Galvanostatic Chronopotentiometry Research Articles

TiO2 top layer improving the performance of sulfur/carbon composite cathode in Li-sulfur cells

Facile preparation of the TiO2 top layer on the sulfur/carbon cathode in a Li-sulfur battery is presented. The layer significantly improves the initial charge capacity of composite cathodes. To demonstrate the versatility of the TiO2 top layer, its effect is evaluated on the sulfur composite cathodes with three kinds of carbonaceous additives. The electrochemical performance of these sulfur composite cathodes in the Li-sulfur battery is studied by cyclic voltammetry, galvanostatic chronopotentiometry, and electrochemical impedance spectroscopy. The sulfur/composite cathode with TOB carbon provides the highest charge capacity of 816 mAh g−1 from cyclic voltammetry, however, due to its structural disorder, exhibits the most pronounced capacity fade during galvanostatic cycling at 0.1C rate. The graphene nanoplatelets/sulfur composite cathode provides a charging capacity of 739 mAh g−1 in cyclic voltammetry and excellent cycling stability over 100 cycles of galvanostatic charging/discharging. A TiO2 top layer on the cathode and a TiO2-modified separator increase substantially the initial charge capacities of sulfur composite cathodes with all three kinds of carbon. The voltammetric charge capacities are 1427 mAh g−1, 1349 mAh g−1, and 952 mAh g−1 for TOB carbon, graphene nanoplatelets, and Penta carbon, respectively. This represents the relative enhancement by 75%, 83%, and 44%, respectively, as referenced to the cells with titania-free materials. Galvanostatic chronopotentiometry confirms the beneficial effect of inorganic additive on the charge capacity of Penta carbon and graphene nanoplatelets, however, the long-term cycling stability of the composite electrode is determined exclusively by the carbonaceous additive.

Composite cathode for Li-sulfur system: Effect of inorganic additives on electrochemical performance

The influence of five different inorganic additives with different composition and morphology, viz. nanofibrous rutile/TiOxNy, Li4Ti5O12 (LTS) from Altair, TiO2-P90 from Evonik, TiOxNy-anatase and nano-TiO2 on the electrochemical performance of the activated carbon/sulfur composite cathode is evaluated by cyclic voltammetry at the scan rate of 0.1 mV s-1 and by galvanostatic chronopotentiometry at the 0.1 C rate. The composites are prepared by facile mechanical mixing of activated carbon with the inorganic additive and subsequent melting-diffusion with sulfur. The addition of nano-TiO2 from titanium isopropoxide, TiOxNy-anatase, rutile/TiOxNy, and LTS Altair to the carbon/sulfur composite cathode increased the charge capacity of the corresponding Li-sulfur cell. The negative effect of the P90 additive can be attributed to the blocking of its surface by Al2O3 and SiO2, hindering the adsorption of polysulfides. TiOxNy-anatase additive exhibits the highest capacity improvement due to its surface-enhanced redox chemistry of conductive and sulphiphilic surface resulting in a 7 % increase of the voltammetric charge capacity. In addition, this additive has a beneficial effect on the cycling stability of the sulfur composite cathode during galvanostatic cycling.

Supercapacitors for storing energy from coffee bean waste

Activated carbon (AC) was made from coffee bean waste, which was prepared by chemical activation, using potassium hydroxide (KOH) at 2 M as activating agent, with impregnation times of 24 and 48 h, temperatures carbonization of 600 and 700 ° C, once the activated carbon samples were obtained, they were doped with nickel oxide (NiO), in order to modify the electrical properties of CA, later they were characterized (physical adsorption of N2, FT-IR, XRD). The CA / NiO composites were prepared by the chemical method and electrodes were compacted into forms of self-consistent tablets, which were placed in a two-electrode cell using sulfuric acid (H2SO4) as electrolyte at 2 M. The electrochemical part was evaluated by means of Cyclic voltammetry and galvanostatic chronopotentiometry, obtaining the electrical behavior of the electrodes for their application in supercapacitors (SCS). Finally, the specific capacitance of the SCS was determined from CA / NiO, as a result it was obtained that the CA / NiO-48-700 ° C-KOH samples showed a maximum capacitance of: 405.405 F / g respectively. This proves that nickel oxide improved the properties of AC for use as electrodes in supercapacitors.

The TiO2-Modified Separator Improving the Electrochemical Performance of Lithium-Sulfur Battery

Electrochemical performance of activated carbon/sulfur composite cathode in the Li-S cell with standard and TiO2-modified separator is evaluated by cyclic voltammetry and galvanostatic chronopotentiometry. The modification of the separator by TiO2 impregnation has beneficial effect on the charge capacity of the activated carbon/sulfur cathode in the Li-S cell. The specific capacity of the cathode in the cell with TiO2-modified separator is 632 mAh g-1 (calculated from cyclic voltammetry) and 673 mAh g-1 (determined from galvanostatic chronopotentiometry). Facile impregnation of the separator with nanocrystalline TiO2 results in the 10-20 % stable increase of the charge capacity of corresponding activated carbon/sulfur cathode as compared to its electrochemical performance in the system with non-modified separator.

Solvothermal synthesis of Bi2S3 nanoparticles for active photocatalytic and energy storage device applications

High edge energy storage with large life-span stable materials have become the most significant and major requirement in near future. Bismuth sulfide (Bi2S3) nanoparticles (NPs) was effectively synthesized by utilizing bismuth diethyldithiocarbamate (Bi[DTC]3) complex as single-source antecedent. The synthesized Bi2S3 NPs were affirmed by structural, morphological and thermal analysis with various analytical studies. The electrochemical performance of Bi2S3 NPs reveals that, exhibit redox behavior from cyclic voltammetry analysis, the charge–discharge analysis was examined by the galvanostatic chronopotentiometry. Bi2S3 NPs exhibit excellent supercapacitor behavior with value of the specific capacitance 470 Fg−1 at current density 0.5 Ag−1 and the retentivity of 79% after 1000 cycles. The Bi2S3 NPs were further utilized as photocatalytic discoloration of Congo Red (CR) dye in aqueous medium under UV light irradiation. Which shows, excellent catalytic behaviour, up to 98% of CR dye degrade within 150 min and it is exhibit good catalytic stability and reusability.

Nanocrystalline TiO2/Carbon/Sulfur Composite Cathodes for Lithium-Sulfur Battery.

This paper evaluates the influence of the morphology, surface area, and surface modification of carbonaceous additives on the performance of the corresponding cathode in a lithium–sulfur battery. The structure of sulfur composite cathodes with mesoporous carbon, activated carbon, and electrochemical carbon is studied by X-ray diffraction, nitrogen adsorption measurements, and Raman spectroscopy. The sulfur cathode containing electrochemical carbon with the specific surface area of 1606.6 m2 g−1 exhibits the best electrochemical performance and provides a charge capacity of almost 650 mAh g−1 in cyclic voltammetry at a 0.1 mV s−1 scan rate and up to 1300 mAh g−1 in galvanostatic chronopotentiometry at a 0.1 C rate. This excellent electrochemical behavior is ascribed to the high dispersity of electrochemical carbon, enabling a perfect encapsulation of sulfur. The surface modification of carbonaceous additives by TiO2 has a positive effect on the electrochemical performance of sulfur composites with mesoporous and activated carbons, but it causes a loss of dispersity and a consequent decrease of the charge capacity of the sulfur composite with electrochemical carbon. The composite of sulfur with TiO2-modified activated carbon exhibited the charge capacity of 393 mAh g−1 in cyclic voltammetry and up to 493 mAh g−1 in galvanostatic chronopotentiometry. The presence of an additional Sigracell carbon felt interlayer further improves the electrochemical performance of cells with activated carbon, electrochemical carbon, and nanocrystalline TiO2-modified activated carbon. This positive effect is most pronounced in the case of activated carbon modified by nanocrystalline TiO2. However, it is not boosted by additional coverage by TiO2 or SnO2, which is probably due to the blocking of pores.

Use of Coffee Beans to Obtain Activated Carbon with Potential Applications as Supercapacitors

Activated carbons (AC) from coffee bean waste were prepared by chemical activation using as activating compounds potassium hydroxide (KOH) and potassium carbonate (K2CO3) respectively, impregnation times of 24 and 48 hours, 600°C and 700°C as temperatures calcination. After that coals samples were synthesized. They were doped with nickel oxide (NiO) in order to modify the electrical properties of the AC. Later they were characterized (physical adsorption of using N2, FT-IR, XRD). The AC/NiO composites were prepared by the chemical method and the electrodes were compacted into pellet forms, which were placed in a two-electrode cell using 2M sulfuric acid (H2SO4) as electrolyte. Activity electrochemical was evaluated by cyclic voltammetry and galvanostatic chronopotentiometry. Finally, the specific capacitance of the supercapacitors (SCS) was determined from AC/NiO. Results of AC/NiO-48-700°C-KOH and AC/NiO-48-700°C-K2CO3 materials showed maximum capacitances of 405.40 and 394.73 F/g respectively.

LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O 2 with morphology optimized for novel concept of 3D Li accumulator

An array of LiNi1/3Mn1/3Co1/3O2 (NMC 111) samples with a hollow-sphere morphology enabling the use of binder-free, millimeter-thick electrodes in a battery are prepared by a combination of ball milling, hydrothermal treatment and calcination. Materials are studied by powder X-ray diffraction, nitrogen adsorption measurements, X-ray fluorescence analysis, and scanning electron microscopy. Their electrochemical performance for Li+ extraction/insertion is tested by cyclic voltammetry and galvanostatic chronopotentiometry on thin-film electrodes. Optimized materials, prepared by mechanical and thermal treatment with surface areas of 7 to 10 m2 g−1, provide charge capacity values of 141 to 156 mAh g−1. The concentration of the crystalline phase in NMC 111 materials with a hollow-sphere morphology is found to be the decisive parameter for their galvanostatic cycling stability. Hollow spheres with well-developed NMC nanocrystals and a low concentration of amorphous phase in the walls, exhibiting excellent cycling stability and charge capacity in thin-film electrodes are incorporated into a NMC/graphite 3D-battery module. This 122 Ah/451 Wh 3D-battery provides 78% of theoretical capacity and 73% of theoretical energy after 10 formatting cycles. Additionally, the battery prototype exhibits stable performance over more than 200 cycles at C/10 rate. A series of analogous 3D Li accumulators, currently assembled and tested in a pilot plant, represent the first step toward large-scale production of novel 3D Li accumulator.

The use of activated carbon from coffee endocarp for the manufacture of supercapacitors

Activated carbon (AC) was obtained from the dry endocarp of coffee for the manufacture of electrodes for supercapacitors. Four different AC samples were prepared via chemical methods at different proportions of impregnation (Xp) and two temperatures of activation (600 and 700 °C). Scanning Electron Microscopy technology and the measurement of the adsorption of N2 via the Brunauer–Emmett–Teller (BET) method were used to identify the morphological characteristics of AC, revealing high surface areas. Energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy techniques were applied for chemical composition analysis, identifying oxygenated functional groups which contribute to the increase in capacitance. The supercapacitor comprised two electrodes mounted on a tantalum cell, which was electrochemically evaluated by means of cyclic voltammetry and galvanostatic chronopotentiometry charge/discharge measurements. The maximum specific capacitance encountered was 186 Fg−1, which was obtained from the AC sample with a surface area of 734 m2g−1 and prepared at an Xp of 150% and an activation temperature of 700 °C. All AC samples exhibited good electrochemical performance.

Layered LiNi1/3Mn1/3Co1/3O2 (NMC) with Optimized Morphology for Li-Ion Batteries

Commercial LiNi1/3Mn1/3Co1/3O2 material is treated in appropriate way to provide cathode material with reasonable charge capacity and high cycling stability upon different charging/discharging rates. Electrochemical performance of the tested materials is studied by cyclic voltammetry of Li insertion and galvanostatic chronopotentiometry. An influence of calcination, surface area and particle size uniformity on the charge capacity and cycling stability is evaluated and the parameters of the optimized samples providing charge capacity of 141 mAh/g (cyclic voltammetry) and 144 and 135 mAh/g (galvanostatic chronopotentiometry) at 1 and 10C, respectively, represent a platform for scale up during the next period of the research.

Electrochemical performance of sol-gel-made Na2Ti3O7 anode material for Na-ion batteries

Nanocrystalline Na2Ti3O7 material is prepared by a newly developed sol-gel procedure. The sol-gel made Na2Ti3O7 calcined at 500 °C possesses mesoporous structure and BET surface area of 89 m2 g−1. X-ray diffraction and scanning electron microscopy confirm the presence of sintered nanosheets or very small crystals of the size of 10–20 nm with short-range ordering. Electrochemical behavior of nanocrystalline Na2Ti3O7 is evaluated by cyclic voltammetry of Na insertion and by galvanostatic chronopotentiometry at different charging rates. The sol-gel made Na2Ti3O7 exhibits improved performance as compared to that of the microcrystalline Na2Ti3O7 prepared by solid-state synthesis. Discharge capacities of optimized material at charging rates 1, 2, and 5C reach 109, 86, and 63 mAh g−1, respectively, with 100% coulombic efficiency and zero capacity drop over 50 cycles after initial conditioning. Excellent performance of Na2Ti3O7_500 is obviously an effect of its large surface area giving rise to predominantly capacitive mechanism of charge storage. Hence, sol-gel made nanocrystalline Na2Ti3O7 represents promising anode material for Na-ion batteries due to its charge capacity and outstanding cycling stability.

Li insertion into Li4Ti5O12 spinel prepared by low temperature solid state route: Charge capability vs surface area

Li4Ti5O12 spinel powders with different surface areas are prepared by a novel low temperature solid state route with subsequent mechanical disintegration. X-ray diffraction analysis proves the presence of majority of Li4Ti5O12 phase with small amount of rutile and WC impurities. Transmission electron microscopy analysis evidences the presence of two morphologies, larger Li4Ti5O12 crystals surrounded by nanocrystals of Li4Ti5O12. This finding is supported by cyclic voltammetry of Li insertion and electrochemical impedance spectroscopy. The concentration ratio of these two morphologies in particular sample depends on its post ball milling time. Cyclic voltammetry of Li insertion and galvanostatic chronopotentiometry at 1C rate confirm the highest charge capacity for Li4Ti5O12 spinel with surface area of 21 m2 g−1. Due to optimized ratio of two particular morphologies this material (coded LTO_21) without any carbonaceous additive possesses excellent long time cycling stability during galvanostatic chronopotentiometry at 1, 2 and 5C. Its discharge capacities reach 170 mAh g−1 at 1C, 167 mAh g−1 at 2C and 160 mAh g−1 at 5C rates with 100% coulombic efficiency. The capacity drop was less than 1% for charging rates of 1 and 2C and about 5% at 5C. The discharge capacity of all the reported samples significantly outperforms that of commercial lithium titanate (Aldrich) with surface area of 12.5 m2 g−1 exhibiting discharge capacities of 95 mAh g−1 (cyclic voltammetry) and 77 mAh g−1 or 35 mAh g−1 in galvanostatic chronopotentiometry at 1 or 2C rates, respectively. Hence, our novel low temperature solid state route with subsequent mechanical disintegration represents energy saving pathway towards promising anode materials for fast and stable Li-ion batteries.

Theory for the chronopotentiometry on rough and finite fractal electrode: Generalized Sand equation

A theoretical model for the galvanostatic chronopotentiometry on a randomly rough electrode is developed for the diffusion controlled mass transport. The proposed model addresses the influence of various morphological characteristics of roughness on the transition time, interfacial concentration and potential transients. The potential transient and transition time of rough electrode is expressed in terms of average interfacial concentration. Expression for the average surface concentration is obtained in terms of the power spectrum of roughness while detailed analysis of simulated chronopotentiograms is performed for the finite fractal model. Power spectrum of finite fractal roughness is characterized through three controlling parameters of roughness, viz. fractal dimension (DH), lower cutoff length scale of fractality (ℓ) and topothesy length (ℓτ), significantly influence the chronopotentiometric response. Theoretical result show that the transition time at a centered random or pitted surface decreases with increase in their roughness. Experimental data on rough Pt electrode corroborate this observation and quantitative agreement over all time scale is achieved after inclusion of correction for the electric double layer and ohmic contributions.

Na insertion into nanocrystalline Li4Ti5O12 spinel: An electrochemical study

Na insertion into sol-gel made nanocrystalline spinel, Li4Ti5O12 (nano LTS) and reference commercial spinel (Aldrich LTS) is studied by cyclic voltammetry and galvanostatic chronopotentiometry at 1C and 2C charging/discharging rates. Nanocrystalline LTS exhibits the best performance for Na storage, its charge capacities reach 156 mAhg−1 and are twice as high as those of reference Aldrich LTS. A capacity drop of nano LTS taking place during galvanostatic cycling is ascribed to irreversible structural changes induced by Na accommodation in the Li4Ti5O12 lattice. Raman spectroscopy of nano LTS after Na insertion reveals a formation of orthorhombic Li0,5TiO2 phase in original nanocrystalline Li4Ti5O12. The occurrence of this phase, which is commonly formed during Li insertion into anatase, is discussed in terms of induced Li redistribution and its accommodation in very minor anatase impurities detectable by Raman spectroelectrochemistry and HRTEM, but visible neither by X-ray diffractometry nor cyclic voltammetry of Na insertion.

Electrooxidation of trifloxystrobin at the boron-doped diamond electrode: electrochemical mechanism, quantitative determination and degradation studies

ABSTRACTThe boron-doped diamond (BDD) presents attractive electrochemical sensing characteristics that are useful in analytical applications based on voltammetry and amperometry. It has a wide potential window in aqueous solutions enabling the quantification of the fungicide trifloxystrobin, measured at +1744 mV (versus Ag/AgCl), by square-wave anodic voltammetry in a Britton–Robinson (BR) buffer (0.04 mol L−1; pH 4.00)/acetonitrile 70/30% v/v. The activation of the electrode was made using galvanostatic chronopotentiometry and cyclic voltammetry (CV). The linear analyte addition curve, Ip (µA) = (1.0 × 10–1 ± 4.8 × 10–6) C (mol L−1) + (8.8 × 10–2 ± 1.1 × 10–3); R2 = 0.997, was obtained using amplitude of 40 mV, frequency of 30 Hz, step potential of 20 mV. The instrumental limit of detection (LOD) was 1.4 × 10–7 mol L−1 (0.058 mg L−1) and the dynamic linear range covered three decades (up to 1 × 10–5 mol L−1 or 4.1 mg L−1). The samples were analysed with recoveries about 80% in orange juice samples and from 92.4% to 104.0% in water samples. A study to evaluate potential interferences was made in the presence of other fungicides. Diagnostic studies indicated that oxidation of trifloxystrobin in aqueous medium at the surface of the BDD is irreversible, involving two steps, each one with two electrons. The UV degradation of trifloxystrobin was evaluated using the proposed electrochemical method and the kinetics of degradation established with half-life of 1.07 min.

Spray pyrolysed titanium oxide thin films using different ingredients for supercapacitive charaterizations

Titanium oxide (TiO2) thin films have been prepared on stainless steel at 673 K using spray pyrolysis technique. Equimolar Aqueous solutions of different ingredients like titanium tri chloride, titanium iso propoxide, and potassium titanium oxalate were used for the deposition of TiO2 thin films. As-prepared thin films were characterized using X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy (FT-IR). Prepared samples exhibit tetragonal type crystal structure with dense surface morphology. Electrochemical characterizations were carried out using cyclic voltammetery, Galvanostatic chronopotentiometry and electrochemical impedance spectroscopy. TiO2 thin films of potassium titanium oxalate shows good physical and electrochemical performance, with a high value of specific capacitance 557.50 F/g, Specific energy 20.41 Wh/kg, specific power 28.00 kW/kg and observed internal resistance 0.382 Ω.

Chemical Fabrication and Electrochemical Characterization of Graphene Nanosheets Using a Lithium Battery Platform

Graphene has opened up new opportunities for scientific and technological innovations because of its astonishing electrical, mechanical, chemical, and thermal properties. For instance, graphene-based nanocomposites have found extensive applications in Li-ion batteries (LIBs) as scientists and engineers seek to achieve superior electrochemical performances. The laboratory module reported herein includes both chemical fabrication and electrochemical characterizations of graphene nanosheets (GNSs). The GNS powders are fabricated through the chemical exfoliation of graphite, and the resulting morphological and structural changes are evaluated by means of scanning electron microscopy and X-ray diffraction. Li storage electrochemical characteristics of GNSs are then assessed via galvanostatic chronopotentiometry and compared with that of graphite, a commonly used anode material in LIBs. This novel laboratory module, suitable for a wide range of students with a general chemistry background, has been successfully implemented in a multidisciplinary laboratory and lecture course entitled Experimental Nanomaterials and Nanoscience. Because the laboratory connects chemistry and materials engineering to a real-world application, it raises students’ interest in and awareness of nanomaterials’ contribution to the renewable and clean energy field.

Synthesis of Anatase TiO2 Nanosheets with Enhanced Pseudocapacitive Contribution for Fast Lithium Storage

Anatase TiO2 nanosheets (ATNs) are successfully prepared by a biomimetic layer-by-layer titania mineralization approach, and the electrochemical performance of the ATNs as negative electrode for lithium-ion batteries is investigated by the galvanostatic chronopotentiometry and cyclic voltammetry. A high initial discharge capacity (311 mA h g(-1)) and initial Coulombic efficiency (81.7%) were obtained for ATNs, and capacities of 252, 202, 186, 158, 136, and 119 mA h g(-1) were obtained at 0.2, 1, 5, 10, 20, and 30 C, respectively. Particularly, the ATNs can still maintains a capacity of 108 mA h g(-1) after 4000 cycles at 30 C (only a capacity loss of 10%), which indicated a superior rate capabilities and cyclability. The CVs analysis revealed that the ANTs have both diffusive lithium storage in the bulk and pseudocapacitive lithium storage at the surface (also called interfacial lithium storage), and the pseudocapacitive lithium storage dominates the total capacity when the scan rates are above 1 mV s(-1). The fast and stable lithium storage of ATNs might be attributed to the high pseudocapacitive lithium storage contribution in the material, and it was suggested the pseudocapacitive lithium storage could occurred at grain-grain interfaces as well as nanosheet surfaces.

Activated carbon derived from marine Posidonia Oceanica for electric energy storage

In this paper, the synthesis and characterization of activated carbon from marine Posidonia Oceanica were studied. The activated carbon was prepared by a simple process namely pyrolysis under inert atmosphere. The activated carbon can be used as electrodes for supercapacitor devices. X-ray diffraction result revealed a polycrystalline graphitic structure. While scanning electron microscope investigation showed a layered structure with micropores. The EDS analysis showed that the activated carbon contains the carbon element in high atomic percentage. Electrochemical impedance spectroscopy revealed a capacitive behavior (electrostatic phenomena). The specific capacity per unit area of the electrochemical double layer of activated carbon electrode in sulfuric acid electrolyte was 3.16Fcm−2. Cyclic voltammetry and galvanostatic chronopotentiometry demonstrated that the electrode has excellent electrochemical reversibility. It has been found that the surface capacitance was strongly related to the specific surface area and pore size.

The Effects of Nd on Lead Anode for Zinc Electrowinning

A detailed investigation of the effects of Nd on the microstructure, mechanical properties and electrochemical properties of lead anode in 160g.L-1 at 35°C was carried out. Galvanostatic polarization and Chronopotentiometry (CP) were used to study the electrochemical behavior ( such as anodic potential, corrosion rate and the composition of passive film) of the Pb and Pb-Nd anodes. The metallographic structure and passive film morphology of Pb and Pb-Nd anodes were observed and analyzed using polarizing microscope and scanning electronic microscopy (SEM), respectively. The experimental results show the grains become smaller and aggregation of PbxNdy become severe as the content of Nd increases. The addition of Nd enhances the formation of PbO2, inhibits the formation of PbSO4 and PbO and reduces the anodic potential. However, Holes presenting on rough passive film of high Nd content Pb-Nd anodes accelerate the corrosion.