Showing papers in "Journal of Solid State Electrochemistry in 2016"

Fabrication, characterization and photoelectrochemical performance of chromium-sensitized titania nanotubes as efficient photoanodes for solar water splitting

Abstract: Chromium-sensitized titanium dioxide nanotubes (CTNT) with high photocatalytic activity were prepared by a chemical bath deposition technique. The resulting films were characterized by SEM, EDX, and XRD. Results showed that the fabricated films have the ordered nanotubes with diameter of 90–140 nm, wall thickness of 20–50 nm, and tube lengths in the range of 24 μm. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare titanium dioxide nanotubes (TNT). The photoelectrochemical performance was examined under light irradiation in 1 M NaOH electrolyte. Photoelectrochemical characterization shows that chromium sensitizing efficiently enhances the photocatalytic water splitting performance of CTNT composite. The sample (C3TNT) exhibited better photocatalytic activity than the TNT and CTNT fabricated using other chromium concentrations. This inexpensive photoanodes prepared free of noble metals showed enhanced high photocurrent density with good stability and is a highly promising photoanode for solar hydrogen production.

On the gassing behavior of lithium-ion batteries with NCM523 cathodes

Abstract: Gas evolution has a profound effect on the functioning of state-of-the-art lithium-ion batteries. On one hand, it is the natural concomitant of solid electrolyte interphase (SEI) formation on the anode (reduction of electrolyte components). On the other hand, because of the demand for high terminal voltages, it is also the consequence of electrolyte and/or cathode material oxidation. Overall, gassing happens on the expense of Coulombic efficiency and additionally raises safety issues. Herein, the gassing behavior of one of the most important commercialized cathode materials, namely Ni-rich Li1 + xNi0.5Co0.2Mn0.3O2 (NCM523 with 0.01 < x < 0.05), is reported for the first time. We analyze the generation pattern of the most typical gases H2, C2H4, CO2, and CO during 30 cycles by means of differential electrochemical mass spectrometry combined with Fourier transform infrared spectroscopy. In a long-term test of an NCM523/graphite cell, we monitor its potential-resolved gas evolution and evaluate the total amount of gas from cycle to cycle. An explanation on the characteristic features of pressure versus time curves during cycling is given by combining the spectrometric and total gas pressure data. With additional information from graphite/lithium cells, the identity of gases formed during SEI formation is revealed.

Electrodeposited conductive polymers for controlled drug release: polypyrrole

Abstract: Over the last 40 years, electrically conductive polymers have become well established as important electrode materials. Polyanilines, polythiophenes and polypyrroles have received particular attention due to their ease of synthesis, chemical stability, mechanical robustness and the ability to tailor their properties. Electrochemical synthesis of these materials as films have proved to be a robust and simple way to realise surface layers with controlled thickness, electrical conductivity and ion transport. In the last decade, the biomedical compatibility of electrodeposited polymers has become recognised; in particular, polypyrroles have been studied extensively and can provide an effective route to pharmaceutical drug release. The factors controlling the electrodeposition of this polymer from practical electrolytes are considered in this review including electrolyte composition and operating conditions such as the temperature and electrode potential. Voltammetry and current-time behaviour are seen to be effective techniques for film characterisation during and after their formation. The degree of take-up and the rate of drug release depend greatly on the structure, composition and oxidation state of the polymer film. Specialised aspects are considered, including galvanic cells with a Mg anode, use of catalytic nanomotors or implantable biofuel cells for a self-powered drug delivery system and nanoporous surfaces and nanostructures. Following a survey of polymer and drug types, progress in this field is summarised and aspects requiring further research are highlighted.

Ionic liquid-based sodium ion-conducting composite gel polymer electrolytes: effect of active and passive fillers

Abstract: We report the studies on composite gel polymer electrolytes (GPEs) comprising 0.5 M solution of sodium trifluoromethane sulfonate (Na-triflate or NaTf) in ionic liquid 1-ethyl 3-methyl imidazolium trifluoromethane sulfonate (EMITf) entrapped in poly (vinylidinefluoride-co-hexafluoropropylene) (PVdF-HFP) dispersed with passive filler Al2O3 and active filler NaAlO2 particles. The free-standing films of the composite GPEs, prepared from solution-cast method, offer optimum ionic conductivity at room temperature (6.3–6.8 × 10−3 S cm−1 and 5.5–6.5 × 10−3 S cm−1 for Al2O3- and NaAlO2-dispersed GPEs, respectively), with sufficient electrochemical stability and excellent thermal stability up to 340 °C. As observed from XRD and SEM, the composites are of predominantly amorphous and porous character, which support the high ionic conduction. The sodium ion transport number has been found to be ∼0.27 for Al2O3-dispersed GPE and 0.42 for NaAlO2-dispersed GPE, which indicates the predominant role of passive and active fillers, Al2O3 and NaAlO2, respectively. The dispersion of NaAlO2 enhances the sodium ion conductivity in composite GPE substantially. The overall ionic conductivity is same as in the case of Al2O3 dispersion. The performance characteristics of GPE, particularly, dispersed with active filler NaAlO2 show its potential applicability as electrolyte/separator in sodium batteries.

NiCo 2 O 4 /rGO hybrid nanostructures for efficient electrocatalytic oxygen evolution

Abstract: We report the synthesis of NiCo2O4/reduced graphene oxide (NiCo2O4/rGO) hybrid hierarchical structures with unique nanonet and microsphere morphologies by organic polar solvent-assisted solvothermal method. The electrocatalytic oxygen evolution reaction (OER) activity of these materials is studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods in O2-saturated 0.1 M KOH solution. The NiCo2O4/rGO hybrid nanocomposite materials are found to be highly active electrocatalysts for OER at lower overpotentials. The nanonet and microsphere-like NiCo2O4/rGO catalysts require overpotentials of 0.450 and 0.530 V at a current density of 10 mA cm−2, and their corresponding Tafel slopes are 53 and 62 mV dec−1, which are much lower than values reported for non-precious electrocatalysts. Further, both NiCo2O4/rGO catalysts show good catalytic stability with current retention more than 92 % over long period of 15,000 s determined by chronoampirometry and at the end of 1000th cycle determined by linear sweep voltammetry. The enhanced OER activity of nanostructured NiCo2O4/rGO hybrid catalysts is attributed to synergistic interaction between rGO and NiCo2O4, which seems to be essential for maintaining the large contact area at the electrode-electrolyte interface, better mass, and charge transport and to minimize the aggregation of NiCo2O4 nanoparticles.

Studies of porous solid polymeric electrolytes based on poly (vinylidene fluoride) and poly (methyl methacrylate) grafted natural rubber for applications in electrochemical devices

Abstract: The potential of new porous solid polymer electrolyte (SPE) for poly (vinylidene fluoride)–poly (methyl methacrylate) grafted natural rubber (PVDF-MG49) doped with LiCF3SO3 based on application in electrochemical device system has been investigated. The characteristics of the samples are analyzed and studied using electron impedance spectroscopy (EIS), X-ray diffraction (XRD), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and linear sweep voltammetry (LSV). Ionic conductivity of 3.25 × 10−4 S cm−1 is achieved at room temperature, and the studies suggested that ion transport proceeds in these materials via a hopping mechanism similar to what is found in an ionic crystal. It is found that dielectric constant and dielectric loss increase with salt contents. A similar situation is also observed in electrical modulus. Analysis of XRD shows a decrease in crystallinity peaks of methyl methacrylate (MMA) in MG49 with the amount of added salt. The observations from SEM micrographs show porosity structure of polymer electrolyte. Based on the FTIR results, we are able to conjecture that interactions between the lithium ion and with the oxygen atoms from the MMA likely occur. Electrochemical studies show that polymer electrolyte has high electrochemical stability windows and is favorable for application in electrochemical devices.

Electrochemical supercapacitive properties of polypyrrole thin films: influence of the electropolymerization methods

Abstract: A detailed study of the effects of different electropolymerization methods on the supercapacitive properties of polypyrrole (PPy) thin films deposited on carbon cloth is reported. Deposition mechanisms of PPy thin films through cyclic voltammetry (CV), potentiostatic (PS), and galvanostatic (GS) modes have been analyzed. The resulting PPy thin films have been characterized by X-ray photoelectron spectroscopy (XPS), SEM, and TEM. The electrochemical properties of PPy thin films were investigated by cyclic voltammetry and galvanostatic charge/discharge. The results showed that the different electrodeposition modes of synthesis significantly affect the supercapacitive properties of PPy thin films. Among different modes of electrodeposition, PPy synthesized by a potentiostatic mode exhibits maximum specific capacitance of 166 F/g with specific energy of 13 Wh/kg; this is attributed to equivalent proportions of the oxidized and neutral states of PPy. Thus, these results provide a useful orientation for the use of optimized electrodeposition modes for the growth of PPy thin films to be applied as electrode material in supercapacitors.

MnO2/polyaniline hybrid nanostructures on carbon cloth for supercapacitor electrodes

Abstract: A facile two-step strategy is developed for synthesis of MnO2/polyaniline (PANI) hybrid nanostructures on carbon cloth (CC). Vertically aligned PANI nanofiber arrays were firstly grown on CC via chemical oxidative polymerization, and MnO2 nanoparticles were then deposited on the surface of PANI nanofibers via redox reaction between PANI and KMnO4 solution. Structural and morphological characterizations of composites were investigated by FESEM, Raman, and XPS techniques, respectively. Electrochemical performance of the composites as supercapacitor electrode materials was evaluated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. The results demonstrate that the morphology and areal specific capacitance of the MnO2/PANI/CC composite vary with MnO2 deposition time. The ternary composite with 6 h MnO2 deposition exhibits a high areal capacitance of 1.56 F cm−2 at the scan rate of 10 mV s−1 and 0.99 F cm−2 at a current density of 2 mA cm−2 and still maintains 88.1 % of the original capacitance after 1000 charge-discharge cycles at a large current density of 10 mA cm−2.The excellent performance is due to the synergistic effect from the combination of two active pseudo materials and 3D conductive CC backbone. This study further highlights the importance of optimal design and control of material structures in supercapacitor applications.

The application of activated carbon modified by ozone treatment for energy storage

Abstract: Activated carbon modified by ozone treatment was examined. The process was carried out in a glass reactor under a continuous flow of ozone through a bed of activated carbon for 15, 30, 60, 120, and 240 min. The modified and unmodified carbon materials were characterized by Raman spectroscopy and observed by scanning electron microscopy (SEM). Thermogravimetric analysis was used to estimate the presence of oxygen groups in the carbon structure. The surface area and pore size distribution were examined by nitrogen adsorption method at 77 K. Moreover, Fourier transform infrared (FTIR) spectroscopy was used to estimate the functional groups of modified activated carbon. The carbon content was estimated using the elemental analysis. The process of ozonation increases oxygen functionalities, thus the activated carbon was tested as electrodes for an electrochemical capacitor. The performance of an electrochemical capacitor was estimated by selected alternating (AC) and direct current (DC) methods in 1 M H2SO4, 1 M Na2SO4, and 6 M KOH electrolytes.

Effect of solvents on the morphology of NiCo2O4/graphene nanostructures for electrochemical pseudocapacitor application

Abstract: The large internal surface areas and outstanding electrical and mechanical properties of graphene have prompted to blend graphene with NiCo2O4 to fabricate nanostructured NiCo2O4/graphene composites for supercapacitor applications. The use of graphene as blending with NiCo2O4 enhances the specific capacitance and rate capability and improves the cyclic performance when compared to the pristine NiCo2O4 material. Here, we synthesized two different nanostructured morphologies of NiCo2O4 on graphene sheets by solvothermal method. It has been suggested that the morphologies of oxides are greatly influenced by dielectric constant, thermal conductivity, and viscosity of solvents employed during the synthesis. In order to test this concept, we have synthesized nanostructured NiCo2O4 on graphene sheets by facile solvothermal method using N-methyl pyrrolidone and N,N-dimethylformamide solvents with water. We find that mixture of N-methyl pyrrolidone and water solvent favored the formation of nanonet-like NiCo2O4/graphene (NiCoO-net) whereas mixture of N,N-dimethylformamide and water solvent produced microsphere-like NiCo2O4/graphene (NiCoO-sphere). Electrochemical pseudocapacitance behavior of the two NiCo2O4/graphene electrode materials was studied by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy techniques. The supercapacitance measurements on NiCoO-net and NiCoO-sphere electrodes showed specific capacitance values of 1060 and 855 F g−1, respectively, at the current density of 1.5 A g−1. The capacitance retention of NiCoO-net electrode is 93 % while that of NiCoO-sphere electrode is 77 % after long-term 5000 charge-discharge cycles at high current density of 10 A g−1.

Lignin-derived hierarchical porous carbon for high-performance supercapacitors

Abstract: Lignin as the second most abundant natural polymer was applied to prepare a hierarchical porous carbon (HPC) for supercapacitors (SCs). Direct activation with various KOH dosages was applied to obtain HPC. Both pore size distribution and electrochemical performance were evaluated and compared to optimize the KOH dosages. Field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), Fourier transform infrared spectrometry (FT-IR), and Raman spectroscopy were also applied to better understand the structure change of HPC with KOH dosages. High gravimetric capacities (C g) of 268 and 162 F g−1 were obtained in aqueous and organic solutions, respectively. Excellent rate and cycle performance demonstrated the stable structure of HPC. Energy density could reach as high as 40.89 W h kg−1 in organic solution. Besides, it was also concluded that a high C g can be obtained with low KOH dosage in aqueous solution while high KOH dosage was needed in organic solution. In a word, lignin was indeed a suitable precursor for the preparation of HPC in SCs.

Enzyme-free impedimetric glucose sensor based on gold nanoparticles/polyaniline composite film

Abstract: A non-enzymatic impedimetric glucose sensor was fabricated based on the adsorption of gold nanoparticles (GNPs) onto conductive polyaniline (PANI)-modified glassy carbon electrode (GCE). The modified electrode (GCE/PANI/GNPs) was characterized by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The determination of glucose concentration was based on the measurement of EIS with the mediation of electron transfer by ferricyanide ([Fe(CN)6]3−). The [Fe(CN)6]3− is reduced to ferrocyanide ([Fe(CN)6]4−), which in turn is oxidized at GCE/PANI/GNPs. An increase in the glucose concentration results in an increase in the diffusion current density of the [Fe(CN)6]4− oxidation, which corresponds to a decrease in the faradaic charge transfer resistance (R ct). A wide linear concentration range from 0.3 to 10 mM with a lower detection limit of 0.1 mM for glucose was obtained. The proposed sensor shows high sensitivity, good reproducibility, and stability. In addition, the sensor exhibits no interference from common interfering substances such as ascorbic acid, acetaminophen, and uric acid.

Electrospun cellulose acetate/poly(vinylidene fluoride) nanofibrous membrane for polymer lithium-ion batteries

Abstract: The membranes for gel polymer electrolyte (GPE) for lithium-ion batteries were prepared by electrospinning a blend of poly(vinylidene fluoride) (PVdF) with cellulose acetate (CA). The performances of the prepared membranes and the resulted GPEs were investigated, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), porosity, hydrophilicity, electrolyte uptake, mechanical property, thermal stability, AC impedance measurements, linear sweep voltammetry, and charge–discharge cycle tests. The effect of the ratio of CA to PVdF on the performance of the prepared membranes was considered. It is found that the GPE based on the blended polymer with CA:PVdF =2:8 (in weight) has an outstanding combination property-strength (11.1 MPa), electrolyte uptake (768.2 %), thermal stability (no shrinkage under 80 °C without tension), and ionic conductivity (2.61 × 10−3 S cm−1). The Li/GPE/LiCoO2 battery using this GPE exhibits superior cyclic stability and storage performance at room temperature. Its specific capacity reaches up to 204.15 mAh g−1, with embedded lithium capacity utilization rate of 74.94 %, which is higher than the other lithium-ion batteries with the same cathode material LiCoO2 (about 50 %).

Nano oxides incorporated sulfonated poly(ether ether ketone) membranes with improved selectivity and stability for vanadium redox flow battery

Abstract: Three kinds of sulfonated poly(ether ether ketone) (SPEEK)/nano oxide (Al2O3, SiO2, and TiO2) composite membranes are fabricated for vanadium redox flow battery (VRFB) application. The composite membranes with 5 wt% of Al2O3, SiO2, and TiO2 (S/A-5 %, S/S-5 %, and S/T-5 %) exhibit excellent cell performance in VRFB. Incorporation of nano oxides (Al2O3, SiO2, and TiO2) in SPEEK membrane improves in aspect of thermal, mechanical, and chemical stabilities due to the hydrogen bonds’ interaction between SPEEK matrix and nano oxides. The energy efficiencies (EEs) of composite membranes are higher than that of Nafion 117 membrane, owing to the good balance between proton conductivity and vanadium ion permeability. The discharge–capacity retentions of composite membranes also overwhelm that of Nafion 117 membrane after 200 cycles, indicating their good stability in VRFB system. These low-cost SPEEK/nano oxide composite membranes exhibit great potential for the application in VRFB.

A sensitive electrochemical sensor for lead based on gold nanoparticles/nitrogen-doped graphene composites functionalized with l-cysteine-modified electrode

Abstract: Glassy carbon electrodes (GCEs) modified with l-cysteine (l-cys)/gold nanoparticles (AuNPs)/nitrogen-doped graphene (NG) composite were prepared to fabricate a novel electrochemical sensor for lead. AuNPs were uniformly dispersed into NG and l-cys was successfully decorated on AuNPs through the S–Au bond. The l-cys/AuNPs/NG exhibited a well-distributed nanostructure and high responsivity toward Pb(II). The results indicated that l-cys/AuNPs/NG/GCE exhibited the highest peak current, reflecting that the l-cys/AuNPs/NG composites showed the best response signal toward Pb2+. Under optimized conditions, a linear relationship between the current intensity and Pb2+ concentration was obtained in a range of 0.5–80 μg L−1 with a detection limit of 0.056 μg L−1 (S/N = 3). The analytical interference procedure and practical application were investigated using the prepared electrode, which exhibited an acceptable result.

Activity volcanoes for the electrocatalysis of homolytic and heterolytic hydrogen evolution

Abstract: This paper derives a simple kinetic model for the electrochemical current generated by a heterolytic model for hydrogen evolution, as it would apply to the reaction taking place on molecular catalysts, and compares the activity trends to the classical Volmer-Heyrovsky-Tafel models. It is demonstrated that in the heterolytic mechanism, pH plays a crucial role in optimizing the overall activity.

Preparation of polyacrylamide via surface-initiated electrochemical-mediated atom transfer radical polymerization (SI-eATRP) for Pb2+ sensing

Abstract: Acrylamide polymer brushes (PAM) were prepared on the surface of Au electrode for Pb2+ ion sensing via surface-initiated electrochemical-mediated atom transfer radical polymerization (SI-eATRP). The electrode modified with PAM (PAM/Au) was carefully examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), polarization modulation infrared reflection–absorption spectroscopy (PM-IRRAS), and scanning electron microscope (SEM). Further, the PAM/Au electrode was successfully used for the determination of Pb2+ ion by differential pulse anodic stripping voltammetry (DPASV). Under the optimal conditions, the PAM/Au electrode showed a linear correlation for Pb2+ concentrations in the range of 3.0 × 10−3 to 2.0 × 103 μg/L. The limit of detection (S/N = 3.3) was estimated to be 3.7 × 10−4 μg/L. Finally, polymer brush electrodes were applied to analyze Pb2+ ion in an effluent. The results of the experiment indicated that PAM/Au electrode has good accuracy and potential application in practical sample analysis. In a word, the work of this paper established a useful way for the synthesis and application of polymer brush.

The search for a solid electrolyte, as a polysulfide barrier, for lithium/sulfur batteries

Abstract: Composite Li10SnP2S12 (LSPS)/polyethylene oxide (PEO) films, containing 25 to 50 % polymer, were electrophoretically deposited from acetone-based suspension and tested as possible candidates for polysulfide barriers in Li/S batteries. It was found by XRD and XPS tests that saturation of composite films by LiI salt, followed by prolonged annealing at 90 °C, diminishes the crystallinity of neat LSPS and results in the formation of a novel composite Li10+xIxSnP2S12 (LISPS)/P(EO)3/LiI solid electrolyte (x < 1). The high room-temperature ion conductivity of amorphous sulfide Li10+xIxSnP2S12 (0.1–0.3 mS cm−1) is restricted by slow ion transport via the polymer electrolyte (PE) imbedded in ceramics and grain boundaries between the PE and sulfide. Increase in polymer content and temperature improves total ion transport in the LISPS/PEO system. Conformal EPD coating of sulfur and lithium sulfide cathodes by the developed composite electrolyte increased the reversible capacity and Faradaic efficiency of the Li/S and Li/Li2S cells and enabled their operation at 60 °C.

Sulfur encapsulated in porous carbon nanospheres and coated with conductive polyaniline as cathode of lithium–sulfur battery

Abstract: We report a novel composite, sulfur (S) encapsulated in porous carbon nanospheres (PCNS) and coated with conductive polyaniline (PANI) (PCNS-S@PANI), as cathode of lithium–sulfur battery. PCNS is prepared by convenient and controllable hydrothermal synthetic route and loaded with S via chemical deposition and then coated with conductive polyaniline via in situ polymerization under the control of ascorbic acid. The physical and electrochemical performances of the resulting PCNS-S@PANI are investigated by scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherms, thermogravimetric analysis, electronic conductivity measurement, galvanostatic charge–discharge test, and electrochemical impedance spectroscopy. It is found that PCNS-S@PANI exhibits excellent charge–discharge performances as cathode of lithium–sulfur battery: delivering a discharge capacity of 881 mAh g−1 at 0.2 C (1 C = 1672 mA g−1) with a capacity retention of 72 % after 100 cycles and a rate capacity of 324 mAh g−1 at 2 C. These natures can be attributed to the co-contribution of PCNS and conductive PANI to the improvement in electronic conductivity and chemical stability of sulfur cathode.

On the structural composition and stability of Fe–N–C catalysts prepared by an intermediate acid leaching

Abstract: The development of highly active and stable non-noble metal catalysts (NNMC) for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEM-FC) becomes of importance in order to enable cost reduction. In this work, we discuss the structural composition as derived from Fe-57 Mosbauer spectroscopy and X-ray diffraction, catalytic performance determined by a rotating (ring) disk electrode (RRDE) technique and stability evaluation of our Fe–N–C catalysts prepared by an intermediate acid leaching (IAL). The advantage of this IAL is given by a high density of active sites within the catalyst, as even without sulphur addition, an iron carbide formation and related disintegration of active sites are inhibited. In addition, our accelerated stress tests illustrate better stability of the sulphur-free IAL catalyst in comparison to the sulphur-added one.

Emulsion polymerization method for polyaniline-multiwalled carbon nanotube nanocomposites as supercapacitor materials

Abstract: Nanocomposites consisting of the conducting polymer, polyaniline (PANI), and multiwalled carbon nanotubes (MWNT) were prepared by in situ emulsion polymerization of aniline monomer on the surface of MWNT, using sodium dodecyl sulfate as an emulsifier and by varying the wt% of the MWNT. The morphology, composition, and thermal stability of the PANI-MWNT nanocomposites and pure PANI were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and field emission electron microscopy (FE-SEM). The PANI-MWNT nanocomposites were found to be crystalline in nature, with the PANI corals grown uniformly on the MWNT. Symmetric supercapacitors were constructed using the PANI-MWNT nanocomposites and pure PANI. Electrochemical analysis of the nanocomposites was performed using cyclic voltammetry and the galvanostatic charge-discharge method. The cyclic voltammetry analysis showed a synergistic increase in the specific capacitance of the PANI-MWNT nanocomposites. The unique structure of the PANI-MWNT nanocomposites led to a high specific capacitance of 240 F g−1 at a current density of 4.0 A g−1, with good rate performance, and 93 % retention of specific capacitance after 5000 CD cycles, indicating their potential as an electrode material for supercapacitors.

Surface structure and composition effects on electrochemical reduction of carbon dioxide

Abstract: Carbon dioxide electrochemical reduction has attracted significant attention due to its great potential in environmental protection and energy storage In this mini-review, some recent progress in heterogeneous electrochemical reduction of carbon dioxide is summarized, with a particular emphasis on the effects of catalyst surface modification Several structural (metal overlayers, particle size adjustment, roughness creation, special 2D or 3D structure patterning) and compositional (alloy, doping, oxide, and composite) modification techniques are reviewed and discussed Research directions towards more advanced catalysts design are proposed

PVDF/PAN/SiO2 polymer electrolyte membrane prepared by combination of phase inversion and chemical reaction method for lithium ion batteries

Abstract: PVDF/PAN/SiO2 polymer electrolyte membranes based on non-woven fabrics were prepared via introducing a chemical reaction into Loeb-Sourirajan (L-S) phase inversion process. It was found that physical properties (porosity, electrolyte uptake and ionic conductivity) and electrochemical properties were obviously improved. A favorable membrane structure with fully connective porous and uniform pore size distribution was obtained. The effects of PVDF/PAN weight ratio on the morphology, crystallinity, porosity, and electrochemical performances of membranes were studied. The optimized PVDF/PAN (70/30 w/w) (designated as Mpc30) polymer electrolyte membrane delivered excellent electrolyte uptake of 246.8 % and the highest ionic conductivity of 3.32 × 10−3 S/cm with electrochemical stability up to 5.0 V (vs. Li/Li+). In terms of cell performance, the Li/Mpc30 polymer electrolyte/LiFePO4 battery exhibited satisfactory electrochemical properties including high discharge capacity of 149 mAh/g at 0.2 C rate and good discharge performance at different current densities. The promising results reported here clearly indicated that PVDF/PAN/SiO2 polymer electrolyte membranes prepared by the combination of phase inversion and chemical reaction method were promising enough to be applied in power lithium ion batteries.

The polyacrylic latex: an efficient water-soluble binder for LiNi1/3Co1/3Mn1/3O2 cathode in li-ion batteries

Abstract: The polyacrylic latex (LA132) was firstly reported as a water-soluble binder for LiNi1/3Co1/3Mn1/3O2 (NCM) cathode in Li-ion battery. The electrochemical performances of NCM cathode with LA132 binder were investigated and compared with the conventional water-soluble sodium carboxymethyl cellulose (CMC) and commercial non-aqueous polyvinylidene difluoride (PVDF). NCM cathode with LA132 binder exhibited a much higher specific capacity of 146 mAh g−1 and capacity retention of 96.4 % after 100 cycles as compared with 122 mAh g−1/88 % and 121 mAh g−1/75% for the NCM electrode with CMC and PVDF, respectively. In addition, NCM cathode with LA132 binder exhibited better rate capability than that of CMC and PVDF, e.g., retaining 34.3 % capacity of C/5 at 5 C rate as compared with 28.5 and 10.9 % for CMC and PVDF, respectively.

Identification of low-index crystal planes of polycrystalline gold on the basis of electrochemical oxide layer formation

Abstract: The electrochemical oxidation of single-crystal gold surfaces has been well studied, and the exposed crystal planes can be reliably distinguished based on the peak potentials of oxide formation. However, the multiple oxidation peaks of polycrystalline gold have not yet been unambiguously related to crystal planes. In this work, we used cyclic voltammetric responses of activated polycrystalline gold electrodes recorded in sulfuric acid solutions to allow constructing relationships between crystal planes and oxide peaks. The studies of oxide formation were complemented by measuring double-layer non-faradaic currents, lead underpotential deposition (Pb-upd), the oxygen reduction reaction (ORR), and the hydrogen evolution reaction (HER).

Use of screen-printed electrodes for quantification of cocaine and Δ 9 -THC: adaptions to portable systems for forensic purposes

Abstract: The worldwide attention for illicit drug consumption is known, mainly cocaine and marijuana, which were the most commonly apprehended drugs. In this study, we adapted conventional systems for voltammetric analysis for identifying these drugs using screen-printed electrode (SPE) devices in a portable potentiostat. For cocaine determination, a commercial platinum screen-printed electrode (Pt-SPE) with a cobalt hexacyanoferrate film (CoHCFe) presented the best results in comparison to other available models, and for Δ9-tetrahydrocannabinol (Δ9-THC), no chemical modification was required on the carbon screen-printed electrodes (C-SPEs). The results allowed the use of the adapted systems with good analytical parameters: cocaine and Δ​9-THC determination presented a sensibility equal to 2.02 × 10−2 and 2.65 × 10−7 A L mol−1 , respectively. Finally, the developed procedures showed an application for electrochemical analysis in forensic context, besides the results obtained to comply with reliable results which forensic analysis must have.

Effect of electrolyte concentration on the capacitive properties of NiO electrode for supercapacitors

Abstract: The capacitive performances of NiO as electrode-active material in aqueous KOH electrolyte with different concentrations are systematically studied by cyclic voltammetry (CV), galvanostatic charge/discharge technique (GCD), and electrochemical impedance spectroscopy (EIS). CV and GCD data show that NiO delivers higher specific capacitance and better long-term cyclicity in 6 M KOH than in 2 or 4 M solution. EIS spectra reveal both charge transfer resistance (R ct) and solution resistance (R s) reduce with the increase of the KOH concentration, indicating the smoother charge and ion transfer pathways in both electrode and bulk electrolyte solution in the denser electrolyte.

Poly(3-octylthiophene) as solid contact for ion-selective electrodes: contradictions and possibilities

Abstract: The hydrophobic conductive polymer, poly(3-octylthiophene) (POT), is considered as uniquely suited to be used as an ion-to-electron transducer in solid contact (SC) ion-selective electrodes (ISEs). However, the reports on the performance characteristics of POT-based SC ISEs are quite conflicting. In this study, the potential sources of the contradicting results on the ambiguous drift and poor potential reproducibility of POT-based ISEs are compiled, and different approaches to minimize the drift and the differences in the standard potentials of POT-based SC ISEs are shown. To set the potential of the POT film, it has been loaded with a 7,7,8,8-tetracyanoquinodimethane (TCNQ/TCNQ·−) redox couple. An approximately 1:1 TCNQ/TCNQ·−ratio in the POT film has been achieved through potentiostatic control of the potential of the redox couple-loaded conductive polymer. It is hypothesized that once the POT film has a stable, highly reproducible redox potential, it will provide similarly stable and reproducible interfacial potentials between the POT film and the electron-conducting substrate and result in SC ISEs with excellent reproducibility and potential stability. Towards this goal, the potentials of Au, GC, and Pt electrodes with drop-cast POT film coatings were recorded in KCl solutions as a function of time. Some of the POT films were loaded with TCNQ and coated with a K+-selective membrane. The improvement in the potential stabilities and sensor-to-sensor reproducibility as a consequence of the incorporation of TCNQ in the POT film and the potentiostatic control of the TCNQ/TCNQ·−ratio is reported.

Reed straw derived active carbon/graphene hybrids as sustainable high-performance electrodes for advanced supercapacitors

Abstract: Reed straw-derived active carbon@graphene (AC@GR) hybrids were prepared by one-step carbonization/activation process using a mixture of reed straw and graphene oxide (GO) as raw materials and ZnCl2 as activation agent. The as-prepared hybrids exhibit high specific surface area in a range of 1971–2497 m2 g−1, abundant porosity, as well as excellent energy storage capability. The symmetric C//C supercapacitor using the hybrid obtained at 700 °C as electrodes demonstrates superior cycling durability, ca. 90 % retention after 6000 cycles at 2 A g−1, and a high energy density of 6.12 Wh kg−1 at a power density of up to 4660 W kg−1 in 6 M KOH aqueous electrolyte. The excellent capacitive performance is attributed to the synergistic effect of AC and GR.

The use of different types of reduced graphene oxide in the preparation of Fe-N-C electrocatalysts: capacitive behavior and oxygen reduction reaction activity in alkaline medium

Abstract: Three different types of reduced graphene oxide (rGO) were prepared starting from graphite oxide (GO) produced with the Hummers’ method using three different exfoliation-reduction strategies: thermal annealing under N2 atmosphere at 700 °C, thermal annealing under H2–N2 (1:1 vol.) atmosphere at 500 °C and ultrasonication. Then, three non-noble metal catalysts (NNMC) for the oxygen reduction reaction (ORR) were synthesized using these three different rGO as carbon supports, by impregnation of a complex formed between Fe(II) ions and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) as source of nitrogen, followed by a pyrolysis at 800 °C. The physical-chemical properties of rGO and Fe-N/rGO catalysts were characterized by N2 physisorption, XRD, XPS, SEM, and EDX. The capacitive behavior and the ORR activity of rGO and Fe-N/rGO catalysts were measured in alkaline conditions by cyclic voltammetry (CV) and rotating disk electrode (RDE), respectively. The three different reduction-exfoliation methods used for the rGO preparation influenced the physical-chemical properties, as well as the capacitive currents and the ORR activity of both rGO and Fe-N/rGO. This provides an insight about which synthesis process could be the most convenient for the final application.