Potential Sweep Rate Research Articles

Anodic behaviour of indium doped zinc alloy TsAMSv4-1-2,5 in NaCl Electrolyte

Zinc-aluminium alloys find a wide application in different industries. Approximately half of the produced zinc is used as corrosion protection coatings for steel structures. Corrosion resistance is one of the essential properties of zinc alloys as well. Zinc alloys are highly resistant to atmospheric and marine corrosion, as well as basic and acidic solutions. They have low density and are easily workable by cutting. As is well-known, lead serves as the main concomitant metal for metallic zinc, and its concentration may reach 2.5 wt. % (for TsZ grade of zinc). This research is aimed at designing a new alloy on the basis of zinc alloy TsAM 4-1, which is obtained from a low zinc grade TsZ labelled as TsAMSv4-1-2,5. The alloys were analyzed following potentiostatic technique in a potentiodynamic mode at the potential sweep rate of 2 mV/s in NaCl electrolyte on the pulse potentiostat PI-50-1.1. The TsAMSv4-1-2,5 alloy was doped with 0.05–1.0 wt. % of metallic indium. It was found that as the chloride ion concentration in NaCl electrolyte rises, the free corrosion, pitting and repassivation potentials tend to shift in the negative region while the corrosion rate increases by 28%. It is shown that indium additions cause a 10% drop in the corrosion rate while the alloys’ electrochemical potentials tend to shift in the positive region. Due to increased corrosion resistance of the zinc alloy TsAMSv4-1-2,5 doped with indium, one can save 10% of metal and thus achieve a more cost-effective production of zinc alloy items.

Anodic Stripping Voltammetric Analysis of Trace Arsenic(III) on a Au-Stained Au Nanoparticles/Pyridine/Carboxylated Multiwalled Carbon Nanotubes/Glassy Carbon Electrode.

A Au-stained Au nanoparticle (Aus)/pyridine (Py)/carboxylated multiwalled carbon nanotubes (C-MWCNTs)/glassy carbon electrode (GCE) was prepared for the sensitive analysis of As(III) by cast-coating of C-MWCNTs on a GCE, electroreduction of 4-cyanopyridine (cPy) to Py, adsorption of gold nanoparticles (AuNPs), and gold staining. The Py/C-MWCNTs/GCE can provide abundant active surface sites for the stable loading of AuNPs and then the AuNPs-initiated Au staining in HAuCl4 + NH2OH solution, giving a large surface area of Au on the Aus/Py/C-MWCNTs/GCE for the linear sweep anodic stripping voltammetry (LSASV) analysis of As(III). At a high potential-sweep rate of 5 V s−1, sharp two-step oxidation peaks of As(0) to As(III) and As(III) to As(V) were obtained to realize the sensitive dual-signal detection of As(III). Under optimal conditions, the ASLSV peak currents for oxidation of As(0) to As(III) and of As(III) to As(V) are linear with a concentration of As(III) from 0.01 to 8 μM with a sensitivity of 0.741 mA μM−1 and a limit of detection (LOD) of 3.3 nM (0.25 ppb) (S/N = 3), and from 0.01 to 8.0 μM with a sensitivity of 0.175 mA μM−1 and an LOD of 16.7 nM (1.20 ppb) (S/N = 3), respectively. Determination of As(III) in real water samples yielded satisfactory results.

The versatile behavior of diamond electrodes — Electrochemical examination of the anti-psychotic drug olanzapine (OL) oxidation as a model organic aqueous solution

The electrochemical degradation of dilute aqueous solutions of olanzapine (OL), using boron-doped diamond (BDD) anodes as electrocatalysts, was investigated. The studies were carried out in a single-compartment electrochemical cell at three different current densities (10, 30, and 50 mA cm−2), 25 °C, and 50 mg L−1 of OL in 0.05 M Na2SO4 pH (2.0, 4.0 and 6.0) as supporting electrolyte. The OL concentration and feasible by-products of the oxidized solution were monitored during the oxidation process using UV spectrophotometry, chemical oxygen demand (COD), total organic carbon (TOC), and high-performance liquid chromatography-mass spectrometry (HPLC-MS) techniques. Through voltametric studies, it was revealed that OL oxidation involved a direct oxidation stage, characterized by a current peak at +0.8 V (vs Ag/AgCl3M) that behaved as a quasi-reversible process, and an irreversible oxidation stage as well as an indirect oxidation step at +1.65 V (vs Ag/AgCl3M) mediated by physiosorbed ●OH radicals on BDD surface, which were formed by the discharge of water. The dependence of the peak current (ip), as well as the peak potential (Ep), with the potential sweep rate ν (mV s−1), showed that the oxidation depended on the diffusion of OL towards the BDD surface. By using a chronoamperometric analysis, a value of 6.6 × 10−4 cm2 s−1 was estimated for the diffusion coefficient of OL in 0.05 M Na2SO4 pH 2.0, confirming the transport effects. The results of UV and HPLC showed that the OL removal rate increased as the applied current density increased, although the COD and TOC data showed that a better oxidation is achieved at 30 mA cm−2. The results of HPLC-MS were consistent with the removal processes, involving both direct and indirect OL oxidation steps with BDD electrode. In any case, the results clearly confirmed the OL removal from the aqueous solution, achieving 80% of mineralization at applied current densities greater than 30 mA cm−2.

Effect of calcium additives on the anodic behavior of the conductive aluminum alloy E-AlMgSi (Aldrey) in the medium of the NaCl electrolyte

When creating new materials designed to work in particularly harsh conditions, the task of giving them corrosion resistance arises, the practical solution of which is associated with the level of knowledge in the field of high-temperature oxidation of metals and alloys. When using conductive aluminum alloys for the manufacture of thin wire, for example, winding wire, etc., certain difficulties may arise due to their insufficient strength and a small number of kinks before failure. In recent years, aluminum alloys have been developed, which even in a soft state have strength characteristics that allow them to be used as a conductor material. One of the conductive aluminum alloys is the E-AlMgSi alloy (Aldrey), which refers to thermally strengthened alloys. It is characterized by high strength and good ductility. This alloy under appropriate heat treatment acquires high electrical conductivity. The wires made from it are used almost exclusively for overhead power lines.The results of the study of the anodic behavior of the aluminum conductor alloy E-AlMgSi (Aldrey) with calcium, in an electrolyte medium of 0.03; 0.3 and 3.0% NaCl are presented. Corrosion-electrochemical study of alloys was carried out by the potentiostatic method on the PI-5.0-1.1 potentiostat at a potential sweep rate of 2 mV/s. It is shown that alloying the aluminum alloy E-AlMgSi (Aldrey) with calcium increases its corrosion resistance by 20%. The potentials of corrosion, pitting and repassivation of alloys during doping with calcium are shifted to the positive range of values, and from the concentration of sodium chloride in the negative direction of the ordinate axis.

Electrochemical oxidation of Pt(111) beyond the place-exchange model

Oxide formation plays an important role in the degradation of Pt electrocatalysts. However, the exact oxide structure and reaction mechanism are not fully understood. Here, we used in situ surface X-ray diffraction experiments to resolve the oxide formation at a Pt(111) model electrode at potentials near the onset of the oxygen evolution reaction. Fast experiments are possible by using X-ray photons with a high kinetic energy in combination with a large 2D detector. By employing very low potential sweep rates we obtain a more ordered oxidized surface compared to literature data from potential step experiments. This demonstrates that the oxidation process is strongly governed by the reaction kinetics. The increased surface order enables us to disentangle two subsequent oxidation process; initially the place-exchange process, followed by the formation of a partially disordered oxide in which still 50% of the surface atoms reside on sites commensurate to the Pt(111) surface. The reduction experiments indicate that the place-exchange process is structurally reversible, whereas the disordered oxide causes the surface roughening observed during potential cycling. Despite the increased surface order, oxide superstructures are not observed. These results provide important insights in the oxidation and degradation process of Pt(111), which are valuable for the design of improved electrocatalysts and they rationalize operating procedures.

Electrochemical Tip-Enhanced Raman Spectroscopy for the In Situ Characterization of Functional Materials

The understanding of the mechanism of operation and failure of functional (nano)materials and surfaces is a prerequisite to the optimization of their performance and design. This can be address with nanoscale-sensitive techniques which can be implemented, in situ/operando under the operating conditions of such functional material. Tip-Enhanced Raman Spectroscopy (TERS) has already demonstrated its ability to characterize functional materials at the nanoscale, though its operation in liquid conditions and under polarization remains challenging.[1] After the first demonstration of liquid TERS in organic solvent in 2016 in our group [2], we could access electrochemical TERS (EC-TERS) mapping with 8-nm resolution in 2019.[3]Our most recent work focuses on the in situ investigation of the reactivity of electrochemically-active molecular architectures immobilized on electrode surfaces by EC-TERS. To this purpose we have developed a configurations enabling EC-TERS implementation in the Scanning Tunneling Microscopy mode (EC-STM-TERS). In this setup using a home-made bipotentiostat synchronized to the CCD detector, relatively high potential sweep rate[4] and broad potential ranges are accessible, enabling real-time assessments of electrochemical processes without compromising the plasmonic coupling at the tip-sample junction. A complex electrochemical mechanism, involving reaction intermediates and multiple reaction paths, could be resolved on electroactive architectures based on nitrobenzene derivatives. Further EC-TERS investigations on nitrobenzene derivatives assembled as mono- or multilayers on the electrode surface emphasized the influence of the structure of the molecular assemblies on their reactivity.In our latest developments, EC-TERS measurements implemented in the Atomic Force Microscopy mode (EC-AFM-TERS) are also accessible, therefore broadening the range of functional materials which can be studied in situ/operando.[1] T Touzalin, S Joiret, E Maisonhaute, IT Lucas “Capturing electrochemical transformations by tip-enhanced Raman spectroscopy”, Current Opinion in Electrochemistry 6 (2017) 46-52[2] T Touzalin, AL Dauphin, S Joiret, IT Lucas, E Maisonhaute “Tip enhanced Raman spectroscopy imaging of opaque samples in organic liquid”, Physical Chemistry Chemical Physics 18 (2016) 15510-15513[3] T Touzalin, S Joiret, IT Lucas, E Maisonhaute “Electrochemical tip-enhanced Raman spectroscopy imaging with 8 nm lateral resolution”, Electrochemistry Communications 108 (2019) 106557[4] M Mattei, G. Kang, G. Goubert, D.V. Chulhai, G.C. Schatz, L. Jensen and R.P. Van Duyne., “Tip-Enhanced Raman Voltammetry: Coverage Dependence and Quantitative Modeling” Nano Lett.(2017) 17, 590−596 Figure 1

Oxidation kinetics and behaviour of Pb – Zn alloy anodes

Lead and its alloys are widely used in hydroelectric metallurgy, in the production of chemical power sources, electroplating, as well as in electrochemical methods of corrosion protection. To increase the resistance and reduce the anodic potential of lead-based electrodes, various methods are used which allow to solve new problems in industrial electrolysis. Currently, the main task is the creation of new anode alloys, which will allow for the optimal selection of the anode for each specific case. In this regard, lead and its alloys in the foreseeable future will remain the main material in the electrolysis production. Taking into account the operation of lead alloys at high temperatures and corrosive environments, the kinetics of oxidation of alloys of the Pb – Zn system containing up to 0.5 wt% zinc was investigated by thermogravimetry. It has been found that the addive of zinc to lead increases its resistance to oxidation in the solid state. It is shown that the oxidation of alloys occurs according to a hyperbolic mechanism and has the order of 10–4 kg·m–2·s–1. The anodic behavior of the alloys in the NaCl electrolyte medium was studied by the potentiostatic method at a potential sweep rate of 2 mV/s. It was found that zinc as an alloying component does not significantly improve the corrosion resistance of lead. In this case, with an increase in the additive of zinc to lead, the main electrochemical potentials (corrosion, pitting formation, and repassivation) of the alloys will mix in the field of positive values. With an increase of the concentration of chloride ion in the NaCl electrolyte, the corrosion rate of alloys increases, while the values of electrochemical potentials decrease.

A New Approach for the Voltammetric Determination of Amoxicillin in the Dosage Form Using Azo Coupling Reaction with Sulphanilamide

AbstractThe novel method of amoxicillin (AM) determination has been developed using single‐sweep polarography. The proposed method is based on the obtaining of yellow coloured azo compound due to azo coupling reaction of previous diazotized sulphanilamide (SA) (in the medium of 0.6 M hydrochloric acid) with amoxicillin at pH=9.0 with the further reduction of the formed analytical form on a dropping mercury electrode. Voltammetric determination of amoxicillin is carried out due to the reduction peak of azo group of the obtained azo compound in the presence of 0.05 mol ⋅ L−1 Na2B4O7 as a background electrolyte at the potential Ecp2=−0.55 V and potential sweep rate of 2.5 V ⋅ s−1. The developed voltammetric method has two linear ranges of the determined concentrations (0.05–2.0) ⋅ 10−5 mol ⋅ L−1 and (0.2–1.0) ⋅ 10−4 mol ⋅ L−1 and the high sensitivity: LOD without the removing of unreacted sodium nitrite is 1.1 ⋅ 10−6 mol ⋅ L−1, and 7.2 ⋅ 10−7 mol ⋅ L−1, when NaNO2 excess is removed using urea. The developed voltammetric technique of AM determination has been approved during the analyses of tablets and oral suspension.

Introducing Electrochemically Active Oxygen Species to Boost the Pseudocapacitance of Carbon‐based Supercapacitor

AbstractLow energy density is the main bottleneck for carbon‐based supercapacitors, which can be addressed by introducing extra faradaic pseudocapacitance. Herein, a cyclic voltammetry oxidation method in 1 M H2SO4 electrolyte was employed for carbon electrode to produce electrochemically active oxygen functional groups that are in contact with the conductive substrates, which facilitates the implementation of the pseudocapacitance. Moreover, the influence of potential window and sweep rate on the components and performances of oxidized electrodes in the cyclic voltammetry oxidation process was systematically investigated. The results reveal that a broad potential window of −0.65∼2 V can enhance the oxygen content to 16.4 wt.% (vs. 7.6 wt.% within −0.65∼1.5 V). Additionally, a selective oxygen component dominated with redox active C−OH and C=O groups was achieved by a rapid potentiodynamic sweep at 20 mV s−1, simultaneously suppressing the ‐COOH groups with inferior conductivity. The oxidized AC electrodes could substantially improve the specific capacitance (534 vs. 150.3 F g−1 at 1 A g−1) without sacrifice of rate performance (retained 418 F g−1 at 20 A g−1), accompanying excellent cycling stability of 94 % of initial capacitance after 10000 cycles. Such finding would provide some reference for tailoring oxygen species to fabricate advanced carbon‐based supercapacitor electrodes.

Anodic behaviour of Zn0.5Al doped with molybdenum in acidic, neutral and alkaline media

The paper presents the results of a potentiodynamic study of the anodic behaviour of Zn0.5Al doped with molybdenum in the acidic (0.1 M, pH = 1; 0.01 M, pH = 2; 0.001 M, pH = 3), neutral (0.03, 0.3, 3%, pH = 7) and alkaline (0.001 M, pH = 10; 0.01 M, pH = 11; 0.1 M, pH = 12) media of HCl, NaCl and NaOH electrolytes. In the potentiodynamic mode with an electrode potential sweep rate of 2 mV/s, all Zn0.5Al-Mo samples containing from 0.01 to 1.0 wt% of molybdenum demonstrated a shift in the potentials of corrosion, pitting formation and repassivation. These potentials shift towards negative values in acidic and alkaline media, while shifting to positive values in a neutral medium. It was established that an increase in the concentration of electrolytes led to a shift of all the considered potentials towards negative values in all media - acidic, neutral and alkaline. This dependence is associated with the specific features of the process of anodic dissolution of alloys during the formation of an oxide film on their surface. The significance of the dependence of the stationary potential of free corrosion of alloys on time for establishing the passivity of surfaces in acidic, neutral and alkaline media was shown. It was determined that zinc alloys doped with molybdenum are resistant to pitting corrosion in all the investigated media. This resistivity is particularly high in acidic (0.001 M), neutral (0.03%) and alkaline (0.001 M) media of HCl, NaCl and NaOH electrolytes. The favourable effect of molybdenum on both the anodic behaviour of Zn0.5Al and the overall increase in the corrosion resistance of alloys was demonstrated. In comparison with undoped Zn0.5Al alloys, the corrosion rate of alloys doped with molybdenum (0.01-1.0 wt%) is 2-2.5 times lower. The proposed compositions of Zn0.5Al-Mo alloys can be used as noncorrosive coatings for steel products.

Features of the discharge of zinc in the background solution of sodium sulphate under stirring conditions

The production technology of hydrometallurgical zinc uses various surfactants to thicken pulps, stabilise the electrolysis process, and obtain high-quality cathode deposits. Numerous researches were conducted to study the cathodic and anodic processes in a wide range of the composition of aqueous solutions using various solid electrodes in the absence of intense stirring of the electrolyte and with a high contribution of the migration component of the discharge of metals. This approach to the study of the surfactants’ influence rarely provided a high degree of statistical reliability in observing the effect of differently charged surfactants on electrode processes, which is of great importance in the hydrometallurgical production of zinc. In this work, the task was to practically eliminate the contribution of the migration component due to the followingfactors: conducting electrolysis in a background solution of sodium sulphate, organising electrolyte stirring, performing calculations of current densities at the beginning of electrolysis, and establishing polarisation curves at an increased potential sweep rate from 20 to 100 mV/s. This approach provided a greater degree of statistical reliability in presenting the mechanism of the effect of additions of cationic and anionic surfactants during the stage of zinc discharge on a solid electrode, which was the purpose of the article.Electrolysis was conducted in the potential range from -1050 to -1250 mV relative to the silver chloride electrode (AgCl/Ag) in the presence of a background sodium sulphate solution (0.5 M of Na2SO4 solution) containing 0.005, 0.0125, and 0.025 M ZnSO4 with the introduction of high-molecular surfactants: cationic and anionic coagulants (flocculants) and foaming agents (lignosulphonate – LSTP).During the electrolysis in a background solution of sodium sulphate with stirring, it was found that the process of discharge of zinc ions on a solid electrode occurs in a mixed-kinetic mode. It was shown that positively charged additives, such as lignosulphonate and cationic coagulant (flocculant) Besfloc K6645, have a negative effect on the dynamics of zinc cation discharge, while negatively charged Besfloc K4034 has practically no effect. The approach proposed in this work allows evaluating the influence of additions of cationic and anionic surfactants on the stage of zinc discharge on a solid electrode, which was the practical and scientific value of this work

Capacitive Hysteresis Effects in Ionic Liquids: 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate on Polycrystalline Gold Electrode

Ionic liquids (ILs) add complexity to electrochemical interfaces that cannot be adequately treated with traditional double layer models. We present a series of carefully controlled capacitance measurements to optimize the collection of reproducible and uniform capacitance-potential datasets. We quantitatively evaluate analysis methods on the experimentally observed capacitance of l-ethyl-3-methylimidazolium trifluoromethauesulfonate [Emim][TFO] IL at the gold-IL interface. The major outcomes of our work are to identify how experimental data collection methods affect capacitive hysteresis, and to suggest a systematic approach to collect reproducible capacitance data for IL systems. We evaluate different potential scan directions, examine varying potential sweep rates, and capacitance collection methods. We find that faster scan rates can mitigate the capacitive hysteresis between the anodic and cathodic scans for a particular collection technique. However, faster scan rates also result in more variation between the collection techniques. We also find that decreasing the effective potential sweep rate reduces hysteresis between different collection techniques when other factors are held constant. It is crucial for researchers to consistently report the direction of the potential sweep and the effective rate of potential sweep. Our data suggest that using slower effective potential perturbation rates would reduce discrepancies in capacitance data collected from different laboratories under different experimental conditions.

Electrodeposition and Growth of Iron from an Ethylene Glycol Solution

The electrochemical reduction of iron (III) ions into zero-valent iron from a solution of ethylene glycol was accomplished. The kinetics and mechanism of the electroreduction process were investigated by cyclic and linear polarization techniques. The influence of temperature, potential sweep rate, and concentration of iron (III) ions on the electroreduction process was also studied. The observed values of effective activation energy revealed that the investigated electroreduction process is accompanied by mixed kinetics control. Moreover, the results of SEM and X-ray diffraction analysis confirmed the deposition of thin Fe films under the optimized conditions.

Voltammetric sensor based on the copper (II) amino acid complex for the determination of tryptophan enantiomers

A voltammetric sensor based on a composite of polyarylene phthalide and graphitized carbon black Carboblack C modified with chelate complexes of L-argenato-L-alaninate of copper (II) has been developed for the recognition and selective determination of tryptophan enantiomers. The conditions for modifying the sensor are optimized, the effective surface area (A = 4.38 ± 0.06 mm2) and the effective resistance (Ret = 1.29 ± 0.08 kΩ) are calculated. The optimal conditions for recording voltammograms of tryptophan enantiomers are selected: the range of operating potentials is 0.5-1.2 V, the potential sweep rate is 20 mV/s, the holding time of the electrode in the test solution is 5 s. The electrochemical and analytical characteristics of the sensor were studied when registering differential pulse voltammograms of tryptophan enantiomers. It is shown that the dependence of the analytical signal on the concentration is linear in the range from 1.25·10-6 to 1·10-3 M with detection limits of 0.90·10-6 M for L-Trp and 0.66·10-6 M for D-Trp. The developed sensor shows the greatest sensitivity to D-Trp. The sensor has been successfully tested to determine the content of L- and D-Trp in enantiomer solutions in the presence of excipients that are part of medicines and biologically active additives. The proposed sensor allows the determination of tryptophan enantiomers in human urine and blood plasma. To evaluate the analytical capabilities of the sensor, the "entered-found" method was used. When determining tryptophan enantiomers in model solutions, the relative standard deviation does not exceed 2.3 %, and the relative error is 1.7 %. When determining D- and L-Trp in biological fluids, the relative standard deviation ranges from 0.3-1.7 %, and the relative error ranges from 0.3-5.6 %. The research results show that there is no significant systematic error.

Mathematical modeling of nonstationary 1:1 electrolyte transfer and study of the space charge region in membrane systems taking into account electric convection and water dissociation/recombination reactions

The article formulates a mathematical model of non-stationary transfer of 1:1 electrolyte in potentiodynamic mode, taking into account electroconvection and non-catalytic reaction of dissociation/recombination of water molecules in membrane systems, which are considered the channel of desalting of the electrodialysis apparatus. Using this model, the main regularities of the space charge distribution are theoretically established, the influence of the input parameters is determined: initial concentration, potential sweep rate, etc. It is shown that the desalination channel consists of narrow quasi-equilibrium regions of space charge adjacent to ion-exchange membranes; an electric double layer appears in the central part, caused by the recombination reaction. Regions of electroneutrality are located between this double electric layer and the near-membrane space charge regions. This study will further be used to analyze the combined effect of the noncatalytic reaction of dissociation of water molecules and recombination and electroconvection on the current-voltage characteristic of the desalting channel.

Разработка вольтамперометрической методики количественного определения бендазола гидрохлорида

In connection with the wide field of application of bendazole hydrochloride in medicine and its use as a part of combined drugs, an assessment of the effectiveness of the novel dosage forms and the determination of pharmacokinetic parameters are required. For this purpose, it is necessary to obtain data on the concentration of the studied drug in biological fluids. The aim of this research is to develop a voltammetric method for the bendazole hydrochloride quantification. In the course of the study, the optimal electrolysis conditions were established: potential was –1.8 V, time 15 s, and potential sweep rate 50 mV/s. The opti-mum pH value for electrolysis of bendazole hydrochloride is 6–7. The proposed method is validated by tests: specificity and linearity, detection limit; the range of the procedure and its analytical precision were determined. Thus, the developed method can be used for the quantification of bendazole hydrochloride in pharmaceutical substances.

ВЛИЯНИЕ КАЛЬЦИЯ НА АНОДНОЕ ПОВЕДЕНИЕ АЛЮМИНИЕВОГО ПРОВОДНИКОВОГО СПЛАВА AlTi0.1 В СРЕДЕ ЭЛЕКТРОЛИТА NaCl

The article presents the results of an experimental study of the effect of calcium on the anodic behavior of the aluminum alloy AlTi0.1, in the medium of NaCl electrolyte. The study was carried out by the potentiostatic method in the potentiodynamic mode at the potential sweep rate of 2 mV / s. It is shown that the modification of the aluminum alloy AlTi0.1 with calcium promotes the displacement of the potentials of free corrosion, pitting formation, and repassivation to the positive range of values. The corrosion rate of the aluminum alloy AlTi0.1 when modified with 0.01-0.5 wt % calcium decreases by 10-17 %.

Linear sweep and cyclic voltammetry of porous mixed conducting oxygen electrode: Formal study of insertion, diffusion and chemical reaction model

The classical 1D continuum model of oxygen exchange in a porous mixed conductor (bulk path) is presented in terms of Linear Sweep Voltammetry (LSV) and Cyclic Voltammetry (CV). We show that, from a formal point of view, it corresponds to an insertion, diffusion and chemical reaction mechanism. Some general rules for LSV/CV curves are established. Using a dimensionless description, we evidence eight different limiting behaviors of the electrochemical model, which depend on four dimensionless parameters. For an almost full insertion level at equilibrium, these parameters can be reduced to only two, i.e. the dimensionless electrode thickness L and the dimensionless chemical rate constant λ. We show that the resulting zone diagram, plotted using the representation log L versus log λ, is useful to predict the possible sequences of model behaviors as a function of the potential sweep rate and the electrode thickness. This theoretical analysis is applied to a porous LSCF oxygen electrode under air at high temperature.

Nanoarchitectonics of Lotus Seed Derived Nanoporous Carbon Materials for Supercapacitor Applications.

Of the available environmentally friendly energy storage devices, supercapacitors are the most promising because of their high energy density, ultra-fast charging-discharging rate, outstanding cycle life, cost-effectiveness, and safety. In this work, nanoporous carbon materials were prepared by applying zinc chloride activation of lotus seed powder from 600 °C to 1000 °C and the electrochemical energy storage (supercapacitance) of the resulting materials in aqueous electrolyte (1M H2SO4) are reported. Lotus seed-derived activated carbon materials display hierarchically porous structures comprised of micropore and mesopore architectures, and exhibited excellent supercapacitance performances. The specific surface areas and pore volumes were found in the ranges 1103.0–1316.7 m2 g−1 and 0.741–0.887 cm3 g−1, respectively. The specific capacitance of the optimum sample was ca. 317.5 F g−1 at 5 mV s−1 and 272.9 F g−1 at 1 A g−1 accompanied by high capacitance retention of 70.49% at a high potential sweep rate of 500 mV s−1. The electrode also showed good rate capability of 52.1% upon increasing current density from 1 to 50 A g−1 with exceptional cyclic stability of 99.2% after 10,000 cycles demonstrating the excellent prospects for agricultural waste stuffs, such as lotus seed, in the production of the high performance porous carbon materials required for supercapacitor applications.

Peat-Derived Hard Carbons for High Capacity Sodium-Ion Batteries: Synthesis and Characterization

Hard carbons have emerged as one of the most promising candidates for high capacity anode materials in sodium-ion batteries (SIB). It has been demonstrated that the degree of graphitization, disorder, and porosity of obtained hard carbons have an enormous effect on capacity.1 Various biomass precursors (banana peels, peanut shells, leaves, etc.) have been used for obtaining hard carbons, which have shown promising results as SIB anodes.2–4 In this study, peat was used as the precursor for obtaining peat-derived hard carbon anode materials (PDCs). Peat has a distinctive advantage as a precursor for its ease of collection. It can be excavated in millions of tons, as opposed to collecting shells or peels of different fruit. Hard carbons were synthesized using three steps – pre-pyrolysis at 300-800 oC, base-acid treatment, and post pyrolysis at 1000-1500 oC (Fig. 1). Each step was deemed necessary to improve the capacity of obtained hard carbon material (Fig. 1a). The materials were labeled as follows: PDC – pre-pyrolysis temperature – post-pyrolysis temperature A (A appended if KOH-HCl treatment was used).5 The structure of hard carbon materials was investigated with XRD, SEM-EDX, TEM, Raman spectroscopy, and laser powder diffraction methods. The specific surface area was examined by gas sorption analysis (with N2 and Ar). XRF was used to determine the elemental composition of hard carbon materials before and after the KOH-HCl treatment. TGA was performed to evaluate the burn-off of peat’s organic content during pre-pyrolysis.Cycling performance of hard carbon electrodes was investigated using the galvanostatic charge-discharge method at current densities ranging from 25 to 2000 mA g-1 and cyclic voltammetry at a potential sweep rate of 0.1 mV s-1. NaClO4 in EC:DEC (1:1) and NaPF6 EC:PC (1:1) were used as electrolytes to compare two rather common electrolytes and their effect on capacity (Fig. 1b).The highest capacities were achieved for PDC-450-1400 A. The constant current measurements show very high capacities of 350 mAh g -1 with a plateau region (E < 0.2 V vs. Na/Na+) of 250 mAh g-1 at the current density of 25 mA g -1. At the current density of 50 mA g-1, a capacity of 328 mAh g-1 with a plateau region of 243 mAh g -1 was achieved. Long-term stability of PDC-450-1400 A was also demonstrated, after 130 charge-discharge cycles at the current density of 25 mA g-1, the capacity stabilized at 280 mAh g-1 with the initial capacity of 320 mAh g-1.Overall, the highest capacities were achieved with materials that had the lowest impurity contents and specific optimal physical properties – low surface areas of around 6 m2 g-1, broad 002 reflexes in XRD diffractograms, interlayer spacing of about 3.9 Å and optimal I D/I G values of approximately 1.50. These characteristics might indicate the existence of local graphitic domains and therefore explain the high capacities.5 Acknowledgments This work was supported by ‘Strengthening of sectoral R&D’ project LLTOM17351, by EU through the European Regional Development Fund project 2014-2020.3.01.15-0011 and Personal Research under Grant PRG676. References I. El Moctar et al., Functional Materials Letters, 11, 1830003 (2018).E. M. Lotfabad et al., ACS Nano, 8, 7115–7129 (2014).J. Ding et al., Energy Environ. Sci., 8, 941–955 (2015).H. Li et al., ACS Appl. Mater. Interfaces, 8, 2204–2210 (2016).A. Adamson et al., RSC Adv., 10, 20145–20154 (2020). Figure 1