Chronopotentiometry Experiments Research Articles

On the selective transport of mixtures of organic and inorganic anions through anion-exchange membranes: A case study about the separation of nitrates and citric acid by electrodialysis

Electrodialysis is finding an increasing number of applications, recently also in the separation and purification of organic acids. This technology involves reducing the use of chemicals and the generation of wastes, as compared to conventionally used processes. Gaining insights about the competitive transport between organic and inorganic ions in ED systems is key to achieving efficient separation processes in the bioresource industry. In the present study, the competitive transport of organic (citrates) and inorganic anions (nitrates) through anion-exchange membranes is investigated, under varying pH conditions, ion concentrations, and applied currents, by means of chronopotentiometry and ED experiments. In the absence of nitrate ions and under acidic conditions (pH 2), the resistance of the membrane system is very high because citric acid is mainly present in its undissociated and uncharged form. In the case of sodium citrate (pH 8), the membrane resistance decreases, especially at high current densities, which promote dissociation reactions and the subsequent concentration increase in ionic species near the membrane. Such phenomenon is identified both in chronopotentiometric curves and in long-term ED experiments by a gradual drop in membrane voltage with time. Although being less concentrated than citrates, the selective removal of nitrates is the most effective choice for the separation of both types of species. The selectivity factor of nitrates over citrates reaches the highest values at low applied current densities (below the limiting current density), with stable permselectivity values higher than 20. Such conditions also lead to the least specific energy consumption per nitrates removed (<0.5 kW·hr·kgNO3--1). Therefore, ED can be used under such favorable operating conditions after a clarification step in order to remove inorganic ions from fermentation broths and increase the purity of organic acids. At higher current densities, the enhanced transport of citrate anions produces a significant drop in selectivity towards nitrates and increases the specific energy consumption.

Performance of Transition Metals in Imidazolium‐Assisted CO2 Reduction in Acetonitrile

AbstractThis study explores the electrochemical reduction of CO2 in dry acetonitrile containing 1,3‐dimethyl imidazolium cations, utilizing late‐transition metals (Au, Ag, Zn, Cu, and Ni). All metals exhibit remarkable selectivity, nearing 100 %, for CO formation. Particularly noteworthy is Au, which manifests the lowest (−2.37 V vs. Ag/Ag+) overpotential in chronopotentiometry experiments. We propose that, for metals with lower CO binding energies compared to Au (Ag and Zn electrodes) – calculated by DFT, the rate‐determining step is the adsorption of CO2. This distinction in CO2 adsorption is reinforced by the examination of partial charge transfer from negatively charged slabs to CO2 (−0.241 a.u with the Au electrode and +0.002 a.u with the Zn electrode). Conversely, the greater CO binding energy calculated for Cu and Ni likely diminishes electrocatalytic activity relative to the Au electrode. Our results unveil a volcano trend in catalyst activity, albeit with smaller performance disparities between the late‐transition metals and Au than previously observed in aqueous conditions, possibly due to the co‐catalytic influence of imidazolium cations. This study suggests that metals unsuitable for aqueous environments hold promise for cost‐effective and viable electrochemical conversion of CO2 to CO in non‐aqueous media containing imidazolium compounds.

A rational study of transduction mechanisms of different materials for all solid contact-ISEs

The new era of solid contact ion selective electrodes (SC-ISEs) miniaturized design has received an extensive amount of concern. Because it eliminated the requirement for ongoing internal solution composition optimization and created a two-phase system with stronger detection limitations. Herein, the determination of venlafaxine HCl is based on a comparison study between different ion- to electron transduction materials (such as; multiwalled carbon nanotubes (MWCNTs), polyaniline (PANi), and ferrocene) and illustrating their mechanisms in their applied sensors. Their different electrochemical features (such as bulk resistance (Rb**), double-layer capacitance (Cdl), geometric capacitance (Cg), and specific capacitance (Cp)) were evaluated and discussed by using the Electrochemical Impedance Spectroscopy (EIS), Chronopotentiometry (CP), and Cyclic Voltammetry (CV) experiments. The results indicated that each transducer's influence on the proposed sensor's electrochemical characteristics is determined by their unique chemical and physical properties. The electrochemical features vary for different solid contact materials used in transduction mechanisms. The results confirm that the MWCNT sensor revealed the best electrochemical behavior with the potentiometric response of a near-Nernestian slope of 56.1 ± 0.8 mV/decade with detection limits of 3.8 × 10−6 mol/L (r2 = 0.999) and a low potential drift (∆E/∆t) of 34.6 µV/s. Also, the selectivity study was performed in the presence of different interfering species either in single or complex matrices. This demonstrates excellent selectivity, stability, conductivity, and reliability as a VEN-TPB ion pair sensor for accurately measuring VEN in its various formulations. The proposed method was compared to HPLC reported technique and confirmed no significant difference between them. So, the proposed sensors fulfill their solutions' demand features for VEN appraisal.

Improving the electrochemical characteristics and performance of a neutral all-iron flow battery by using the iron reduction bacteria

At present, the all-iron redox flow batteries (RFBs) have greater application potential due to high accessibility of electrolytes compared to traditional RFBs. Meanwhile, although electroactive bacteria can accelerate the electrons transfer, their potential to improve the performance of RFBs has been overlooked. Previously, we had confirmed that ferrous-oxidizing bacteria (FeOB) could enhance the performance of an all-iron RFB, therefore we conducted several batch experiments and chronopotentiometry experiments by using the ferric-reducing bacteria (FeRB) or mixed culture (FeOB and FeRB) to demonstrate whether they have the same or stronger effects on Fe3+-DTPA/Na4[Fe(CN)6] RFB. The results showed that the experimental reactors could achieve higher charging current density and initial cathodic potential during constant voltage charging process. The electrochemical impedance spectroscopy data and cyclic voltammetry curves demonstrated that the polarization impedance increased slower and reduction peak potential of experimental groups also emerged a positive shift compared to CK. According to chronopotentiometry experiments results, the microbes could function at maximum 0.3 M, 12 mA/cm2, and also improved the charging specific capacity. Combined the SEM pictures and microbial composition analysis, the main functional electroactive FeRB were Alcaligenes, Corynebacterium and Bacillus, which indicated to have important potential in improving the performance of RFBs.

Is Ethanol Essential for the Lithium-Mediated Nitrogen Reduction Reaction?

Ammonia is used extensively as a fertilizer in agriculture and in the chemical industry. It also has the potential to store carbon-neutral fuel (hydrogen) in the future. To help meet the future demand for ammonia, the electrochemical nitrogen reduction reaction (NRR) has received much attention. It would serve as a decentralized method of synthesizing ammonia at low temperature and pressure. [1]To this day, the most promising NRR results have been shown via the lithium-mediated approach, in which lithium metal is electroplated in an organic electrolyte containing a lithium salt, saturated nitrogen gas, and a proton shuttle. The saturated nitrogen in the electrolyte reacts with electrodeposited lithium and protons are subsequently delivered by the shuttle. The local availabilities of protons and nitrogen are crucial for achieving a high selectivity towards ammonia rather than hydrogen evolution. The selectivity is heavily affected by the solid electrolyte interphase (SEI) which is formed between the electrodeposited lithium and bulk electrolyte. [2,3,4,5]This study investigates the role of ethanol as the proton shuttle in the lithium-mediated nitrogen reduction reaction (Li-NRR). In situ mass spectrometry and electrochemical quartz crystal microbalance are used to elucidate the importance of ethanol. Furthermore, particularly designed chronopotentiometry experiments are designed to provide additional information, allowing for a detailed discussion of ethanol’s multifaceted role in the Li-NRR. It is shown that ethanol is crucial for the formation of the SEI, but not necessary for the actual synthesis of ammonia. The SEI formation in the Li-NRR system is critically influenced by ethanol at the onset of lithium plating. Ethanol is not necessary to shuttle protons from the anode to the cathode. Furthermore, it is shown that lithium is an active species in the Li-NRR system even without electrochemistry. Finally, it is revealed that ethanol plays an important role in the context of anodic electrode potentials and electrolyte stability.References MacFarlane, D. R. et al. Adv. Mater. 32, 1904804 (2020)Du, H-L et al. Nature 609, 722 (2022)Lazaouski, N. et al. ACS Catal. 12, 5197-5208 (2022)Andersen, S. Z. et al. Energy Environ. Sci. 13, 4291-4300 (2020)Andersen, S. Z. et al. Nature 570, 504 (2019)

In-Situ Analysis of Chronopotentiometry Data to Predict Electrodeposition Rates

Often in MEMS or NEMS microfabrication R&D, many single layer “test” samples are created prior to committing more complex multiple layer “device” samples which require more time and effort to create. Ideally, much of the R&D can focus on less critical test samples and the experimental results can then be applied to more valuable device wafers. We investigated tin electroforming into patterned polymer molds creating Meissner-Effect Transition-Edge-Sensor (ME-TES) devices1 and found multiple variables changed between the test and device samples making it difficult to target a desired tin metal thickness. These variables were analyzed and distilled down to two: (I) area and (II) the measured voltage at constant current 30 seconds after plating started. In addition to the underlying analysis, a Graphical User Interface (GUI)2 was developed in R to quickly calculate and predict in-situ tin electroplating rates regardless of uncontrolled variables in the sample.ME-TES devices required a final tin plating feature height of 8-12 microns for 50-micron diameter discs coupled with patterned niobium electrical traces3. During chronopotentiometry experiments, two samples were plated for 1 minute and 18 minutes, respectively – both achieving the target height of 10 microns. This extreme variability in rate caused the height to undershoot or overshoot within just a few minutes of plating. Many variables were collected into a database and analyzed including wafer design layout, electrochemical methods, chemistry make-up, electrochemical setup, the use of a reference electrode, current density, voltage, mounting technique, height, device size, and surface roughness across the substrate. The resulting GUI resulted in fewer necessary test samples, reduced processing time, and improved accuracy in plating thickness.(1) Finnegan, P. Packaging & Solid-state Materials and Fabrication Processes. In Packaging & Solid-state Materials and Fabrication Processes, June 2023.(2) St. John, C. “R Shiny User Interface for Electrochemical Development.” In CoDA, Santa Fe NM, March 2023.(3) Arrington, C.L. Optimizing Tin Electroplating for MEMS Meissner-Effect Transition Edge Sensors. In 243rd ECS Meeting with SOFC-XVIII, Boston, MA, 2023.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.SAND2022-10287A

Optimizing Tin Electroplating for MEMS Meissner-Effect Transition-Edge Sensors

Electroforming metal features into patterned polymer molds targeting MEMS microfabrication allows for the enhancement of electrical, mechanical, magnetic, and thermal properties1. Uniform and repeatable electroforming processes are important to achieve the final desired metal geometry to optimize performance. MEMS fabrication processes typically rely on average plating rates based on historical depositions to determine future plating rates and offer the user options to vary electroplating time, among other options, to meet the desired device height(s). Process repeatability is often difficult to achieve in these scenarios and can be challenging in R&D applications with limited throughput. Inherent changes from one sample to the next can occur in many forms including a change in active area of lithographically patterned photoresist molds, resistance of substrates/seed layers below electroplated layers, geometry of the layout, chemistry make-up, electroplating setup, and fast deposition rates can all affect plating rates from sample to sample. Some changes can be controlled through careful inspection and tracking, then accounted for. However, some changes cannot be observed, and deposition rates can change from sample to sample leading to ever-changing plating rates.These challenges were encountered during electroplating of tin disks coupled with planar superconducting coils of niobium targeting the microfabrication of Meissner-Effect Transition-Edge Sensor devices (ME-TES)2. We investigated two and three electrode setups using a modified Dow Chemical Solderon make-up chemistry targeting pure tin depositions as opposed to tin and silver alloy depositions. Those changes were coupled with chronopotentiometry, chronoamperometry, and pulse plating experiments to optimize tin electrodeposition. Once found, the optimum tin deposition process was built into a graphical user interface (GUI)3 that predicts electroplating rates and was then successfully applied to microfabricate ME-TES’s. This process methodology could benefit other metal MEMS-based electrodeposition processes such as nickel, copper, gold, magnetic alloys, etc. to optimize electroplating.(1) Buchheit, T. E.; Christenson, T. R.; Schmale, D. T.; Lavan, D. A. Understanding and tailoring the mechanical properties of LIGA fabricated materials. Materials Science of Microelectromechanical Systems (Mems) Devices 1999, 546, 121-126. DOI: Doi 10.1557/Proc-546-121.(2) Finnegan, P. Packaging & Solid-state Materials and Fabrication Processes. In Packaging & Solid-state Materials and Fabrication Processes, June 2023.(3) St. John, C. In-Situ Analysis of Chronopotentiometry Data to Predict Electrodeposition Rates. In 243rd ECS Meeting with SOFC-XVIII, Boston, MA, 2023.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525 SAND2022-10288A

A Bipolar Separator for Autonomous Suppression of Dendrite Penetration in Zinc Metal Batteries

Zinc metal anodes are attracting much attention to enable more economical and sustainable energy storage devices. However, like other metal anodes, dendritic growths and penetrations of porous separators are still challenging to eliminate. Introducing negative surface charges on the pore walls of separators have been exploited to enforce a uniform incoming Zn-ion flux toward more uniform electrodeposition, but penetrations induced by localized high current densities still remain in available systems. In this work, we report, for the first time, a bipolar separator that exploits the distinct electroosmotic effects of the negative and the positive surface charges. The surface charge effects on Zn dendrite growths were first verified in transparent capillary cells via operando video microscopy. By stacking the positively charged separator over the negatively charged separator as our proof-of-concept, the system offers preemptively a uniform Zn-ion flux through the negative layer yet starve-stops local metal growths that already penetrated the negative layer autonomously. Chronopotentiometry experiments with the symmetric cells reveal extended short-circuit time compared to control cells. Galvanostatic cycle-life experiments of full cells with the bipolar separator showed excellent cycle life of 5,000 cycles at the rate of 10 C, without signs of metal penetration.

Evaluation by Means of Electrochemical Impedance Spectroscopy of the Transport of Phosphate Ions through a Heterogeneous Anion-Exchange Membrane at Different pH and Electrolyte Concentration

Electrodialysis is an innovative technique to reclaim phosphates from municipal wastewater. However, chemical reactions accompany the transport of these ions through ion-exchange membranes. The present study investigates the dependence of these phenomena on the initial pH and concentration of the phosphate-containing solution using a heterogeneous anion-exchange membrane. Linear sweep voltammetry, electrochemical impedance spectroscopy, and chronopotentiometry experiments were conducted for different phosphate-containing systems. For the most diluted solution, two limiting current densities (ilim) have been observed for pH 5 and 7.2, while only one ilim for pH 10, and correlated with the appearance of Gerischer arcs in EIS spectra. For pH 7.2, sub-arcs of Gerischer impedance were separated by a loop, indicating the involvement of the membrane functional groups. Increasing the phosphate concentration changed the system’s characteristics, reporting a single ilim. In the EIS spectra, the absence of Gerischer elements determined the attenuation of chemical reactions, followed by the development of a diffusion boundary layer, as indicated by the finite-length Warburg arcs. Chronopotentiometry clarified the mass transport mechanism responsible for distorting the diffusion boundary layer thickness at lower concentrations. The obtained results are expected to contribute to the phosphates recovery using electrodialysis in the most varied conditions of pH and concentration available in the environment.

Lithium Dependent Electrochemistry of p‐Type Nanocrystalline CuCrO2 Films

AbstractCuCrO2 nanocrystals were synthesized and fabricated into mesoporous thin films to study their electrochemical properties, where a strong [Li+] dependence was observed. An anodic shift in the Cu2+/+ redox potential was observed with increased [Li+] in the electrolyte, in addition to the growth of a new redox feature at E1/2=−0.43 V vs Fc+/0. This new feature was attributed to Cu2+/+ redox chemistry accompanied by Li+ occupation in copper vacancy surface defects. The equilibrium constant and maximum charge for Li+ occupation were determined to be K=0.057 M−1 and 15.5 mC, respectively. The maximum charge was close to the expected value of 11 mC based on the measured concentration of copper vacancies. The pronounced Li+ dependent electrochemistry suggests that CuCrO2 behaves similarly to cathodes in Li‐ion batteries. Thus, chronopotentiometry experiments revealed a 7.8 mA h g−1 charge capacity at cycle 2 and increasing cycling efficiency from 83 to 91 % over 10 cycles. However, a pronounced decrease in charge capacity was observed with increased cycles, attributed to a loss in lithium‐coupled electrochemistry. These studies add to our understanding of surface defects in p‐type oxides and their effect on hole recombination in solar cell devices.

Divergent C-H Amidations and Imidations by Tuning Electrochemical Reaction Potentials.

Electrochemical C-H functionalizations are attractive transformations, as they are capable of avoiding the use of transition metals, pre-oxidized precursors, or suprastoichiometric amounts of terminal oxidants. Herein an electrochemically tunable method was developed that enabled the divergent formation of cyclic amines or imines by applying different reaction potentials. Detailed cyclic voltammetry analyses, coupled with chronopotentiometry experiments, were carried out to provide insight into the mechanism, while atom economy was assessed through a paired electrolysis. Selective C-H amidations and imidations were achieved to afford five- to seven-membered sulfonamide motifs that could be employed for late-stage modifications.

Cross-linked anion-exchange membrane with side-chain grafted multi-cationic spacer for electrodialysis: Imparting dual anti-fouling and anti-bacterial characteristics

Polyimide (SPI) was functionalized using dianhydride with a high electron density in the carbonyl carbon atoms, and on active-sites (2,4,6-tris(dimethylaminomethyl) phenol: TAP) multi-cationic groups were grafted. Further, we fabricated multi-cationic cross-linked anion-exchange membrane (AEM) with tuneable polymer design by varying number of carbon chain in cross-linker spacer. CrQSPI@3 AEM with C3 spacer, exhibited 2.85 meq/g ion-exchange capacity, 21.4% water uptake, 20.7% swelling ratio, 13.87 × 10–2 S/cm membrane conductivity, and assessed as optimized membrane for further experimental analysis. Architectural strategy including cross-linking, and side chain grafting of multi-cationic groups provides fine control over properties, stabilities, hydrophilic-hydrophobic characteristics, anti-fouling and anti-bacterial nature. Anti-fouling nature of CrQSPI@3 AEM were gaged by impedance spectroscopy, chronopotentiometry, and electrodialysis experiments, while anti-bacterial nature was studied against water borne Escherichia coli (E. coli). High electro-dialytic performance of CrQSPI@3 AEM (current efficiency: 97.4%, and energy consumption: 0.92 kW h/kg of NaCl removed) along with better stabilities, anti-fouling and anti-bacterial properties, revealed its suitability for water desalination and other diversified electrochemical applications. Described method provides facile membrane fabrication with superior performance to obtain deep in-sight understanding of structural features.

Intrinsic bipolar membrane characteristics dominate the effects of flow orientation and external pH-profile on the membrane voltage

The practical energy required for water dissociation reaction in bipolar membrane (BPM) is still substantially higher compared to the thermodynamic equivalent. This required energy is determined by the bipolar membrane voltage, consisting of (1) thermodynamic potential and (2) undesired voltage losses. Since the pH gradient over the BPM affects both voltage components, in this work, pH gradient is leveraged to decrease the BPM-voltage. We investigate the effect of four flow orientations: 1) co-flow, 2) counter-flow, 3) co-recirculation, and 4) counter-recirculation, on the pH gradient and BPM-voltage, using an analytical model and chronopotentiometry experiments. The analytical model predicts the experimentally obtained pH accurately and confirms the importance of the flow orientation in determining the longitudinal pH gradient profile over the BPM in the bulk solution. However, in contrast to the simulated results, our observations show the effect of flow orientations on the BPM-voltage to be insignificant under practical operating conditions. When the water dissociation reaction in the BPM is dominant, the internal local pH inside of the membrane determines its final voltage, shadowing the effect of the external pH-gradient in the bulk solution. Therefore, although changing the flow orientation affects the bulk pH, it does not influence the local pH at the BPM junction layer and hence the BPM-voltage. Instead, opportunities for reducing the membrane voltage are in the realm of improved catalysts and ion exchange layers of the BPM.

Understanding the Catalytic Site in RuOx-TiOx Electrodes for Chlorine Evolution Reaction

As late as in 2017, there were still at least one third of world population suffering from water sanitation problems. Electrochemical oxidation (EO) technology, which relies on anodic generation of reactive chlorine and oxygen species as oxidants and disinfectants, has been shown feasible for human wastewater onsite treatment and recycling. Pivotal to the EO system is anodic chlorine evolution reaction (CER). Traditionally, oxides of platinum group metals (PGMs) have shown excellent catalytic activity for CER, with RuO2 identified as the golden standard. However, fast acid dissolution and prohibitive price prevents its real application. On the other hand, RuOx-TiOx binary electrodes (denoted as RTO electrodes) have demonstrated both enhanced activity and stability compared to pure RuO2, and it has been used in chloro-alkali industry for centuries as one of the dimensionally stable anodes (DSA). Previous research has ascribed the exceptional activity of RTO electrodes to Ti-Ru polarizations pairs (denoted as RuOx \U0001d6ff +-TiOx \U0001d6ff -). Nevertheless, the actual catalytic site (RuOx \U0001d6ff + or TiOx \U0001d6ff -), as well as the specific mechanism, has remained elusive.In this work, ultrathin sandwich electrodes were fabricated by sequentially depositing nanometer-thick uniform crystalline TiO2 and RuO2 films onto HF-treated atomically flat Si wafers to study the active sites in RTO electrodes. The electrodes were characterized with scanning electron microscope (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), while the CER catalytic activity was probed by chronopotentiometry experiments in 5 M NaCl solution. The structure of the sandwich electrodes was varied to investigate the activity of both components, and layer thickness was varied to quantify the effective range of Ti-Ru polarizations. Density functional theory (DFT) computation was used to help understand the catalytic mechanism.In order to promote further application of EO systems in developing countries, electrodes at lower price are essential. Not only does this work shed light on the catalytic mechanism of RTO electrodes, it also provides important guidance for design of low-PGM or PGM-free electrodes towards high-efficiency CER catalysis and wastewater treatment.

Snowflake-like Cu2S as visible-light-carrier for boosting Pd electrocatalytic ethylene glycol oxidation under visible light irradiation

Photo-assisted electrocatalytic oxidation alcohol molecule holds promise for both sustainable energy generation and energy conversion in direct alcohol fuel cells (DAFCs). Herein, we demonstrate that snowflake-like Cu2S on which Pd nanoparticles are grown, which acts as an excellent catalyst for ethylene glycol oxidation reaction (EGOR) under visible light irradiation. The peak current density of Pd–Cu2S electrode reaches to 3254 mA mg−1Pd under visible light irradiation, which is 1.7 and 5.5 times than that of Pd–Cu2S electrode and commercial Pd/C electrode under dark condition. In the chronopotentiometry experiments, the sustained time of Pd–Cu2S electrode under visible light illumination is 2.9 and 5.0 times longer than that of Pd–Cu2S electrode and commercial Pd/C electrode in dark. These results indicate that Pd–Cu2S catalyst exhibits excellent catalytic activity and stability for EGOR under photoelectric cooperation. Meanwhile, the present work indicates that Cu2S snowflake as the traditional noble metal electrocatalyst carrier demonstrates promising prospects in efficient and stable solar fuel conversion and fuel cell reaction.

2D Bi2WO6/MoS2 as a new photo-activated carrier for boosting electrocatalytic methanol oxidation with visible light illumination

ABSTRACT In this paper, a new two-dimensional (2D)/2D composite of Bi2WO6/MoS2 was facile synthesized, and then was used as supporting material for depositing Pt nanoparticles. The as-synthesized Pt-Bi2WO6/MoS2 was extended into photo-assisted electrocatalytic oxidation of methanol, which is a model anode reaction for direct methanol fuel cell. Compare with traditional electrocatalytic process, Pt-Bi2WO6/MoS2 displays 1.5 times enhanced electrocatalytic performance on methanol oxidation with assistance of visible light irradiation and 2.2 times for commercial Pt/C. Besides, from the results of chronoamperometric and chronopotentiometry experiments, the stability of Pt-Bi2WO6/MoS2 electrode is clearly improved under visible light irradiation. The synergistic effects of photo- and electro-catalytic in the heterojunction of Pt-Bi2WO6/MoS2 in favor of the above enhancement. This research gives more insights in the fields of photo-assisted traditional electrocatalytic application by constructing of semiconductor heterojunction carrier.

Ultra Micro Neural Stimulation and Recording Electrodes

With recent interest in increasing selectivity and reducing foreign body reaction to neural implants by using small-scale indwelling electrode arrays, the necessity of using ultramicroelectrodes (UME) in the implant design is inevitable. UMEs have been widely used as sensors for detecting biological elements such as neurotransmitters and oxygen in living tissue. Thus, their behavior in vitro under similar experimental conditions has been well investigated by performing electrochemical experiments such as cyclic voltammetry and chronoamperometry. However, the behavior of UMEs under neural stimulation and recording conditions has not been well characterized. In this study we have investigated the behavior of UMEs in cyclic voltammetry, electrochemical impedance spectroscopy, chronopotentiometry, and chronoamperometry experiments in phosphate buffered saline (PBS) electrolyte. Comparisons are made between macro, micro, and ultra micro platinum electrode behavior in PBS with ionic reactive species, hydrogen and hydroxyl ions, in galvanostatic and potentiostatic experiments. As migration is also a charge transfer mechanisms besides diffusion in electrochemical cells with ionic reactive species, the effect of hemispherical diffusion on the total current flux in such conditions has been evaluated by means of finite element analysis. A transient two-dimensional axisymmetric finite element model is developed to solve the Poisson-Nernst-Planck equation (Equations (1-2)) using COMSOL Multiphysics software. It has been assumed that the ionic flux is due to migration and diffusion and there is no convection flux. where V is the electric potential, ε the permittivity of the electrolyte, e the electron charge, ci the ionic concentration of ion i, Ni the flux of ion i, Di the diffusion coefficient of ion I, R the Boltzmann constant, T the temperature, zi the balance of ion i, umi the mobility of ion I, F the Faraday constant. Butler-Volmer equation (Equation 3) was assigned to the electrode-electrolyte interface to represent the interfacial reactions. where iloc is the local charge transfer current density, i0 the exchange current density, cr is the concentration of reduced species, co the concentration of oxidized species, crb the bulk concentration of reduced species, cob bulk concentration of oxidized species, η the overpotential, ac the cathodic transfer coefficient. Gouy-Chapman-Stern model was used to simulate the electric double layer. Based on the Gouy-Chapman-Stern model the electric double layer is the capacitance of the Stern and Gouy-Chapman layers in series (Equations (4-5)). Where CH is the Stern layer capacitance, CGc the Gouy-Chapman layer capacitance, εr the relative permittivity of the electrolyte, ε0 the electric permittivity of free space,λD the Debye length, e the elementary charge, UT the thermal voltage, c0 the concentration of ions in the bulk. Cyclic voltammetry experiments were performed in PBS electrolyte purged with Argon gas with a scan rate of 50 mV/s. Charge storage capacity of a 10 mm diameter UME, 100 mm diameter microelectrode, and 1.6 mm diameter macroelectrode platinum electrodes (Bioanalytical Systems) in PBS electrolyte were compared. Upon 99% decrease in geometric surface area, the increase in cathodic and anodic charge storage capacities are 82% and 140% from microelectrode to UME, while these increases are only 16% and 11% from macro to microelectrode, respectively. Figure 1

Green synthesis of Fe3O4 nanoparticles using aqueous extracts of Pandanus odoratissimus leaves for efficient bifunctional electro-catalytic activity

Iron oxide (Fe3O4) nanoparticles (NPs) were prepared at room temperature by one-step synthesis via green chemistry using aqueous extracts of Pandanus odoratissimus leaves. Fe3O4 NPs show uniform particle size distribution with an average diameter of ~ 5.0 nm. BET surface area and average pore diameter of the nanoparticles were found to be ~ 150 m2/g and ~ 3.0 nm, respectively. FTIR, Raman, EDAX and XPS studies were also carried out to confirm the phase purity of the prepared materials. Electrochemical water splitting reactions have been carried out using Fe3O4 NPs as electrocatalysts in 0.1 M KOH electrolyte solution. Polarization studies confirm dual nature of Fe3O4 electro-catalysts in water electrolysis for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Potentiodynamic polarization curves reveal low Tafel values of 295 and 126 mV/dec (± 2) for OER and ORR, respectively. The overpotential for water oxidation reaction was found to be ~ 390 mV (± 5) at the current density of 1 mA/cm2 in 0.1 M KOH. Chronoamperometry and chronopotentiometry experiments were conducted for stability tests of the electrodes.

Monitoring the State-of-Charge in All-Iron Aqueous Redox Flow Batteries

Monitoring the state-of-charge (SOC) in redox flow batteries is indispensable as a diagnosis tool to detect changes in the electrolyte concentration that can deteriorate the battery performance. Existing methods, which measure electrical variables of the cell or are dependent on recalibration during battery operation, become time consuming for practical uses. Here we present a simple and absolute method for monitoring the SOC in iron aqueous redox flow batteries. The method is based on the determination of the Fe(II) concentration with photometry after forming the complex of Fe(II)-1,10-phenanthroline. It can be applied in both the negative and positive electrolytes, and it is independent of the pH, concentration, and temperature of the electrolytes. The SOC values are compared with the redox potential of the negative electrolyte during chronopotentiometry experiments using different cells in a ferro/ferricyanide (positive electrolyte) and Fe(III)/(II)-triethanolamine (negative electrolyte) system. The SOC values as a function of the redox potential measurements follow a Nernst equation, which demonstrates the validity of the method.

Endeavor toward competitive electrochlorination by comparing the performance of easily affordable carbon electrodes with platinum

ABSTRACTKinetics of chloride ion oxidation was studied on graphite, glassy carbon (GC), and platinum electrodes. The performance of the electrodes was monitored using the cumulative productivity and current efficiency of the cell as indicators. It was seen that the performance of the working electrode improved with repeated uses, the current efficiency increased from 22% in the third use to about 46% in the tenth use. The study also revealed that the role of diffusion to the total anodic current was insignificant and chloride ions were transported at the electrode surface only by conduction. The hypochlorite production in case of platinum was about 3.66 times than that of graphite and GC with the current efficiency of 75% in contrast to 46% found in graphite and GC. But platinum undergoes passivation to a significant extent unlike the graphite and GC electrodes. Chronopotentiometry experiments confirmed the passivation process in platinum electrodes, showed a steep rise in potential from 1.2 to 2 V while the electrode potential was uniformly maintained at 1.7 V in carbon electrodes. The highest io, exchange current density value was observed at 0.45 mA/cm2 in 0.5 M electrolyte, which is an indication of improved electrocatalytic activity with increased molar concentration. After continuous uses the corrosion rate studies revealed that platinum and GC electrodes were corrosion resistant whereas graphite underwent corrosion at the rate of 0.006 mm/h. The study dictated that carbon electrodes has great potential to be used as an alternatives to platinum electrodes, however, further investigations are required to assess its practical applicability in the public water supply system.