Electrochemical Gas Research Articles

RTILs as Electrolytes in Electrochemical Gas Sensors for O2 and Other Gases

Oxygen is the third-most abundant element on this planet and is essential to life, the lifestyle of humans and virtually all sentient life. We need O2 to live and additionally use it for both heating and transportation. Since O2 is so essential in our everyday life, there are several applications where the oxygen levels need to be controlled or maintained within a certain range. To make sure that the O2 level is within the necessary range, devices are needed that can monitor and feedback/communicate O2 levels continuously. There are several types of chemical gas sensors for O2 which include chemoresistive gas sensors and electrochemical gas sensors. The Clark-type electrochemical sensor is the oldest and probably the most used sensor for oxygen especially in medical applications. One of the most well-known industrial applications for gas-phase oxygen sensors is probably the control of oxygen levels in combustion engines with the help of a Lambda probe, a solid-state electrochemical cell operated in amperometric and potentiometric modes.Electrochemical sensors have evolved over the past decades. By finding the suitable combination of electrolyte, electrode material, cell design and operation conditions, electrochemical sensors are tunable to meet the specific requirements of the many different applications. For example, by changing the electrode material from gold to platinum while keeping everything else the same, you can reduce the response to CO by orders of magnitude improving the selectivity in low level measurements. Further, by adjusting the thermodynamic voltage of the sensing electrode, the electrochemical reactivity is adjusted to maximize the sensor’s selectivity for the target analyte. While these developments have occurred over time, recent work implements room temperature ionic liquids (RTILs) as electrolytes. This idea has some serious merit to it for multiple reasons. Firstly, many electrochemical sensors have aqueous electrolytes which freeze at low temperatures and rapidly evaporate at elevated temperatures. Additionally, aqueous electrolytes can change in real time with variations in background humidity levels. To be more exact, aqueous electrolytes dry out when operated in low humidity backgrounds and significantly increase in volume (swell) in high humidity background levels. While drying out is an issue because this leads to poor ionic conductivities, swelling is an issue because the electrolyte needs expansion room in the sensor, typically an extensive cavity within the cell body. RTILs have shown promise because they can extend the operating temperature range as well as lead to new sensor designs operatable over a wider range of environmental conditions. The implementation of RTILs might even allow for smaller sensor designs due to a smaller volume change of the electrolyte in dependence of changing humidity levels.Several research groups have investigated the oxygen sensing capabilities of RTILs in electrochemical devices. Silvester et al. investigated the oxygen solubility in several different imidazolium cations combined with [bis(trifluoromethylsulfonyl)imide] ([NTf2]-) anions and found a high oxygen solubility in 3-butyl-1-methyl imidazolium [NTf2]- [1]. They further investigated the influence of humidity on the oxygen reduction reaction and found the most stable behavior for [3-etyhl-1-methyl imidiazolium] [NTf2]- over a broad range of different humidity levels [2]. Yin et al. investigated 1-butyl-1-methylpyrrolidinium [NTf2]- as an electrolyte in oxygen sensors and found good linear correlation of the sensor output to the oxygen concentration [3].In this work, we investigated different RTILs, including the before mentioned 1-butyl-1-methylpyrrolidinium [NTf2]- and 3-butyl-1-methyl imidazolium [NTf2]-, regarding their suitability for thin layer electrochemical oxygen sensors in a background of mostly nitrogen. The performance was investigated using CV (cyclic voltammetry) and other time dependent voltametric techniques. The ability to detect oxygen of sensors with different RTILs as electrolyte was compared to that of aqueous H2SO4.[1] S. Doblinger, D.S. Silvester, M. Costa Gomes, Functionalized Imidazolium Bis(trifluoromethylsulfonyl)-imide Ionic Liquids for Gas Sensors: Solubility of H2, O2 and SO2, Fluid Phase Equilib. 549 (2021). https://doi.org/10.1016/j.fluid.2021.113211.[2] S. Doblinger, J. Lee, D.S. Silvester, Effect of Ionic Liquid Structure on the Oxygen Reduction Reaction under Humidified Conditions, Journal of Physical Chemistry C. 123 (2019) 10727–10737. https://doi.org/10.1021/acs.jpcc.8b12123.[3] H. Yin, H. Wan, L. Lin, X. Zeng, A.J. Mason, Miniaturized Planar RTIL-based Electrochemical Gas Sensor for Real-Time Point-of-Exposure Monitoring, 2016 IEEE Healthcare Innovation Point-Of-Care Technologies Conference (HI-POCT). (2016) 85–88. https://doi.org/10.1109/HIC.2016.7797703.

Discovering a catholyte free design for gas phase electrocatalytic NO gas reduction to NH3 at room temperature

Nitric oxide (NOx) is one of the most contributors to the health risks associated with breathing in flue gases and it is crucial to eliminate this pollutant from the air when solid waste is burned. Electrochemical gas phase reduction of NO to NH3 is the promising method to mitigating the accumulation of NO gas pollutants and producing a valuable NH3 as a product at room temperature. In this investigation, for the first time, we designed a catholyte-free cell for gas phase electrochemical NO to NH3 conversion using K2[Ni(CN)4] coated carbon felt (CF) electrode as a electrocatalyst at room temperature. Herein, K2[Ni(CN)4] heterogeneous mediator transfers the electron between the NO gas molecule and electrode. The NO removal efficiency and NH3 formation were simultaneously monitored by using online gas phase FTIR spectroscopy. In the catholyte-free gas phase NORR process, the K2[Ni(CN)4]/CF electrode exhibits excellent NORR performance, with a high NH3 yield rate of 1128.9 µmol h−1 cm−2, an excellent 89.5 % NH3 faradaic efficiency at − 1 V vs quasi reference Ag and enhanced long term NORR durability. It is noteworthy that, this is the highest yield rate and faradaic efficiency of NH3 during gas phase NORR at room temperature. In addition, K2[Ni(CN)4]/CF electrocatalyst exhibits 99 % of NO removal efficiency with the formation of value-added product (NH3). Moreover, the proposed electrocatalyst shows excellent chemical, and morphological stability after long durability NORR operations. Furthermore, the detailed electrode-electrolyte free cell, NORR reduction mechanism was proposed. Present discovery provides great insights for sustainable NORR operations in real-site applications.

Solutal Marangoni effect determines bubble dynamics during electrocatalytic hydrogen evolution.

Understanding and manipulating gas bubble evolution during electrochemical water splitting is a crucial strategy for optimizing the electrode/electrolyte/gas bubble interface. Here gas bubble dynamics are investigated during the hydrogen evolution reaction on a well-defined platinum microelectrode by varying the electrolyte composition. We find that the microbubble coalescence efficiency follows the Hofmeister series of anions in the electrolyte. This dependency yields very different types of H2 gas bubble evolution in different electrolytes, ranging from periodic detachment of a single H2 gas bubble in sulfuric acid to aperiodic detachment of small H2 gas bubbles in perchloric acid. Our results indicate that the solutal Marangoni convection, induced by the anion concentration gradient developing during the reaction, plays a critical role at practical current density conditions. The resulting Marangoni force on the H2 gas bubble and the bubble departure diameter therefore depend on how surface tension varies with concentration for different electrolytes. This insight provides new avenues for controlling bubble dynamics during electrochemical gas bubble formation.

Evaluation NO2 Detection Using Low-Cost Folded-Path Photometer

As it impacts both environmental and health conditions, the measurement of nitrogen dioxide (NO2) in industrial and residential areas needs comprehensive and reliable instrumentation providing long-interference-free operation and minimum maintenance and re-calibration. Differential optical absorption spectroscopy can be used as a direct measurement technique based on the specific absorption characteristics of NO2 following the Beer-Lambert law. This paper proposes a low-cost folded-path photometer to measure NO2 in the air. Cheap tubular acrylic was used as a detection cell with a 3D printed framework, making it compact, modular, and flexible. Evaluation of this differential optical absorption spectroscope (DOAS) was conducted by instrument test responses using NO2 gas. The estimated LOD was ~1263 ppb using a 2-nm resolution of the spectrometer and a 6-meter detection cell length. Deviation of the DOAS was estimated to be 0.8% at high concentration and 2.85% at low concentration based on the calibrated DOAS. Intercomparison of the results was conducted using two different instruments to evaluate the DOAS’s performance by measuring NO2 from motorcycle emissions, which indicated that there was a good correlation between the results. The coefficient correlation (R) was 0.649 for the DOAS- ASTM D1607 Griesz Saltzmann method pairing and 0.846 for the DOAS- electrochemical gas analyzer pairing.

Ionic Liquid-Packed Microfluidic Device with Non-Planar Microelectrode as a Miniaturized Electrochemical Gas Sensor

Integrating transducer/sensing materials into microfluidic platforms has enhanced gas sensors′ sensitivity, selectivity, and response time while facilitating miniaturization. In this manuscript, microfluidics has been integrated with non-planar microelectrode array and functionalized ionic liquids (ILs) to develop a novel miniaturized electrochemical gas sensor architecture. The sensor employs the IL 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM][2-CNpyr]) as the electrolyte and capture molecule for detecting carbon dioxide (CO2). The three-layer architecture of the sensor consists of a microchannel with the IL sandwiched between glass slides containing microelectrode arrays, forming a non-planar structure. This design facilitates electric field penetration through the IL, capturing CO2 binding perturbations throughout the channel volume to enhance sensitivity. CO2 binding with [EMIM][2-CNpyr] generates carboxylate ([EMIM]+-CO2−]), carbamate ([2-CNpyr]-CO2−]), and pyrrole-2-carbonitrile (2-CNpyrH) species, significantly decreasing the conductivity. The viscosity is also increased, leading to a further decrease in conductivity. These cumulative effects increase charge transfer resistance in the impedance spectrum, allowing a linear calibration curve obtained using Langmuir Isotherm. The sensitivity and reproducibility in CO2 detection are demonstrated by two electrode configurations using the calibration curve. The developed sensor offers a versatile platform for future applications.

Design and theoretical error analysis of wireless electrochemical reader to be integrated in smart mask for breath monitoring

Herein, we describe the development of a mask for electrochemical breath gas measurement. The readout board, with dimensions of 16 × 43 × 12 mm, enables Bluetooth connectivity. The device exhibits a current measurement range of up to 582 µA. Sources of measurement error were identified and quantified using the generalized Randles model with 10% accuracy. Device accuracy was determined to be 5% of current signals. Other sources of error included hardware noise (0.021 µA), sampling time error (19.6 µA), and voltage resolution error (4.6 µA at 1 mV). Enhancing the voltage resolution of the LMP91000 chip from 66 mV to 1 mV was achieved by utilizing the microcontroller DAC output voltage as the chip reference voltage, leading to a reduction in the measurement error from 293 to 4.6 µA. The mask was successfully tested for ammonia measurement within the 0–1000 ppm range, indicating its potential for breath monitoring applications.

Solution-based self-assembly synthesis of two-dimensional-ordered mesoporous conducting polymer nanosheets with versatile properties.

Conducting polymers with conjugated backbones have been widely used in electrochemical energy storage, catalysts, gas sensors and biomedical devices. In particular, two-dimensional (2D) mesoporous conducting polymers combine the advantages of mesoporous structure and 2D nanosheet morphology with the inherent properties of conducting polymers, thus exhibiting improved electrochemical performance. Despite the use of bottom-up self-assembly approaches for the fabrication of a variety of mesoporous materials over the past decades, the synchronous control of the dimensionalities and mesoporous architectures for conducting polymer nanomaterials remains a challenge. Here, we detail a simple, general and robust route for the preparation of a series of 2D mesoporous conducting polymer nanosheets with adjustable pore size (5-20 nm) and thickness (13-45 nm) and controllable morphology and composition via solution-based self-assembly. The synthesis conditions and preparation procedures are detailed to ensure the reproducibility of the experiments. We describe the fabrication of over ten high-quality 2D-ordered mesoporous conducting polymers and sandwich-structured hybrids, with tunable thickness, porosity and large specific surface area, which can serve as potential candidates for high-performance electrode materials used in supercapacitors and alkali metal ion batteries, and so on. The preparation time of the 2D-ordered mesoporous conducting polymer is usually no more than 12 h. The subsequent supercapacitor testing takes ~24 h and the Na ion battery testing takes ~72 h. The procedure is suitable for users with expertise in physics, chemistry, materials and other related disciplines.

Field evaluation of low-cost electrochemical air quality gas sensors under extreme temperature and relative humidity conditions

Abstract. Modern electrochemical gas sensors hold great potential for improving practices in air quality (AQ) monitoring as their low cost, ease of operation and compact design can enable dense observational networks and mobile measurements. Despite that, however, numerous studies have shown that the performance of these sensors depends on a number of factors (e.g. environmental conditions, sensor quality, maintenance and calibration), thereby adding significant uncertainties in the reported measurements and large discrepancies from those recorded by reference-grade instruments. In this work we investigate the performance of electrochemical sensors, provided by two manufacturers (namely Alphasense and Winsen), for measuring the concentrations of CO, NO2, O3 and SO2. To achieve that we carried out collocated yearlong measurements with reference-grade instruments at a traffic AQ monitoring station in Nicosia, Cyprus, where temperatures ranged from ca. 0 ∘C in the winter to almost 45 ∘C in the summer. The CO sensors exhibit the best performance among all the ones we tested, having minimal mean relative error (MRE) compared to reference instruments (ca. −5 %), although a significant difference in their response was observed before and after the summer period. At the other end of the spectrum, the SO2 sensors reported concentration values that were at least 1 order of magnitude higher than the respective reference measurements (with MREs being more than 1000 % for Alphasense and almost 400 % for Winsen throughout the entire measurement period), which can be justified by the fact that the concentrations of SO2 at our measuring site were below their limit of detection. In general, variabilities in the environmental conditions (i.e. temperature and relative humidity) appear to significantly affect the performance of the sensors. When compared with reference instruments, the CO and NO2 electrochemical sensors provide measurements that exhibit increasing errors and decreasing correlations as temperature increases (from below 10 to above 30 ∘C) and RH decreases (from >75 % to below 30 %). Interestingly, the performance of the sensors was affected irreversibly during the hot summer period, exhibiting different responses before and after that, resulting in a signal deterioration that was more than twice that reported by the manufacturers. With the exception of the Alphasense NO2 sensor, all low-cost sensors (LCSs) exhibited measurement uncertainties that were much higher, even at the beginning of our measurement period, compared to those required for qualifying the sensors for indicative air quality measurements according to the respective European Commission (EC) Directive. Overall, our results show that the response of all LCSs is strongly affected by the environmental conditions, warranting further investigations on how they are manufactured, calibrated and employed in the field.

Scale-up of Co–Ni cathodes produced from spent Ni–Cd batteries for hydrogen production in an oxy-hydrogen gas cell

Ni(II) and Co(II) ions are recovered from real leached positive electrodes of spent Ni–Cd batteries, and subsequently co-deposited on A36 carbon steel using direct and pulsed currents. The idea is to evaluate how variations in texture and composition of recycled coatings affect their catalytic activities for H2 production at microelectrolysis levels, and using an oxy-hydrogen gas (HHO) cell. The most active Ni–Co electrocatalyst in 0.1 M HClO4 or KOH towards hydrogen evolution reaction (HER) is formed using pulsed current at −50 mA cm−2, according to electrochemical measurements and gas chromatography (GC). This plating mode favors grain size refinement and pH rise during metal deposition, to prevent the formation of oxides/hydroxides with low catalytic activity arising in direct current. In the HHO cell, the most active Co–Ni coating produces 21.63 mL min−1 H2, while A36 carbon and 304 stainless steels present lower generations of 7.30 and 7.55 mL min−1, respectively.

Improving mass transfer in anion exchange membrane water electrolysis by ordered gas diffusion layer

For tight assembly electrochemical gas evolution devices, such as anion exchange membrane water electrolysis (AEMWE), bubbles blocking gas diffusion layer (GDL) channels is one of the key reasons for cell performance degradation under high current densities. To enhance mass transport in GDLs at high current densities, herein we report a 3D printed Ni GDL (GDL3D print) with straight-through pores and three-dimensional periodic structures. Due to its periodic structures and high hydrophilicity, GDL3D print is more conducive to the rapid escape of bubbles and timely replenishment of water, showing higher mass transfer efficiency and lower ohmic resistance. Therefore, compared with the commercial nickel foam (NF), GDL3D print exhibits better cell performance not only in 1 mol/L KOH solutions but also in pure-water-fed AEMWE, and the cell voltage of AEMWE using GDL3D print as the anode GDL is only 1.8 V at 1 A cm−2. This work provides a useful guidance for GDL design for tight assembly electrochemical gas evolution devices.

Printed, Flexible, Ionic Liquid-Based Hydrogen Sensor via Aerosol Jet Printing of Nanomaterials

Low-cost, high-performance hydrogen sensors are highly demanded in hydrogen leakage detection. To increase the sensitivity and reliability of the hydrogen sensor, an ionic liquid (IL)-based electrochemical gas sensor is fabricated with bimetallic Platinum–Nickel (Pt-Ni) nanoparticles (NPs) with aerosol jet printing technology for continuous monitoring of hydrogen concentration. The Pt-Ni NPs covering the top surface of the metal electrodes can accelerate the catalysis and expand the sensing surface area. When hydrogen gas is sensed at room temperature, the uniquely reversible and rapid redox reactions of hydrogen at the IL/Pt electrode interface, thereby creating continuous measurement capability in a real-time manner with little signal drift. The full coverage of the sensor electrodes will increase the robustness and accuracy of the device. The fabricated sensors demonstrate excellent analytical sensing performance, reaching a limit of detection up to 19.3 ppm. The device takes advantage of an easy fabrication process, simple structure, high sensing response, and low cost, providing a promise for hydrogen sensing at room temperatures.

Excluding the Trouble from Interfacial Water by Covalent Organic Polymer to Realize Extremely Reversible Zn Anode

AbstractThe side reactions related to water are the major issue hindering practical application of Zn metal batteries. To exclude the trouble from interfacial water, a covalent organic polymer (COP) layer with N, N′‐Bis(salicylidene)ethylenediamine structure is designed, whose strong coordination ability with Zn2+ enhances the de‐solvation kinetics of solvated Zn2+ which is conducive to interfacial water removal thus alleviating the side reactions related to water. This function has been certified by density functional theory along with molecular dynamics analysis. Moreover, measurements including in situ electrochemical gas chromatography, in situ optical microscopy, in situ X‐ray diffraction and in situ Raman spectroscopy verify the weakened side reactions (including hydrogen evolution and corrosion) along with homogenous Zn deposition contributed from the covalent organic polymer layer. Benefiting from these merits, when assemble into cells based on common ZnSO4‐based aqueous electrolyte, the COP layer‐decorated anode exhibits excellent electrochemical performance of a high average Coulombic efficiency value 99.5% at a high capacity of 5.0 mA h cm−2. What's more, the symmetric cells can operate at −20 °C and the full cell with N/P ratio as low as 1.2 can cycle stably for 100 cycles, which would carry forward the promising practical application of Zn metal batteries.

Short Term Silver Electrode Microstructure Changes Under Epoxidation Conditions for Solid Oxide Electrolysis Cells

Ethylene epoxidation is an important reaction to form ethylene oxide (EO), which is a precursor to many other critical chemicals. This study links short-term EO production to the effects on the microstructure of Ag/yttria-stabilized zirconia cells with and without an electrochemically promoted catalyst (EPOC). Nano scale features called striations were observed using a Scanning Electron Microscope (SEM) on the silver under all reaction conditions tested. While appearing in both cases, the striations for the EPOC case are finer in size (~150 to 250 nm) compared to the no current case (~400 to 500 nm). These features did not appear when epoxidation conditions were not present. Striation formation was further linked to the epoxidation reaction through electrochemical impedance spectroscopy (EIS) and gas chromatography (GC). Ethylene conversion to EO declines over the course of hours as striations form, indicating that striations have a negative influence on the reaction. Striation formation further effected the electrochemical performance of the cells, resulting in the low frequency depressions observed in EIS to shrink in both cases after 10 hours of epoxidation.

Co-Electrolysis of CO2 and H2O Using an Exsoluted Perovskite Layer

Solid oxide electrolysers (SOECs) are a key class of technology that offers an efficient solution to storing renewable energy. One of the key characteristics of this technology is its ability to reduce both H2O and CO2. Currently, commercial cells are adapted from those made for power generation (i.e. SOFCs) and are not suitable for generating gas of higher quality than syngas due to the limited behaviour of the cells. Electrochemical analyses and gas chromatography were used to examine the ability of SOEC cells to improve gas quality. With the addition of a functional layer to the cathode, we achieved a complementary effect between electrochemical mechanisms taking place at the cathode and catalytic mechanisms involving CO2 and CO methanation. In spite of the fact that the results could be significantly improved, this approach demonstrated the potential for CO2 and H2O co-electrolysis at intermediate temperatures.

Errors in ambient gas concentration measurement caused by acoustic response of electrochemical gas sensors

Electrochemical sensors are used to measure electroactive gases in ambient air monitoring applications. These sensors typically contain sulfuric acid electrolyte, and porous carbon working, reference, and counter electrodes. Current fluctuations caused by fluctuations in the meniscus contact shape or area at the 3 phase gas-electrolyte-electrode interface as a result of ambient pressure fluctuations have been suggested as a potentially significant source of error in sensor measurements. We confirm in the present work that the pressure oscillations associated with ambient sound can indeed lead to significant signals. We show, for a variety of commercial sensors for ambient nitrogen dioxide (NO2), that acoustic noise equivalent to that from a nearby motorcycle or heavy goods vehicle can cause transient current fluctuations at 2 Hz sampling rate equivalent in the sensor output to as much as that due to 100 parts per billion by volume (ppb) of NO2, and with a root mean square (RMS) variation averaged over 10 s of approximately 40 ppb equivalent. These observations indicate that electrochemical gas sensors can behave as “microphones” in response to loud noise. The impact of acoustic noise should be considered when using electrochemical sensors to measure ambient air quality in areas of significant noise pollution, particularly if the aim is to resolve local transient concentration variations.

Corrosion inhibition of aluminium in 0.3 M HCl using starch mucor in potassium iodide as inhibitor

Purpose The purpose of this study is to investigate starch mucor (SM) in potassium iodide (KI) as corrosion inhibitor of aluminium in hydrochloric acid (HCl) medium. Design/methodology/approach The SM in KI was characterized by gravimetric, scanning electron microscopy, electrochemical impedance spectroscopy measurements, potentiodynamic polarization and gas chromatography-mass spectrometer techniques. The inhibition efficiency was optimized using response surface methodology. Findings The result revealed that the inhibitor inhibited corrosion at a low concentration with the rate of inhibition increasing as the concentration of the inhibitor increased. The inhibition efficiency increases as the temperature was increased with slight incorporation of the inhibitor (SM in KI). This indicates that the corrosion control is both inhibitor (SM in KI) and temperature dependent. Originality/value The research results can provide the basis for using SM in KI as corrosion inhibitor of aluminium in HCL medium. Mixed-type inhibitor nature of SM was proved by cathodic and anodic nature of the polarization curves.

Classification of [formula omitted]-defect holes on a graphene sheet

Holey graphene sheet is a promising nano-scaled material with a number of applications for electrochemical energy storage and gas sensors. Further, the joining of a carbon nanotube on a holey flat graphene creates new 3D material combining remarkable mechanical properties from both materials. In order to join a carbon nanotube with defect atoms on its end, we need a hole in graphene sheet with an equal number of defect atoms on its border. A k-defect hole on a graphene sheet is defined to be a simply-connected region that has k carbon atoms on the edge of the hole with one missing bond. In this study, a mathematical technique is presented to enumerate and classify all possible k-defect holes on the graphene sheet. The predicted joining structure for each hole formation is also determined. We introduce the least square and the discrepancy variance parameters that assess the hole’s joining quality in order to choose the best k-defect holes to join with a carbon nanotube.

Air Pollution Monitoring via Wireless Sensor Networks: The Investigation and Correction of the Aging Behavior of Electrochemical Gaseous Pollutant Sensors

The continuously growing human activity in large and densely populated cities pollutes air and consequently puts public health in danger. This is why air quality monitoring is necessary in all urban environments. However, the creation of dense air monitoring networks is extremely costly because it requires the usage of a great number of air monitoring stations that are quite expensive. Instead, the usage of wireless sensor networks (WSNs) that incorporate low-cost electrochemical gas sensors provides an excellent alternative. Actually, sensors of this kind that are recommended for low-cost air quality monitoring applications may provide relatively precise measurements. However, the reliability of such sensors during their operational life is questionable. The research work presented in this article not only experimentally examined the correlation that exists between the validity of the measurements obtained from low-cost gas sensors and their aging, but also proposes novel corrective formulae for gas sensors of two different types (i.e., NO2, O3), which are aimed at alleviating the impact of aging on the accuracy of measurements. The following steps were conducted in order to both study and lessen the aging of electrochemical sensors: (i) a sensor network was developed to measure air quality at a place near official instruments that perform corresponding measurements; (ii) the collected data were compared to the corresponding recordings of the official instruments; (iii) calibration and compensation were performed using the electrochemical sensor vendor instructions; (iv) the divergence between the datasets was studied for various periods of time and the impact of aging was studied; (v) the compensation process was re-evaluated and new compensation coefficients were produced for all periods; (vi) the new compensation coefficients were used to shape formulae that automatically calculate the new coefficients with respect to the sensors’ aging; and (vii) the performance of the overall procedure was evaluated through the comparison of the final outcomes with real data.

Analytical Methods for Oxalate Quantification: The Ubiquitous Organic Anion

Oxalate is a divalent organic anion that affects many biological and commercial processes. It is derived from plant sources, such as spinach, rhubarb, tea, cacao, nuts, and beans, and therefore is commonly found in raw or processed food products. Oxalate can also be made endogenously by humans and other mammals as a byproduct of hepatic enzymatic reactions. It is theorized that plants use oxalate to store calcium and protect against herbivory. Clinically, oxalate is best known to be a major component of kidney stones, which commonly contain calcium oxalate crystals. Oxalate can induce an inflammatory response that decreases the immune system's ability to remove renal crystals. When formulated with platinum as oxaliplatin (an anticancer drug), oxalate has been proposed to cause neurotoxicity and nerve pain. There are many sectors of industry that are hampered by oxalate, and others that depend on it. For example, calcium oxalate is troublesome in the pulp industry and the alumina industry as it deposits on machinery. On the other hand, oxalate is a common active component of rust removal and cleaning products. Due to its ubiquity, there is interest in developing efficient methods to quantify oxalate. Over the past four decades, many diverse methods have been reported. These approaches include electrochemical detection, liquid chromatography or gas chromatography coupled with mass spectrometry, enzymatic degradation of oxalate with oxalate oxidase and detection of hydrogen peroxide produced, and indicator displacement-based methods employing fluorescent or UV light-absorbing compounds. Enhancements in sensitivity have been reported for both electrochemical and mass-spectrometry-based methods as recently as this year. Indicator-based methods have realized a surge in interest that continues to date. The diversity of these approaches, in terms of instrumentation, sample preparation, and sensitivity, has made it clear that no single method will work best for every purpose. This review describes the strengths and limitations of each method, and may serve as a reference for investigators to decide which approach is most suitable for their work.

Effect of calcination temperature on sensing performance of YSZ based electrochemical H2S gas sensor with a NiFe2O4 electrode

Electrochemical gas sensors based on yttria-stabilized zirconia (YSZ) film have attracted ascending attention for detecting H2S. Due to the poor sinterability of YSZ film, high-temperature calcination is usually required in the preparation procedure to ensure the good contact between YSZ and sensing electrode, which could particularly limit the triple phase boundary (TPB) length at the interface of H2S|YSZ|sensing electrode as well as the porosity of sensing electrode. Therefore, the calcination temperature would significantly affect the sensing performance, which has been ignored in reported studies. In this work, YSZ based electrochemical gas sensors with NiFe2O4 (NFO) sensing electrode are prepared to detect H2S at ppb-level. The effect of the calcination temperature of NFO sensing electrode on the sensing performance is investigated. The sensor with an optimal calcination temperature of 1000 °C delivers a response value of − 42 mV for 500 ppb H2S at 460 °C with a detection limitation of 10 ppb H2S. Good linear slopes with a sensitivity of − 13.1 mV/decade toward 20–100 ppb H2S and a sensitivity of − 46.9 mV/decade toward 100–500 ppb H2S are obtained. Meanwhile, the sensor also displays attracting stability and short response/recovery time. The good sensing performance is attributed to enhanced TPB length, good porosity of NFO electrode and limited interaction between the NFO and YSZ film by optimizing the calcination temperature of NFO sensing electrode.