https://iopscience.iop.org/article/10.1149/1945-7111/ab77a0/pdf

Review—Recent Advances in Electrochemical Impedance Spectroscopy Based Toxic Gas Sensors Using Semiconducting Metal Oxides

First-principles calculations are used to study the structural, electronic, transport and optical properties of buckled bismuthene with the adsorption of various gas molecules such as CO, O2, H2O, NH3, SO2, NO and NO2. By considering the van der Waals interactions between the gas molecules and buckled bismuthene, we find that the buckled bismuthene shows superior gas sensing performance to other 2D materials such as graphene and MoS2. The adsorption of CO, O2, H2O and NH3 molecules is physisorption, whereas SO2, NO and NO2 are chemisorbed on the buckled bismuthene with large charge transfer and strong adsorption energy. After adsorption, charges are transferred from buckled bismuthene to the molecules and the quantum conductance is changed by the adsorbed molecules. Furthermore, the work function of buckled bismuthene is changed with the adsorption of different molecules. Our results show that the electronic, transport and optical properties of buckled bismuthene are sensitive to the adsorption of gas molecules, which suggests that buckled bismuthene holds great potential for application in gas sensors.

Gas sensing properties of buckled bismuthene predicted by first-principles calculations.

Review—Electrochemical NOx Gas Sensors Based on Stabilized Zirconia

/pdf/metal-oxides-nanomaterials-and-nanocomposite-based-1tv7aol3.pdf

Metal Oxides Nanomaterials and Nanocomposite-Based Electrochemical Sensors for Healthcare Applications

In the present study, changes in the sensing properties of SnO2 on Carbon incorporation have been investigated in detail. The gas sensing response of size-selected SnO2 and SnO2:C alloy nanoparticles prepared by gas phase deposition method have been investigated for H2 and ethanol over a varied temperature range (50 °C–200 °C). The incorporation of carbon into SnO2 lattice results in a large change in the sensing behaviour towards the two gases both having reducing nature. SnO2:C nanoparticles show positive sensing response for H2 and negative sensing response for ethanol, whereas SnO2 nanoparticles show a normal sensing response of an n-type semiconductor towards both the reducing gases. Observed values of activation energy of sensing and energy levels of O-vacancies observed in the PL spectra of SnO2 and SnO2:C are consistent with these results. (i) Catalytic C–H interaction and (ii) modified work function of SnO2 and C on hydrogenation resulting in alteration of electronic exchange between SnO2 and C, and (iii) passivation effect of carbon during SnO2-ethanol interaction along with a possibility of reduction in SnO2 sites in SnO2:C nanoparticles, are responsible for the observed behaviour. The present study shows that the incorporation of C in SnO2 nanoparticles results in excellent selectivity towards H2 and ethanol (both having reducing nature) in the low temperature range, normally not observed in oxide based resistive sensors.

Improved selectivity of SnO2:C alloy nanoparticles towards H2 and ethanol reducing gases; role of SnO2:C electronic interaction

Influence of Microstructure on the Sensing Behavior of NOx Exhaust Gas Sensors

Using impedance spectroscopy the electrical response of sensors with various porous Y-stabilized ZrO2 (YSZ) microstructures was measured for gas concentrations containing 0–100 ppm NO with 10.5%O2 at temperatures ranging from 600–700 °C. The impedance response increased substantially as the sensor porosity increased from 46%–50%. Activation energies calculated based on data from the impedance measurements increased in magnitude (97.4–104.9 kJ/mol for 100 ppm NO) with respect to increasing YSZ porosity. Analysis of the oxygen partial pressure dependence of the sensors suggested that dissociative adsorption was the dominant rate limiting. The PWC/DNP theory level was used to investigate the gas-phase energy barrier of the 2NO+O2→2NO2 reaction on a 56-atom YSZ/Au model cluster using Density Functional Theory and Linear Synchronous Transit/Quadratic Synchronous Transit calculations. The reaction path shows oxygen surface reactions that begin with NO association with adsorbed O2 on a Zr surface site, followed by O2 dissociative adsorption, atomic oxygen diffusion, and further NO2 formation. The free energy barrier was calculated to be 181.7 kJ/mol at PWC/DNP. A qualitative comparison with the extrapolated data at 62% ± 2% porosity representing the YSZ model cluster indicates that the calculated barriers are in reasonable agreement with experiments, especially when the RPBE functional is used.

/pdf/kinetics-of-nitric-oxide-and-oxygen-gases-on-porous-y-2u7w0u9jbx.pdf

Kinetics of Nitric Oxide and Oxygen Gases on Porous Y-Stabilized ZrO2-Based Sensors

The influence of electrode configuration on the impedancemetric response of nitric oxide (NO) gas sensors was investigated for solid electrochemical cells [Au/yttria-stabilized zirconia (YSZ)/Au)]. Fabrication of the sensors was carried out at 1050 °C in order to establish a porous YSZ electrolyte that enabled gas diffusion. Two electrode configurations were studied where Au wire electrodes were either embedded within or wrapped around the YSZ electrolyte. The electrical response of the sensors was collected via impedance spectroscopy under various operating conditions where gas concentrations ranged from 0 to 100 ppm NO and 1%–18% O2 at temperatures varying from 600 to 700 °C. Gas diffusion appeared to be a rate-limiting mechanism in sensors where the electrode configuration resulted in longer diffusion pathways. The temperature dependence of the NO sensors studied was independent of the electrode configuration. Analysis of the impedance data, along with equivalent circuit modeling indicated the electrode configuration of the sensor effected gas and ionic transport pathways, capacitance behavior, and NO sensitivity.

Effect of Electrode Configuration on Nitric Oxide Gas Sensor Behavior

The role of porosity on impedancemetric NOx sensing is discussed for sensors com‐ posed of a porous yttria-stabilized zirconia (YSZ) electrolyte and dense Au electrodes. NOx sensors considered here were fabricated at firing temperatures of 950–1200°C, which established a range of electrolyte microstructures where the porosity ranged from approximately 50% to 44%. Analysis of the electrical response of the NOx sensors indicated that sensors fired at 1050°C resulting in an electrolyte porosity of 46% demonstrated higher NOx sensitivity based on the operating conditions studied. The impedance of the sensors demonstrated a strong dependence on the electrolyte porosity. The activation energy of the sensors, which ranged from 109.2 to 81.1 kJ/mol, decreased with decreasing electrolyte porosity. Sensors with an electrolyte porosity ≥46% were limited by dissociated adsorption, whereas gas diffusion was rate limiting for sensors with an electrolyte porosity <46%. The impedancemetric response of the porous sensors to NO concentrations ≤10 ppm was distinguishable at operating frequencies as high as 40 Hz, thereby suggesting rapid sensing capabilities. Overall, the microstructure of the sensors composed of a YSZ electrolyte with 46% porosity promoted a strong, rapid, and highly sensitive response to NOx.

/pdf/advances-in-electrochemical-nitric-oxide-exhaust-gas-sensors-29hlsowugu.pdf

Advances in Electrochemical Nitric Oxide Exhaust Gas Sensors

The emulsified feedstock technique is to improve the performance of
products by using the micro-explosion phenomenon of emulsion. However,
an obstacle to some applications of this technology is the contradiction
between emulsion stability and micro-explosion intensity. For the first
time, adding water-soluble polymers was proposed to solve this problem.
Two polymers of xanthan gum (XG) and nonionic polyacrylamide (NPAM) were
investigated and the results show that micro-explosions have five forms.
As one of these five forms, the intensity of optimal micro-explosion is
three orders of magnitude higher than other forms, and adding 0.5% XG
increases the probability of optimal micro-explosion from 0% to 60%
due to the low surface activity, strong thickening and pseudoplasticity
of XG solutions. By contrast, NPAM does not promote micro-explosion
because of its strong surface activity. Finally, a new mechanism for
micro-explosions related to surface tension, interfacial tension and
viscosity is proposed.

Achieving optimal micro-explosions in stable emulsions by adding water-soluble polymers

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