Electrolyte Ionic Strength Research Articles

A New 3D Printing Milli-Fluidic Device with Integrated Nanojunction for On-Site Colorimetric Analysis of Iron in Water and Soil Samples

Fabrication and bonding represent significant challenges in the production of micro- and milli-fluidic devices with integrated functions. Here, to investigate the formation of nanojunction through controlled dielectric breakdown, a thermoplastic material was utilized to create a three-dimensional (3D) printed milli-fluidic device. The device was constructed using a fused deposition modeling three-dimensional printer with acrylonitrile butadiene styrene (ABS). With the application of a voltage between 20 and 25 kV, which was cut off when the current threshold was reached, a controlled dielectric breakdown was used to create a nanojunction in the thin slice of ABS. Both altering the current threshold and the electrolyte ionic strength used for breakdown allowed for different sizes of the nanojunction to be created. The size and transport characteristics of the nanojunctions were observed using electrophoretic transport of two proteins: fluorescamine-labeled bovine serum albumin (f-BSA; 2-4 nm) and R-phycoerythrin (RPE; <10 nm in size), and a small molecule (fluorescein, ∼0.5–1.0 nm) and ions (thiocyanate, ∼0.3 nm). Colorimetric measurement of iron from water and soil slurry samples was utilized to examine the suitability of the 3D-printed device for on-site analysis. Samples were freshly introduced to the 3D-printed milli-fluidic device after Fe3+ was reduced to Fe2+ using hydroxylammonium chloride. The nanojunction captured particle matter, allowing for particulate-free smartphone camera detection for imaging the orange-brown complex produced using 1,10-phenanthroline. The calibration curve covered 1 to 100 μg/mL of Fe2+ using the 3D printed device, which showed good agreement (97.5%) with ICP-MS.

Multiphysics Modeling of Electrode Dissolution Under Hydrodynamic Conditions in Low Conductivity Water

Efficient plug-flow electrochemical reactors are characterized by their ability to effectively convert species with significant ionic strength and/or with the assistance of a well-behaved electrolyte. Because of the classic electroconductivity requirement, electrochemical reactors are not particularly attractive options for applications with low-conductivity conditions, especially for low-pressure feeds. However, these reactors can still find application in dedicated processes such as ultra-clean water conditioning and biological-coupled separation systems. Consequently, a multi-physics model was developed using COMSOL Multiphysics to characterize different reactor-design conditions based on the Tertiary Current Distribution which accounts for the effects of expected variations in electrolyte composition and ionic strength on the electrochemical process, as well as solution resistance and electrode kinetics. The modelling framework presented here employs single-phase laminar fluid flow, the Nernst-Planck equation, the water-based electroneutrality condition, and concentration-dependent overpotentials. This investigation particularly explores the electrolysis process of “anodic dissolution,” in which elemental species dissociate from the solid matrix of the electrode and enter the liquid phase of the electrolyte as soluble ions. The reactor configuration of interest has a rectangular parallel-electrode design and is operated galvanostatically. A series of parametric studies are carried out to inspect the response of the system when hydrodynamic, kinetic, and geometric conditions are changed. The parametric sweep resulted in variable effluent concentrations and system voltage, which reveal underlaying optimization patterns for electrode dissolution in low conductivity water.

Durability and Performance of Poly(norbornene) Anion Exchange Membrane Alkaline Electrolyzer with High Ionic Strength Anolyte

Anion exchange polymer electrolytes enable low-temperature alkaline water electrolysis for reliable green hydrogen production. Anion exchange membrane water electrolysis (AEMWE) with alkaline electrolytes has several advantages over the proton exchange membrane water electrolysis using acid-based polymer electrolytes. The advantages include low-cost catalysts, all hydrocarbon non-fluorinated polymer membrane, and low-cost cell components. Long-term durability of AEMWEs in high pH operation has been challenging, although there have been significant performance improvements. AEMWE operated at low hydroxide anolyte provides improved chemical stability.In this study, an understanding of the high ionic-strength anolyte is provided along with demonstration of the AEMWE performance and durability. Anion exchange poly(norbornene) solid polymer electrolytes show high-performance, durable membrane electrode assemblies for alkaline electrolysis. Covalently bonded, self-adhesive solid polymer ionomers were used in electrodes for durable electrolysis. Hydration problem with the low pH alkaline anolyte in dry-cathode AEMWE is presented. The effect of anolyte concentration and mobile cations on the cathode electrolysis performance using a low hydroxide anolyte was investigated. High ionic strength anolyte was prepared by changing the mobile cation concentration while maintaining a constant anolyte pH. The mechanism of cathode hydration improvement through use of a high ionic strength anolyte is presented. Long-term durability with the optimal high ionic strength electrolyte is discussed.

An organic artificial soma for spatio-temporal pattern recognition via dendritic integration

A novel organic neuromorphic device performing pattern classification is presented and demonstrated. It features an artificial soma capable of dendritic integration from three pre-synaptic neurons. The time-response of the interface between electrolytic solutions and organic mixed ionic-electronic conductors is proposed as the sole computational feature for pattern recognition, and it is easily tuned in the organic dendritic integrator by simply controlling electrolyte ionic strength. The classifier is benchmarked in speech-recognition experiments, with a sample of 14 words, encoded either from audio tracks or from kinematic data, showing excellent discrimination performances in a planar, miniaturizable, fully passive device, designed to be promptly integrated in more complex architectures where on-board pattern classification is required.

Attachment of various-shaped polystyrene microplastics to silica surfaces: Experimental validation of the equivalent Cassini oval extended DLVO model

Microplastics (MPs) vary in shape and surface characteristics in the environment. The attachment of MPs to surfaces can be studied using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, this theory does not account for the shape MPs. Therefore, we investigated the attachment of spherical, pear-shaped, and peanut-shaped polystyrene MPs to quartz sand in NaCl and CaCl2 solutions using batch tests. The attachment of MPs to quartz sand was quantified using the attachment efficiency (alpha). Subsequently, alpha behaviors were interpreted using energy barriers (EBs) and interaction minima obtained from extended DLVO calculations, which were performed using an equivalent sphere model (ESM) and a newly developed equivalent Cassini model (ECM) to account for the shape of the MPs. The ESM failed to interpret the alpha behavior of the three MP shapes because it predicted high EBs and shallow minima. The alpha values for spherical MPs (0.62–1.00 in NaCl and 0.48–0.96 in CaCl2) were higher than those for pear- and peanut-shaped MPs (0.01–0.63 in NaCl and 0.02–0.46 in CaCl2, and 0.01–0.59 in NaCl and 0.02–0.40 in CaCl2, respectively). Conversely, the ECM could interpret the alpha behavior of pear- and peanut-shaped MPs either by changes in EBs or interaction minima as a function of orientation angles and electrolyte ionic strength. Therefore, the particle shape must be considered to improve the attachment analyses.

Performance of Anion Exchange Membrane Water Electrolysis with High Ionic Strength Electrolyte

Anion exchange membrane water electrolysis (AEMWE) provides the advantages of conventional alkaline water electrolysis and proton exchange membrane water electrolysis for low-temperature hydrogen production. This study investigates the effect of ionic strength in low hydroxide concentration anolyte on AEMWE performance. The anolyte was recirculated at the anode, and the cathode was operated dry. Different alkali cations in the high ionic strength anolyte improved the cathode overpotential by increasing the water transport from the anode to the cathode. Li+, Na+, K+, and Cs+ cations were tested with K+ providing the lowest electrolysis overpotential among the cations tested. The transference number of the alkali cations was measured by a modified Bruce-Vincent method using a membrane electrode assembly, composed of a hydrogen-evolving cathode and oxygen-evolving anode and anion exchange polymer membrane. The result shows that the cathode overpotential is influenced by the cation mobility, which is related to the hydration shell width. The electrolysis overpotential trend with different alkali cations in the anolyte scaled with the alkali dynamic ionic radius. Durable electrolysis was performed in 1,000 h test at 60 °C and 1 A cm−2.

Optimization of Electrolytes with Redox Reagents to Improve the Impedimetric Signal for Use with a Low-Cost Analyzer.

The most well-known criterion for POC devices is ASSURED, and affordability, i.e., using low-cost instrumentation, is the most challenging one. This manuscript provides a pathway for transitioning ESSENCE, an impedance-based biosensor platform, from using an expensive benchtop analyzer-KeySight 4294A (~$50k)-to using a significantly portable and cheaper USB oscilloscope-Analog Discovery 2 (~$200) -with similar sensitivity (around 100 times price difference). To achieve this, we carried out a fundamental study of the interplay between an electrolyte like potassium chloride (KCl), and an electrolyte buffer like phosphate buffered saline (PBS) in the presence and absence of a redox buffer like ferro/ferricyanide system and ([Ru(bpy)3]2+). Redox molecules in the electrolyte caused a significant change in the Nyquist curve of the impedance depending on the redox molecule type. The redox species and the background electrolyte have their own RC semicircles in the Nyquist curve, whose overlap depends on the redox concentration and electrolyte ionic strength. We found that by increasing the electrolyte ionic strength or the redox concentration, the RC semicircle moves to higher frequencies and vice versa. Importantly, the use of the buffer electrolyte, instead of KCl, led to a lower standard deviation and overall signal (lesser sensitivity). However, to achieve the best results from the biorecognition signal, we chose a buffered electrolyte like PBS with high ionic strength and lowered the redox probe concentrations to minimize the standard deviation and reduce any noise from migrating to the low-cost analyzer. Comparing the two analyzers shows similar results, with a lowered detection limit from the low-cost analyzer.

Multiscale modelling of species transport in hydrophilic Nafion®-coated Cu catalysts for CO2 electro-reduction

Ionomers such as Nafion are being used for engineering the microenvironment of the CO2RR towards selectivity to higher hydrocarbons. Their cationic exchange qualities mitigate homogeneous bicarbonate reactions, providing favourable conditions for production of C2-C3 products. The proximity of Nafion® layers to the negatively charged electrode surface results in complex effects that have yet to be explored computationally. We combine mass transport equations and density functional theory (DFT) calculations to model the hydrophilic moieties in Nafion® layer on a 1D planar copper electrode. We vary the Nafion® layer thickness in the thick film regime (200–1100 nm), the ionic strength of supporting aqueous electrolyte and the applied voltage to investigate the concentration profile of participating species within the Nafion® layer. We find that the bicarbonate ion concentration and local pH decrease with decreasing thickness which makes thinner films better at mitigating bicarbonates at the cost of a relatively lower pH. We observe the breakdown of Donnan exclusion effects with higher ionic strength electrolytes which allows diffusion of both co-ions and counter-ions, promoting the bicarbonate reactions. Further, we find that the pKa of Nafion® generally increases as the local dielectric constant of the reaction medium decreases. This is primarily due to the accumulation of K+ and production of low dielectric constant products such as ethanol, albeit their concentrations are low on planar Cu electrodes. The lower permittivity of the reaction medium weakens the exclusion forces and changes the morphology of Nafion® which ultimately impacts its ability to mitigate homogeneous bicarbonate reactions.

Fine-Tuning the Surface and Interfacial Chemistry of Silica Nanoparticles to Control Stability in High Ionic Strength Electrolytes and Modulate Assembly at Oil–Water Interfaces

Fine-Tuning the Surface and Interfacial Chemistry of Silica Nanoparticles to Control Stability in High Ionic Strength Electrolytes and Modulate Assembly at Oil–Water Interfaces

Live Cell and Hybrid Material Based Bio-Photoelectrochemical Cells for Clean Solar Energy Conversion

Photosynthetic organisms and complexes are attractive starting materials for solar energy conversion (SEC). I will describe here how the remarkable photocatalytic activity of the photosynthetic apparatus can provide overall water splitting with oxygen and hydrogen production in Bio-Photo-Electro-Chemical (BPEC) cells (Fig. 1). Use of isolated photosynthetic systems tightly associated with different electrodes has the benefit of potentially high reaction center density. However, the cross-section for light absorption is poor, leading to sub-optimal activity. Disconnection from biological repair mechanisms leads to limited lifetime. On the other hand, use of intact, live systems have the benefit of evolutionarily optimized light harvesting antennas for improved energy absorption and transfer, and all of these organisms have excellent repair systems leading to essentially endless activity. However, how these intact systems can be functionally connected to the BPEC depends on the morphology, permeability and flux of electron carriers. We will show here that we can obtain significant electrical current using a variety of live photosynthetic organisms, each with benefits and drawbacks. Cyanobacteria1,2 and microalgae3 are applied directly to the BPEC anode, providing continuous current densities in the 10’s of μA/cm2. Use of photosynthetic tissues from macroalgae (seaweeds)4 or higher plants5 require tight association with metallic anodes (stainless steel, aluminum, etc.) leading to current densities of >50mA/cm2, with high ionic strength electrolyte solutions supporting these increased current densities. Succulents can serve as their own BPEC6. In all cases, the major electron carrier is NADPH which is released by the cells and tissues into the electrolyte. A different strategy is to use isolated photosynthetic complexes and chemically connect them to the electrochemical cell. To overcome the problem of lower number of light absorbing chromophores connected to each reaction center we can use either isolated biological light harvesting (LH) complexes or nanoparticles (NPs). As Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation, we focus on its use in these systems. PSII can be isolated from a wide variety of organisms, each with relative benefits or disadvantages: isolation ease and cost, quantity per cell, stability to heat or other external stress, etc. PSII contains chlorophyll a which absorbs well in the 400-500nm and 600-700nm region, limiting the quantum efficiency in the gap in the green absorption region (500 - 600 nm). To overcome this limitation, we have used two strategies: stabilizing the interaction between PSII and isolated thermophilic cyanobacterial Phycobilisomes LH complex within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO). This results in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies7. Another strategy was to isolate market-purchased spinach PSII (cheap and abundant) and associate them via a unique binding shell to gold-nanoparticles (Au-NPs)8. These Au-NP were shown to serve as both light harvesting modules in the green gap, as well as conduits of electrons from the bound PSII to the BPEC, leading to record current densities were obtained. Figure 1

Solid State Zinc and Aluminum ion batteries: Challenges and Opportunities.

Solid-state zinc ion batteries (ZIBs) and aluminum-ion batteries (AIBs) are deemed as promising candidates for supplying power in wearable devices due to merits of low cost, high safety, and tunable flexibility. However, their wide-scale practical application is limited by various challenges, down to the material level. This Review begins with elaboration of the root causes and their detrimental effect for four main limitations: electrode-electrolyte interface contact, electrolyte ionic conductivity, mechanical strength, and electrochemical stability window of the electrolyte. Thereafter, various strategies to mitigate each of the described limitation are discussed along with future research direction perspectives. Finally, to estimate the viability of these technologies for wearable applications, economic-performance metrics are compared against Li-ion batteries.

Characterization of liquid flow and electricity generation in a glass channel based evaporation-driven electrokinetic energy conversion device

Evaporation-driven spontaneous capillary flow presents a promising approach for driving electrolytes through electrically charged channels and pores in electrokinetic energy conversion devices. However, there are no literature reports of detailed flow visualization in these systems and/or experimental observations relating the liquid velocity and evaporation rate to the generated voltage and current. In this manuscript, we describe such a visualization study for a glass channel based electrokinetic energy conversion device with one of its channel terminals left open to ambient air for facilitating the evaporation process. Fluorescence microscopy was used to measure the liquid velocity in the electrokinetic energy conversion channel by observing the advancement of an electrolyte solution dyed with a neutral tracer. The accumulation of the same dye tracer was also imaged at the open terminal of this glass conduit to estimate the rate of solvent evaporation, which was found to be consistent with the flow velocity measurements. Additionally, an electrochemical analyzer was employed to record the electrical voltage and current produced by the device under different operating conditions. The highest electrical power output was derived in our experiments upon flowing de-ionized water through a 1 μm deep channel, which also produced the fastest liquid velocity in it. Moreover, the energy conversion efficiency of our device was observed to increase for shallower channels and lower ionic strength electrolytes, consistent with previous literature reports on electrokinetic energy conversion platforms.

Streaming Potentials of Hyaluronic Acid Hydrogel Films.

The streaming potentials of hyaluronic acid (HA) hydrogel films are measured and theoretically interpreted by systematically varying the HA concentration and the streaming electrolyte pH and ionic strength. While Donnan potentials are expected to vanish with sufficient added salt, apparent ζ-potentials from the Helmholtz-Smoluchowski interpretation remain of the order -20 mV. To theoretically interpret these data, we derived an electrokinetic model (valid in the Debye-Hückel regime) that accounts for ionic and hydrodynamic permeability of the gels. The films could then be ascribed an effective acid dissociation constant pKa ≈ 4.2, specific HA charge ≈-0.1e mmol g-1, and Brinkman/hydrodynamic permeability ∼ S1/3, where is the Brinkman length for HA solutions in the as-prepared reference state and S is the hydrogel swelling ratio. At an ionic strength of 10 mmol L-1, for example, the HA surface potentials are only ψD/2 ≈ -8 mV, where ψD is the Donnan potential, considerably lower than ζ-potentials furnished by the Helmholtz-Smoluchowski interpretation. This insight significantly changes how the films are expected to interact with other surfaces and colloids via Derjaguin-Landau-Vervey-Overbeek-type forces. Our analysis furnishes formulas for the swelling ratio S and hydrodynamic permeability , expressed explicitly as simple power-law functions of the as-prepared HA concentration cha (wt %), consistent with independent assessments of the HA solution permeability and polyelectrolyte-hydrogel swelling theory. These may prove valuable for extrapolating the results to other combinations of ionic strength, pH, and HA and cross-linking concentrations.

An Interfacial Label-Free Electrochemical Approach to in-Situ Soil pH Monitoring

Soil is a critical entity of Earth’s ecosystem. Healthy soil supports a landscape that is more resilient to the impacts of drought, flood, or fire. It also helps regulate the Earth’s climate. Real time assessment of soil health is imperative to improving crop yield as well to sustain an ever growing human population. Soil health encompasses moisture content, phosphorus, pH, nitrate, and other parameters. One of the most important parameters is soil pH which affects nutrients availability to plants and nutrients leaching in the soil. Current soil pH assessment techniques require destructive sampling of the soil where a core of soil is collected then treated at a lab before measuring the pH. This method measures pH at time points and doesn’t provide a continuous real time monitoring of pH. This work utilizes commercial screen printed electrodes with a pH sensitive coating for low cost continuous in-situ soil pH measurement. The coating is made up from alizarin an anthraquinone compound that undergoes a redox reaction in the presence of hydrogen ions and nafion an ion permeable membrane. Square wave voltammetry (SWV) is utilized since the output current signal shows the redox of alizarin while rejecting the capacitive current that’s inherent in soil. This redox peak current potential is dependent on the concentration of hydrogen ions which is gives a direct measure of pH. Due to the sensitivity of SWV, it is possible to measure unbuffered soil ph (without CaCl2 and KCl to improve the electrolyte ionic strength) accurately. The nafion layer protects the alizarin from dissolving in water present in soil as well as promoting the diffusion of hydrogen ions into the coating thus improving sensitivity. The alizarin has been used previously in screen printed electrodes however, this is the first work to our knowledge to utilize it to measure soil pH in-situ over a period of time. The sensor output was first calibrated in different unbuffered soil textures against the gold standard glass electrode. The calibrated response of the sensor in unbuffered sandy loam soil slurry is shown in Fig. 1. Then the sensor accuracy was validated by testing different soil samples using the sensor and later mixing it with deionized water and measuring the pH using the glass electrode. The sensor’s stability was evaluated by taking a measurement every hour for 48 hours without removing it from the soil sample. The temporal study showed a coefficient of variation less than 1% and an average reading of within 0.3 pH of the actual pH of the soil sample.Fig. 1 Calibrated response of proposed sensor in sandy loam soil slurries with 40% water Figure 1

Dual-frequency comb spectroscopy studies of ionic strength effects in time-resolved ATR-SEIRAS

• DFCS allows sub-millisecond resolution of temporal processes occurring at an electrode surface. • IR transient time constants are directly proportional to the RC cell constant. • Absorption spectra line shape depends on coverage. Attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies of the potential induced desorption/adsorption of a model organic monolayer is described using a paradigm-challenging dual frequency comb spectrometer. Experimentally measured ATR-SEIRAS transients reveal that both the rates of adsorption and desorption of 4-dimethylaminopyridine (DMAP) are dependent on the ionic strength of the supporting electrolyte. The characteristic time scales of monolayer desorption are found to be directly proportional to the spectroelectrochemical cell time constant indicating that the rate of film dissolution is much faster than the RC charging of the interface. The slow response of the interfacial charging process relative to the kinetics of the film re-organization/desorption processes means that the transient is parametrically linked to the potential dependent DMAP adsorption isotherm. The transients also reveal that the line shape of the molecular IR absorption feature exhibits a temporal dependence. A Lorentzian band is seen at early stages of the desorption transient but increasingly exhibit an anomalous bimodal line-shape at longer times. The development of the anomalous line shape is more pronounced at equivalent times in higher ionic strength electrolytes. Such an effect has been modelled using effective medium theory and is explained by the fact that the fraction of organic layer in the SEIRAS active film influences the observed apparent absorption features. The observation of a coverage dependence on SEIRAS line shapes adds new complexity to previous reports that linked anomalous absorption features exclusively to the metal film morphology and metal volume fraction.

On-Chip Electrokinetic Micropumping for Nanoparticle Impact Electrochemistry.

Single-entity electrochemistry is a powerful technique to study the interactions of nanoparticles at the liquid-solid interface. In this work, we exploit Faradaic (background) processes in electrolytes of moderate ionic strength to evoke electrokinetic transport and study its influence on nanoparticle impacts. We implemented an electrode array comprising a macroscopic electrode that surrounds a set of 62 spatially distributed microelectrodes. This configuration allowed us to alter the global electrokinetic transport characteristics by adjusting the potential at the macroscopic electrode, while we concomitantly recorded silver nanoparticle impacts at the microscopic detection electrodes. By focusing on temporal changes of the impact rates, we were able to reveal alterations in the macroscopic particle transport. Our findings indicate a potential-dependent micropumping effect. The highest impact rates were obtained for strongly negative macroelectrode potentials and alkaline solutions, albeit also positive potentials lead to an increase in particle impacts. We explain this finding by reversal of the pumping direction. Variations in the electrolyte composition were shown to play a critical role as the macroelectrode processes can lead to depletion of ions, which influences both the particle oxidation and the reactions that drive the transport. Our study highlights that controlled on-chip micropumping is possible, yet its optimization is not straightforward. Nevertheless, the utilization of electro- and diffusiokinetic transport phenomena might be an appealing strategy to enhance the performance in future impact-based sensing applications.

Electrostatic Secondary‐Sphere Interactions That Facilitate Rapid and Selective Electrocatalytic CO2 Reduction in a Fe‐Porphyrin‐Based Metal–Organic Framework

AbstractMetal–organic frameworks (MOFs) are promising platforms for heterogeneous tethering of molecular CO2 reduction electrocatalysts. Yet, to further understand electrocatalytic MOF systems, one also needs to consider their capability to fine‐tune the immediate chemical environment of the active site, and thus affect its overall catalytic operation. Here, we show that electrostatic secondary‐sphere functionalities enable substantial improvement of CO2‐to‐CO conversion activity and selectivity. In situ Raman analysis reveal that immobilization of pendent positively‐charged groups adjacent to MOF‐residing Fe‐porphyrin catalysts, stabilize weakly‐bound CO intermediates, allowing their rapid release as catalytic products. Also, by varying the electrolyte's ionic strength, systematic regulation of electrostatic field magnitude was achieved, resulting in essentially 100 % CO selectivity. Thus, this concept provides a sensitive molecular‐handle that adjust heterogeneous electrocatalysis on demand.

Electrostatic Secondary-Sphere Interactions That Facilitate Rapid and Selective Electrocatalytic CO2 Reduction in a Fe-Porphyrin-Based Metal-Organic Framework.

Metal–organic frameworks (MOFs) are promising platforms for heterogeneous tethering of molecular CO2 reduction electrocatalysts. Yet, to further understand electrocatalytic MOF systems, one also needs to consider their capability to fine‐tune the immediate chemical environment of the active site, and thus affect its overall catalytic operation. Here, we show that electrostatic secondary‐sphere functionalities enable substantial improvement of CO2‐to‐CO conversion activity and selectivity. In situ Raman analysis reveal that immobilization of pendent positively‐charged groups adjacent to MOF‐residing Fe‐porphyrin catalysts, stabilize weakly‐bound CO intermediates, allowing their rapid release as catalytic products. Also, by varying the electrolyte's ionic strength, systematic regulation of electrostatic field magnitude was achieved, resulting in essentially 100 % CO selectivity. Thus, this concept provides a sensitive molecular‐handle that adjust heterogeneous electrocatalysis on demand.

Ion Exchange Resin Modified Carbon Paste Electrode Applied to Simultaneous Determination of Cd (II) and Pb (II)

A new, simple, sensitive and fast analytical method was developed to simultaneous quantification of Cd(II) and Pb(II) in cooling water by anodic square wave redissolution voltammetry (SWASV) using a modified carbon paste electrode composite with carbon black, resin functionalized with sulphonic group and paraffin. The experimental conditions such as supporting electrolyte (composition, pH and ionic strength) and SWASV parameters were optimized. The best conditions of Cd(II) and Pb(II) (higher peak current) were obtained in 0.1 mol l−1 BR buffer (pH 4.6) from −1.1 to 0.3 V, amplitude of 60 mV, frequency of 40 Hz, potential step of 5 mV, potential and deposition time of −1.1 V and 240 s, respectively. The analytical curve of Cd(II) and Pb were linear from 10 to 50 μg l−1 (R2 = 0.999) with quantification limit of 0.06 and 0.12 μg l−1, respectively. The method was successfully applied in cooling water from thermoelectric industry and the concentrations of Cd(II) and Pb(II) were 3.27 ± 0.30 and 2.80 ± 0.18 mg l−1, respectively. The method accuracy was evaluated through the comparison with the comparative method (SWV with Hanging Mercury Drop Electrode) and the relative error obtained was smaller than 9.8%.

Parallel Potentiometric and Capacitive Response in a Water-Gate Thin Film Transistor Biosensor at High Ionic Strength.

We show that an SnO2-based water-gate thin film transistor (WGTFT) biosensor responds to a waterborne analyte, the spike protein of the SARS-CoV-2 virus, by a parallel potentiometric and capacitive mechanism. We draw our conclusion from an analysis of transistor output characteristics, which avoids the known ambiguities of the common analysis based on transfer characteristics. Our findings contrast with reports on organic WGTFT biosensors claiming a purely capacitive response due to screening effects in high ionic strength electrolytes, but are consistent with prior work that clearly shows a potentiometric response even in strong electrolytes. We provide a detailed critique of prior WGTFT analysis and screening reasoning. Empirically, both potentiometric and capacitive responses can be modelled quantitatively by a Langmuir‒Freundlich (LF) law, which is mathematically equivalent to the Hill equation that is frequently used for biosensor response characteristics. However, potentiometric and capacitive model parameters disagree. Instead, the potentiometric response follows the Nikolsky-Eisenman law, treating the analyte ‘RBD spike protein’ as an ion carrying two elementary charges. These insights are uniquely possible thanks to the parallel presence of two response mechanisms, as well as their reliable delineation, as presented here.