Galvanostatic Procedure Research Articles

Improved performance of the NaFePO4/Hardcarbon sodium-ion full cell

Chronoamperometry and galvanostatic procedures were applied in the LiFePO4-based ion exchange approach for the production of NaFePO4 cathodes. The materials obtained by various processes were employed as the cathode electrode in Na-ion half cells, and their structural and electrochemical properties were investigated. According to XRD patterns for both processes, it is seen that the Na-ions were successfully replaced with Li-ions. In addition of this, XPS and EDX-dot mapping analyses were supports the ion exchange procedure. The electrochemical properties of the cathode were investigated using CR2032 cells, and the diffusion coefficient and diffusion activation energy were calculated using the CV graphs at various scan rates and environmental temperatures. It was found that the Na-diffusion rate in the cell is faster at higher temperatures than at lower temperatures. The galvanostatic cycling tests were performed for C/10 and 1C rates at room temperature, 10 °C, and 50 °C and determined that the first capacities for C/10 and 1C at room temperature were 140mAh/g and 60mAh/g, respectively, with good stability. The full cells of NaFePO4/hard carbon were fabricated by pre-sodiation technique and the battery performance tests revealed that the cells have a 74 mAh/g for C/10-rate with a voltage window of 2–4 V.

Catalytic synergism in Mn-heterostructured molybdenum oxysulfide hybridized with transition metal phosphides: A robust amorphous water oxidation catalyst

This work aimed to improve the catalytic behavior of semi-conductive amorphous molybdenum oxysulfide (aMoOxSy) as a weak oxygen evolution reaction (OER) catalyst. A simple galvanostatic procedure is employed to hybridize Nickel foam (NF)/Mn-doped aMoOxSy with some amorphous transition metal phosphides (TMPs). Mn-heterostructuring causes an impressive improvement in both morphological properties and OER activity by more than 300% compared with NF/MoOxSy. The hybridization with TMPs (Fe, Co, Ni and Cu) gives a trimetallic composite with strong interfacial interaction, long-term stability, and pronounced OER activity. Further consideration unveils how Mn-doping endows a dramatic synergism upon hybridization of MoOxSy with CoP and NiP (with current boosting≥600%). While no synergism was observed after multiple examinations of CuP and FeP. Density functional theory (DFT) calculations are performed to theoretically address the role of Mn on the electronic features of the hybridized MoOS and the included transition metals. The defined theoretical synergism coefficient (TSC,τ) adhered to the observed trends in the electrochemical measurements. Two independent suggested schemes demonstrate the interfacial coordination pathway of MoOS-based composite. Finally, the NF/Mn-MoOxSy/petals-like 2D NiP nanosheets are recommended as a robust and cost-effective electrocatalyst for OER. It requires overpotentials as low as 191, 299 and 366 mV at the current densities of 10, 100 and 500 mA cm−2, respectively, which are much superior to the benchmark NF/IrO2 catalyst.

Electrochemical stability of hexagonal tungsten carbide in the potential window of fuel cells and water electrolyzers investigated in a half-cell configuration

Tungsten carbide has attracted much interest as possible support for oxygen reduction and hydrogen oxidation in fuel cells and as catalyst itself for the hydrogen evolution reaction in water electrolyzers in the last years. Herein, we investigate the dissolution behavior of hexagonal tungsten carbide in acidic media with cyclovoltammetric and galvanostatic procedures under steady-state and dynamic conditions. The tungsten dissolution rate in the electrolyte was monitored in-situ and time resolved via coupling of the scanning flow cell with an inductively coupled plasma mass spectrometer (SFC-ICP-MS), allowing a direct correlation of potential and amount of dissolved species. The stability and passivation behavior of tungsten carbide was compared to pristine tungsten metal and its highest oxide WO3 in fuel cell/electrolyzer relevant potential ranges. It was found that partial passivation in the oxygen reduction region takes place, accompanied by steady dissolution of tungsten slightly above these potentials. In the HER/HOR region, no significant dissolution was observed. The dissolution rate of WC at high potentials was found to be in many cases almost one order of magnitude lower than for the pristine metal, yet two orders of magnitude higher than for its corresponding highest oxide.

Metal Organic Frameworks/Ionic Liquid Composites As Electrolytes for Li-Ion Batteries

Metal Organic Frameworks (MOFs), as a novel class of crystalline porous material have gained great attention in the fields of gas storage, separation, drug delivery, catalysis, sensors and so forth. The supramolecular design of MOFs allow a number of organic ligands, with two or more functional groups, to be linked to metal ion coordination centers giving myriad variations and tunable properties in synthesized structures. Metal Organic Frameworks (MOFs) are of great interest due to several unique features and their applications have been extended to the field of Li-ion batteries. Simultaneously, ionic liquids (ILs) are becoming popular in a range of areas including biphasic reaction catalysis, electromechanical actuator membranes and diluents and separation membranes. Many studies have been conducted for the application of MOFs in energy storage devices [1]-[3], but scarcely any investigation was performed to understand the effect of ionic liquid incorporated MOFs in electrochemical storage devices especially batteries. Hence, an attempt has been made by our group with ionic liquid incorporated modified MOFs to serve as a better electrolyte system for Li-ion batteries with increased thermal and electrochemical stability, high ionic conductivity and other electrochemical aspects. Further, dimensionally and morphologically controlled MOFs will be carefully used to ease the ion transport in the electrolyte system by the regulation of ion conductive path. MOF-1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AMImTFSI), synthesized by a facile in-situ electrochemical method [4] was doped with a lithium salt, lithium bis (triflouromethylsulfonyl) imide (LiTFSI) by a modified procedure for electrochemical measurements. Morphological features and crystal size of these matrices were evaluated by TEM (Transmission Electron Microscopy) and XRD measurements. Temperature dependence of ionic conductivity of the MOF/ionic liquid matrix was studied by AC-impedance method. Combination of AC-impedance and DC-polarization method was used to determine the lithium ion transference number of the samples. Electrochemical window of different electrolyte compositions was studied by linear sweep voltammetry. A coin cell was fabricated to study the charge discharge characteristics of the resulting cell. Synthesis of MOF-5/ionic liquid matrix by electrochemical method - MOF was successfully synthesized by a mild in-situ electrochemical method using 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AMImTFSI) as a templating agent employing a modified procedure of reported method [4]. Synthesis of the MOF (AMImTFSI) was achieved by a constant dissolution of Zn2+ ion from Zn anode. The dissolution was carried out by applying a constant direct current (DC) of 0.15A. A titanium electrode was employed as cathode. The electrolyte used in this procedure was a solution containing 0.07 M terephthalic acid and 0.04 M zinc nitrate hexahydrate in DMF. The electrochemical galvanostatic procedure was carried out for 3hrs. A white powder formed during the above mentioned procedure, was filtered and washed with DMF first and then, with chloroform. The sample was then dried in oven at 80 oC to get pure MOF (IL). For further electrochemical analysis, MOF (IL) was doped with lithium salt, LiTFSI. A set of samples were synthesized with varying content of MOF (IL) in ionic liquid system and ionic conductivity was measured by AC-impedance method. Three samples with different weight % of MOF (IL) in AMImTFSI were prepared and temperature dependent ionic conductivity measurements were performed by AC impedance method. All the samples showed linear profiles in Arrhenius plots. As expected the ionic conductivity decreased with increase in wt% of MOF (IL) because of change in state from liquid to gel. Interestingly a decrease in activation energy of ion transport was observed. The ionic conductivities of the samples were calculated by the Vogel-Fulcher-Tammann (VFT) equation, resulting out to be highest for the sample with 10 wt% of MOF (IL) in AMImTFSI i.e. 1.0 x 10-2 Scm-1 at 51 oC . The highest tLi + of 0.31 was observed for 20 wt% MOF (IL) in AMImTFSI. The systems showed a potential window of 5.22-5.55 V. Charge discharge studies were also carried out after fabricating a coin anodic half-cell composed of Si/electrolyte/Li which showed 90% coulombic efficiency in the presence of 30 mL of EC: DC=1:1 in electrolyte. Conclusion Modified MOF with ionic liquid framework was prepared in ionic liquid system by electrochemical method. Measurements of temperature dependence of ionic conductivity using AC impedance showed relatively high ionic conductivity. These encouraging results affirm the prepared modified MOF (IL) to be a prospective electrolyte in energy storage devices.

Corrosion Protection By MOF-5 Coatings for Sustained Zinc-Air Battery Anodes

Zinc–air is a century-old battery technology but has attracted revived interest recently. With larger storage capacity at a fraction of the cost compared to lithium-ion, zinc–air batteries clearly represent one of the most viable future options to power electric vehicles. Despite of their great potential, the development of zinc–air batteries has been impeded by problems associated with the metal electrode like self-corrosion, dendrite formation on zinc electrode, and poor discharge characteristics. It is therefore urgent to improve their overall device performance. In the present research, an attempt is made to investigate the application of ionic liquid (IL) modified Metal Organic Frameworks (MOFs) in zinc-air batteries. The use of MOF-5 (IL) in zinc-air batteries have never been studied so far, so in this research we will focus on the use of electrochemically modified zinc electrode decorated with MOF-5 (IL) for the fabrication of zinc-air batteries. It can solve issues like self-corrosion and improve discharge performance which would result into high performance zinc-air batteries with prolonged cyclability. The research also deals with the use of polythiophene in zinc air batteries. Electro-polymerization of a conducting polymer like polythiophene [1] proves to be an efficient approach for modification of the Zn anodes as it provides high thermal and chemical stability. Hence, electropolymerized polythiophene coating can aid in the binding of MOF-5 film over the Zn electrode which would provide stability to the latter. Synthesis of MOF-5 (IL) decorated zinc anodes - Modified MOF-5 (IL) was successfully synthesized over zinc electrode by a mild in-situ electrochemical method [2] using 1-butyl-3-methylimidazolium chloride (IL) ionic liquid as a templating agent employing a modified procedure of reported method [2]. Synthesis of the MOF-5 (IL) was achieved by a constant dissolution of Zn2+ ion from Zn anode. The dissolution was carried out by applying a constant direct current of 0.20 A. A titanium electrode was employed as cathode. The electrolyte used in this procedure was a solution containing 0.07 M terephthalic acid and 0.04 M zinc nitrate hexahydrate in DMF. The electrochemical galvanostatic procedure was carried out for 1hr to get uniform coating of MOF (IL) over the zinc electrode. After that, the electrode was kept for drying at room temperature for 6 hours. Synthesis of MOF-5 (IL) / polythiophene decorated zinc anodes – After the synthesis of MOF-5 (IL), thiophene was added in the solution described above and cyclic voltammetry was performed using Ag/Ag+ as reference electrode for 10 cycles. The electrode was then, kept for drying. Similarly, controlled electropolymerization of thiophene was also done over the zinc electrodes for polythiophene coated Zn anodes. The X-ray diffractogram of synthesized MOF-5 (IL) (Fig. 1) was indexed and was found to be in good agreement with the indices of conventional MOF-5. To investigate the corrosion behavior of Zn anode with different surface modifications, potentiodynamic experiment was performed using a three electrode cell including Zn-based electrode as a working electrode, Ag/AgCl as reference electrode and platinum served as counter electrode. The experiment was performed at room temperature in 0.1 M NaOH aq. at a scan rate of 3.6 mV/s in the range of -0.25 V to 0.50 V. To study discharge characteristics, zinc-air battery was fabricated using carbon cloth as air electrode, zinc based electrodes as anode and nickel mesh as current collector. 5.0 M KOH aq. was used as electrolyte. Chronopotentiometry experiment was performed to see the discharge behavior of different Zn based anodes. The potential went down abruptly in case of pure zinc anode while the potential with zinc anodes decorated with MOF-5 (IL) sustained for a longer cycle. The zinc-air battery with pure zinc as anode showed current density of ~ 7 mA cm-2. On the contrary, zinc-air batteries with zinc anodes decorated with MOF-5 (IL) showed 4 times enhanced current density of ~ 30 mA cm-2. Considering corrosion current and corrosion potential, MOF-5 (IL) decorated Zn anodes and MOF-5 (IL) / polythiophene coated Zn anodes showed the most favorable characteristics to be used in zinc-air batteries. The enhanced discharge performance may be due to the formation of conducting passive layer of MOF-5 (IL) and MOF-5 (IL) / polythiophene on the surface of pure zinc electrode which prevented the active Zn metal from direct exposure to the KOH electrolyte and thus, minimizing the spontaneous side reactions that occur in conventional zinc-air batteries like hydrogen evolution. Efforts are underway to study the discharge characteristics of MOF-5 (IL) / polythiophene coated Zn and polythiophene coated Zn materials. Figure 1

POLYPYRROLE COATED CELLULOSIC SUBSTRATE MODIFIED BY COPPER OXIDE AS ELECTRODE FOR NITRATE ELECTROREDUCTION

The aim of this work is to synthesize polypyrrole (PPy) films on nonconducting cellulosic substrate and modified by copper oxide particles for use in the nitrate electroreduction process. Firstly, the chemical polymerization of polypyrrole onto cellulosic substrate is conducted by using FeCl3as an oxidant and pyrrole as monomer. The thickness and topography of the different PPy films obtained were estimated using a profilometer apparatus. The electrochemical reactivity of the obtained electrodes was tested by voltamperometry technique and electrochemical impedance spectroscopy. Secondly, the modification of the PPy film surface by incorporation of copper oxide particles is conducted by applying a galvanostatic procedure from a CuCl2solution. The SEM, EDX and XRD analysis showed the presence of CuO particles in the polymer films with dimensions less than 50 nm. From cyclic voltamperometry experiments, the composite activity for the nitrate electroreduction reaction was evaluated and the peak of nitrate reduction is found to vary linearly with initial nitrate concentration.

Slow magnetic relaxation in radical cation tetrathiafulvalene-based lanthanide(iii) dinuclear complexes

Lanthanide dinuclear complexes involving tetrathiafulvalene-based ligands in their radical cation form were synthesised and crystallised by a galvanostatic procedure. Dynamic magnetic measurements reveal an unprecedented slow magnetic relaxation for the Dy(III) analogue in this kind of molecular edifice.

Structural and activity comparison of self-limiting versus traditional Pt electro-depositions on nanopillar Ni films

We report the fabrication, characterisation, and electro-catalytic activity of <0.3 mg cm−2 platinum deposits onto ∼500 nm long nickel nanopillar substrates (NiNP) synthesised by glancing angle deposition (GLAD). This is the first reported study of GLAD-based Pt–Ni electro-catalysts and the first alcohol oxidation study on any GLAD based electro-catalyst. The Pt was deposited onto NiNP via either 1) an unconventional, self-limiting, relatively high current density galvanostatic deposition, with a Pt counter electrode as the source of Pt, or 2) via a conventional potentiostatic deposition from Pt salts dissolved in acidic electrolytes. X-ray Diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) confirm the successful deposition of Pt onto NiNP, while Scanning Electron Microscopy (SEM) shows that the nanopillar morphology is preserved but the Pt morphology is significantly different between the two methods. The galvanostatic procedure resulted in a conformal Pt deposition over the entire surface of the NiNP. The conventional procedure appeared to be mass-transfer limited, with most of the Pt being deposited on the tops of the NiNP. Cyclic voltammetry in 1 M KOH shows an enhancement of the surface area of the catalysts upon Pt deposition and corroborates the presence of Pt on the NiNP surface. Both prepared catalysts show high electro-catalytic activity towards 2-propanol oxidation in the KOH electrolyte at 60 °C. The activity enhancement below 300 mV vs. RHE (RHE = reversible hydrogen electrode) was attributed to the combined activity of the Pt and Ni components in the catalysts. At higher potentials, a bifunctional mechanism was suggested. Finally, a geometric/composition effect may be at work in the traditionally deposited catalyst, and requires further investigation.

Electrochemical investigation of conformational rearrangements of polypyrrole deposited on Al alloys

Polypyrrole (PPy) films were electrochemically deposited on AA2024 and AA6082 Al alloys by a two-step galvanostatic procedure: (1) activation in nitric acid and (2) deposition in oxalic acid. Polymeric films were electrochemically characterized through a series of cyclovoltammetric experiments, underlining differences due to the two different substrates. Interesting effects are linked to the presence of copper in AA2024, that extracted from the alloy during the deposition, is included into the polymeric matrix increasing its quality and polymerization yield. Methods and experiments based on Otero's Electrochemically Stimulated Conformational Relaxation model (ESCR) were performed in order to investigate structural changes of the polymer in function of an applied potential. PPy on AA2024 manifests a more complex redox process, involving both cations and anions, as compared to the polymer film on AA6082 that involves only anion interchange.

Polypyrrole films on Al alloys: The role of structural changes on protection performance

Polypyrrole (PPy) films were electrochemically synthesized on AA6082, AA5083 and AA2024 Al alloys by a two-step galvanostatic procedure: (1) activation in nitric acid and (2) deposition in oxalic acid. PPy films were characterized by elemental analysis, cyclic voltammetry, SEM/EDX, RAIR, solid-state 13C NMR, and EPR. The corrosion behaviour of PPy-coated alloys was evaluated in near neutral NaCl solution by single-cycle anodic polarization and open circuit potential monitoring. Film adhesion and polymer structure are principally determined by the nature of the Al substrate. Good quality films are obtained on the most reactive AA5083 and AA2024, while highly degraded, partially saturated polymer is electrogenerated on AA6082. The performance of PPy films was observed to depend strongly on the electrochemical test used for corrosion protection evaluation. Accordingly, the rate at which structural changes are driven within the polymeric matrix is of paramount importance to understand the corrosion inhibition properties of conducting polymers.

A novel galvanostatic polymerization for high specific capacitance poly(3-methylthiophene) in ionic liquid

For the first time it is here reported a novel and clean galvanostatic procedure to polymerize poly(3-methylthiophene) in the 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI) ionic liquid (IL). The strategy consists in the use of the acid additive trifluoromethanesulfonimide (HTFSI) displaying the same anion of the IL and which provides an acid proton that is reduced to H 2 at the counter electrode upon the anodic polymer growth on the working electrode and prevents consumption of the ionic liquid with great advantage in terms of costs. This procedure provides a pMeT electrode featuring 250 F g −1 in EMITFSI at 60 °C, a very interesting result in view of application of such pMeT in IL-based hybrid supercapacitors. Here are reported the results of the galvanostatic polymerization of pMeT in EMITFSI–HTFSI as well as the performance in EMITFSI at 60 °C of the obtained pMeT electrode.

Selective electrodeposition of PbO 2 on anodised-polycrystalline titanium

Electrochemical experiments on titanium electrodes were coupled with electron backscattered diffraction (EBSD) experiments. The substrates were thermally treated and electropolished in order to have flat and reproducible polycrystalline surfaces, leading to EBSD orientation mapping. Afterwards, the samples were anodised by a galvanostatic procedure. It was shown that electrodeposition of PbO 2 from a 0.5 M Pb(NO 3) 2+2.5 M HNO 3 solution occurs selectively on the near {0 0 0 1} grains, whereas lead electrodeposition occurs on all the grains, whatever their orientation. These results are discussed, taking into account the fact that on {0 0 0 1} grains, the oxide layers are thinner than on other grains. It was concluded that electrodeposition is observed locally on Ti/TiO 2 electrodes for (i) cathodic electrodeposition of metals at low overvoltage; (ii) anodic electrodeposition of PbO 2, in potentiostatic or galvanostatic conditions.

Lithium insertion electrodes based on niobium telluride thin films

Niobium telluride thin films were evaluated as intercalation electrodes in lithium cells. The films were prepared on Al substrate by sputter deposition under different experimental conditions. Large deposition periods lead to a non-crystalline film material, while short deposition periods allow the formation of layered particles structurally similar to niobium ditelluride. For preparations carried out at 300°C, the particles have sizes of ca 1 μm with their 001 planes oriented parallel to the substrate. At 330°C, particles of ca 10 μm with their 001 axis parallel to the substrate are obtained. Test batteries of the type Li/LiClO4(PC)/niobium telluride film were studied by potentiostatic and galvanostatic procedures. The performance of the batteries is influenced by the preparation conditions. Cell capacities larger than 100 mA h g−1 and a good capacity retention after 50 cycles were observed for films prepared at 300°C when the cells were cycled between 0.5 and 2.0 V.

Structure and composition of passive titanium oxide films

The thickness and composition of several kinds of titanium oxide films formed on a titanium substrate were determined by surface analysis techniques: X-ray photoelectron spectroscopy, Rutherford back scattering, X-ray diffraction and atomic force microscopy. Most titanium oxide samples were prepared by anodisation, using a galvanostatic procedure. The films were shown to be composed of an amorphous TiO 2 outer layer (10–20 nm thick) and an intermediate TiO x layer, in contact with the TiO 2 layer and the metallic substrate. The outer layer is sensitive to the environment: its thickness usually decreases with ageing in a corrosive solution. A stabilisation procedure was proposed in order to improve its ability to withstand corrosion.

The Advantages of Galvanostatic Polarization Resistance Measurements

Abstract A routine versatile galvanostatic procedure is described for measuring corrosion rate by polarization resistance. The galvanostatic procedure has been most useful and effective under transient conditons when corrosion rate and corrosion potential are changing with time or when relatively rapid corrosion potential fluctuations are present due to localized corrosion. At each step of the procedure, it is possible to monitor polarization to steady-state, a condition which has been found essential for accurate measurement of polarization resistance, especially at low corrosion rate. Comparisons are made with potentiodynamic scanning methods which have been favored in recent years.

Electro‐oxidation of Gallium Arsenide: I . Initial Phase of Film Formation in Tartaric Acid‐Water‐Propylene Glycol Electrolyte

A standard galvanostatic procedure was used to study the initial phase of anodic oxidation of in a 3 weight percent (w/o) aqueous solution of tartaric acid mixed with propylene glycol. The initial phase is controlled by a two‐dimensional growth of oxide from nuclei generated at a rate of about 107 cm−2 sec−1. The effect of pH and illumination was examined in terms of the kinetics of nucleation in a heterogeneous system involving the semiconductor as the solid phase.