Concentration Of Electroactive Species Research Articles

Energy Storage Capacity Utilization in Redox Flow Batteries

Redox flow batteries (RFBs) are predicted to be a major contributing technology in the need for four-to-ten-hour energy storage. Other energy storage technologies, such as lithium-ion batteries, provide well-documented performance indicators such as efficiency and especially energy storage capacity utilization. While redox flow batteries are compared similarly based on cost and round-trip efficiency, they often neglect a comparison of their operational energy storage capacity utilization. The breakdown of operational losses that represent the current state of operation for RFBs are pivotal to further compare the development of these technologies to the standard of other electrochemical storage devices. Quantifying the current state-of-the-art in relation to the theoretical potential of RFBs allows us to assess the extent of development required to enhance their effectiveness in contributing to future energy storage goals.In this work, we set out to depict the operational energy storage density (W-h L-1) of various redox flow battery technologies based on consideration from experimental parameters and results from literature as key inputs. After reviewing five RFBs including the all-vanadium RFB, Hydrogen-Bromine RFB, All-Iron RFB, Zinc-Bromine RFB, and the Iron-Chromium RFB, results indicate that the VRFB is the most developed technology attaining around 60% of its theoretical energy storage density. While the Zinc-Bromine RFB has approximately the largest theoretical energy storage density (due to its high electroactive species concentration and standard potential difference), it is currently only able to operate at about a lowly 15% of it, dependent on its operational current density. We also assess the volumetric footprint for each RFB electrolyte system by considering a 6 MWh (6 MW, 1 hr) system. This assessment considers how large the electrolyte component of the RFB would be for operation. The Hydrogen-Bromine RFB would require electrolyte tanks to be more than 1600 m3 based on operational parameters, but if it were able to operate at 100% of its capability, the electrolyte tanks would shrink to be about 400 m3.

Use of Mixed Methanesulfonic Acid/Sulfuric Acid as Positive Supporting Electrolyte and the Study of Ion Crossover in Zn-Ce Redox Flow Battery

The development of a highly efficient and inexpensive energy storage technology is central to the operation of a sustainable smart grid and widespread utilization of intermittent renewable energy sources. An emerging and promising grid-scale technology for electrochemical energy storage is the redox flow battery (RFB). A unique and particularly valuable aspect of the design of RFBs is that their energy and power capacities can be scaled independently. Some of their other advantages include short response time, long life-cycles and no detrimental effects associated with being fully charged or discharged [1]. The Zn-Ce RFB, first developed by Plurion Inc (UK) in 2005 [2], has an open-circuit voltage as high as 2.4 V which is one of the highest among the various RBFs.To further improve the efficiency of Zn-Ce RBFs, the effect of different positive supporting electrolytes on the performance of a bench-scale Zn-Ce RFB has been studied. The effectiveness of mixed methanesulfonic/sulfuric acid, mixed methanesulfonic/nitric acid and pure methanesulfonic acid has been assessed and compared on the basis of the cyclic voltammetry response for the Ce(III)/Ce(IV) redox couple and galvanic charge-discharge of a bench-scale Zn-Ce RFB. We have observed the Ce(III)/Ce(IV) reaction to exhibit faster kinetics and the battery to attain higher coulombic efficiency and long-term performance over ~40 charge-discharge cycles in the mixed 2 mol/L MSA–0.5 mol/L H2SO4 electrolyte compared to that achieved in the commonly used 4 mol/L pure MSA electrolyte due to lower H+ crossover and the prevention of CeO2 precipitation. The coulombic efficiency fade rate in the mixed MSA-H2SO4 electrolyte is 0.55% per cycle over 40 charge-discharge cycles, while the fade rate is 1.26% in the case of 4 mol/L MSA. Furthermore, the positive electrode reaction is no longer the limiting half-cell reaction even at the end of long-term battery charge-discharge operation [3]. Our results show that a mixed MSA–H2SO4 acid electrolyte may be a better option for the positive side of a Zn-Ce RFB as a large-scale energy storage device.At the same time, undesired ion crossover is a practical issue that cannot be neglected since it decreases the concentrations of electroactive species in both negative and positive electrolytes and can cause battery self-discharge and thereby lower battery efficiency and longevity. The concentrations of electroactive species in both the positive and negative electrolytes after each charge-discharge cycle have been monitored as a function of cycle number. We have found that as much as 48.6% of the Zn(II) ions are transported through the Nafion 117 membrane from the negative to the positive electrolyte and 11.1% of Ce(III) ions are transported from the positive to the negative electrolyte by the end of 30 cycles (~55 hours of battery operation). A simple and efficient method to mitigate this problem is to add a certain amount of Zn(II) to the positive electrolyte and Ce(III) to the negative electrolyte at the outset of operation in order to reduce the concentration gradients between the two sides. From our cyclic voltammetry results, the addition of Zn(II) ions into the positive electrolyte has no deleterious effect on the Ce(III)/Ce(IV) redox couple and in fact appears to slightly reduce the separation between the reduction and oxidation peaks, suggesting better reversibility of the positive electrode reaction. In addition, experiments involving 30 cycles of battery charge-discharge have been conducted using Zn(II)-containing pure MSA positive electrolyte as well as Zn(II)-containing MSA-H2SO4 mixed acid electrolytes to analyze battery efficiency. Our results show that both the coulombic and voltage efficiencies are increased compared to that attained using the original electrolytes without Zn(II) initially added to the positive electrolytes. The energy efficiency increases by 19.7% in the case of the Zn(II)-containing pure MSA electrolyte and 6.1% for the Zn(II)-containing H2SO4-MSA mixed acid electrolyte (see Figure 1). Another benefit of adding Zn(II) ions to the MSA pure positive electrolyte is that it prevents the precipitation of CeO2 routinely observed to occur in MSA-only electrolytes after 10 – 15 charge-discharge cycles, which further enhances the energy density of the Zn-Ce RFB.References Nguyen, T. and R.F. Savinell, Flow Batteries. Electrochemical Society Interface, 2010. 19(3), 54.Clarke, R., B. Dougherty, S. Harrison, P. Millington, and S. Mohanta, US Patent 2004/0202925 A1. Cerium Batteries, 2004.Yu, H., M. Pritzker, and J. Gostick, Use of Mixed Methanesulfonic Acid/Sulfuric Acid as Positive Supporting Electrolyte in Zn-Ce Redox Flow Battery. J. Electrochemical Society, 2023. 170(2), 020536. Figure 1

(Invited) Solvation Control in Deep Eutectic Solvent Electrolytes for Stable Plating/Stripping of Zn in Battery Applications

Within the field of battery applications, deep eutectic solvents (DESs) have emerged as innovative electrolytes for rechargeable Zinc-ion batteries (ZIBs) . ZIBs traditionally employ neutral or weakly acidic aqueous electrolytes, which are susceptible to the standard anode drawback such as dendrite formation and passivation. DES-based electrolytes can facilitate the reversible plating and stripping of Zn, mitigating also dendrite growth . One notable benefit of DES solvents over their aqueous counterparts is that the concentration of electroactive species controls the shape evolution of electrodes during electroplating. For this reason, the coordination chemistry and metal complex formed between the Lewis acid of the metal and the Lewis base of the DES play a central role. Moreover, water can be added to the eutectic mixtures to increase the diffusion coefficient of the electroactive species and lower the electrolyte viscosity without destroying the eutectic nature if the concentration is kept under 40%.Regarding metal plating/stripping processes, DESs offer a notable advantage due to their high capacity to dissolve metal salts, oxides, and hydroxides, inhibiting the formation of insoluble oxides and hydroxides . Moreover, the unique coordination properties of Zn2+ in DESs lead to an atypical voltammetric behavior, characterized by a cathodic peak in the cathodic branch of the anodic-going scan. The mechanistic studies of Zn electrodeposition onto glassy carbon (GC) from DESs have concluded that the metal is formed by the reduction of an intermediate Zn-containing species. Finally, the reactivity of choline chloride and ethylene glycol can impact coordination in that these species can be dehydrogenated at negative potential forming RO¯, which can replace one or more chloride ligands in [ZnCl4]2− . The correlation between the chemistry of Zn2+ solutions and DESs is elucidated, and the peculiarities of Zn electrochemistry can be rationalized in terms of the DES–electrode interface structure. Although few studies on hydrated DESs have been conducted, the literature remains scant.Shi et al. conducted a study on DES composed of ZnCl2 and acetamide with different concentration of water. The authors employed various spectroscopic techniques, including FT-IR, Raman, and 17O NMR, to investigate the effect of water on the coordination geometry of Zn2+ and its consequent impact on Zn plating. Interestingly, the authors observed that the addition of small amounts of water, below the threshold for direct water-water interaction, resulted in significant alterations of the Zn2+ coordination geometry. In fact, based on the accepted view that Zn electrodeposition is a process that involves desolvation and charge-transfer steps, [ZnCl(acetamide)2(H2O)]+ was shown to undergo successive deamidation and dehydration, yielding [ZnCl(acetamide)]+ from which the metal center is finally reduced. Although [ZnCl(acetamide)3]+ is the most stable species, the energy barrier for dehydration is significantly lower than that for deamidation. Therefore, [ZnCl(acetamide)2(H2O)]+ with lower dissociation energy is the actual electroactive species . The solvation of Zn also affects the nucleation overpotential, as Zn2+ in hydrated DES exhibits faster desolvation kinetics, resulting in a lower nucleation overpotential. In addition, Zhao et al. investigated the properties of a “water-in-DES” electrolyte (~30 mol.% H2O) based on the urea/LiTFSI/Zn(TFSI)2 mixture and discovered that the preferential interaction between water and metal cations promotes interfacial charge transfer. Notwithstanding the important contribution of these papers, the mechanism of Zn electrodeposition in DES has not been conclusively assessed. To address this knowledge gap, our research aims to investigate Zn electrodeposition from two distinct, hydrated DESs: ChU and ChEG with approximately 30% H2O content. To gain control of the impact of the cathode material, we carried out our electrochemical tests by employing GC, Zn, Pt and Au electrodes. Furthermore, to evaluate the performance of these electrolytes under realistic device conditions, electrochemical cycling tests were conducted on symmetric CR2023 coin cells.In this study, we have demonstrated the beneficial effect of water addition on reducing the electrolyte viscosity, which consequently resulted in lower anodic and cathodic overpotentials and improved charge/discharge cyclability. Specifically, the electrolytes ChEG and ChU failed due to passivation and short circuits, respectively. The ChU electrolyte showed regular chronopotentiometric transients until cell failure, and this was supported by multiple cyclic voltammetry (CV) measurements, which showed reversible Zn plating/stripping in this system. Notably, our cell cycling tests were performed at higher current densities and exhibited longer lifetimes compared to previous literature reports. The unusual CV patterns observed with gold and glassy carbon (GC) electrodes, featuring cathodic peaks on both forward and backward scans, were elucidated using complementary electrochemical and in situ Raman spectroscopy measurements. Figure 1

Spectroelectrochemical Examination of the Ferro-Ferricyanide Redox Reaction: Impacts of Electrode Thickness and Applied Potential

Attenuated total reflection, surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) is a spectrochemical method that can detect changes in concentrations of electroactive species near an electrode surface as well as adsorbed intermediates. However, its application to heterogeneous redox reactions is still infrequent due to complex working electrode fabrication procedures. This study presents a simple procedure for fabricating ATR-SEIRAS platinum electrodes and demonstrates the effectiveness of the procedure with a successful examination of the Fe(CN)6 3−(aq)/Fe(CN)6 4−(aq) reaction. We found that electrode resistance measurements supported by atomic force microscopy were accurate indicators of ATR-SEIRAS response and ATR electrode thickness. Working electrodes with resistances of 600 Ω were approximately 2.4 ± 0.3 nm in thickness and enabled clear detection of the ferrocyanide peak at 2040 cm−1 with universal wafers. Decreasing electrode thickness to 1.0 ± 0.3 nm improved signal strength by 50%. Polarization tests revealed the formation of adsorbed intermediates at 2070 cm−1 with both positive and negative polarizations consistent with an inner sphere reaction mechanism. Applying large positive polarizations (>900 mV vs SHE) formed additional cyanoplatinate complexes, indicating electrode degradation at large applied potentials.

In English

The goal of this study is unraveling the specific features of non-stationary surface concentration distribution of electroactive and inactive species in a model electrochemical process with a preceding homogeneous first-order chemical reaction (CE mechanism). For this purpose, the exact analytical expressions for the non-stationary concentration distributions of electroactive and inactive species in the thin layer attached to a planar electrode are analyzed. The both cases of equal and unequal diffusion coefficients of species taking part in the preceding chemical reaction are considered. In the former case, the exact analytical expressions for the concentration distributions of electroactive and inactive species on a planar electrode are obtained. The peculiarities of the limiting cases of zero and infinite frequency of an applied alternating current for the both cases of equal and unequal diffusion coefficients of species are discussed. It is shown that there is a phase shift between AC and the surface concentration of species that changes under the action of this current. At low frequencies, the phase angle tends to p/2, whereas at high frequencies it decreases to p/4. The phase angle is the function of the two important measures, namely, the ratio of the Nernst diffusion layer thickness to the oscillation diffusion layer thickness, and the ratio of the Nernst diffusion layer thickness to the reaction layer one. It is shown that the phase angle depends on the diffusion coefficient of species in different manner for low and high values of the rate constants of the chemical reaction. At low values of these parameters, the phase angle shifts slightly to the range of high frequencies with an increase of diffusion coefficient. At the high rate constants, the phase angle decreases with frequency more slowly, and its dependence on diffusion coefficient is observed only at middle frequencies. The surface concentration of electroactive and inactive species decreases with an increase of frequency, but for the inactive species this process is faster than that for the electroactive species. The influence of the inactive species on the surface concentration of electroactive species decreases at high frequencies and at low rate constants of the preceding chemical reaction. The results obtained shed the light on complex dynamics at an electrode/electrolyte interface under non-stationary conditions.

Synthesis of Reduced Graphene Oxide by Ethyl Acetate and Its Utilization in Determining Hydroxychloroquine in Wastewater and Pharmaceutical Samples

AbstractAn easy and sensitive sensor made by carbon paste modified with reduced graphene oxide rGO‐CPE was developed for the detection of hydroxychloroquine (HCQ). Graphene oxide GO was reduced using ethyl acetate. Scanning electron microscope and X‐ray diffraction (XRD) were used for the characterization of rGO powder. The reduction of graphene oxide was confirmed by the disappearance of the identical peak of graphite in the XRD pattern. Herein, the modified electrode rGO‐CPE showed stronger electrochemical activity compared to bare CPE. The electrochemical behavior of HCQ was studied by cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The mechanism of the HCQ oxidation in the surface of rGO‐CPE was found to be controlled by an adsorption process with the transfer of 2 electrons. Furthermore, the standard heterogeneous rate constant (Ks) and the surface concentration of electroactive species (Γ) were calculated and the obtained values are 1.03×10−2 cm s−1 and 1.07×10−10 mol cm−2, respectively. Differential pulse voltammetry was used for HCQ quantification as a result a linear relationship between HCQ concentration and the oxidation peak current was obtained in the range from 1.0×10−7 to 8.0×10−6 mol L−1 and from 8.0×10−6 to 1.0×10−4 mol L−1, with a detection limit (LOD) of 6.29×10−8 mol L−1 and a sensitivity of 6.42 A L mol−1 cm−2. Moreover, the rGO‐CPE was successfully applied for the detection of HCQ in wastewater and pharmaceutical samples.

Enhanced dechlorination of an enzyme-catalyzed electrolysis system by ionic liquids: Electron transfer, enzyme activity and dichloromethane diffusion

Enzyme-catalyzed electrolysis system (EES) is a promising technique for the efficient dechlorination of pollutants. In this study, ionic liquids (ILs) was first introduced to enhance the dichloromethane dechlorination performance of an EES. An imidazole-based IL, 1-ethyl-3-methylimidazole tetrafluoroborate ([EMIM][BF4]), was chosen due to its excellent performance on dechlorination enhancement than other three ILs. The cyclic voltammograms with different scan rates shows that the presence of IL increased the apparent electron transfer rate constant (ks) from 0.008 to 0.013 s−1. The calculated surface electroactive species concentration (τc) also increased from 7.8 × 10−9 to 9.5 × 10−9 mol cm−2. Electrochemical impedance spectroscopy analysis illustrates that the IL mainly weakened the interfacial resistance between electrolyte and cathode to accelerate the electron communication in the EES. The introduction of IL facilitated the regeneration of reduced glutathione from oxidized glutathione, whereas inhibited the catalytic activity of dehalogenase via the disruption of secondary structure shown in circular dichroism spectra. The presence of IL was also facilitated the dichloromethane diffusion from electrolyte to cathode. The mass transfer rate constants of dichloromethane (km,d) increased by 6.9 times after the addition of IL. The optimum volume concentration, pH value, reaction temperature and applied voltage were 20%, 7, 35 °C and −0.8 V vs Ag/AgCl, respectively. The study is helpful to understand the promotion mechanism of IL on the dechlorination performance of EES when it is adopted as a treatment technique.

Facile indium recovery from waste liquid crystal displays: Chloride-facilitated indium electroreduction and stepwise Cu/MoO2 and indium electrodeposition

With a huge amount of waste liquid crystal displays (LCDs) generated annually, their proper recycling raises continuous concern to realize pollution control (heavy metal and liquid crystal) and resource recovery (indium). However, due to their multi-metal feature, traditional hydrometallurgy lacks of sufficient selectivity, which makes the recycling route lengthy, costly, and generate more waste. Electrodeposition acts as a promising technique for selective metal extraction from multi-metal system due to its high selectivity and electron as clean reagent. To fully develop its application in metal recovery, stepwise Cu/MoO2 and In electrodeposition from In-Cu-Mo-Fe waste LCD leachate is explored in depth. Electrochemical behavior analysis shows Cu and MoO2 can be first electrodeposited for their higher electroreduction potential. Cl- plays a key role in accelerating indium electroreduction kinetics, which largely shortens the extraction time without the sacrifice of current efficiency. This accelerating effect is attributed to the increased concentration of electroactive species or collision frequency. Under optimized condition, 99.41% of indium (> 99% purity) can be electrodeposited within 13 h with high current efficiency. This study provides a cleaner approach for waste LCDs recycling and gives implications for the potential application of electrochemical technique in e-waste recycling.

Carbon Electrocatalysts for High Performance Bromine and Iodine Redox Flow Battery Electrodes

Redox flow battery (RFB) electrodes act as bi-functional electrocatalysts, improving the kinetics of the redox reactions of interest without being consumed in the reaction itself. This property of flow batteries allows them to be fully discharged without damaging the electrode, and also allows for the power and energy densities of RFBs to be uncoupled and designed separately. The power density is largely dependent on the activity of the electrocatalyst, whereas the energy density is determined by the solubility of the electroactive species in the external electrolyte tank. Due to the advantages of RFBs, they have been heavily studied and implemented for applications in large-scale energy storage and are often used in tandem with renewable energy sources. Zinc-bromine hybrid flow batteries have arguably become the most promising and common flow battery technology behind that of the all-vanadium RFB, but are held back by low power densities that result from the slower Br2/Br- half-cell kinetics compared to that of the Zn2+/Zn half-cell. Analogous zinc-iodine based flow batteries have recently become the subject of much scientific interest as well, as the electrolyte is less toxic and corrosive to common battery materials compared to bromine, and a high concentration of electroactive species can be achieved due to the formation of the triiodide ion (I3 -) (up to ~12 M). In addition, some scientific research has recently shifted towards flow batteries constructed from heteropolyhalides (such as I2Br-or Br2Cl-) by combining different halogen-based electrolytes. Flow batteries constructed with Br2/Br-and I2/I-half-cells have been able to achieve some of the highest energy densities reported for aqueous flow batteries to date, but improvements still need to be made to the electrode materials.We investigated a variety of different carbon electrocatalysts for fabrication of low-cost and durable electrodes for the I2/I-, Br2/Br-, and heteropolyhalide redox couples in RFB technology. A variety of carbon blacks and phosphorus-doped graphitic carbons (PCx) were drop-casted onto a glassy carbon electrode substrate and their electrocatalytic performance was assessed via a variety of techniques including cyclic voltammetry, rotating disc electrode studies, and electrochemical impedance spectroscopy. Phosphorus-doped graphitic carbon was synthesized via the reaction of phosphorus chloride and benzene in different volumes ratios to obtain samples with variable amounts of phosphorus content (PC, PC3, PC5, PC8), characterized by X-ray diffraction analysis and 31P NMR.The electrocatalytic activity of various carbon blacks had a strong dependence on their surface area and porosity. The electrocatalytic activity of the phosphorus-doped graphitic carbons exhibit a bell curve relationship with the degree of phosphorus-doping, where PC5 and PC3 exhibited higher electrocatalytic behaviour towards the halogen/halide redox reactions than PC and PC8. These observations can be explained by 31PNMR indicating an increased amount of P-O bonds with increasing amounts of doping, with the oxygen containing functional group being catalytic. Excessive doping leads to faults in the lattice structure of the P-doped graphite. The surface area of the electrocatalyst material had the largest impact overall on the electrocatalytic performance of the electrode.

Nd-Mg-Ni alloy electrodes modified by reduced graphene oxide with improved electrochemical kinetics

To improve the electrochemical kinetics of Nd-Mg-Ni alloy electrodes, the alloy surface was modified with highly conductive reduced graphene oxide (rGO) via a chemical reduction process. Results indicated that rGO sheets uniformly coated on the alloy surface, yielding a three-dimensional network layer. The coated surfaces contained numerous hydrophilic functional groups, leading to better wettability of the alloy in aqueous alkaline media. This, in turn, increased the concentration of electro-active species at the interface between the electrode and the electrolyte, improving the electrochemical kinetics and the rate discharge of the electrodes. The high rate dischargeability at 1500 mA·g−1 increased from 53.2% to 83.9% after modification. In addition, the modification layer remained stable and introduced a dense metal oxide layer to the alloy surface after a long cycling process. Therefore, the protective layer prevented the discharge capacity from quickly decreasing and improved cycling stability.

Theory for Influence of the Metal Electrolyte Interface on Heterogeneous Electron Transfer Rate Constant: Fractional Electron Transferred Transition State Approach

We develop a theory for outer sphere heterogeneous electron transfer (ET) rate constant (k0) and exchange current density (i0). The model hypothesizes that the transition state is attained by alignment of Fermi and reactant energy levels through exchange of fractional electronic charge (δ≠). This approach accounts the contributions from: (i) work function and Fermi energy of metal, (ii) solvent polarity and size, (iii) electronic nature and size of electroactive species, and (iv) outer Helmholtz plane (OHP) potential-dependent composition. At the outset, we develop a model for the potential ϕ1 at the inner Helmholtz plane accounting the influence of electronic and inner dipolar layer screening on the metal. The equation for ϕ1 is used to obtain the potential ϕ2 at OHP through a modified Gouy–Chapman–Stern approach. The concentration of electroactive species at OHP (ciOHP) under the influence of the Frumkin effect is obtained by substituting ϕ2 in Kornyshev’s packing density restriction model. Our theory o...

Electrodeposition study of the Cu-Zn-Mo system in citrate/sulfate medium

Alloys and composites that contain molybdenum have been studied due to their excellent properties, such as corrosion resistance and catalytic activity. In this work, the parameters for Cu-Zn-Mo system electrodeposition were studied, such as deposition potentials and concentration of electroactive species. The deposition potentials were examined using cyclic voltammetry and anodic linear stripping voltammetry (ALSV), the deposit morphology was evaluated using scanning electron microscopy (SEM) and crystallographic characterization was carried out for X-ray diffraction (XRD). The voltammetry studies indicated co-deposition of the metals in potentials more negative than -1.2 V, and a potential deposition at -1.5 V was chosen. The coatings presented morphology compact with small agglomerated particles with cauliflower structures, and the content of molybdenum, copper, and zinc ranged from 5 to 8%, 30 to 40% and 20 to 28%, respectively.

Synthesis of Cobalt Selenide Thin Films and Their Electrocatalytic Properties in Water Splitting Process

Chalcogens of transition metals thin films may be a cheapest and well-efficient replacement for the noble metals in various chemical and electrochemical processes. This paper presents the results work on the electrochemical deposition of Co-Se coatings from aqueous acidic solutions. Co-Se coatings were obtained by the potentiostatic method on a copper substrate. The elemental composition was determined with the XRF method. Crystallographic structure was investigated according to XRD measurements. The influence of applied potential and concentration of electroactive species on the composition and the quality of the obtained coatings was determined. Additionally, the CV's and chronopotentiometric measurements were used to examine the catalytic activity of different Co-Se alloys in water splitting process.This work was supported by the Polish National Center of Science under grant 2016/21/B/ST8/00431

Investigation of Faradaic Contributions from Bipolar Plates to Areal Current Density in Vanadium Redox Flow Batteries

All-vanadium redox flow batteries (VRFBs) have been identified as a promising technology for bridging the gap to integrating renewables onto grids as well as improving grid-level power generation efficiency. VRFBs are prime candidates for this role on account of their modularity, scalability, and relatively high performance. [1] There are still, however, many design parameters that can be more highly optmized to improve and specialize the aspects of this technology. Capacity fade is a parasitic loss that occurs in all electrochemical enery storage systems and is one of the parameters that can be most improved in VRFBs. Fading capacity is due to a host of variables in the system, such as membrane permeability and electroactive species concentration.[2] Degradation of cell components (electrodes and membranes) can also contribute to capacity decay in the form of increased overpotentials throughout the systems operating range. The kinetics at the negative electrode (V(II) ↔ V(III)) are generally understood to be more sluggish than at the positive electrode [3] as well as being less stable (i.e. degrading more rapidly with respect to time). Several high performance materials have been identified for the negative electrode [4] [5], however extended cycling data on the order of years is uncommon in the literature. Mitigation of this degradation on this time scale is one such optimization that can improve voltage efficiency and mitigate capacity fade. In this work we present our most recent experimental work in which the Faradaic current that can be supported by the plates is quantified on different sets of VRFB hardware and isolated from the current on the combined plates with GFD 2.5 mm carbon felt electrodes. For this work symmetric cells were utilized, to isolate crossover effects, in conjunction with electrochemical impedance spectroscopy and polarization curves to quantify the contributions from the different processes at each overpotential. Likewise, experiments were also performed on a symmetric cell where the plates served as the electrodes to quantify the parallel contribution. The data were assessed via statistical tests in order to determine significance. The results of this study show that, graphitic bipolar plates can support 35-50% of the current density on the negative electrode at low overpotentials and 20 and 30% at higher overpotentials. The open circuit impedance data also show that the ASR of the cell with felt electrodes is increasing at a rate of around 25 mΩ cm2 min−1 at this stage in the electrode’s life. This degradation is nonlinear and asymptotes to a stable ASR, however, this implies that the percentage measured in this context is smaller than the steady state percentage. These combined results suggests a material oriented approach to improving the bipolar plate material in order to achieve a more stable negative electrode.

Effect of Scan Rate and pH on Determination Amoxilline Using Screen Printed Carbon Electrode Modified With Functionalized Graphene Oxide

Graphene oxide GO was functionalized with 4-amino, 3-substituted 1H, 1, 2, 4 Triazole 5(4H) thion (ASTT) to obtain GOT. GOT characterized by FT-IR, XRD.via modification of the working electrode of the SPCE with the prepared nanomaterial ( GOT) the effect of scan rate and pH on the determination of Amoxilline (AMOX) was studied using cyclic voltammetry. AMOX show various responses at pH ranging from 2 to 7 and also was observed sharp increase in the oxidation peaks in the pH 3. The formal potential (midpoint) for AMOX was highly pH-dependent. From the effect of scan rate, surface coverage concentration of electroactive species the values of the electron transfer coefficient and the electron transfer constant rate ket was obtained as 5.39×10-10 molcm-2, 0.5, and 2.45×10-3 cm.s-1respectively.

Cyclic voltammetry study of the electrochemical behavior of vanadyl sulfate in absence and presence of antibiotic

The cyclic voltammetry technique was used to study the electrochemical behavior of vanadyl sulfate in absence and presence of antibiotic (cefazolin) in 0.1 M KCl under different pH values at 300.15 K. The redox behavior of vanadyl sulfate has been studied by using glassy carbon electrode, Ag/AgCl as a reference electrode and Pt wire as a counter electrode under potential from +1500 mV to −1000 mV. One anodic peak and one cathodic peak are observed in cyclic voltammograms. Peak current ratio and peak potential separation (ΔE) was calculated, the higher values of them gave an indication about systems under study are quasi-reversible. The effect of pH, scan rate and concentration of electroactive species on the interaction between vanadyl sulfate and antibiotic were studied. Charge transfer coefficients (α), the heterogeneous electron transfer rate constants (ks) and the diffusion coefficients (D) involved in the redox reaction were evaluated.

Highly sensitive and selective electrochemical sensor for detection of vitamin B12 using an Au/PPy/FMNPs@TD-modified electrode

A new electrochemical sensor for sensitive and selective detection of vitamin B12 (VB12) was constructed by the electropolymerization of pyrrole (Py) in the presence of ferromagnetic nanoparticle-incorporated triazine dendrimer (FMNPs@TD) on a gold electrode (Au). The gold/polypyrrole/ferromagnetic nanoparticles/triazine dendrimer (Au/PPy/FMNPs@TD) electrode showed electrocatalytic activity for the reduction of VB12 in Britton-Robinson buffers. The performance and interaction of the Au/PPy/FMNPs@TD with VB12 were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetric (DPV), UV–vis spectroelectrochemistry, and density functional theory calculations. The resulting sensor exhibited excellent performance for determination of VB12 with a wide linear range (2.50 nM–0.5 μM), highly reproducible response (RSD of 2.3%), low percentage of interferences, and long-term stability. The limit of detection (LOD) and limit of quantitation (LOQ) values for the determination of VB12 were 0.91 and 3.00 nM, respectively. The electron transfer rate constants (ks), charge transfer coefficient (α), surface concentrations of electroactive species (Г), and disproportionation equilibrium constant (KD) for Au/PPy/FMNPs@TD-modified electrodes were calculated. Finally, the constructed sensor was applied to the determination of VB12 in food samples.

Role of electrochemical process parameters on the electrodeposition of silicon from 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid

The electrodeposition from Room Temperature Ionic Liquids (RTILs) has recently emerged as a low cost technique for the growth of group IV thin films or nanostructures giving some promising alternative to classical physical vapour or chemical vapour deposition techniques. As a relatively new field of research, only few studies exist describing the growth mechanism of electrodeposition from RTILs, especially for Si films. In the present work, Cyclic Voltammetry (CV), Electrochemical Quartz Crystal Microbalance (EQCM) and potentiostatic electrodeposition techniques have been used to study the role of the applied potential, the concentration of electroactive species, the temperature, and the use of organic additive on the electrodeposition of Si from 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid. The demonstrated investigation of the influence of these parameters on the purity and morphological features gives a better control over the growth of Si thin films and optimizes the technique to grow Si with structural properties suitable for specific applications.

In Ukrainian

A review of recent literature data on appearance of spontaneous oscillations in electrochemical systems of practical relevance is presented. They include electrocatalytic reactions of electrooxidation of hydrogen and small organic molecules on noble metals, oscillatory processes during preparation of different nanostructured materials such as nanotubes and multilayered structures, electrochemical systems with electrodissolution – passivation -electrodeposition of metals and alloys. Many of these systems belong to N-NDR or HN-NDR type of oscillator. They are investigated by different experimental techniques including electrochemical impedance spectroscopy, differential electrochemical mass spectroscopy, surface-enhanced infrared absorption spectroscopy, electrochemical quartz crystal microbalance/nanobalance, Auger electron analysis etc. It has been shown that electrochemical oscillations and more complex spatio-temporal surface structures in these systems are very sensitive to variation of experimental parameters such as applied potential, current density, solution concentration, structure and composition of electrode/electrolyte interface etc. The influence of these parameters on non-linear behavior of a model N-NDR electrochemical system was presented based on the theory of electrochemical impedance spectroscopy. An electrochemical reaction in the chosen model is related to the potential-dependent adsorption/desorption of electroactive particles on a planar, cylindrical or spherical interface and a preceding chemical reaction in the Nernst diffusion layer under potentiostatic conditions. The obtained results indicate that the range of Hopf instability giving rise to spontaneous oscillations in the system can be regulated by variation of electrode form and radius, thickness of the Nernst diffusion layer, diffusion coefficient of electroactive species, ohmic loses, bulk concentration of electroactive species. The role of mass transfer function in appearance of dynamic instabilities in the non-equilibrium system was determined.

Electrochemical Synthesis of Well-Ordered Macroporous Structures of Nickel – Ruthenium Alloys with Low Overpotential on Hydrogen Evolution Reaction

This work presents the results concerning electrochemical deposition of Ni-Ru alloys from aqueous acidic solutions. The Ni-Ru coatings were obtained by the potentiostatic electrodeposition on copper porous substrates and polystyrene matrix. The influence of applied potential and concentration of electroactive species on the composition and the quality of obtained coatings was determined. The elemental composition was determined with the XRF method. X-Ray analysis has been use to determine phase composition of obtained alloys. The surface morphology was investigated with the use of scanning electron microscopy. Electrochemical measurement as a linear and cyclic voltammetry was used to perform comparative examination of catalytic properties of the obtained 3-D structures in aqueous NaOH solutions. Acknowledgment The authors would like to thank Polish National Science Centre for the financial support provided by the grants: No UMO-2016/21/N/ST8/00222.