Electrochem

This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO₄, for Li-ion batteries operating in the 5-V region. The LiNiMnO₄ compound was synthesized by a sol-gel method assisted by ethylene diamine tetra-acetic acid (EDTA) as a chelator. Structural analyses carried out by Rietveld refinements and Raman spectroscopy, selected area electron diffraction (SAED) and X-ray photoelectron (XPS) spectroscopy reveal that the product is a composite ([email protected]), including non-stoichiometric LiNiMnO_4-δ spinel and a secondary Ni₆MnO₈ cubic phase. Cyclic voltammetry and galvanostatic charge-discharge profiles show similar features to those of LiNi_0.5Mn_1.5O₄ bare. A comparison of the electrochemical performances of 4-V spinel LiMn₂O₄ and 5-V spinel LiNi_0.5Mn_1.5O₄ with those of [email protected] composite demonstrates the long-term cycling stability of this new Ni-rich spinel cathode. Due to the presence of the secondary phase, the [email protected] electrode exhibits an initial specific capacity as low as 57 mAh g⁻¹ but shows an excellent electrochemical stability at 1C rate for 1000 cycles with a capacity decay of 2.7 × 10⁻³ mAh g⁻¹ per cycle. Full article

Ruthenium oxide (RuOx) thin films were spin coated by thermal decomposition of alcoholic solutions of RuCl₃ on titanium foils and subsequently annealed at 400 °C. The effect of spin coating parameters, such as spinning speed, volume, and molar concentration of the precursor as well as the number of deposits, on the morphology and electrochemical performance of the electrodes was investigated. The films were characterized by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV) with and without chloride, and linear sweep voltammetry (LSV). The prepared materials were also compared to drop cast films and spin-coated films obtained by adopting low-temperature intermediate treatments. The results indicate that even dispersion of the oxide layer was always achieved. By tuning the spin coating parameters, it was possible to obtain different electrochemical responses. The most influential parameter is the number of deposits, while the concentration of the precursor salt and the rotation speed were less relevant, under the adopted conditions. Full article

A double layer capacitance (DLC) has mainly been brought about in the Helmholtz layer rather than in the diffuse layer, as was demonstrated with the invariance of DLC to salt concentration, c, less than 0.5 M (M = mol dm⁻³) (Univ. J. Chem. 1 (2013) 162). The DLC measured here increased with concentrations of KCl and HCl solutions as high as 1 M at a platinum electrode by the ac impedance method. It was represented as a sum of the Helmholtz capacitance and the ionic one which had 0.7 power of the concentrations. The simple addition implies that the Helmholtz contribution and the ionic one should be represented by a parallel combination rather than a series one such as in the Stern model. The disagreement of the experimental values of the DLC with the Gouy–Chapman theory at high concentrations has been conventionally attributed to the effects of packing of ions over their sizes. In this paper, a model of avoiding the packing was introduced, in which ions were distributed in the direction normal to the electrode in the balance of electric motive force and the thermal energy, keeping the uniform distribution on a plane projected to the electrode. The energy balance was taken by using the grand canonical ensemble in statistical mechanics. The ionic contribution had a linear relation with the applied voltage rather than exponential dependence. When a series combination was applied to the Helmholtz capacitance and the ionic one under the condition of difference between the locally anionic DLC and the cationic one, we obtained approximately a parallel combination of the two capacitances because either the anionic or the cationic DLC works predominantly. Full article

Nowadays, the self-accelerating increase in global temperatures strengthens the idea that the cutting of CO₂ emissions will not be enough to avoid climate change, thus CO₂ from the atmosphere must be removed. This gas can be easily trapped by converting it to bicarbonate using hydroxide solutions. However, bicarbonate must be converted into a more valuable product to make this technology profitable. Several studies show great efficiency when reducing bicarbonate solutions saturated with pure CO₂ gas to formate. However, those approaches don’t have a real application and our objective was to obtain similar results without pure CO₂ saturation. The method consists of electroreduction of the bicarbonate solution using bulk tin (Sn) as catalysts. Tin is a relatively cheap material that, according to previous studies performed in saturated bicarbonate solutions, shows a great selectivity towards formate. The ¹H NMR analysis of bicarbonate solutions after electroreduction show that, without pure CO₂ gas, the faradic efficiency is around 18% but almost 50% for saturated ones. The formate obtained could be used to power formate/formic acid fuel cells obtaining a battery-like system, with greater energy density than common lithium batteries, but electroreduction efficiency needs to be improved to make them competitive. Full article

This investigation’s primary purpose was to illustrate the cooling mechanism within a lithium titanate oxide lithium-ion battery pack through the experimental measurement of heat generation inside lithium titanate oxide batteries. Dielectric water/glycol (50/50), air and dielectric mineral oil were selected for the lithium titanate oxide battery pack’s cooling purpose. Different flow configurations were considered to study their thermal effects. Within the lithium-ion battery cells in the lithium titanate oxide battery pack, a time-dependent amount of heat generation, which operated as a volumetric heat source, was employed. It was assumed that the lithium-ion batteries within the battery pack had identical initial temperature conditions in all of the simulations. The lithium-ion battery pack was simulated by ANSYS to determine the temperature gradient of the cooling system and lithium-ion batteries. Simulation outcomes demonstrated that the lithium-ion battery pack’s temperature distributions could be remarkably influenced by the flow arrangement and fluid coolant type. Full article

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) employed in industrial processes that causes adverse effects on the environment and human health. Sensitive and inexpensive methods to detect BPA are therefore needed. In this paper, we describe an electrochemical biosensor for detecting low levels of BPA using polymeric electrospun nanofibers of polyamide 6 (PA6) and poly(allylamine hydrochloride) (PAH) decorated with gold nanoparticles (AuNPs), namely, PA6/[email protected], which were deposited onto a fluorine-doped tin oxide (FTO) substrate. The hybrid layer was excellent for the immobilization of tyrosinase (Tyr), which allowed an amperometric detection of BPA with a limit of detection of 0.011 μM in the concentration range from 0.05 to 20 μM. Detection was also possible in real water samples with recoveries in the range of 92–105%. The improved sensing performance is attributed to the combined effect of the large surface area and porosity of PA6/PAH nanofibers, the catalytic activity of AuNPs, and oxidoreductase ability of Tyr. These results provide a route for novel biosensing architectures to monitor BPA and other EDCs in water resources. Full article

In this study, we have evaluated the effect of potassium hydroxide (KOH) on the energy storage performance of metal-free carbon-based materials prepared from molasses. Molasses are a renewable-resource biomass and economical by-product of sugar refinement, used here as a carbon precursor. Two co-doped carbon materials using molasses were synthesized via a time and cost-efficient microwave carbonization process, with ammonium polyphosphate as a phosphorus and nitrogen doping agent. The phosphorus and nitrogen co-doped carbon (PNDC) samples were prepared in the presence and absence of a chemical activating agent (KOH), to study the role of chemical activation on PNDCs. Physical characterizations were performed to gain insight into the composition, pore size and topographical data of each material. Electrochemical characterization via cyclic voltammetry in 1 M sulfuric acid (H₂SO₄) as well as in 6 M KOH as electrolytes, revealed high current density and specific capacitance for the chemically activated material (PNDC2) compared to one without chemical activation (PNDC1). The capacitance value of 244 F/g in KOH electrolyte was obtained with PNDC2. It is concluded that addition of KOH prior to carbonization increases the surface functionality, which significantly enhances the electrochemical properties of the PNDC material such as current density, stability, and specific capacitance. Full article

Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses. Full article

Nanocrystalline Ni-Co alloy deposits with grain sizes less than 30 nm were produced by electrodeposition with a direct current in a sulfamate bath. Surfaces of the Ni-Co alloy deposits showed granular morphology. The size of the granular particles and the Co content decreased when a lower current density was applied. Addition of NiBr₂ and a surface brightener (NSF-E) into the bath resulted in the grain refinement effect and an increase of Co content in the deposit. The grain size reached roughly 14 nm and 60 at.% of Co content in Ni-Co alloys electrodeposited with the bath containing the two additives. Ni-Co alloys obtained in this study showed higher microhardnesses than those of pure Ni and Co deposits prepared under the same condition, which revealed the solid solution strengthening effect. With a decrease in the grain size, the microhardness further increased, and this trend followed the Hall–Petch relationship well. The maximum microhardness value of 862.2 Hv was obtained owing to both the grain boundary and solid solution strengthening effects. Full article

A new heat transfer enhancement approach was proposed for the cooling system of lithium-ion batteries. A three-dimensional numerical simulation of the passive thermal management system for a battery pack was accomplished by employing ANSYS Fluent (Canonsburg, PA, USA). Phase change material was used for the thermal management of lithium-ion battery modules and as the heat transmission source to decrease battery temperature in fast charging and discharge conditions. Constant current charge and discharge were applied to lithium-ion battery modules. In the experimental part of the research, an isothermal battery calorimeter was used to determine the heat dissipation of lithium-ion batteries. Thermal performance was simulated for the presence of phase change material composites. Simulation outcomes demonstrate that phase change material cooling considerably decreases the lithium-ion battery temperature increase during fast charging and discharging conditions use. The greatest temperature at the end of 9 C, 7 C, 5 C, and 3 C charges and discharges were approximately 49.7, 44.6, 38.4, and 33.1 °C, respectively, demonstrating satisfactory performance in lithium-ion battery thermal homogeneity of the passive thermal management system. Full article

Herein, metal-free heteroatom doped carbon-based materials are being reviewed for supercapacitor and energy applications. Most of these low-cost materials considered are also derived from renewable resources. Various forms of carbon that have been employed for supercapacitor applications are described in detail, and advantages as well as disadvantages of each form are presented. Different methodologies that are being used to develop these materials are also discussed. To increase the specific capacitance, carbon-based materials are often doped with different elements. The role of doping elements on the performance of supercapacitors has been critically reviewed. It has been demonstrated that a higher content of doping elements significantly improves the supercapacitor behavior of carbon compounds. In order to attain a high percentage of elemental doping, precursors with variable ratios as well as simple modifications in the syntheses scheme have been employed. Significance of carbon-based materials doped with one and more than one heteroatom have also been presented. In addition to doping elements, other factors which play a key role in enhancing the specific capacitance values such as surface area, morphology, pore size electrolyte, and presence of functional groups on the surface of carbon-based supercapacitor materials have also been summarized. Full article

Micro-hole voltammetry exhibiting rectified current-voltage curves was performed in hydrochloric acid by varying the lengths and the diameters of the micro-holes on one end of which a Nafion film was mounted. Some voltammetric properties were compared with those in NaCl solution. The voltammograms were composed of two line-segments, the slope of one segment being larger than the other. They were controlled by electric migration partly because of the linearity of the voltammograms and partly the independence of the scan rates. Since the low conductance which appeared in the current from the hole to the Nafion film was proportional to the cross section area of the hole and the inverse of the length of the hole, it should be controlled by the geometry of the hole. The conductance of the hydrogen ion in the Nafion film was observed to be smaller than that in the bulk, because the transport rate of hydrogen ion by the Grotthuss mechanism was hindered by the destruction of hydrogen bonds in the film. In contrast, the conductance for the current from the Nafion to the hole, enhancing by up to 30 times in magnitude from the opposite current, was controlled by the cell geometry rather than the hole geometry except for very small holes. A reason for the enhancement is a supply of hydrogen ions from the Nafion to increase the concentration in the hole. The concentration of the hydrogen ion was five times smaller than that of sodium ion because of the blocking of transport of the hydrogen ion in the Nafion film. However, the rectification ratio of H⁺ was twice as large as that of Na⁺. Full article

Atomic-level gold clusters are decorated on a polyaniline (PANI) support by a cyclic atomic electrodeposition process, and the catalytic activity in the oxidation of glucose is studied. The evaluation is conducted by cyclic voltammetry using atomic-level gold clusters-decorated PANI (PANI/Au_N, where N indicates the atomic size of the Au cluster and N = 1~3 in this study) as the working electrode and a solution containing 0 to 50.0 mM of glucose in phosphate-buffered saline. The catalytic activity is determined from the oxidation current observed at around +0.6 V vs. Ag/AgCl. The catalytic activity is found to be affected by the size of gold clusters decorated on the PANI/Au_N, whereby the catalytic activity is low when N is 1 or 3. On the other hand, an obvious enhancement in the catalytic activity is observed for the PANI/Au₂ electrode. Full article

Strengthening of electrodeposited Au-based materials is achieved by co-electrodeposition with TiO₂ nanoparticles dispersed in a sulfide-based gold electrolyte. TiO₂ content in the composite film is adjusted by concentration of the TiO₂ in the gold electrolyte. Effects of the TiO₂ content on surface morphology, crystalline structure and microstructure of the composite film are investigated. Mechanical properties of the Au–TiO₂ composite films are evaluated by micro-Vickers hardness and micro-compression tests. The hardness increases from 135 to 207 H_V when the TiO₂ content is increased from 0 to 2.72 wt%. Specimens used in the micro-compression test are micro-pillars fabricated from the composite film, and the yield strength reaches 0.84 GPa by incorporating 2.72 wt% TiO₂ into the film. Full article

It is essential to understand the adsorption of guest molecules on carbon-based materials for both theoretical and practical reasons. It is crucial to analyze the surface properties of carbon-based materials with a wide range of applications (e.g., catalyst supports, hydrogen storage, sensors, adsorbents, separation media, etc.). Inverse gas chromatography (IGC) as a powerful and sensitive technique can be used to characterize the surface physicochemical properties (i.e., Brunauer-Emmett-Teller (BET) surface area, surface energy heterogeneity, heat of adsorption, specific interaction of adsorption, work of cohesion, glass transition temperatures, solubility, and so forth) of various types of materials such as powders, films, and fibers. In this review, the principles, common methods, and application of IGC are discussed. In addition, the examples of various experiments developed for the IGC to characterize the carbonaceous materials (such as carbon nanotubes, graphite, and activated carbon) are discussed. Full article

Conducting copolymer films were prepared from pyrrole (Py) and 1,12-di-(1-pyrrolyl) dodecane (DiPy) in an attempt to prepare conducting films that can be used as sensitive material of chemiresistor gas sensors. Copolymer thin films were obtained by electrochemical oxidation in a lithium perchlorate/acetonitrile electrolyte with different feed ratios of comonomers. Increasing the portion of DiPy in the comonomer mixture resulted in the formation of thinner and less rough copolymer films and to a modification of their morphology from a granular structure to a clover-like structure. In addition, copolymer films with very different conductivities were obtained by varying the comonomers ratio. Indeed, the conductivity of the copolymer containing 91% of Py was 2 × 10⁵ times higher than the conductivity of the polymer containing 91% of DiPy, indicating that it is possible to tune the conductivity of the film by varying the composition of the initial comonomer mixture. Full article

The energy autonomy of self-powered wearable electronics depends on the adequate development of new technologies for energy harvesting and energy storage devices based on textile fibers to facilitate the integration with truly flexible and wearable devices. Silk fiber-based systems are attractive for the design of biomedical devices, lithium-ion batteries and flexible supercapacitors, due to their nitrogen-rich structure (for preparation of hierarchical carbon-based structures), and available surface for chemical modification reinforcing electroactive properties for use in batteries and supercapacitors. Herein, this paper reviews recent advances on silk fiber-based systems for harvesting and the storage of energy and the corresponding strategies to reinforce the physical and chemical properties of the resulting composites applied as electrodes and battery separators. Full article

The dye regeneration in dye-sensitized solar cells (DSSCs) is improved by optimizing the charge separation at the level of the sensitized semiconductor treatment of the mesoporous electrode by TiCl₄ that passivates the surface for back electron transfer reactions. The dye-regeneration kinetics is analyzed for DN216- and D358-sensitized porous TiO₂ electrodes with and without a TiCl₄ treatment by means of scanning electrochemical microscopy (SECM). Different mass transport limitation of the [Co(bpy)₃]³⁺ mediator through the porous electrode is found for the comparison of the structurally similar dyes but cannot be detected for the thin layer introduced by the TiCl₄ treatment. Phototransient measurements are conducted directly in the SECM cell without any intermediated sample manipulation. The results from those measurements corroborate the findings from steady state SECM measurements. Full article

Oxygen-plasma treatment was performed on an activated carbon sheet obtained from shochu (Japanese distilled liquor) waste using a high-frequency plasma generator. The capacitances of the activated carbon sheet electrode subjected to surface treatment were measured using cyclic voltammetry. The best results were obtained with a processing time of 60 min, an output power of 40 W, an interelectrode distance of 13 cm and an oxygen pressure of 40 Pa. The maximum capacitance was 247 F g⁻¹. Investigation of the surface functional groups of the activated carbon sheet revealed that the oxygen-containing functional groups modified on the surface of the activated carbon sheet electrode contributed to the improvement in the capacitance. High-performance electric double-layer capacitors can be realized using the developed electrodes. Full article