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Integration of bipolar membranes (BPMs) into electrochemical cells is an established method for acid and base generation, as well as desalinization methods. More recently, BPMs have been recognized...

Basic notions linked with concept theory can be accounted for by partial order relations. These orders translate the fact that, for an agent, an object may be seen as a better or a more typical exemplar of a concept than anyother. They adequately model notions linked with categorial membership, typicality and resemblance, without any of the drawbacks that are classically encountered in conjunction theory. An interesting consequence of such a concept representation is the possibility of using the tools of non-monotonic logic to address some well-known problems of cognitive psychology. Thus, conceptual entailment and concept induction can be reexamined in the framework of preferential inference relations. This leads to a rigorous definition of the basic notions used in the study of category-based induction.

The development of sustainable and carbon-neutral alternative energy frameworks and chemical feedstocks requires rapid production of scalable water electrolyzer designs for hydrogen production.[1] Coupling electrolyzers to renewable energy supplies can provide a ‘green’ hydrogen production pathway, enabling clean production of chemical feedstocks as well as an energy storage framework. Current acid-based electrolyzer designs, however, integrate precious metals for stable operation, where drastic reductions in iridium use and increased cell durability are required for scalable deployment.[2] This requires the ability to monitor changes to the cell in operando for rapid diagnostics during initial and long-term operation under sustained or intermittent profiles. One technique proposed is electrochemical impedance spectroscopy (EIS), which can provide a breakdown of the cell resistances based on the timescale of the process.[3] Further analysis by circuit modeling, however, requires significant insight into the system for accurate interpretations. By coupling conventional EIS methods with distribution of relaxation times (DRT) analysis, the number of processes impacting cell operation can be determined without a priori knowledge of the system.[4] This has improved circuit modeling analysis of Li-ion batteries and solid oxide fuel cells.[5] Here, we demonstrate the power of EIS-coupled DRT analysis by analyzing the operation porous cathode and anode films of Nafion-based electrolyzer cells in half-cell and full cell configuration. Analysis of the electrodes in half-cell configurations provides estimates of kinetic parameters, active area, ionic conductivity, and diffusion coefficients associated with the electrode from a single EIS spectrum that are comparable to values obtained from in situ values.[6] Further analysis of the full cell operation with variable cathode gas composition provides insight as to the effect of the cathode gas composition on both the cathode and anode operation and stability. The work presented here will show the versatility and limitations of DRT-coupled EIS analysis of novel fuel cell and electrolyzer designs as well as present key findings for improving electrolyzer performance and stability. [1]Ayers, K. et al. Annu. Rev. Chem. Biomolec. Eng. 2019, 10, 219-239. [2]Pham, C. et al Adv. Energy Mater. 2021, 11, 2101998. [3]Liu, H. et al. J. Phys. Chem. Lett. 2022, 13, 6520-6531. [4]Wan, T. et al. Electrochimica Acta 2015, 184, 483-499. [5]Dierickx, S., Ivers-Tiffee, E. Electrochimica Acta 2020, 355, 136764. [6]Giesbrecht, P.K., Freund, M.S. J. Phys. Chem. C 2022, 126, 132-150.

Vapor-fed electrolysis of water has been performed using membrane-electrode assemblies (MEAs) incorporating earth-abundant catalysts and bipolar membranes (BPMs). Catalyst films containing CoP nanoparticles, carbon black, and Nafion were synthesized, characterized, and integrated into cathodes of MEAs. The CoP-containing MEAs exhibited stable (>16 h) vapor-fed electrolysis of water at room temperature at a current density of 10 mA cm⁻² with 350 mV of additional overvoltage relative to MEA's formed from Pt/C cathodic electrocatalysts due to slower hydrogen-evolution reaction kinetics under vapor-fed conditions and fewer available triple-phase boundaries in the catalyst film. Additionally, catalyst films containing a [NiFe]-layered double hydroxide ([NiFe]-LDH) as well as a hydroxide ion conductor, hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI), were synthesized, characterized, and integrated into the anodes of the MEAs. The [NiFe]-LDH-containing MEAs exhibited overvoltages at 10 mA cm⁻² that were similar to those of IrO_x-containing MEAs for vapor-fed electrolysis of water at room temperature. A BPM was formed by pairing Nafion with HMT-PMBI, resulting in a locally alkaline environment of HMT-PMBI to stabilize the [NiFe]-LDH and a locally acidic environment to stabilize the CoP. BPM-based MEAs were stable (>16 h) for vapor-fed electrolysis of water at room temperature at a current density of 10 mA cm⁻², with a change in the pH gradient of 1 unit over 16 h of electrolysis for IrOx-containing MEAs. The stability of [NiFe]-LDH-based MEAs under vapor-fed conditions was dependent on the catalyst film morphology and resulting BPM interface, with stable operation at 10 mA cm⁻² achieved for 16 h. All MEAs exhibited a drift in the operating voltage over time associated with dehydration. These results demonstrate that earth-abundant catalysts and BPMs can be incorporated into stable, room-temperature, vapor-fed water-splitting cells operated at 10 mA cm⁻².

The field of organic electronics has been heavily impacted by the discovery and development of π-conjugated conducting polymers. These polymers show great potential for integration into future optical and electronic devices due to their capacity to transition between semiconducting and conducting states as well as the ability to alter mechanical properties by controlled doping, chemical modification, and stacking or creating composites with other materials. Among π-conjugated polymers, polythiophene and its derivatives has been one of the most extensively studied and is widely investigated computationally and experimentally for use in electronic devices such as light-emitting diodes, water purification devices, hydrogen storage, and biosensors. Various theoretical modeling studies of polythiophene ranging from an oligothiophene approach to infinite chain lengths (periodic boundary conditions) have been undertaken to study a variety of electronic and structural properties of these polymers. In this review,...

In the presence of an electric field, bipolar membranes (BPMs) are capable of initiating water disassociation (WD) within the interfacial region, which can make water splitting for renewable energy in the presence of a pH gradient possible. In addition to WD catalytic efficiency, there is also the need for electronic conductivity in this region for membrane-integrated artificial photosynthesis (AP) systems. Graphene oxide (GO) was shown to catalyze WD and to be controllably reduced, which resulted in electronic conductivity. Layer-by-layer (LbL) film deposition was employed to improve GO film uniformity in the interfacial region to enhance WD catalysis and, through the addition of a conducting polymer in the process, add electronic conductivity in a hybrid film. Three different deposition methods were tested to optimize conducting polymer synthesis with the oxidant in a metastable solution and to yield the best film properties. It was found that an approach that included substrate dipping in a solution containing the expected final monomer/oxidant ratio provided the most predictable film growth and smoothest films (by UV/Vis spectroscopy and atomic force microscopy/scanning electron microscopy, respectively), whereas dipping in excess oxidant or co-spraying the oxidant and monomer produced heterogeneous films. Optimized films were found to be electronically conductive and produced a membrane ohmic drop that was acceptable for AP applications. Films were integrated into the interfacial region of BPMs and revealed superior WD efficiency (≥1.4 V at 10 mA cm⁻²) for thinner films (, National Science Foundation (Grant CHE‐1305124)

This study describes the use of a benzimidazolium-based anion exchange membrane for creating bipolar membranes and the assessment of their suitability for solar-driven water splitting. Bipolar membranes were prepared by laminating anion exchange membrane with Nafion NR-211 membrane without modification of the interface. Under acidic and basic conditions, proton and hydroxide ion conductivities of 103 and 102 mS cm-1 were obtained for Nafion and benzimidazolium-based membranes, respectively. The fabricated bipolar membranes have an average thickness of 90 μm and show high transmittance, up to 75% of the visible light. The findings suggest that the two membranes create a sharp hydrophilic interface with a space charge region of only a few nanometers, thereby generating a large electric field at the interface that enhances water dissociation.

Membrane-based architectures enable optimization of charge transport and electrochemical potential gradients in artificial photosynthesis. Spatial integration of the membrane-bound components reduces the impact of charge recombination and can reduce electrical resistances associated with ionic and electronic transport processes. In addition to eliminating the need for external electrical circuits, a membrane-based architecture also ensures separation of energetic products, thereby preventing the formation of potentially dangerous fuel/oxidant mixtures. Membrane-based structures may also be coupled with other devices, such as perovskite-based solar cells, to further benefit solar fuel production. This review discusses the key roles that various different types of membranes play in artificial photosynthetic systems.

An artificial olfactory system, capable of detecting and discriminating different volatile organic compounds, has a vast potential to solve several sensing challenges. The conducting polymers are a well-researched class of materials that have a demonstrated sensitivity to a wide range of volatile compounds. This work, presented here, demonstrates an olfaction system developed with the integration of gas sensitive conducting polymers into an array of Si-foundry based floating gate metal oxide semiconductor (FGMOS) sensors. The design of the sensor and the post silicon processing steps required to ensure compatibility of this silicon system with the conducting polymers is presented. The system’s response to several different analytes have been measured and analyzed. A statistical method, principle component analysis (PCA), is used to extract information from the experimental data. The PCA analysis confirms successful detection and discrimination of the tested analytes.

X-ray photoelectron spectroscopy (XPS) is a powerful surface characterization technique often relied on for quantification of surface species and coverages. Investigation of silicon microrods, considered a model for high-aspect-ratio structures, at different angles with respect to substrate normal was determined to have a significant impact on the relative sensitivity of surface-bound species on rods relative to the base substrate. Comparison between planar silicon and microrod arrays demonstrates that the angular dependence is complicated and that careful studies must optimize conditions to differentiate between surfaces. In addition, the use of reverse angle resolved XPS, where the substrate is turned away from the X-ray source, is shown to assist in simplifying the spectrum by removing underlying signal from the substrate near the base. Copyright © 2016 John Wiley & Sons, Ltd.

Machine sensing has progressed through innovative breakthroughs. Perhaps the most significant advancements have been in the field of machine vision through the advent of the charge-coupled-device (CCD) chip and the development of artificial neural networks. This is evident in the range of sophisticated behaviors that have been replicated including facial recognition and object tracking. Due to parallel processing of large amounts of temporally evolving data, these systems can rapidly learn, adapt and predict in changing environments. While there have been significant advances in chemically diverse sensor arrays that mimic the mammalian olfactory system under well-defined conditions, relatively little work has been done to understand the temporal response of these systems and to develop neural architectures that will enable machines to become chemically aware of their surroundings. In this work, the temporal response behavior for sensors is investigated, demonstrating that both the response evolution and steady-state provide useful information about the chemical environment under dynamic conditions and that neural networks are ideally suited to combine this information in unsupervised learning to perceive odors in a dynamic environment.

The development of chemically diverse arrays has gained the attention of researchers due to their anticipated capacity to mimic the function of olfactory receptors in the mammalian olfactory system. A major hurdle facing the field is the limited ability to generate large numbers of different sensing elements out of the relatively limited number of conducting polymers. In this work, chemically distinct electrocopolymerized sensors were created with pyrrole by using different substituted vinyl groups (e.g., styrene, m-styrene, 4-chlorostyrene, 4-chloromethylstyrene, 4-t-butylstyrene, 4-t-butoxystyrene, divinyl benzene and vinyl pyridine) as monomers. Copolymer films were grown at different potentials that created an additional level of sensor diversity by altering the relative amount of each of the components. By controlling the deposition conditions in this way, as well as setting different redox potentials to the films after growth changes the copolymer's composition and the amount of dopant anion that is incorporated into the sensing films respectively. The composition of the sensing films was also altered by changing the dopant-type during copolymer growth, thereby providing another mechanism for varying the chemical nature of the sensing materials. The chemical diversity among the 27 different sensing polymers used in this work is demonstrated with differential partitioning of 12 analytes, ranging from alcohols and solvents to fuels. This process of generating significant numbers of chemically distinct sensors represents a significant advancement in the efforts to approach the number of olfactory receptors in mammals. The fact that the sensing polymers can be electropolymerized onto very small conducting contacting electrodes shows that this approach is compatible with integrated circuit technology.

Methyl-terminated (110)-oriented silicon surfaces have been prepared from monohydride-terminated, H–Si(110) surfaces using a chlorination/alkylation procedure. Transmission infrared spectroscopy of the H–Si(110) surfaces showed absorption features indicating monohydride structures along the [−110] direction. X-ray photoelectron spectroscopy was used to characterize the methyl-terminated, CH3–Si(110), surfaces. Surface coverage calculations revealed 0.83 of an equivalent monolayer coverage for methyl-terminated Si(110) surfaces. No oxidation of silicon was observed in the high-resolution Si 2p spectra and the samples were stable against oxidation over time, with only 0.2 of a monolayer of surface oxide observed a month after the sample preparation. Thus, the chlorination/alkylation procedure can be used for the functionalization of monohydride Si(110) surfaces with improved long term stability.

UNLABELLED Organic/inorganic solid-state junctions play a critical role in tandem artificial photosynthetic devices supported by conducting polymer membranes. Recent work with n-Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) hybrid junctions has shown that the electrical behavior is dominated by the passivating groups present on the silicon surface. In this work, the photovoltaic behavior of n-Si/ PEDOT PSS was investigated with methyl, thiophene, and 3,4-ethylenedioxythiophene (EDOT) groups covalently attached to the Si(111) surface. X-ray photoelectron spectroscopy results demonstrated that complete monolayer coverage was achieved in 3 h and that the organic passivating groups were retained over two months of exposure to ambient conditions with minimal silicon oxidation. All surfaces investigated exhibited similar light-limited photocurrents and bulk-limited open-circuit voltages, and thiophene produced a dramatic reduction of the fill factor attributed to the formation of trap states at the interface. Furthermore, shunt behavior observed near the power-producing regions for the thiophene and EDOT surfaces is indicative of increased recombination events under forward bias and suggests that hole transport across the interface is enhanced. Thus, thiophene- and EDOT-functionalized Si(111) offer similar stabilities and efficiencies to those of methylated surfaces as well as enhanced hole transport to the PEDOT PSS interface from the n-Si surfaces.

A fully integrated, freestanding device for photoelectrochemical fuel generation will likely require covalent attachment of catalysts to the surface of the photoelectrodes. Ferrocene has been utilized in the past as a model system for molecular catalyst integration on planar silicon; however, the surface structure of high-aspect ratio silicon microwires envisioned for a potential device presents potential challenges with respect to stability, characterization, and mass transport. Attachment of vinylferrocene to Cl-terminated surfaces of silicon microwires was performed thermally. By varying the reaction time, solutions of vinylferrocene in di-n-butyl ether were employed to control the extent of functionalization. X-ray photoelectron spectroscopy (XPS) and electrochemistry were used to estimate the density and surface coverage of the silicon microwire arrays with ferrocenyl groups, which could be controllably varied from 1.23 × 10(-11) to 4.60 × 10(-10) mol cm(-2) or 1 to 30% of a monolayer. Subsequent backfill of the remaining Si-Cl sites with methyl groups produced ferrocenyl-terminated surfaces that showed unchanged cyclic volammograms following two months in air, under ambient conditions, and repeated electrochemical cycling.

Chemically diverse sensor arrays were synthesized directly on interdigitated array electrodes by electrodepositing copolymers of pyrrole and substituted styrene monomers. By selecting a range of substituted styrenes and controlling deposition conditions (growth potentials) it was possible to create a wide range of chemical variations, resulting in differential partitioning and in turn differential sensor responses. The effectiveness of the electrochemical copolymerization deposition was investigated with FT-IR spectroscopy to determine the relative amounts of co-monomer and the morphology of the films was studied with SEM. The impact of composition on film sensitivity was explored by determining changes in response (e.g., changes in resistance) of sensors to various odorants as a function of degree of functionalization. Performance of the chemically diverse arrays was determined using statistical analysis of response patterns which demonstrate the chemical diversity capable of differentiating different odorants can be achieved with this approach. Figures of merit including reproducibility, sensitivity and selectivity were determined. This report represents a significant advancement in the use of electronically conducting polymers in sensor array technology by moving past the limited number of conducting polymer monomers. The ease by which diversity can be imparted during electrodeposition makes this approach ideal for use in integrated circuit technology, allowing deposition on chip microstructures without the need for additional lithographic steps.

Bifunctional films with higher electrochemical and bioactive properties have many promising applications including tissue engineering, drug delivery, nerve regeneration and bone healing. Since bone possesses natural bio-potential and electromechanical properties, the idea of utilizing small electrical pulses to induce bone-tissue growth has been explored in recent decades. Studies have revealed that electric stimulation (in the order of μV) has positive effects on the osteogenesis, and enhances the mineral formation in osteoblast-like cells. However, the mechanisms behind these effects are not well understood. Electric stimulation is generally performed through the implantation of metal electrodes that need to be removed after the treatment. This sometimes requires surgery that can lead to complications including infection and damaging newly formed bone-tissue. Therefore, in the search for new implant materials that are bioactive (allowing different cells to grow over it) and electrically conductive (to perform electrical stimulation), a composite material has been synthesized by integrating the electro-active properties of the conducting polymer (poly-3,4-ethylenedioxythiophene, doped with polystyrene sulfonate, PEDOT:PSS) with the biological properties of collagen (protein, which is present in the cornea) and collagen–calcium phosphate membranes (which mimics the composition of bone). It is shown that by varying the concentration of PEDOT:PSS, the composite (collagen–PEDOT:PSS) or the hybrid (collagen–hydroxyapatite–PEDOT:PSS) membrane could be altered to be highly biocompatible and highly electrically conductive.

The mammalian olfactory system is highly complex, with more than 1000 non-specific binding receptors. The chemical diversity among these receptors yields differential responses resulting in a ‘fingerprint’ response pattern characteristic of a particular gas phase odorant or mixture. It is through these response-patterns that our brain perceives its chemical environment. While the concept of an electronic nose has been explored over the past several decades, the emergence of integrated circuits analogous to charge-coupled device (CCD) devices with this kind of chemical sensitivity have yet to emerge. One of the main stumbling blocks is the ability to deposit large numbers of chemically diverse sensing layers within large-scale integrated circuits. The use of electronically conducting polymers (ECP) as sensing layers are attractive since they can be electrodeposited on existing fabricated structures without the need for additional lithographic steps, however they are limited by the number of chemically different monomer units available. In this study, we demonstrate the ability to significantly increase the level of diversity through the control of the dopant and the oxidation level of the deposited polymer layers. By using two polymers, several dopants and different oxidation states determined by applied electrochemical potential, fifty-five chemically diverse sensing elements are produced. These results suggest that by using these orthogonal variables, a chemically diverse integrated sensor array chip can be generated through a combinatorial approach of deposition conditions.

Bipolar membranes are formed by the lamination of an anion- and cation-exchange layer. Upon a sufficient applied reverse bias, water molecules at the layer junction dissociate, generating OH(-) and H(+), which can be useful in electrodialysis and electrosynthesis applications. Graphene oxide has been introduced into bipolar membrane junctions (illustrated in the adjacent graphic) and is shown to be an efficient new water dissociation catalyst, lowering the overpotential by 75% compared to a control membrane. It was found that adjusting deposition conditions changes the nature of the graphene oxide films, leading to tunable membrane performance. Additionally, it is shown that their low overpotentials are stable, making for industrially viable, high-performance bipolar membranes.

A passive embeddable coupled coil sensor for remote bioprocess pH monitoring is described. The sensor is sterilizable, able to operate in a fluid medium, and small enough to fit inside a small bioreactor or test tube. It consists of a planar spiral inductor connected parallel to a varactor forming an LC resonant circuit. A pH combination electrode made of an iridium/iridium oxide sensing electrode and a silver/silver chloride reference electrode is connected parallel to the varactor. A potential difference change across the electrodes due to pH variation of the medium changes the voltage-dependent capacitance and shifts the resonant frequency of the sensor. An interrogator coil is inductively coupled to the sensor coil and remotely tracks the resonant frequency of the sensor. For in-fluid monitoring, the sensor is encapsulated in a manner that reduces the influence of the permittivity and conductivity of the medium. The sensor, calibrated over 2-12 pH range, exhibits a rapid response with 2.477-MHz/pH sensitivity. The sensor was used for remote pH monitoring of Yarrowia lipolytica and Saccharomyces cerevisiae fermentation in a shake flask over 63 and 25 h, respectively. The experiments demonstrate that the medium pH can be monitored repeatedly with an accuracy of 0.08 pH.

Temperature must be accounted for in order to provide accurate measurements in electrode-based pH sensors. We present an integrated wireless passive sensor for remote pH monitoring employing temperature compensation. The sensor is a resonant circuit consisting of a planar spiral inductor connected in parallel to a temperature-dependent resistor (thermistor) and a voltage-dependent capacitor (varactor). A pH combination electrode consisting of an iridium/iridium oxide sensing electrode and a silver/silver chloride reference electrode, is connected in parallel with the varactor. A potential difference change across the electrodes due to pH variation of the solution changes the voltage-dependent capacitance and shifts the resonant frequency, while temperature of the solution affects the resistance and changes the quality factor of the sensor. An interrogator coil is inductively coupled to the sensor inductor and remotely tracks the resonant frequency and quality factor of the sensor. The sensor is calibrated for temperature over a range of 25 $^{\circ}{\rm C}$ –55 $^{\circ}{\rm C}$ and pH over a 1.5–12 dynamic range. By employing temperature compensation, a measurement accuracy of less than 0.1 pH is achieved and the response time of the sensor is demonstrated to be less than 1 s. The sensor overcomes the pH measurement error due to the temperature dependence of electrode-based passive pH sensors and has applications in remote pH monitoring where temperature varies over a wide range.

In this paper, the temperature dependency of conventional polymer-based gas sensors is addressed and a novel polymer-based chemicapacitor sensor is presented for application in early detection of deterioration of grain in storage facilities. 3-D heat transfer simulations are used to investigate several heated platforms with the sensing area in millimeter range dimensions to enhance spoilage-induced analyte detection. A resistive heater is employed to heat and maintain the sensor at the desired operating temperature. The platform is optimized to achieve a uniform heat distribution throughout the sensing area with a temperature variation of ΔT ≤ 1°C. Capacitive measurements are performed as a more sophisticated technique for analyte detection, where mechanisms other than swelling are involved. In this method, the need for conductive filler is eliminated, resulting in an improvement in sensor reproducibility and repeatability. 1-octanol and relative humidity measurements are performed, as they are the two key volatiles due to grain deterioration. The results verify functionality of the fabricated sensors at different temperatures, in ppm range for 1-octanol, and up to 75% RH. Responses at the elevated temperature of 40 °C, above the grain bins ambient temperature, are insensitive to ambient temperature fluctuations. Sensitivity measurements demonstrate that an array of detectors, each held at different temperatures and operating at different frequencies, can be utilized to further enhance the sensor sensitivity and selectivity to a desired analyte.

In this paper, the structural and electronic properties of polythiophene and polyprrrole-based systems have been investigated using first-principles calculations both in periodic and oligomer forms. Of particular interest is the band gap modulation through substitutions and bilayer formation. Specifically, S has been substituted by Se and Te in polythiophene, leading to polyseleophene and polytellurophene, respectively, and N has been substituted by P and As in polypyrrole. The values obtained of the binding energy suggest that all the systems studied can be realized experimentally. Stacking (bilayer formation) of pure polythiophene, polypyrrole and their derivatives leads to linear suppression of the band gap or HOMO-LUMO gap as a function of the stacking. Mixed bilayers, including one formed from polythiophene on top of polypyrrole, have also been considered. Overall, a wide range of band gaps can be achieved through substitutions and stacking. Hybrid (B3LYP) calculations also suggest the same trend in the band gap as PBE calculations. Trends in the binding energy are similar for both periodic and molecular calculations. In addition, the $\Gamma$-point phonon calculation are performed in order to check the stability of selected systems., Comment: 22 pages, 13 figures, and 4 Tables

Based on first-principles calculations, the materials properties (structural, electronic, vibrational, and optical properties) of out-of-plane heterostructures formed from the transiti on metal dichalcogenides, specifically MoS$_2$-WSe$_2$ and WS$_2$-MoSe$_2$ were investigated. The heterostructures of MoS$_2$-WSe$_2$ and WS$_2$-MoSe$_2$ are found to be direct and ind irect band gap semiconductors, respectively. However, a direct band gap in the WS$_2$-MoSe$_2$ heterostructure can be achieved by applying compressive strain. Furthermore, the excitoni c peaks in both monolayer and bilayer heterostructures are calculated to understand the optical behavior of these systems. The suppression of the optical spectrum with respect to the c orresponding monolayers is due to interlayer charge transfer. The stability of the systems under study is confirmed by performing phonon spectrum calculations.

During storage, grain can experience significant degradation in quality due to a variety of physical, chemical, and biological interactions. Most commonly, these losses are associated with insects or fungi. Continuous monitoring and an ability to differentiate between sources of spoilage are critical for rapid and effective intervention to minimize deterioration or losses. Therefore, there is a keen interest in developing a straightforward, cost-effective, and efficient method for monitoring of stored grain. Sensor arrays are currently used for classifying liquors, perfumes, and the quality of food products by mimicking the mammalian olfactory system. The use of this technology for monitoring of stored grain and identification of the source of spoilage is a new application, which has the potential for broad impact. The main focus of the work described herein is on the fabrication and optimization of a carbon black (CB) polymer sensor array to monitor stored grain model volatiles associated with insect secretions (benzene derivatives) and fungi (aliphatic hydrocarbon derivatives). Various methods of statistical analysis (RSD, PCA, LDA, t test) were used to select polymers for the array that were optimum for distinguishing between important compound classes (quinones, alcohols) and to minimize the sensitivity for other parameters such as humidity. The performance of the developed sensor array was satisfactory to demonstrate identification and separation of stored grain model volatiles at ambient conditions.

Sensor arrays are currently used for classifying liquors, perfumes, and the quality of food products by mimicking the mammalian olfactory system. The use of this technology for the monitoring of stored grains and identifying the source of spoilage is a new application, which has the potential for broad economic impact. Carbon black polymer sensor array was fabricated and optimized for monitoring of incipient grain spoilage in a simulated stored grain bin. Various aspects of sensor array (flow rate, relative humidity, temperature, presence of background gas) were evaluated at stored grain conditions. Sensor response at low concentration (2% of vapour pressure) of 1-octanol, 1,4-benzoquinone, acetone was checked in presence of water vapour and 400 ppmv CO2 as background. Slightly variable sensor responses were observed compared to in absence of background gases. The responses were decreased by 6–15% on an average for poly(vinyl acetate), poly(bisphenol-A-carbonate) and poly(vinyl butaryl) sensor while exposed in presence of 50% water vapour. Polymers with high sensitive to background gases (H2O and CO2), such as PVP and P4VP were excluded from the array in this study. Co-polymers with styrene showed low sensitivity drop compared to non-styrene copolymers based on 9 months observation. Therefore, styrene copolymer sensors were best suited to build a stable sensor for the sensor array. Selected polymers for the sensor array retained their sensing properties despite being stored under a wide range of temperatures (−20 to 25°C). The sensor array could recognize pure wheat as well as was able to determine the presence of red flour beetle on it.

Identification of the volatile organic compounds released by insects can be used to detect insects in stored grains. An attempt was made to identify the volatile organic compounds released by Tribolium castaneum (red flour beetle) and Cryptolestes ferrugineus (rusty grain beetle) by headspace analysis. Feasibility of the automatic headspace sampler in headspace analysis was found to be positive. The amount of volatiles produced by T. castaneum adults increased with an increase in insect density. The concentration of methyl-1,4-benzoquinone; ethyl-1,4-benzoquinone; and 1-tridecene released by ten adult insects were: 8.5, 9.1 and 10.6 μg/100 μL compared to 7, 8 and 4.2 μg/100 μL for five adult insects. Extreme high or low temperature leading to death produced very high amounts of volatiles compared to insects kept at 35 °C. The larvae of the T. castaneum insects did not produce any volatiles at ambient condition or at extreme cold or hot condition. The C. ferrugineus adults did not produce any detectable amount of volatiles even at very high insect density after up to 3 days. The results of the combination of T. castaneum and C. ferrugineus insects gave the same volatile compounds as produced by T. castaneum insects alone.

The electrical properties of individual p- and n-type silicon microwires have been investigated using a direct contact formation technique, in which an Ohmic contact between the tungsten probe and microwire was produced by applying mechanical force to the probe/microwire junction. This method alleviated the need for lithography or a high-temperature process to form a metal/Si ohmic contact. The technique was also used to characterize the Si microwire/conducting polymer junctions in a single cell of a membrane-supported bilayer Si microwire structure that is of interest for the direct production of fuels from sunlight. The data indicate that the combination of PEDOT–PSS–Nafion and highly doped Si microwires is suitable, from an electrical resistance perspective, to be used in a solar fuels generation device.

We present a coupled coil pH sensor for high-resolution remote pH monitoring. The sensor is based on a passive LC coil resonator whose resonant frequency is monitored remotely by measuring the change in impedance of an interrogator coil coupled to the sensor coil. The sensor resonator consists of an inductive coil connected in parallel with a voltage dependent capacitor and a pH combination electrode. When the pH of the contact solution changes, the electrode potential changes the capacitance, and therefore the resonant frequency of the sensor. A linear response with a 0.1 pH resolution is achieved over a 2-12 pH dynamic range at room temperature. The response time of the sensor is demonstrated to be less than 30 s and is limited by the response time of the pH combination electrode. Effects of varying separation distance and temperature change on the sensor's performance are shown. The described sensor technology has potential application for remote pH monitoring in numerous fields such as biomedical sensing, environmental monitoring, industrial and chemical processing, and structural health monitoring.

Artificial photosynthetic (AP) approaches to convert and store solar energy will require membranes capable of conducting both ions and electrons while remaining relatively transparent and chemically stable. A new approach is applied herein involving previously described in situ chemical polymerization of electronically conducting poly(3,4-ethylenedioxythiophene) (PEDOT) in the presence of proton conducting heteropoly acid (HPA) phosphomolybdic acid (PMA). The electrochemical behaviour of the PEDOT/PMA hybrid material was investigated and it was found that the conducting polymer (CP) is susceptible to irreversible oxidative processes at potentials where water is oxidized. This will be problematic in AP devices should the process occur in very close proximity to a conducting polymer-based membrane. It was found that PEDOT grants the system good electrical performance in terms of conductivity and stability over a large pH window; however, the presence of PMA was not found to provide sufficient proton conductivity. This was addressed in an additional study by tuning the ionic (and in turn, electronic) conductivity in creating composites with the proton-permselective polymer Nafion. It was found that a material of this nature with near-equal conductivity for optimal chemical conversion efficiency will consist of roughly three parts Nafion and one part PEDOT/PMA.

The electrical (DC) behavior of single silicon microwires has been determined by the use of tungsten probes to make ohmic contact to the silicon microwires. The basic electrical properties of the microwires, such as their DC resistivity and the doping distribution along the length of the microwires, were investigated using this approach. The technique was also used to characterize the junction between silicon microwires and conducting polymers to assess the suitability of such contacts for use in a proposed artificial photosynthesis system.

A straightforward approach to the synthesis of electrically conducting PEDOT thin films using metastable and organic-solvent processable mixtures that rapidly polymerize upon solvent evaporation is presented. This one-step synthetic procedure, previously used to prepare well behaved polypyrrole and polythiophene films, has now been extended to one of the most academically/industrially studied and commercially successful polythiophene-based polymers, PEDOT. The methodology can be used to synthesize smooth, uniform, homogeneous, crack and pinhole free, conducting (0.02−0.47 S/cm), and highly transmissive PEDOT films with well-defined spectroelectrochemistry by spin-coating organic-solvent processable mixtures of EDOT monomer and phosphomolybdic acid oxidant onto conductive and nonconductive glass substrates.

Polymer-based sensors have several advantages for gas detection. They can utilize different polymer composite films as their sensing materials, which results in their ability to respond to a wide range of volatiles. However, it is shown that polymer-based sensors suffer from a large temperature sensitivity that causes shift in their volatile response. To overcome this disadvantage, a new design of interdigitated electrodes on a micro-hotplate is proposed. This detector employs a micromachined sensor structure on silicon wafer that maintains a constant temperature throughout the device. Different micromachined sensor structures and substrates were investigated as candidates for constant temperature platforms. COMSOL simulations were performed to investigate the heat transfer profile. Sensor structure and dimensions together with the heater structure were optimized based on the simulation results.

Dissolution experiments on single crystals of uranophane and uranophane-β, Ca(H2O)5[(UO2)(SiO3(OH)]2, from the Shinkolobwe mine of the Democratic Republic of Congo, were done in an aqueous HCl solution of pH 3.5 for 3 h, in HCl solutions of pH 2 for 5, 10 and 30 min, and in Pb2+–, Ba–, Sr–, Ca– and Mg–HCl solutions of pH 2 for 30 min. The basal surfaces of the treated uranophane crystals were examined using atomic-force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Solutions after dissolution experiments on single crystals and synthetic powders were analysed with inductively coupled plasma-optical emission spectroscopy (ICP-OES) and mass spectroscopy (ICP-MS). The morphology of the observed etch pits (measured by AFM) were compared to the morphology, predicted on the basis of the bond-valence deficiency of polyhedron chains along the edges of the basal surface. Etch pits form in HCl solutions of pH 2. Their decrease in depth with the duration of the dissolution experiment is explained with the stepwave dissolution model, which describes the lowering of the surrounding area of an etch pit with continuous waves of steps emanated from the etch pit into the rest of the crystal surface. Hillocks form in an HCl solution of pH 3.5, and the chemical composition of the surface (as indicated by XPS) shows that these hillocks are the result of the precipitation of a uranyl-hydroxy-hydrate phase. Well-orientated hillocks form on the surface of uranophane in a SrCl2–HCl solution of pH 2. They are part of an aged silica coating of composition Si2O2(OH)4(H2O)n. An amorphous layer forms on the surface of uranophane in a MgCl2–HCl solution of pH 2, which has a composition and structure similar to silicic acid. Small crystallites of uranyl-hydroxy-hydrate phases form on the surface of uranophane after treatment in Pb(NO3)2–HCl and BaCl2–HCl solutions of pH 2. Dissolution experiments on synthetic uranophane powders show that in the early stage of the experiments, the dissolution rate of uranophane increase in the sequence Pb(NO3)2–HCl

The O 1s spectrum is examined for 19 uranyl minerals of different composition and structure. Spectra from single crystals were measured with a Kratos Axis Ultra X-ray Photoelectron Spectrometer with a magnetic-confinement charge-compensation system. Well-resolved spectra with distinct maxima, shoulders and inflections points, in combination with reported and measured binding energies for specific O2− species and structural data of the uranyl minerals are used to resolve the fine structure of the O 1s envelope. The resolution of the O 1s spectra includes, for the first time, different O2− bands, which are assigned to O atoms linking uranyl with uranyl polyhedra (U O U) and O atoms of uranyl groups (O U O). The resolved bands in the O 1s spectrum occur at distinct ranges in binding energy: bands for (U O U) occur at 529.6–530.4 eV, bands for (O U O) occur at 530.6–531.4 eV, bands for O2− in the equatorial plane of the uranyl polyhedra linking uranyl polyhedra with (TOn) groups (T = Si, S, C, P, Se) (T O) occur at 530.9–532.2 eV; bands for (OH) groups in the equatorial plane of the uranyl polyhedra (OH) occur at 532.0–532.5 eV, bands of (H2O) groups in the interstitial complex of the uranyl minerals (H2Ointerst) occur at 533.0–533.8 eV and bands of physisorbed (H2O) groups on the surface of uranyl minerals (H2Oadsorb) occur at 534.8–535.2 eV. Treatment of uranyl minerals with acidic solutions results in a decrease in U O U and an increase in OH. Differences in the ratio of OH : O U O between the surface and bulk structure is larger for uranyl minerals with a high number of U O U and T O species in the bulk structure which is explained by protonation of underbonded U O, U O U and T O terminations on the surface. The difference in the ratio of H2Ointerst : O U O between the bulk and surface structures is larger for uranyl minerals with higher percentages of H2Ointerst as well as, with a higher number of interstitial H2O groups that are not bonded to interstitial cations, resulting in easier dehydration of interstitial H2O groups in uranyl minerals during exposure to a vacuum.

Poly(anilineboronic acid)/phosphate nanoparticle dispersions are produced in high yields using the reactivity of the boronic acid moiety with phosphate in the presence of fluoride. The poly(anilineboronic acid)/phosphate dispersions have been characterized using spectroscopic, microscopic and electrochemical techniques. According to 11 B NMR studies, the formation of anionic tetrahedral boronate group in phosphoric acid in the presence of fluoride forms the basis of self-doped, stabilized PABA nanoparticle dispersion. Transmission electron microscope images show that 25-50 nm diameter PABA nanoparticles are formed under these conditions. UV-vis, FT-IR-ATR spectroscopic and cyclic voltammetric results confirm the formation of the conducting form of PABA. Films produced from these particles exhibit enhanced redox stability and potential dependant conductivity under neutral and basic pH conditions due to the formation of a boron- phosphate complex containing fluoride, which results in a self-doped form of the polymer.

Self-doped poly(anilineboronic acid) (PABA) nanostructures have been prepared by chemical polymerization in an aqueous acid solution and aliphatic alcohols. In aliphatic alcohols, PABA is soluble under the polymerization conditions. According to 11 B NMR studies, the formation of anionic tetrahedral boronate ester in aliphatic alcohols in the presence of fluoride forms the basis of self-doped, soluble PABA. Transmission electron microscope images show the formation of nanostructures with different shapes and forms in different solvents after precipitation of the polymer as a result of ion exchange in the presence of 0.5 M HCl. The spectroscopic and cyclic voltammetric results confirm the formation of conducting PABA nanostructures in high yield. The conductivity of PABA thin films made from the nanostructures prepared in aqueous acid, methanol, ethanol and 1-propanol is approximately 15 and 3.0, 2.1 and 1.9 S cm -1 , respectively. The conducting PABA nanostructures are processable since they are easily re-dispersed in the various solvents up to approximately 5 mg mL -1 . UV-vis kinetic measurements, XPS and 11 B NMR results suggest that the formation of various nanostructures is influenced by the polymerization rate, the degree of self-doping versus external doping, and the polarity of the solvents used. The PABA nanostructured films produced from these structures exhibit enhanced redox stability in a wider potential window in non-aqueous media compared to polyaniline due to formation of six-member heterocyclic complexes containing a boron- imine dative bond resulting in a self-doped self-cross- linked polymer. The degree of cross-linking depends on the nature of nanostructures. In non-aqueous media, the self-doped, self-cross-linked PABA nanostructured films are much less susceptible to cathodic and anodic degradation at extreme potentials, overcoming a major limitation of more common conducting polymers.

Conducting polythiophene films are produced by the oxidation of bithiophene or terthiophene monomers using phosphomolybdic acid, wherein the reagents are first combined to form a metastable solution, the solution is then cast as a film, and polymerisation ultimately initiated by evaporation of the solvent The equivalent formation of polypyrrole via the oxidation of pyrrole using phosphomolybdic acid has been previously demonstrated, but this approach cannot be applied directly to thiophene, which has too high an oxidation potential Bithiophene and terthiophene have lower oxidation potentials, close to that of pyrrole This work suggests the previously demonstrated method is suitable for general application, requiring only the proper matching of monomer and oxidant redox potentials, and the selection of a suitable solvent and starting concentration Smooth, spin-coated polythiophene films having thicknesses of 100 to 200 run and conductivities in the range 0.2 to 0.3 S-cm-1 have been prepared.

First-principles calculations were performed to investigate the electronic structure of two-dimensional (2-D) Ge, Sn, and Pb without and with the presence of an external electric field in combination with spin-orbit coupling. Tight-binding calculations based on four orbitals per atom and an effective single orbital are presented to match with the results obtained from first-principles calculations. In particular, the electronic band structure and the band splitting are investigated with both models. Moreover, the simple $k\cdot p$ model is also considered in order to understand the band splitting in the presence of an external electric field and spin-orbit coupling. A large splitting is obtained, which is expected to be useful for spintronic devices. The fair agreement between the first-principle, $k\cdot p$ model, and tight-binding approaches leads to a table of parameters for future tight-binding studies on hexagonal 2-D nanostructures. By using the tight binding parameters, the transport properties of typical 0-D triangular quantum dots between two semi-infinite electrodes in the presence of spin-orbit coupling are addressed., 23 pages, 6 figures, and 3 tables

Exploration of the unusual properties of the two-dimensional materials silicene and germanene is a very active research field in recent years. This article therefore reviews the latest developments, focusing both on the fundamental materials properties and on possible applications., Comment: 9 pages, 9 figures, and 2 tables