Solid contact (SC) ion-selective electrodes (ISEs) utilizing conductive polymers (CPs) as ion-to-electron transducers are plagued with poor potential stability, sensor-to-sensor standard potential reproducibility, and long equilibration times which hinders their use as minimal calibration or calibration-free sensors for clinical diagnostics. Some imperfections in the SC sensor performance are thought to be due to the presence of an undesired water layer beneath the ion-selective membrane; a result of the unsatisfactory hydrophobicity of the CP layer. The time-dependent change in the redox potential of the CP layer is the other major factor. To address these issues, in this work, the benefits of the implementation of highly hydrophobic CP layers with controlled redox potentials are investigated.ISEs built with PEDOT(PSS) as SC on Au and GC had short equilibration times while those on Pt had sluggish equilibration. These results were among the first to suggest that the substrate electrode|CP interface plays a significant role in the electrochemical behavior of the SC ISE. Due to the hydrophilicity and hydrogel-like properties of PEDOT(PSS), pH ISEs with PEDOT(PSS) as SC showed significant CO2 interference, which limits its use as a universal SC. To minimize the CO2 interference, PEDOT(PSS) was replaced by POT and PEDOT-C14(TPFPhB) as ion-to-electron transducers in SC ISEs. SC ISEs with POT as SC had unacceptable potential reproducibility partly due to the significant light sensitivity of the POT film. However, the performance characteristics of the POT-based sensors were significantly improved through the incorporation of a TCNQ redox couple into the POT film along with adjusting the TCNQ oxidized/reduced ratio. In contrast to the POT-based SC ISEs, electrodes with the superhydrophobic PEDOT-C14(TPFPhB) as SC exhibited short equilibration times, excellent potential stability, and no light sensitivity. In addition, the PEDOT-C14(TPFPhB) film eliminated CO2 interference, which has been experienced with PEDOT(PSS) as SC. Consequently, the pH sensors with PEDOT-C14(TPFPhB) as SC allow accurate pH determination in whole blood samples with fluctuating CO2 levels. In summary, the data collected with PEDOT-C14(TPFPhB)-based SC K+, Na+, and pH sensors suggest that PEDOT-C14(TPFPhB) may be the ideal SC for SC ISEs which may lead to ISEs requiring minimal to no calibration

Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2

Half-cell potentials of the electrochemical cell Au, VWT | YSZ | Au are analyzed in dependence on oxygen and ammonia concentration at 550 °C. One of the gold electrodes is covered with a porous SCR catalyst, vanadia-tungstenia-titania (VWT). The cell is utilized as a potentiometric ammonia gas sensor and provides a semi-logarithmic characteristic curve with a high NH(3) sensitivity and selectivity. The analyses of the Au | YSZ and Au, VWT | YSZ half-cells are conducted to describe the non-equilibrium behavior of the sensor device in light of mixed potential theory. Both electrode potentials provide a dependency on the NH(3) concentration, whereby VWT, Au | YSZ shows a stronger effect which increases with increasing VWT coverage. The potential shifts in the anodic direction confirm the formation of mixed potentials at both electrodes resulting from electrochemical reactions of O(2) and NH(3) at the three-phase boundary. Polarization curves indicate Butler-Volmer-type kinetics. Modified polarization curves of the VWT covered electrode show an enhanced anodic reaction and an almost unaltered cathodic reaction. The NH(3) dependency is dominated by the VWT coverage and it turns out that the catalytic properties of the VWT thick film are responsible for the electrode potential shift

Kirigami-inspired, highly stretchable micro-supercapacitor patches fabricated by laser conversion and cutting.

The recent developments in material sciences and rational structural designs have advanced the field of compliant and deformable electronics systems. However, many of these systems are limited in either overall stretchability or areal coverage of functional components. Here, we design a construct inspired by Kirigami for highly deformable micro-supercapacitor patches with high areal coverages of electrode and electrolyte materials. These patches can be fabricated in simple and efficient steps by laser-assisted graphitic conversion and cutting. Because the Kirigami cuts significantly increase structural compliance, segments in the patches can buckle, rotate, bend and twist to accommodate large overall deformations with only a small strain (<3%) in active electrode areas. Electrochemical testing results have proved that electrical and electrochemical performances are preserved under large deformation, with less than 2% change in capacitance when the patch is elongated to 382.5% of its initial length. The high design flexibility can enable various types of electrical connections among an array of supercapacitors residing in one patch, by using different Kirigami designs

Perovskites-Based Nanomaterials for Chemical Sensors

The perovskite structure is adopted by many compounds in solid-state chemistry. The sensitivity, selectivity, and stability of many perovskite nanomaterials have been devoted the most attention for chemical sensors. They are capable to sense the level of small molecules such as O2, NO, and CO. This chapter provides a comprehensive overview of perovskite nanoscale materials that concentrate on chemical sensors. The perovskite structure, with two differently sized cations, is amenable to a variety of dopant additions. This flexibility allows for the control of transport and catalytic properties, which are important for improving sensor performance. We devote the most attention on the synthesis, structural information, and sensing mechanism. We will later elaborate on the development mechanism of chemical sensors based on perovskite nanomaterials. We conclude this chapter with the personal perspectives on the directions toward future works on a novelty of nanostructured chemical sensors

A High-Temperature Electrochemical Carbon Monoxide Sensor with Nanostructured Metal Oxide Electrode

Carbon monoxide (CO) is one of the major air pollutants which are emitted due to the incomplete combustion of hydrocarbon fuels. It is a colorless, odorless and tasteless gas that is highly toxic to humans and animals. Hence, a CO sensor not only serves as an alarm system for threat of CO, but also be used for monitoring the combustion process to improve the combustion efficiency. The currently existing technologies to detect CO such as gas chromatography and optical absorption spectrometry are cumbersome, costly, and lack the capability of on-line monitoring. Thus there is a critical need for developing CO sensors that can give accurate and fast response to change in the concentrations of CO as low as 20 ppm at high temperature (\u3e 500 °C).;In the present work, La0.8Sr0.2MnO3 (LSM) nanofibers were prepared by electrospinning method and utilized as a mixed potential sensor electrode for sensing CO at high temperature. The nanofibers show good thermal stability even after heat treatment at 1050 °C. This nano-fibrous structure possesses several advantages such as high porosity, high surface to volume ratio and high activity towards CO electrochemical oxidation. The nanofibers bring improved sensitivity and lower the limit of detection as compared with bulk LSM powders. Electrochemical impedance (EIS) analysis indicated that the nano-fibrous electrode shows better charge transfer capability, leading to improved catalytic activity for CO oxidation and sensor performance. The developed sensor can be used for monitoring emissions from coal-fired power plants and vehicle exhausts