Buffer Electrolyte Research Articles

Enhanced Photoelectrochemical Water Splitting Using NiMoO4/BiVO4/Sn-Doped WO3 Double Heterojunction Photoanodes.

Efficient photoelectrochemical (PEC) water splitting systems in photoelectrodes are primarily challenged by electron-hole pair recombination. Constructing a heterostructure is an effective strategy to overcome this issue and to enhance PEC efficiency. In this study, we integrated NiMoO4, known for its proper electrocatalytic conductivity, into a BiVO4/Sn-doped WO3 heterojunction using solution-based hydrothermal and spin-coating methods, forming an innovative double heterojunction concept. The resulting NiMoO4/BiVO4/Sn:WO3 triple-layer heterojunction photoanode exhibits a photocurrent density of 2.06 mA cm-2 in a potassium borate buffer (KBi) electrolyte at 1.23 V vs RHE, outperforming the bilayer BiVO4/Sn:WO3 heterojunction (1.45 mA cm-2) and Sn:WO3 photoanodes (0.55 mA cm-2) by approximately 1.4 and 3.7 times, respectively. Remarkably, the NiMoO4/BiVO4/Sn:WO3 double heterojunction photoanode exhibits notable stability, showing only an approximate 30% reduction in initial photocurrent density after 10 h of measurement in the KBi electrolyte without a hole scavenger. This stability is attributed to the excellent corrosion resistance of the thin NiMoO4 layer, effectively protecting the bilayer BiVO4/Sn:WO3 heterojunction photoanode from photocorrosion. Our findings show how this novel double heterojunction, established through simple and cost-effective solution-based methods, offers a promising approach to enhancing PEC water splitting applications.

Electric Field of DNA in Solution: Who Is in Charge?

In solution, DNA, the “most important molecule of life,” is a highly charged macromolecule that bears a unit of negative charge on each phosphate of its sugar-phosphate backbone. Although partially compensated by counterions (cations of the solution) adsorbed at or condensed near it, DNA still produces a substantial electric field in its vicinity, which is screened by buffer electrolytes at longer distances from the DNA. This electric field is experienced by any charged or dipolar species approaching and interacting with the DNA. So far, such a field has been explored predominantly within the scope of a primitive model of the electrolytic solution, not considering more complicated structural effects of the water solvent. In this paper, we investigate the distribution of electric field around DNA using linear response nonlocal electrostatic theory, applied here for helix-specific charge distributions, and compare the predictions of such a theory with specially performed, fully atomistic, large-scale, molecular dynamics simulations. Both approaches are applied to unravel the role of the structure of water at close distances to and within the grooves of a DNA molecule in the formation of the electric field. As predicted by the theory and reported by the simulations, the main finding of this study is that oscillations in the electrostatic potential distribution are present around DNA, caused by the overscreening effect of structured water. Surprisingly, electrolyte ions at physiological concentrations do not strongly disrupt these oscillations and are rather distributed according to these oscillating patterns, indicating that water structural effects dominate the short-range electrostatics. We also show that (i) structured water adsorbed in the grooves of DNA leads to a positive electrostatic potential core relative to the bulk, (ii) the Debye length some 10 Å away from the DNA surface is reduced, effectively renormalized by the helical pitch of the DNA molecule, and (iii) Lorentzian contributions to the nonlocal dielectric function of water, effectively reducing the dielectric constant close to the DNA surface, enhance the overall electric field. The impressive agreement between the atomistic simulations and the developed theory substantiates the use of nonlocal electrostatics when considering solvent effects in molecular processes in biology. Published by the American Physical Society 2024

Enhancing the Electrocatalytic Hydrogenation of Furfural via Anion-Induced Molecular Activation and Adsorption.

The electrocatalytic hydrogenation (ECH) of furfural (FF) to furfuryl alcohol, which does not require additional hydrogen or high pressure, is a green and promising production route. In this study, we explore the effects of anions on FF ECH in two buffer electrolytes (KHCO3 and phosphate-buffered saline [PBS]). Anions influence the yield of furfuryl alcohol through molecular activation and adsorption. Molecular dynamics simulations show that bicarbonate is present in the first shell layer of the FF molecule and induces strong hydrogen bonding interactions. In contrast, hydrogen phosphate is present only in the second shell layer, resulting in weak hydrogen bonding interactions. Owing to the interfacial anions and hydrogen bonding, FF molecules exhibit strong flat adsorption on the electrode surface in the KHCO3 solution, while weak adsorption is observed in the PBS solution, as confirmed by operando synchrotron-radiation Fourier-transform infrared spectroscopy and in situ Raman spectroscopy. Density-functional theory calculations reveal that the overall anionic hydrogen bonding network promotes the activation of the carbonyl group in the FF molecule in KHCO3, whereas electrophilic activity is inhibited in PBS. Consequently, FF ECH demonstrates much faster kinetics in KHCO3, while it exhibits sluggish ECH kinetics and a severe hydrogen evolution reaction in PBS. This work introduces a new strategy to optimize the catalytic process through the modulation of the microenvironment.

Buffering Donor Shuttles in Proton-Coupled Electron Transfer Kinetics for Electrochemical Hydrogenation of Hydroxyacetone to Propylene Glycol.

Electrochemical hydrogenation reactions demand rapid proton-coupled electron transfer at the electrode surface, the kinetics of which depend closely on pH. Buffer electrolytes are extensively employed to regulate pH over a wide range. However, the specific role of buffer species should be taken into account when interpreting the intrinsic pH dependence, which is easily overlooked in the current research. Herein, we report the electrochemical hydrogenation of hydroxyacetone, derived from glycerol feedstock, to propylene glycol with a faradaic efficiency of 56 ± 5% on a polycrystalline Cu electrode. The reaction activities are comparable in citrate, phosphate, and borate buffer electrolytes, encompassing different buffer identities and pH. The electrokinetic profile reveals that citrate is a site-blocking adsorbate on the Cu surface, thereby decreasing buffer concentration and increasing pH will enhance the reaction rate; phosphate is an explicit proton donor, which promotes the interfacial rate by increasing buffer concentration and decreasing pH, while borate is an innocent buffer, which can be used to investigate the intrinsic pH effect. Combined with in situ SEIRAS, we demonstrate that water is the primary proton source in citrate and borate electrolytes, reiterating the rationality of the proposed mechanism based on the microkinetic modeling. Our results emphasize the intrinsic complexity of the buffer system on the kinetic activity for electrocatalysis. It calls for special care when we diagnose the mechanistic pathway in buffer electrolytes convoluted by different buffer identities and pH.

(Invited) Electrolyte Engineering for Disruptive Cost Reduction of Electrolyzer: Hydrogen Generation from Dense Carbonate Buffer Solution

Water electrolysis using renewable electricity is a key process for generating green hydrogen, a crucial element in the pursuit of a sustainable society. To make substantial strides in lowering the cost of green hydrogen, it is imperative to address not only the expense of the electricity involved but also the cost associated with the electrolyzer itself [1]. The current challenge lies in the materials chosen for electrolyzers operating under extreme acidic or alkaline conditions, which necessitate the use of costly corrosion-resistant components. A viable solution involves considering non-extreme pH water as an electrolyte, allowing for the utilization of affordable and readily available materials, such as iron or stainless steel, in key electrolyzer components like the frame or bipolar plate [2]. Despite the reported inferior performance of non-extreme pH electrolysis compared to extreme pH conditions, primarily due to inevitable pH shifts (resulting in concentration overpotential) and elevated solution resistance, advancements in technology and research hold the potential to overcome these challenges.Our research group has been actively engaged in the exploration of electrolyte engineering, a concept centered on optimizing the diffusion flux of buffer ions to mitigate the previously mentioned challenges in non-extreme pH conditions [3,4]. Our approach involves leveraging a dense buffer solution to maximize the flux of buffer ions, resulting in a significant reduction in concentration overpotential. This strategy becomes even more impactful when the operating temperature is elevated to the commercially viable range of 80-100 °C [5]. The synergistic effect of employing a dense buffer solution, combined with elevated temperatures, proves to be a promising avenue for advancing electrolyte engineering and optimizing the performance of electrolysis systems in non-extreme pH conditions. In this presentation, we will delve into our discoveries concerning non-noble metal electrocatalysts, specifically focusing on their efficacy in both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER).Our research has led us to identify transition metal-based electrocatalysts that demonstrate exceptional efficiency in catalyzing OER within a carbonate buffer electrolyte at near-neutral pH [6]. Among the diverse materials we explored, the iron-nickel composite, coupled with copper or gold on electrochemically activated Ni (ECA-Ni) substrates [7], stands out as a superior performance. Notably, these electrodes exhibited a remarkable OER catalysis rate of 1 A cm−2 and an overpotential of approximately 330 mV, becoming competitive with highly alkaline counterpart.Next, our research has uncovered noteworthy electrocatalysts based on copper and molybdenum, demonstrating exceptional efficiency in catalyzing the hydrogen evolution reaction (HER) within a carbonate buffer electrolyte at pH 10.5 [8]. The most promising sample achieved a current density of 1 A cm−2 at an overpotential of approximately 0.2 V, a performance comparable to previously reported HER results in highly alkaline conditions. Detailed characterization of these electrocatalysts unveiled that the addition of copper resulted in a rougher surface structure, contributing to the largest double-layer capacitance. These characteristics are indicative of an enlarged active surface area, which is pivotal for enhanced catalytic activity. Furthermore, the introduction of copper element correlated with a decreased apparent Tafel slope, suggesting a tailored nature of the active sites. These insights not only shed light on the structural modifications induced by copper but also underscore its role in optimizing the electrocatalytic performance.Finally, we integrated the previously developed HER and OER catalysts with a carefully selected polyether sulfone (PES) diaphragm [8]. This strategic combination resulted in a notable enhancement of overall cell performance within a 3.0 mol kg− 1 K-carbonate solution at pH 10.5 and a temperature of 353 K. The resultant cell performance, factoring in the series resistance, achieved a 1 A cm− 2 at a voltage of approximately 2.0 V. This achievement stands competitively against the top-class commercial alkaline electrolyzers. These findings not only highlight the feasibility of non-extreme pH electrochemical electrolyzers in industrial applications but also underscore the potential for further advancements and optimizations. The demonstrated success serves as a compelling indicator of the viability of our approach and opens avenues for refining non-extreme pH electrolysis for even greater efficiency and applicability in industrial settings.Reference[1] M. Chatenet, et al., Chem. Soc. Rev. 2022, 51, 4583.[2] M. Pourbaix, “Atlas of Electrochemical Equilibria in Aqueous solutions”, 1974.[3] T. Shinagawa and K. Takanabe, ChemSusChem 2017, 10, 1318.[4] T. Shinagawa et al., ChemCatChem 2019, 11, 5961.[5] T. Naito, et al., ChemSusChem 2022, 8, e202102294.[6] T. Nishimoto, et al., ChemSusChem 2022, e202201808.[7] T. Shinagawa, et al., Angew. Chem. Int. Ed. 2017, 56, 5061.[8] T. Nishimoto, et al., ACS Catal. 2023, 13, 14725.

Progress of highly reproducible capillary electrophoresis

Following rapid developments in capillary electrophoresis (CE), this technology has become an established analytical technique owing to its microscale characteristics, high speed, high efficiency, and versatility. However, the challenges of poor peak stability and/or reproducibility have consistently hindered its wider applications. CE has long been used as a measurement tool for plotting signal intensities versus the migration time; however, the migration time is not an independent variable in CE, but is affected by many direct and indirect parameters, including capillary (length, diameter, and inner surface properties), electric field (or voltage, current, and/or power), temperature, and running buffer (electrolytes, additives, solvents, and their concentration, buffering pH, etc.). These intricacies render the acquisition of reproducible electropherograms difficult. Various studies ranging from those on the early stages of CE development to those on the exploration of three important strategies have been conducted to address this issue. In the first strategy, the CE conditions, especially those parameters that can maintain a stable electro-osmotic flow, are strictly controlled and stabilized to significantly improve peak repeatability. In the second strategy, either the peak position is corrected using internal standards or the peak time is converted into other variables, such as electrophoretic mobility, to offset or eliminate some unstable factors, thereby improving the repeatability and even reproducibility of the peaks; this strategy is useful when plotting signals versus the migration time ratio, correlated migration time, effective mobility, or temperature-correlated mobility. In the third strategy, a new methodology called highly reproducible CE (HRCE) is established using theoretical studies to explore better principles for real-time CE with the aim of the complete removal of the challenge from the root. This strategy includes the development of novel methods that plot electropherograms based on weighted mobility, migrated charge, charge density, or partial differential molar charge density. Similar to ordinary CE approaches, this strategy can also draw electropherograms based on the ratios of these properties. As theoretically predicted, these novel methods can offset or resist changes in critical CE conditions (mainly electric field strength, capillary length and diameter, and/or some buffer parameters such as concentration). Our experimental results demonstrate that given certain prerequisites, a new set of methods can produce highly reproducible electropherograms. This review focuses on the theoretical basis and advancements of HRCE, and elucidates the link between electrophoretic migration/peak expression theories and their impact on reproducibility. Studies on the transformation of time-scale electropherograms in the CE literature are summarized and analyzed in general. However, this review does not directly discuss research on and progress in improving CE repeatability or reproducibility through instrument upgrades, parameter optimization, or practical method refinements.

Electrolyte Influence on Properties of Ultra-Thin Anodic Memristors on Titanium

Titanium anodic memristors were prepared in phosphate buffer (PB) and citrate buffer (CB) electrolytes. Studying their I-U sweeps, the memristors presented self-rectifying and volatile behaviors. Transmission electron microscopic analysis revealed crystalline protrusions inside a semi-crystalline Ti oxide. Grounded in this, a hybrid interfacial memristive switching mechanism relaying on partial filaments was proposed. Moreover, both analyzed memristor types demonstrated multilevel switching capabilities. The memristors anodized in the PB and CB showed high-to-low resistance ratios of 4 × 104 and 1.6 × 102, respectively. The observed (more than two order of magnitude) ratio improvement of the PB memristors suggests their better performance, in spite of their modestly high resistive state instabilities, attributed to the thermal stress caused by consecutive switching. The endurance and retention of both the PB and CB memristors was measured over up to 106 cycles, indicating very good lifetimes. Phosphate incorporation into the anodic oxide was confirmed by photoelectron spectroscopy analysis and was related to the improved memristive behavior of the PB sample. The presence of phosphate inside the memristively active layer modifies the availability of free O species (vacancies and ions) in the oxide. Taking all this into consideration, Ti anodic memristors anodized in PB are emphasized as candidates for neuromorphic computing.

Electrokinetic instability of a highly charged and weakly diffusing analyte in a buffer electrolyte near an ion-selective surface

Electrokinetic instability of a highly charged and weakly diffusing analyte in a buffer electrolyte near an ion-selective surface

Corrosion resistance of electroplated coatings based on chromium trivalent-baths

Cr-C coatings were obtained from two different Cr(III)-baths based on sulphate and chloride salts, respectively. A tailored characterization was carried out by scanning electron microscopy, several spectroscopies and Mott-Schottky approaches (including Point Defect Model) to find out the impact in the corrosion performance of the morphology, composition, and semiconducting properties of the native oxide layers. The polarisation curves using 0.01 M NaCl have shown better corrosion resistance capabilities for the chloride-based Cr(III) coatings which is in agreement with the lower crystal size and the less defective native oxide layer (using a borate buffer electrolyte).

Electrochemical sulfate production from sulfide-containing wastewaters and integration with electrochemical nitrogen recovery

Electrochemical methods can help manage sulfide in wastewater, which poses environmental and health concerns due to its toxicity, malodor, and corrosiveness. In addition, sulfur could be recovered as fertilizer and commodity chemicals from sulfide-containing wastewaters. Wastewater characteristics vary widely among wastewaters; however, it remains unclear how these characteristics affect electrochemical sulfate production. In this study, we evaluated how four characteristics of influent wastewaters (electrolyte pH, composition, sulfide concentration, and buffer strength) affect sulfide removal (sulfide removal rate, sulfide removal efficiency) and sulfate production metrics (sulfate production rate, sulfate production selectivity). We identified that electrolyte pH (3 × difference, i.e., 25.1 to 84.9 μM h−1 in average removal rate within the studied pH range) and sulfide concentration (16 × difference, i.e., 82.1 to 1347.2 μM h−1 in average removal rate) were the most influential factors for electrochemical sulfide removal. Sulfate production was most sensitive to buffer strength (6 × difference, i.e., 4.4 to 27.4 μM h−1 in average production rate) and insensitive to electrolyte composition. Together, these results provide recommendations for the design of wastewater treatment trains and the feasibility of applying electrochemical methods to varying sulfide-containing wastewaters. In addition, we investigated a simultaneous multi-nutrient (sulfur and nitrogen) process that leverages electrochemical stripping to further enhance the versatility and compatibility of electrochemical nutrient recovery.

A NiO-nanostructure-based electrochemical sensor functionalized with supramolecular structures for the ultra-sensitive detection of the endocrine disruptor bisphenol S in an aquatic environment.

Herein, NiO nanoparticles (NPs) functionalized with a para-hexanitrocalix[6]arene derivative (p-HNC6/NiO) were synthesized by using a facile method and applied as a selective electrochemical sensor for the determination of bisphenol S (BPS) in real samples. Moreover, the functional interactions, phase purities, surface morphologies and elemental compositions of the synthesized p-HNC6/NiO NPs were investigated via advanced analytical tools, such as Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Additionally, the synthesized p-HNC6/NiO NPs were cast on the surface of a bare glassy carbon electrode (GCE) via a drop casting method, which resulted in uniform deposition of p-HNC6/NiO/GCE over the surface of the GCE. Additionally, the developed p-HNC6/NiO/GCE sensor demonstrated an outstanding electrochemical response to BPS under optimized conditions, including a supporting electrolyte, a Briton-Robinson buffer electrolyte at pH 4, a scan rate of 110 mV s-1 and a potential window of between -0.2 and 1.0 V. The wide linear dynamic range was optimized to 0.8-70 μM to obtain a brilliant linear calibration curve for BPS. The limit of detection (LOD) and limit of quantification (LOQ) of the developed sensor were estimated to be 0.0059 and 0.019 μM, respectively, which are lower than those of reported sensors for BPS. The feasibility of the developed method was successfully assessed by analyzing the content of BPS in waste water samples, and good recoveries were achieved.

Электрохимические сенсоры на основе сеток из однослойных углеродных нанотрубок для вольтамперометрического определения аскорбиновой кислоты

Modern highly sensitive and selective sensors are able to determine biologically active substances, which makes this direction one of the most popular areas of analytical chemistry. The study featured the electrochemical properties of new fiber materials based on single-wall carbon nanotubes with prospects of using them in the voltammetry of ascorbic acid. 
 The authors developed a new technology to synthesize films from disordered single-wall carbon nanotubes by chemical vapor deposition. Fibers were produced from a solvent by wet-pulling of single-wall carbon nanotubes networks. Thin films of randomly oriented single-wall carbon nanotube bundles were deposited downstream of a floating aerosol CVD reactor, which included a high temperature furnace with a quartz tube. The synthesis of the single-wall carbon nanotube samples was performed at 825°C. Ethanol served as carbon source while ferrocene was used as catalyst precursor. The single-wall carbon nanotubes were collected on a nitrocellulose filter in the form of films with transmittances of 10% in the middle of the visible wavelength (550 nm). The method was optimized to involve air annealing at 300–320°C and a treatment with strong inorganic acids, i.e., HCl, HNO3 + H2SO4. The voltammetric curves recording included background electrolyte, scan rate, and preconditioning. These parameters were selected experimentally to obtain the maximal sensor response to ascorbic acid content. The anodic peak of ascorbic acid in the phosphate buffer electrolyte (pH 6.86) was observed at a potential of +0.2 V. The current and peak area of ascorbic acid oxidation depended neither on the time nor on the conditioning potential of the sensor. The linear dependences of these parameters on the concentration of ascorbic acid stayed within 50–500 μmol/L (8.8–90 mg/L) at a scan rate of 0.1 mV/s. The single-wall carbon nanotube microsensor had a length of 0.5 cm and an average width of 400 μm. Its sensitivity was two times as high as that of a disk glassy carbon electrode with a diameter of 5 mm. 
 The experimental sensors proved effective in determining ascorbic acid in food products, pharmaceuticals, and biological fluids.

(Invited) High Productivity Electrocatalytic Water Splitting Using Diverse Water Sources

Water electrolysis is a commercially established process. However, significant cost reductions are desired for the large scale applications anticipated in the future. Electrolysis is typically performed under extreme pH conditions due to the high reaction rate of the electrocatalyst and low solution resistance. On the other hand, energy conversion using electricity generated from renewable energy requires a water splitting electrocatalyst that is versatile, safe, and durable. Recent water splitting research has focused on the development of catalyst materials and elucidation of their efficient action under non-extreme pH conditions. However, there are several problems associated with water splitting in the mild pH range. The first problem is the lack of protons and hydroxide ions at mild pH, which leads to large concentration overpotentials. To solve these problems, concentrated buffered electrolytes are used to suppress local pH shifts and to compensate for the steady-state proton or hydroxyide ion. To maximize the buffering effect, concentrated buffer electrolyte solutions should be applied near the pKa values where protonated and deprotonated species coexist. A second problem at near-neutral pH levels is the inherently lower conductivity of the electrolyte solution compared to strongly acidic or strongly alkaline solutions. The ohmic potential (iR) drop between the anode and cathode is critical to the cell voltage of water splitting devices, especially at the high current densities that are industrially important. The conductivity at pH 7.0 of phosphate buffer can be maximized by varying the molar ratio and selecting the appropriate counter cation (K among Li, Na, K, and Cs). The choice of conditions essentially reduces viscosity and maximizes solubility, which strongly affects the conductivity of the solution. The conductivity of saturated K phosphate reaches a maximum of ~20 S m−1, but this value is still not as high as the alkaline one (~130 S m−1). Viscosity and solution resistance can be adjusted by mixing different electrolytes and fine-tuning the position of pKa within the target pH range. In water containing Mg2+ and Ca2+, precipitation of these ionic salts can be a problem. Keeping the pH between 8 and 10 prevents such precipitation. We are also attempting to intentionally use chloride ions, which have the highest concentration anion in seawater. In this way, solution resistance is further improved. Thus, it is emphasized that electrolyte engineering is an important technology for cost-effective water electrolysis by finding new reaction environments to efficiently electrolyze water under more moderate conditions.

Electrochemical CO2 Reduction to Formic Acid As Feedstock for Biotechnological Processes

Substituting fossil-based production methods with methods utilizing renewable resources is experiencing growing interest. Incorporating intermittent renewable electricity into such processes is highly desirable, especially for energy storage purposes. In this context, electrocatalytic conversion of renewable raw materials into platform chemicals is an important approach. Biogenic raw materials can be converted into platform chemicals through electrocatalysis, which can then be used in power-to-X-to-Y processes to generate a range of products. One notable example of this approach is the electrochemical conversion of CO2 into formic acid, which has numerous applications in the chemical, textile, agricultural, and pharmaceutical industries [1, 2]. Utilization of CO2-based formate as a microbial substrate is a fascinating research topic that expands the range of possible products. The work presented here focuses on optimizing a compatible interface between efficient electrochemical processs and biotechnology, by identifying key factors, including the choice of catalyst, electrolyte, electrochemical setup, and formate production rate. This study also involves testing of an electrochemical microreactor for the scalable production of formate from CO2. Our results show that formate concentrations of up to 3 mol L-1 can be achieved in a bio-compatible buffer electrolyte using an optimized electrochemical process at high current densities. Additionally, this research successfully demonstrates the biochemical utilization of electrochemically produced CO2-based formate in coupled electro-biochemical processes. The developed process is a sustainable and efficient method for producing value-added products from CO2 and renewable electric energy, contributing to bridging the gap between electrochemical and biological processes.

Enhancing Carbon Efficiency in Electrochemical CO2 Reduction at Silver Gas Diffusion Electrodes – The Effect of Acidic Electrolytes Explained via TFFA Modeling

Recently, there has been a growing focus on enhancing carbon efficiency in the field of electrochemical CO2 reduction, quantifying the proportion of CO2 converted electrochemically relative to the total amount consumed. The competition between homogeneous reactions forming carbonates and the electrochemical conversion of CO2 is causing lowered carbon efficiencies in typical buffer or alkaline electrolytes. Consequently, strategies aimed at shifting the equilibrium of these reactions have to be employed. In this work, the application of acidic electrolytes is presented as a promising pathway to overcome this limitation. Experimental investigations at silver gas diffusion electrodes (GDEs) in acidic 0.5 M K2SO4 electrolyte show an improvement of carbon efficiency by up to 20% compared to 1 M KHCO3 electrolyte, while the Faradaic efficiency at high current densities is unaffected. Nevertheless, degradation of silver GDEs occurs in acidic conditions, emphasizing the need for development of more stable catalysts. Furthermore, a spatially resolved mathematical model provides insights into the local reaction environment within the GDE. This highlights the importance of local alkalinity to control the rate of electrochemical CO2 reduction. While the formation of hydroxide ions by the electrochemical reactions creates an alkaline environment favoring CO2 reduction, the acidic bulk electrolyte hinders the formation of carbonates.

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.

General synthesis of metal selenides embedded in N-doped carbon nanofibers covered with in-situ grown carbon nanotubes as binder-free anodes for sodium-ion storage

Due to the high theoretical capacity, metal selenides are considered to be promising materials for energy storage. Unfortunately, their practical use is still hampered by their flat electronic conductivity, large volume change and poor ion transport kinetics. In this work, a general synthesis method is presented for the preparation of metal selenides embedded in N-doped carbon nanofibers with in-situ grown carbon nanotubes (CNTs) on the surface (MSe2@NCF/CNTs, M=Co, Ni, Fe) as binder-free anodes for sodium-ion batteries. Metal precursors can be used as catalysts and as active materials after selenization treatment. The metal selenides are dispersed in the carbon nanofibers and CNTs, which effectively prevents agglomeration of the particles. The in-situ grown CNTs are strongly coupled to the surface of nanofibers, which improves the electrical conductivity, allows for efficient electrolyte infiltration and buffers the volume expansion during the charge/discharge processes. As a result, CoSe2@NCF/CNTs achieves extremely high reversible capacity, stable cycling stability (441.2 mAh g−1 after 1000 cycles at 200 mA g−1), and excellent rate properties (375.4 mAh g−1 at 2 A g−1) when used as binder-free anodes for sodium-ion batteries. The fast charge transport and Na+ diffusion rates, as well as a pseudocapacitance Na+ storage mechanism, are revealed by kinetic analysis. This synthetic approach is extendable to assembling CNTs in-situ on other substrates for advanced energy storage systems.

Construction of FeSe2 nanoparticles encapsulated in TiN/N-doped carbon nanofibers intertwined with in-situ grown CNTs for pseudocapacitive Na+ storage

Metal selenides are recognized as potential anodes for sodium-ion batteries because of their high theoretical capacity. However, they face the hurdles of low electronic conductivity and significant volume change. In this study, a composite material consisting of FeSe2 nanoparticles enclosed within TiN/N-doped carbon nanofibers intertwined with in-situ grown carbon nanotubes (FeSe2@TNCF/CNTs) is successfully prepared by electrospinning, carbonization, and selenization approach. The TiN/N-doped carbon nanofibers enhance electronic conductivity, active sites for sodium-ion storage, and structural stability. Moreover, carbon nanotubes (CNTs) that in-situ grown on the carbon nanofibers not only enhance conductivity but also facilitate electrolyte penetration and buffer volume expansion. Benefiting from the synergistic effects of FeSe2, TiN, N-doped carbon nanofibers and CNTs, the hybrid FeSe2@TNCF/CNTs anode demonstrates long-term cycling stability and ultrafast pseudocapacitive sodium storage capability, with a specific capacity of 388.5 mAh/g delivered at 0.2 A/g after 1000 cycles. This work could provide inspiration for further research into the design and manufacture of high-performance materials for use in energy storage systems.

Oxidized Copper and Molybdenum Species Exclusively Boosting Electrocatalytic Hydrogen Evolution in Non-Extreme pH Carbonate Buffer Electrolyte

Oxidized Copper and Molybdenum Species Exclusively Boosting Electrocatalytic Hydrogen Evolution in Non-Extreme pH Carbonate Buffer Electrolyte

Shear dispersion of multispecies electrolyte solutions in the channel domain

In multispecies electrolyte solutions, even in the absence of an external electric field, differences in ion diffusivities induce an electric potential and generate additional fluxes for each species. This electro-diffusion process is well-described by the advection Nernst–Planck equation. This study aims to analyse the long-time behaviour of the governing equation under electroneutrality and zero current conditions, and to investigate how the diffusion-induced electric potential and shear flow enhance the effective diffusion coefficients of each species in channel domains. The exact solutions of the effective equation with certain special parameters, as well as the asymptotic analyses for ions with large diffusivity discrepancies, are presented. Furthermore, there are several interesting properties of the effective equation. First, it is a generalization of the Taylor dispersion, with a nonlinear diffusion tensor replacing the scalar diffusion coefficient. Second, the effective equation exhibits a scaling relation, revealing that the system with a weak flow is equivalent to the system with a strong flow under scaled physical parameters. Third, in the case of injecting an electrolyte solution into a channel containing well-mixed buffer solutions or electrolyte solutions with the same ion species, if the concentration of the injected solution is lower than that of the pre-existing solution, then the effective equation simplifies to a multi-dimensional diffusion equation. However, when introducing the electrolyte solution into a channel filled with deionized water, the ion–electric interaction results in several phenomena not present in the advection–diffusion equation, including upstream migration of some species, spontaneous separation of ions, and non-monotonic dependence of the effective diffusivity on Péclet numbers. Finally, the dependence of effective diffusivity on concentration and ion diffusivity suggests a method to infer the concentration ratio of each component and ion diffusivity by measuring the effective diffusivity.