The synergistic effect between graphene oxide nanocolloids and silicon dioxide nanoparticles for gallic acid sensing

For the first time, the synergistic effect of graphene oxide nanocolloids (nano-GO) and silicon dioxide (silica) nanoparticles (SiO₂-nanoparicles) has been used to modify a glassy carbon electrode (GCE) for the determination of gallic acid (GA). The modified electrode surface was characterised by using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXA) and Fourier transform infrared spectroscopy (FTIR). The electrochemical behaviour of the modified electrode was then studied, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), showing that the electrode was sensitive to GA in a concentration range of 6.25 × 10⁻⁶ to 1.0 × 10⁻³ mol L⁻¹, with a correlation coefficient R² of 0.9956 and a limit of detection of 2.09 × 10⁻⁶ mol L⁻¹ (S/N = 3). The proposed method was successfully used for the determination of GA in red wine, white wine and orange juice, with recoveries of 102.3, 95.4 and 97.6%, respectively.

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Discerning the oscillatory electrochemical response during electrodeposition of cobalt in the presence of but-2-yne-1,4-diol

We present a new observation of electrochemical oscillation during the reduction of Co²⁺ from sulfate solution in the presence of but-2-yne-1,4-diol (butynediol) as an additive. Cyclic voltammetry, hydrodynamic voltammetry at galvanostatic condition, and electrochemical impedance spectroscopic studies suggest that the electrochemical oscillation observed was a relaxation type and was the manifestation of adsorbed hydrogen formation by electrochemical reduction of protons on cobalt and their chemical removal by semi-hydrogenation of butynediol to butenediol during the initial stages of electrodeposition.

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Facile synthesis of layered reduced graphene oxide–copper sulfide (rGO-CuS) hybrid electrode for all solid-state symmetric supercapacitor

A straightforward process for synthesis of hybrid porous electrode material composed of reduced graphene oxide (rGO) and copper sulfide (CuS) with layered structure on the stainless steel substrate is developed. As-synthesized hybrid electrode shows hexagonal crystal structure of CuS with 77 m² gm⁻¹ specific surface area and 22 nm average pore size. The specific capacitance obtained with rGO-CuS5 hybrid electrode is 1201 F g⁻¹ at the sweep rate of 5 mV s⁻¹ in 1 M LiClO₄ aqueous electrolyte. The majority of charge stored by diffusion-controlled process indicates benefits of layered structures for solid-state energy storage. The rGO-CuS5-based hybrid symmetric supercapacitor delivers a specific capacitance (C_s) as high as 109 F g⁻¹ at a sweep rate of 5 mV s⁻¹ with polyvinyl alcohol (PVA)-LiClO₄ gel electrolyte. Also, the specific energy of 44 Wh kg⁻¹ and specific power of 1.4 kW kg⁻¹ with 87% stability after 6000 cycles at an applied current of 5 mA are obtained. The simple process of synthesis of layered hybrid electrode material for flexible supercapacitor promises its use in smart textile and wearable electronic devices.

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One-step CZT electroplating from alkaline solution on flexible Mo foil for CZTS absorber

In this work, Cu-Zn-Sn (CZT) is co-electrodeposited onto a flexible Mo substrate exploiting an alkaline bath (pH 10). The plating solution is studied by cyclic voltammetry, highlighting the effects of potassium pyrophosphate (K₄P₂O₇) and EDTA-Na₂ on the electrochemical behavior and stability of the metallic ionic species. The optimized synthesis results in a homogeneous precursor layer, with composition Cu 44 ± 2 at. %, Zn 28 ± 1 at. %, and Sn 28 ± 2 at. %. Soft and reactive annealing are employed respectively to promote intermetallic phase formation and sulfurization of the precursor to obtain CZTS. Microstructural (XRD, Raman), morphological (SEM), and compositional (EDX, XRF) characterization is carried out on CZT and CZTS films, showing a minor presence of secondary phases. Finally, photo-assisted water splitting tests are performed considering a CZTS/CdS/Pt photoelectrode, showing a photocurrent density of 1.01 mA cm⁻² at 0 V vs. RHE under 1 sun illumination.

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Electrolysis energy efficiency of highly concentrated FeCl2 solutions for power-to-solid energy storage technology

An electrochemical cycle for the grid energy storage in the redox potential of Fe involves the electrolysis of a highly concentrated aqueous FeCl₂ solution yielding solid iron deposits. For the high overall energy efficiency of the cycle, it is crucial to maximize the energy efficiency of the electrolysis process. Here we present a study of the influence of electrolysis parameters on the energy efficiency of such electrolysis, performed in an industrial-type electrolyzer. We studied the conductivity of the FeCl₂ solution as a function of concentration and temperature and correlated it with the electrolysis energy efficiency. The deviation from the correlation indicated an important contribution from the conductivity of the ion-exchange membrane. Another important studied parameter was the applied current density. We quantitatively showed how the contribution of the resistance polarization increases with the current density, causing a decrease in overall energy efficiency. The highest energy efficiency of 89 ± 3% was achieved using 2.5 mol L⁻¹ FeCl₂ solution at 70 °C and a current density of 0.1 kA m⁻². In terms of the energy input per Fe mass, this means 1.88 Wh g⁻¹. The limiting energy input per mass of the Fe deposit was found to be 1.76 Wh g⁻¹_.

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Conflicting roles of Na-doped layered cathode material LiCoO2 for Li-ion batteries

In this work, the electrochemical performance of Na-doped layered cathode material LiCoO₂ for Li-ion batteries is studied using first-principles calculations. The results show that the doped Na ion acts as a pillar, which can greatly increase the diffusion rate of Li ions, but it is not conducive to improving cycle performance and delithiation potential. These research results provide a theoretical reference for the study of Li-ion batteries with high-rate performance. Due to the conflicting role of single element doping, the multi-element co-doping strategy will be the best way to develop high-performance Li-ion batteries.

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Connection of CVs and impedance spectra of reversible redox systems,as used for the validation of a dynamic electrochemical impedance spectrum measurement system

With the purpose of fast characterization of electrode reactions, a dynamic electrochemical impedance spectrum (dEIS) measurement system has been assembled which permits the continuous collection of audio-frequency impedance spectra while performing cyclic voltammetry measurements with the usual scan rates of up to 200 mV/s. The performance of this system was tested by analyzing the CV curves and impedance spectra taken simultaneously in ferro-/ferricyanide containing aqueous solutions yielding an experimental demonstration of the connection of the semi-integrated reversible voltammograms and the Warburg coefficients.

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The Inverted Philosopher’s Stone: how to turn silver to a base metal

Metals often are classified as “noble” or “base”—characterizing their reduction potential as one of the most important chemical properties. We show that metals are only as noble as allowed by their environment, i.e. this is a relative term, and the “frame of reference” simply is the solvent in which the redox system is present. We prove that silver is a prime example for a noble metal that forfeits its noble character in the simple ionic liquid HMIM Br (1-hexyl-3-methylimidazolium bromide) as an example for such a solvent.

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Mixed oxide growth on combinatorial aluminium–gadolinium alloys — a thermodynamic and first-principles approach

Metal surfaces covered with oxides have attracted considerable scientific attention in various applications. In particular, anodic films fabricated by cost-effective anodizing have been widely used in nano-structured engineering to provide various surface functionalities. However, understanding of alloy film stability, having individual elements with widely varying structures and morphologies, is very limited due to lack of thermodynamic information and effects of electrolyte chemistry. This requires many tedious efforts on a trial and error basis in selecting suitable electrolytes that can produce the protective film at high efficiency on alloys having mixed chemistries. It is, therefore, crucial to develop a combination of high throughput theoretical analysis and automated rapid localized electrochemical probing that provides a fast and simple solution for electrolyte choice and paves the way to the remarkable expansion of industrial applications of oxides. Herein, we demonstrate that combinatorial Al–Gd alloys covering 1.0 to 10.0 at.% Gd can be oxidized into ultra-thin anodic films of controlled thickness through a selection of electrolyte based on thermodynamics (phosphate buffer with a pH of 8.20). We propose that growth of anodic films on alloys at high efficiency is possible if Gibbs free energy minimization criteria would be systematically contemplate.

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Zein film as a novel natural biopolymer membrane in electrochemical detections

Permselective modifier films are very important in preparing highly sensitive electrochemical sensors. In this work, for the first time, the behavior of gold and glassy carbon electrodes coated with biocompatible zein film as a permselective membrane for the electrochemical detection of various compounds has been investigated. For this purpose, several electroactive cationic (methylene blue, brilliant green, and thionine) and anionic (potassium ferricyanide, alizarin red S, and riboflavin-5’-phosphate) compounds have been used as model. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that zein membranes prepared from casting solution containing 1% zein in ethanol/water have porous structures with high nanometric roughness. The capacitance values of electrical double layers of electrodes modified with zein film were very high for hydrophilic ions in comparison with hydrophobic ions. Point of zero charge pH (pH_pzc) of zein membrane was 4.8. The results of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) as well as pH_pzc study indicated that zein permselective membrane acts as ion exchanger film for selected cationic compounds with fast electrochemical kinetics responses in aqueous solution (pH=7). This behavior was confirmed by circulating solutions containing model compounds from homemade continuous cell equipped with polyamide membranes modified with zein film.

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Reduced graphene oxide supported 2D-NiO nanosheets modified electrode for urea detection

Nickel oxide (NiO) nanosheets (NSs) deposited on different amounts (0.025, 0.05, 0.1, and 0.2 wt%) of reduced graphene oxide (rGO) are synthesized through hydrothermal method. The NiO NSs on rGO (rGO-NiO) are characterized by using X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) analyses, and electrochemical analysis. Electrocatalytic activity of rGO-NiO nanocomposite modified glassy carbon (GC/rGO-NiO) electrode is examined towards electrocatalytic oxidation of urea in 0.1 M NaOH using cyclic voltammetry and amperometry techniques. The GC/rGO_0.1-NiO nanocomposite modified electrode shows enhanced electrocatalytic oxidation of urea than that of other modified electrodes due to the incorporation of NiO NSs on an optimum amount of rGO. The GC/rGO_0.1-NiO modified electrode is used for designing electrochemical sensor for urea, and the detection limit is estimated as 0.47 μM using the amperometry technique. The sensitivity of GC/rGO_0.1-NiO modified electrode is found to be 2450 μA mM⁻¹ cm⁻². In addition to good electroanalytical performance, the present urea sensor displayed good stability and acceptable anti-interference ability in the presence of 20-fold excess concentration of relevant interferents. The GC/rGO_0.1-NiO nanocomposite modified electrode is successfully used for the determination of urea in water sample.

Schematic representation of electrocatalytic oxidation of urea at GC/rGO-NiO nanocomposite modified electrode.

     

Effect of 1-octanethiol as an electrolyte additive on the performance of the iron-air battery electrodes

It has recently been established that 1-octanethiol in the electrolyte can allow iron electrodes to be discharged at higher rates. However, the effect of thiol additives on the air electrode has not yet been studied. The effect of solvated thiols on the surface positive electrode reaction is of prime importance if these are to be used in an iron-air battery. This work shows that the air-electrode catalyst is poisoned by the presence of octanethiol, with the oxygen reduction overpotential at the air electrode increasing with time of exposure to the solution and increased 1-octanethiol concentration in the range 0–0.1 mol dm⁻³. Post-mortem XPS analyses were performed over the used air electrodes suggesting the adsorption of sulphur species over the catalyst surface, reducing its performance. Therefore, although sulphur-based additives may be suitable for nickel-iron batteries, they are not recommended for iron-air batteries except in concentrations well below 10 × 10⁻³ mol dm⁻³.

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Dual solid electrolytes for aluminium-air batteries based on polyvinyl alcohol acidic membranes and neutral hydrogels

Water-based electrolytes are generally preferable to organic electrolytes due to their low cost and higher safety standard. However, their widespread use is generally limited by recharging issues. In the case of Al-air cells, water on the anode prevents aluminium deposition during recharging by producing hydrogen at more positive standard potentials. This promotes parasitic reactions that consume the anode and shorten the cell shelf life. On the cathode side, depending on the pH, water allows efficient oxygen reduction or oxygen evolution reactions. To produce electrolytes with different water contents on the two electrodes, we prepared solid electrolytes using polyvinyl alcohol (PVA) and aqueous HCl solutions with ionic conductivity ranging from 0.7 to 2.2 × 10⁻³ S cm⁻¹ and electrochemical windows wider than 2.2 V. The new materials resembled a thin plastic membrane (0.6–0.9 mm thick) and were able to oxidise the Al-air cell anode. We also explored the possibility of using a dual electrolyte to allow the presence of water mainly on the cathode side. Specifically, cells assembled with two electrolytes in contact, with an acidic PVA membrane as anolyte and saline hydrogel as catholyte without separator, showed discharge capacity more than one order of magnitude greater than cells with single acidic PVA electrolytes. Electrochemical impedance spectroscopy (EIS) characterisation verified that the improved cell discharge capacity was attributed to the soft aqueous catholyte on the cathode-electrolyte interface and to the membrane conductivity stabilisation during cell use through the saline gel water. Cyclic voltammetry (CV) characterisation suggested the possibility of recharging the dual electrolyte cells thanks to the substantial absence of water on the anode side.

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Inorganic solids for dual magnesium and sodium battery electrodes

Despite the success of lithium-ion batteries, recognized through the award of the 2019 Nobel Prize in Chemistry, the forecast of a wide application of these systems to avoid the use of fossil fuels and their effect on global warming has raised doubts about their safety, sustainability, and performance. To make a post-lithium era possible, other reducing metals are investigated. While sodium shows certain analogies with lithium, some advantages with respect to its abundance and availability or the lack of Al alloy that could substantially reduce production costs make sodium-ion batteries a good alternative, particularly for stationary applications. On the other hand, other abundant multivalent elements such as Mg can provide even higher energy densities. The possibility of using dual ions can be a strategy to get the best of each element in a synergistic battery system. Dual Na⁺/Mg²⁺ systems have been considered a potential option by different researchers. In this review, we shall discuss different results on dual-metal-ion systems studied in our laboratory, particularly vanadium oxides and phosphates and layered manganese oxides.

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Selective and sensitive detection of cyanate using 3-amino-2-naphthoic acid-based turn-on fluorescence probe

The cyanate anion (CNO⁻), formed spontaneously within cells from urea and carbamoyl phosphate, usually functions as a biomarker of some diseases such as chronic kidney disease. Therefore, accurate determination of CNO⁻ is highly demanded. Herein, a 3-amino-2-naphthoic acid-based “turn-on” fluorescence probe was developed for specific detection of CNO⁻. Upon the addition of sodium cyanate, the weak-fluorescent 3-amino-2-naphthoic acid could react with CNO⁻, which triggered intense emission of green fluorescence. And up to 9-fold fluorescence enhancement was observed. The fluorescence enhancement ratios displayed a good linear relationship with the concentrations of CNO⁻ in the range of 0.5–200 μM. The high selectivity and sensitivity for CNO⁻ detection were investigated with the detection limit as low as 260 nM. The probe was further successfully applied to determine CNO⁻ in real samples such as tap water, human urine and serum samples, which offered a promising approach in practical applications.

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Electrochemistry of metal adlayers on metal chalcogenides

Electrodeposition of metal adlayers on semiconductor metal chalcogenides (CdSe, CdS, PbTe, PbSe, PbS, Bi₂Te₃) is reviewed. Cathodic underpotential deposition of metal adlayer on metal chalcogenide is the electrochemically irreversible surface limited reaction. The irreversibility of the upd increases in the row from tellurides to selenides and further to sulfides. The underpotential shift on chalcogenide nanoparticles increases with particle size. Metal upd on chalcogenides is applied as a means of measurement of electroactive surface area of chalcogenide electrodes. The method is especially advantageous for multicomponent systems with other component not supporting upd, such as CdSe-TiO₂, CdSe-ZnO. Differences of voltammetric profiles of Pb upd on Bi₂Te₃ and Te are applied for detection of Bi₂Te₃ surface contamination by elemental tellurium. The further tasks in the electrochemistry of metal adlayers are their incorporation as interlayers in layered chalcogenides and electrodeposition of superlattices.

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Processes associated with ionic current rectification at a 2D-titanate nanosheet deposit on a microhole poly(ethylene terephthalate) substrate

Films of titanate nanosheets (approx. 1.8-nm layer thickness and 200-nm size) having a lamellar structure can form electrolyte-filled semi-permeable channels containing tetrabutylammonium cations. By evaporation of a colloidal solution, persistent deposits are readily formed with approx. 10-μm thickness on a 6-μm-thick poly(ethylene-terephthalate) (PET) substrate with a 20-μm diameter microhole. When immersed in aqueous solution, the titanate nanosheets exhibit a p.z.c. of − 37 mV, consistent with the formation of a cation conducting (semi-permeable) deposit. With a sufficiently low ionic strength in the aqueous electrolyte, ionic current rectification is observed (cationic diode behaviour). Currents can be dissected into (i) electrolyte cation transport, (ii) electrolyte anion transport and (iii) water heterolysis causing additional proton transport. For all types of electrolyte cations, a water heterolysis mechanism is observed. For Ca²⁺ and Mg²⁺ions, water heterolysis causes ion current blocking, presumably due to localised hydroxide-induced precipitation processes. Aqueous NBu₄⁺ is shown to ‘invert’ the diode effect (from cationic to anionic diode). Potential for applications in desalination and/or ion sensing are discussed.

     

Highly sensitive and rapid determination of sunset yellow in drinks using a low-cost carbon material-based electrochemical sensor

Starting from simple graphite flakes, an electrochemical sensor for sunset yellow monitoring is developed by using a very simple and effective strategy. The direct electrochemical reduction of a suspension of exfoliated graphene oxide (GO) onto a glassy carbon electrode (GCE) surface leads to the electrodeposition of electrochemically reduced oxide at the surface, obtaining GCE/ERGO-modified electrodes. They are characterized by cyclic voltammetry (CV) measurements and field emission scanning electron spectroscopy (FE-SEM). The GCE/ERGO electrode has a high electrochemically active surface allowing efficient adsorption of SY. Using differential pulse voltammetry (DPV) technique with only 2 min accumulation, the GCE/ERGO sensor exhibits good performance to SY detection with a good linear calibration for concentration range varying 50–1000 nM (R² = 0.996) and limit of detection (LOD) estimated to 19.2 nM (equivalent to 8.9 μg L⁻¹). The developed sensor possesses a very high sensitivity of 9 μA/μM while fabricated with only one component. This electrochemical sensor also displays a good reliability with RSD value of 2.13% (n = 7) and excellent reusability (signal response change < 3.5% after 6 measuring/cleaning cycles). The GCE/ERGO demonstrates a successful practical application for determination of sunset yellow in commercial soft drinks.

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Development of metal oxide incorporated Al-Zn-Sn sacrificial anodes processed by stir casting and heat treatment

Aluminum sacrificial anodes are currently the first choice for cathodic protection in numerous applications. The galvanic performance of aluminum-based sacrificial anodes is considerably enhanced by addition of certain alloying elements called activators. Recent researches proved that incorporation of specific metal oxides like MnO₂, CeO₂, RuO₂, and IrO₂ into the aluminum matrix could enhance the galvanic efficiency of aluminum anodes; however, the mechanism by which metal oxides improve galvanic properties of aluminum is still subject to discussion. The present work investigates the effect of incorporating commercially available low-cost manganese dioxide concentrate into Al-5Zn-0.1Sn sacrificial anodes in different volume fractions. It also studies the influence of heat treatment on anode’s galvanic performance by performing solution treatment at 3 different temperatures (250 °C, 400 °C, 550 °C). The electrochemical testing results proved an increase in efficiency of anodes incorporated with metal oxides and solution treated at 550 °C. The SEM imaging and EDX elemental mapping declared that the presence of SiO₂ particles in the anode matrix which might cause effective and uniform corrosion of Al anodes and decreased non-coulombic losses.

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Novel photosensitizer for dye-sensitized solar cell based on ionic liquid–doped blend polymer electrolyte

The existing energy situation demands not only the huge energy in a short time but also clean energy. In this regard, an integrated photo-supercapacitor device has been fabricated in which photoelectric conversion and energy storage are achieved simultaneously. A novel carbazole-based dye is synthesized and characterized for photosensitizer. The silver-doped titanium dioxide (Ag-TiO₂) is synthesized, and it is used as photoanode material. Different concentrations of tetrabutylammonium iodide (TBAI)-doped polyvinyl alcohol–polyvinylpyrrolidone (PVA-PVP) blend polymer electrolytes are prepared, and their conductivity and dielectric properties were studied. Reduced graphene oxide (r-GO) is synthesized by a one-pot synthesis method and confirmed using Raman spectroscopy for counter electrode material in dye-sensitized solar cell (DSSC) and supercapacitor electrodes. The DSSC having 4% Ag-TiO₂–based photoanode showed the highest efficiency of 1.06% (among r-GO counter electrodes) and 2.37% (among platinum counter electrodes). The supercapacitor before integration and after integration exhibits specific capacitance of 1.72 Fg⁻¹ and 1.327 Fg⁻¹, respectively.

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