Electrochemical insertion of lithium in thin tin films

The behavior of model electrodes made of lithiated thin films of tin during their cycling is studied. The electrodes show high values of useful specific capacity for the extension of several tens of operation cycles. Dependences of the diffusion coefficient for lithium into tin on the initial electrode potential, temperature, and direction of the electrode process are determined by a chronopotentiometric method. The dependences have a complex character, which is connected with the phase composition of the lithium-tin alloy.     

Electrochemical deposition and characterization of SnS thin films

Thin films of SnS were cathodically deposited onto stainless steel substrates from bath containing 0.025 M SnSO₄, 0.25 M KSCN and 0.25 M Na₂SO₄. The mechanism of electrochemical co-deposition of tin and sulphur was investigated by cyclic voltammetry. Analysis of the chronoamperometric current–time transients suggested that, in the potential range −560 to −590 mV vs saturated calomel electrode, the electrodeposition of SnS involved progressive nucleation model. However, at a potential −600 mV, the electrodeposition involved instantaneous nucleation model. The deposits have been characterized by scanning electron microscopy, X-ray diffraction and optical measurements. SnS films were found to be polycrystalline with an optical energy gap of 1.38 eV.     

Manganese oxide thin films prepared by potentiodynamic electrodeposition and their supercapacitor performance

Manganese oxide film for supercapacitor applications was prepared by potentiodynamic electrodeposition in a manganese acetate plating solution. The effects of the potential sweep rate on the oxide microstructure, crystallinity, and chemical states were examined using a scanning electron microscope, an X-ray diffractometer, and an X-ray photoelectron spectrometer, respectively. Electrochemical performance of the film electrodes was evaluated using a cyclic voltammetric measurement. The experimental results indicate that the deposition potential sweep rate significantly affected the material properties of the prepared oxide films. The oxide-specific capacitance increased from 262 to 337 F/g when the sweep rate was increased from 100 to 400 mV/s. The key material factors that govern the specific capacitance and cyclic stability of the oxide electrodes were discussed.     

Novel chemical synthesis of polypyrrole thin film electrodes for supercapacitor application

Present investigation describes the cost-effective, novel and simple chemical synthesis of polypyrrole (PPy) thin films for supercapacitor application. These PPy films are characterized by different techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The XRD pattern reveals the amorphous nature of PPy thin film, which is highly feasible for supercapacitors. Further, FTIR study confirms the formation of PPy. The surface morphological study exhibit the coverage of uniform and smooth morphology on thin film. The electrochemical supercapacitive properties of PPy thin films are evaluated using cyclic voltammetry (CV) in 0.5 M H₂SO₄ electrolyte, which exhibits the maximum specific capacitance of 329 Fg⁻¹ at the scan rate of 5 mV s⁻¹. Additionally, an equivalent series resistance (ESR) of PPy thin films is found to be 1.08 Ω using electrochemical impedance measurement.     

Electrochemical texturing of Al-doped ZnO thin films for photovoltaic applications

The processes during chemical and electrochemical etching of Al-doped ZnO are investigated utilizing a scanning flow cell setup with online detection of dissolved Zn ions. The rate of chemical dissolution was found to be a linear function of buffer and proton concentration in near neutral pH solutions according to a transport limited reaction. In contrast, electrochemical etching is limited by the kinetics of the reaction and increases linearly with the imposed current density. Due to this fundamental difference, the dissolution of Zn can be either uniform over the whole surface or highly localized at active sites like grain boundaries. A combined approach of chemical etching and the well-controllable galvanostatic dissolution thus allows a fine adjustment of the ZnO:Al surface texture for applications in silicon thin film photovoltaic cells in order to improve their overall energy conversion efficiency.     

Electrochemical behavior of silver thin films interfaced with yttria-stabilized zirconia

Thin silver films (100–800 nm) were deposited by physical vapor deposition (PVD) on yttria-stabilized zirconia solid electrolyte. The electric percolation as a function of the film thickness was studied during deposition and annealing using a two-electrode in-situ resistance measurement technique. Electrical percolation was achieved in as-deposited films greater than 5.4?±?0.4 nm; however, thermal treatment (550 °C in air) resulted in film dewetting for Ag films as thick as 500 nm and formation of electronically isolated Ag nanoparticles, as was confirmed by SEM and XPS. In thermally treated samples, stable electronic conductivity associated with a continuous percolated network was only observed in samples greater than 600 nm in thickness. The effect of polarization on the electrochemical reactions at the three-phase (electrode-gas-electrolyte) and two-phase (electrode-electrolyte) boundaries of the electrode was investigated by solid electrolyte cyclic voltammetry (SECV) at 350 °C and P _O2?=?6 kPa. With the application of positive potential, silver oxide (Ag₂O) was found to form along the three-phase boundary and then extends within the bulk of the electrode with increasing anodic potentials. By changing the hold time at positive potential, passivating oxide layers are formed which results in a shift in favor of the oxygen evolution reaction at the working electrode. This oxide forms according to a logarithmic rate expression with thick oxides being associated with decrease in current efficiency for subsequent oxide formation.     

Optical iris application of electrochromic thin films

We have successfully developed an electrochromic device (ECD) as the “optical iris” of a camera lens that could potentially control the transmittance intentionally. To realize this goal, we have applied photolithography and subsequent wet etching to fabricate the patterned complementary electrochromic systems where tungsten oxide and prussian blue were electrodeposited. At this point it is important to note that such a device could be directly attached onto a camera lens without any mechanical equipment. In this way the device will reduce power consumption and will be much smaller and thinner which results would also further the miniaturization of cameras.     

Electrochemical and XPS measurements on thin oxide films on zirconium

The potentiodynamic growth of thin oxide films on zirconium electrodes was investigated by coulometric and simultaneous impedance measurements, as a function of the electrode potential (0 V ⩽ E ⩽ 9 V), the pH (0 ⩽ pH ⩽ 14) and the surface preparation (electropolishing, etching and mechanical polishing). The initial film thickness d₀ is at least 4–6 nm; with increasing potential, the oxide grows irreversibly by 2.6 nm/V (pH 0.3) up to 3.2 nm/V (pH 14). In Cl⁻- and ClO⁻₄-containing solutions the oxide growth is limited by localized corrosion. The oxide behaves like a typical insulator with a donor concentration N_D < 10¹⁹ cm⁻³ and a dielectric constant D = 31. Below −0.5 V (vs. SHE) only, th film behaves like an n-type semiconductor with N_D ≈ 3 × 10¹⁹ cm⁻³. From photoelectrochemical measurements a direct and an indirect transition with band gap energies of E_g = 5 eV and E_g = 2.8 eV could be derived. Anodic electron-transfer reactions (ETRs) are blocked at the homogeneous oxide surface, but cathodic ETRs are possible at larger overvoltages. Near the flatband potential E_fb ≈ −1.3 ± 0.2 V (vs. SHE) hydrogen evolution takes place with a simultaneous increase of the capacity which may be attributed to hydrogen incorporation. With XPS measurements the stoichiometry of the oxide film was determined as ZrO₂ at all the pH values examined, but a thin outer layer contained some hydroxide. Components of the forming electrolyte could not be detected (sulphate, borate and perchlorate < 1%), but etching in HF caused accumulation of F⁻ at the inner boundary.     

Electrochemical reductive dechlorination of carbon tetrachloride on nanostructured Pd thin films

The nanostructured Pd thin films prepared via cyclic voltammetric deposition method are proved to be a promising electrocatalyst for electrochemical reductive dechlorination of carbon tetrachloride (CT). The use of as-prepared Pd thin films as the working electrode material provides a possibility to separately study the role of various forms of hydrogen in the dechlorination reactions. Electrochemical characterization and gas chromatography analysis clearly indicate for the first time that the adsorbed hydrogen has excellent ability to remove CT from acidic solutions through the surface reaction with the chemisorbed CT molecules, which is of fundamental importance to have a better understanding of the reaction mechanism of electrochemical dechlorination.     

Electrochemical template synthesis of adherent polyaniline thin films with tubular structure

The synthesis of nano and microstructured thin polyaniline (PANI) films by a simple and very efficient template-assisted method is presented. This work shows the synthesis and characterization of acoustically rigid thin films structured at nanotubular shape by using methyl orange (MO) as a template-assisted system. The amount of the tubes can be easily controlled by the charge passed. The morphology for different films growth was characterized by field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), and quartz crystal microbalance with dissipation mode (QCM-D). Raman spectroscopy results show important changes in the conformational PANI chain of the tubular material compare with a non-tubular one that provokes the increase of bipolarons population. This should be responsible by some changes in the electrochemical behavior of tubular film compared with the granular material, due to the higher conductivity when the emeraldine form starts to be formed.     

Electrodeposited PbO2 thin film on Ti electrode for application in hybrid supercapacitor

PbO₂ thin films were prepared by pulse current technique on Ti substrate from Pb(NO₃)₂ plating solution. The hybrid supercapacitor was designed with PbO₂ thin film as positive electrode and activated carbon (AC) as negative electrode in the 5.3 M H₂SO₄ solution. Its electrochemical properties were determined by cyclic voltammetry (CV), charge–discharge test and electrochemical impedance spectroscopy (EIS). The results revealed that the PbO₂/AC hybrid supercapacitor exhibited large specific capacitance, high-power and stable cycle performance. In the potential range of 0.8–1.8 V, the hybrid supercapacitor can deliver a specific capacitance of 71.5 F g^?1 at a discharge current density of 200 mA g^?1(4 mA cm^?2) when the mass ratio of AC to PbO₂ was three, and after 4500 deep cycles, the specific capacitance remains at 64.4 F g^?1, or 32.2 Wh Kg^?1 in specific energy, and the capacity only fades 10% from its initial value.     

Electrochemical behavior of nanocrystalline diamond thin films grown in electrical arc plasma

Nitrogenated nanocrystalline diamond films with controlled electrical conductivity are grown in electrical arc plasma in CH₄/H₂/Ar/N₂ gas mixtures and characterized by scanning electron microscopy and spectroscopic measurements. Their electrochemical properties are studied by electrochemical impedance spectroscopy. Transfer coefficients of reactions in the [Fe(CN)₆]^3−/4− redox system are determined. The electrochemical behavior of the material is controlled by its nitrogenation (3–20% N₂ in the reaction gas mixture). The nitrogenated nanocrystalline diamond has higher differential capacitance in indifferent electrolyte (1 M KCl) solution than not nitrogenated one; the nitrogenation also increases the reversibility of reactions in the [Fe(CN)₆]^3−/4− redox system. By and large, with nitrogenation of diamond, its electrochemical behavior changes from the one characteristic of a “poor conductor” to that characteristic of metallike conductor. In this respect the nanocrystalline diamond electrodes grown in the electrical arc plasma are similar to those grown in microwave plasma.     

Electrochemical evidences of morphological transformation in ordered mesoporous titanium oxide thin films

We provide the first electrochemical evidence of permeability changes in continuous mesoporous TiO2 thin film electrodes induced by nanocrystallisation.     

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

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.     

Electrochemical properties and photoelectrochemical response of vacuum-deposited poly(p-phenylene) thin films

The electrochemical properties of a poly(p-phenylene) (PPP) thin film prepared by vacuum deposition were investigated by cyclic voltammetry in organic and aqueous media with a lithium perchlorate electrolyte. The PPP thin film was able to undergo both n-doping and p-doping reversibly. In an aqueous medium, the cyclic voltammograms indicated the characteristic loop in a potential sweep. The loop was ascribed to the charge transfer on the PPP film surface and to an accumullation effect of the charge in the PPP film. A photocurrent was observed at the PPP film under UV light irradiation.     

Electrochemical exfoliation and in situ carboxylic functionalization of graphite in non-fluoro ionic liquid for supercapacitor application

Simultaneous electrochemical generation and functionalization of nano-sized graphite from graphite had been carried out in a non-fluoroanion-based ionic liquid, namely, triethylmethylammonium methylsulfate (TEMAMS) containing water and acetonitrile (AN) in different weight ratios. The oxygen-based functional groups attached with the exfoliated material had been identified using Fourier transform infrared spectroscopy (FTIR), and morphological changes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A symmetrical supercapacitor was fabricated using the exfoliated nano-sized graphite, and the influence of surface functionalities on its performance was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge–discharge cycles (CC). The highest specific capacitance (C _sp) value of 140 F g^?1 at 0.25 A g^?1 was obtained in 1.0 M H₂SO₄, followed by aqueous TEMAMS (125 F g^?1), TEMAMS/acetonitrile (115 F g^?1), and TEMAMS (106 F g^?1) at 0.10 A g^?1.     

Carbon materials for supercapacitor application

The most commonly used electrode materials for electrochemical capacitors are activated carbons, because they are commercially available and cheap, and they can be produced with large specific surface area. However, only the electrochemically available surface area is useful for charging the electrical double layer (EDL). The EDL formation is especially efficient in carbon pores of size below 1 nm because of the lack of space charge and a good attraction of ions along the pore walls. The pore size should ideally match the size of the ions. However, for good dynamic charge propagation, some small mesopores are useful. An asymmetric configuration, where the positive and negative electrodes are constructed from different materials, e.g., activated carbon, transition metal oxide or conducting polymer, is of great interest because of an important extension of the operating voltage. In such a case, the energy as well as power is greatly increased. It appears that nanotubes are a perfect conducting additive and/or support for materials with pseudocapacitance properties, e.g. MnO(2), conducting polymers. Substitutional heteroatoms in the carbon network (nitrogen, oxygen) are a promising way to enhance the capacitance. Carbons obtained by one-step pyrolysis of organic precursors rich in heteroatoms (nitrogen and/or oxygen) are very interesting, because they are denser than activated carbons. The application of a novel type of electrolyte with a broad voltage window (ionic liquids) is considered, but the stability of this new generation of electrolyte during long term cycling of capacitors is not yet confirmed.     

Hybrid materials for supercapacitor application

In the present study, a manganese oxide obtained by the acid treatment of LiMn₂O₄ spinel has been used as a positive electrode of supercapacitor. Removal of lithium from a spinel allowed to obtain MnO₂ compound with the pores partly distributed in atomic scale, hence, an efficient use of its pseudocapacitive properties could be reached. On the other hand, residual lithium remaining in the structure preserved layered framework of MnO₂ with pathways for ions sorption. Physical properties, morphology, and specific surface area of electrode materials were studied by scanning and transmission electron microscopy, and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge, and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. Neutral Li₂SO₄ aqueous solution has been selected for electrolytic medium. Extension of operating voltage for supercapacitor has been realized through asymmetric configuration with an activated carbon as a negative electrode. The asymmetric capacitor was operating within a voltage range up to 2.5 V (limited to 2.0 V for cycling tests) and was able to deliver a specific capacitance of 60 Fg⁻¹ per capacitor at 100 mA g⁻¹ current density. High specific energy of 36 Wh kg⁻¹ was reached but with a moderate power density.     

Electrochemical preparation and structural characterization of Co thin films and their anomalous IR properties

Nanometer scale cobalt thin films of different structures and thicknesses supported on glassy carbon were prepared by electrochemical deposition under cyclic voltammetric conditions (denoted nm-Co/GC(n)). The thickness of Co thin films was altered systematically by varying the number (n) of potential cycling within a defined potential range in electrodeposition. Electrochemical in situ scanning tunneling microscopy (STM) and ex situ scanning electron microscopy (SEM) were employed to characterize the surface structure of Co thin films. It has been illustrated that the Co thin films were uniformly composed of Co nanoparticles, whose structure and size varied with increasing n. The structure of nanoparticles inside the Co thin films underwent a transition from bearded nanoparticles to multiform nanoparticles and finally to hexagonal nanosheets, accompanying with an increase of average size. In situ FTIR reflection spectroscopic studies employing CO adsorption as probe reaction revealed that the Co thin films all exhibited anomalous IR properties; that is, along with their different nanostructures they presented abnormal IR effects, Fano-like IR effects, and surface-enhanced IR absorption effects. CO adsorbed on Co thin films dominated by bearded nanoparticles yielded abnormal IR absorption bands; that is, the direction of the bands is inverted completely, with enhanced intensity in comparison with those of CO adsorbed on a bulk Co electrode. The enhancement of abnormal IR absorption has reached a maximal value of 26.2 on the nm-Co/GC(2) electrode. Fano-like IR features, which describe the bipolar IR bands with their positive-going peak on the low wavenumbers side, were observed in cases of CO adsorbed on Co thin films composed mainly of multiform nanoparticles, typically on the nm-Co/GC(8) electrode. IR features were finally changed into surface-enhanced IR absorption as CO adsorbed on the nm-Co/GC(30) electrode, on which the Co thin film is dominated by Co hexagonal nanosheets.