Amorphous Electrodes Research Articles

The Electrochemical Properties of Diamond and Tetrahedral Amorphous Carbon Electrodes in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) are emerging as a new medium for redox reactions as these liquids possess high solubilizing power, electrical conductivity, wide breakdown voltage and low volatility. Being composed entirely of ions (no solvent) and possessing wide electrochemical windows ( ca. 5 V), it is not difficult to see why these liquids are viewed by electrochemists to be attractive electrolytes for investigation. Our group is (i) studying the wetting of these ionic fluids on different carbon electrode surfaces and how this wetting affects the capacitance-potential relationships and (ii) investigating how the carbon electrode surface chemistry and microstructure affect the heterogeneous electron-transfer rate constant of different inorganic and organic redox systems in these ionic liquids. It is well established that the in aqueous electrolyte solutions, the heterogeneous electron-transfer rate constant for certain redox-systems at ordered HOPG and more microstructurally-disordered glassy carbon is strongly affected by the electrode surface microstructure and chemistry. We seek to learn if these same trends hold in ionic liquids. In this presentation, we will compare the electrochemical behavior of boron-doped nanocrystalline diamond and nitrogen-incorporated tetrahedral amorphous carbon thin-film electrodes. Specifically, contact angle measurements of the surface wettability, measurements of the double-layer capacitance (C dl) and its variation with potential, and heterogeneous electron-transfer rate constants for redox systems in structurally distinct RTILs will be presented. These two carbon electrodes have distinct microstructures as compared to their sp2 carbon counterparts. Nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) is a composite material consisting of a mixture of sp2 and sp3-bonded carbon. Impurities can be incorporated during growth (e.g., N) further adding to their complex structure. These films typically possess 40-60% sp3-bonded carbon. It has been widely used as a protective coating due to its hardness, high wear resistance and low coefficient of friction. The growth temperature for ta-C is usually from 25 to about 100 °C. This means that non-traditional materials, such as plastics, can be used as substrates for deposition. Importantly, these carbon materials possess some electrochemical properties that are similar to those of diamond.

Improving the capacity of sodium ion battery using a virus-templated nanostructured composite cathode.

In this work we investigated an energy-efficient biotemplated route to synthesize nanostructured FePO4 for sodium-based batteries. Self-assembled M13 viruses and single wall carbon nanotubes (SWCNTs) have been used as a template to grow amorphous FePO4 nanoparticles at room temperature (the active composite is denoted as Bio-FePO4-CNT) to enhance the electronic conductivity of the active material. Preliminary tests demonstrate a discharge capacity as high as 166 mAh/g at C/10 rate, corresponding to composition Na0.9FePO4, which along with higher C-rate tests show this material to have the highest capacity and power performance reported for amorphous FePO4 electrodes to date.

Electron beam deposition of amorphous manganese oxide thin film electrodes and their predominant electrochemical properties

Electron beam evaporated manganese oxide films display excellent electrochemical properties on post deposition oxidative annealing in air. The films annealed below 573 K are amorphous, exhibit minor deficiency in oxygen and are characterized by a specific discharge capacitance of 398 F g−1 at a discharge current of 1.1 A g−1 and 236 F g−1 at a discharge current of 5.5 A g−1. In terms of stability, these films retain 99.6% of their specific capacitance even after 400 cycles. The electrochemical properties of these films are explained in terms of their structure and composition which have been measured by X-ray diffraction and proton elastic backscattering spectrometry. In addition, the electrochemical properties are influenced by their morphology; the oxidatively annealed films contain nanometric, spherical and elongated grains which acquire extensive networking during electrochemical measurements.

Electrode Materials

This review work was focused on conventional and modern electrodes which play an important role in electrochemical systems. Among many types of existing electrode materials, some of the most prominent materials from the conventional (metals and their alloys, graphite and mixed metal oxides) and the modern (amorphous, modified and composite) electrodes, have been outlined. What is also discussed is the recent intensive usability of nanocrystalline electrodes of better properties than their microcrystalline equivalents, and development trend of electrode materials.

Amorphous Ni-P Electrode Materials

Versatile applications and broad interest in amorphous electrode materials, especially the nickel-phosphorus coatings, primarily results from their unique properties and low-production costs in comparison to precious metals. This paper discusses the most important research conducted over several years into the Me-P layers, in particular the Ni-P and Ni-Me-P ones, which led to only partial understanding of these amorphous alloys. Methods of increasing the catalytic activity of the Ni-P layers in the process of electroevolution of hydrogen are also discussed because the electrolytic layers of amorphous nickel still seem to be the promising electrode material.

Effects of stress on lithium transport in amorphous silicon electrodes for lithium-ion batteries

Silicon, as a promising electrode material for high energy density lithium ion batteries, experiences large strains and stresses during lithiation and delithation. The coupling effect between stress and lithium diffusion leads to a grand challenge to optimizing the design of Si electrodes with high capacity and high rate capability, particularly considering the amorphization of Si during initial cycles. In this study, we established a relationship between stress and the diffusion coefficients of Li in amorphous Si by ab initio molecular dynamics calculations (AIMD). The prediction from AIMD was validated by the potentiostatic intermittent titration measurements. Our results showed that two Li diffusion mechanisms can operate depending on the stress state. Specifically, the stress can increase Li diffusion either through increasing free volume under tension or by changing local structure under compression. However, within the range of stress generated during the lithiation and delithation process, diffusion coefficients are expected to vary by only one order of magnitude.

Cathodically induced antimony for rechargeable Li-ion and Na-ion batteries: The influences of hexagonal and amorphous phase

Cathodic corrosion, a green electrochemical method, has been employed to obtain Sb nanomaterials utilized as anode material for lithium-ion batteries and sodium-ion batteries. Interestingly, two different corrosion mechanisms are found, coming from the impact of electrolyte, resulting in the formation of hexagonal and amorphous Sb in aqueous and organic solution, respectively. With the help of water-soluble carboxymethyl cellulose binder and the electrolyte additive fluoroethylene carbonate, both hexagonal and amorphous Sb electrodes exhibit good cycling stability when utilized as anode materials for lithium-ion batteries and sodium-ion batteries. Additionally, both the hexagonal and amorphous Sb electrodes show very good rate capability in lithium-ion batteries. Even at high current density (2000 mA g−1), the hexagonal and amorphous Sb give reversible capacities of 422 and 379 mA h g−1, respectively. Surprisingly, when used as anode materials for sodium-ion batteries, the hexagonal Sb electrode exhibits a good rate performance of 632, 625, 569, 515 and 426 mA h g−1 at a current density of 100, 200, 500, 1000, and 2000 mA g−1, respectively. However, limited rate performance is observed from the amorphous Sb electrode in case of sodium-ion battery due to the large impedance.

Fully transparent and rollable electronics.

Major obstacles toward the manufacture of transparent and flexible display screens include the difficulty of finding transparent and flexible semiconductors and electrodes, temperature restrictions of flexible plastic substrates, and bulging or warping of the flexible electronics during processing. Here we report the fabrication and performance of fully transparent and rollable thin-film transistor (TFT) circuits for display applications. The TFTs employ an amorphous indium-gallium-zinc oxide semiconductor (with optical band gap of 3.1 eV) and amorphous indium-zinc oxide transparent conductive electrodes, and are built on 15-μm-thick solution-processed colorless polyimide (CPI), resulting in optical transmittance >70% in the visible range. As the CPI supports processing temperatures >300 °C, TFT performance on plastic is similar to that on glass, with typical field-effect mobility, turn-on voltage, and subthreshold voltage swing of 12.7 ± 0.5 cm(2)/V·s, -1.7 ± 0.2 V, and 160 ± 29 mV/dec, respectively. There is no significant degradation after rolling the TFTs 100 times on a cylinder with a radius of 4 mm or when shift registers, each consisting of 40 TFTs, are operated while bent to a radius of 2 mm. For handling purposes, carrier glass is used during fabrication, together with a very thin (∼1 nm) solution-processed carbon nanotube (CNT)/graphene oxide (GO) backbone that is first spin-coated on the glass to decrease adhesion of the CPI to the glass; peel strength of the CPI from glass decreases from 0.43 to 0.10 N/cm, which eases the process of detachment performed after device fabrication. Given that the CNT/GO remains embedded under the CPI after detachment, it minimizes wrinkling and decreases the substrate's tensile elongation from 8.0% to 4.6%. Device performance is also stable under electrostatic discharge exposures up to 10 kV, as electrostatic charge can be released via the conducting CNTs.

Effect of mechanical grinding on the electrochemical hydrogen storage properties of Mg–Ni–Y alloy

The nanocrystalline and amorphous Mg2Ni-type electrode alloys with a composition of Mg20 − xYxNi10 (x = 1 and 4) were fabricated by mechanical milling, and the effects of milling time on the structures and electrochemical hydrogen storage performances of the alloys were investigated in detail. Test results of X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) reveal that a nanocrystalline structure can be obtained through mechanical milling, and the amorphization degree of the alloy visibly increases with milling time prolonging. When Y content is x = 1, the substitution of Y for Mg results in the formation of secondary YMgNi4 + YMg3 phases without altering the major phase Mg2Ni, but when Y content is x = 4, the major phase of the alloys changes into YMgNi4 + YMg3 phases. The capacity retaining rate of 20th cycle is reduced from 48.3 to 37.7 % for the x = 1 alloy and from 89.8 to 74.7 % for the x = 4 alloy by increasing milling time from 0 (as-cast is defined as milling time of 0 h) to 70 h. The x = 1 alloy milled for 30 h obtains the maximum discharge capacity of 418.5 mA h g−1, and for x = 4 alloy milled for 10 h, it is 341.5 mA h g−1. The effect of milling time on the electrochemical kinetics of the alloys is related to Y content. When Y content is x = 1, the high rate discharge ability (HRD), diffusion coefficient of hydrogen atom (D), and charge transfer rate all increase with milling time prolonging. However, for x = 4 alloy, the electrochemical kinetics is getting steadily worse with ball milling time increasing.

The performance of a nitrogen-containing tetrahedral amorphous carbon electrode in flow injection analysis with amperometric detection

The performance of a nitrogen-incorporated tetrahedral amorphous (ta-C:N) carbon thin-film electrode was evaluated using flow injection analysis with amperometric detection.

Study on the electromagnetic properties of thin-film solar cell grown with graphene using FDFD method

In recent years amorphous silicon solar cells have been receiving a great deal of interest due to their high energy conversion efficiency and low cost. The positions of absorption peak reflect the good absorption performance at specific frequency point or nearby spectra. However, the absorption peaks of amorphous silicon solar cell which are mainly determined by the properties of amorphous silicon and metal electrode, cannot be tuned. And the absorption efficiency can not be further enhanced also. Therefore, monolayer graphene film will be employed in the solar cells with periodic structure due to its remarkable electro-optic properties. With a suitable chemical potential applied, the dielectric constant of graphene can be tuned. This design mainly aims to tune the position of the absorption peak based on the graphene by using finite-difference frequency-domain method. Also, an approximate fitted function is developed in order to overcome the singularity in the exact expression. Numerical results show that the approximate closed form expression generates results within a maximum absolute error of 0.8%. Theoretical results provide the realistic organic thin-film solar cells with theoretical basis and technical support.

Nanoporous nickel-copper-phosphorus amorphous alloy film for methanol electro-oxidation in alkaline medium

Nanoporous Ni-Cu-P amorphous alloy (NP-NiCuP) and nanoporous Ni-Cu crystalline alloy (NP-NiCu) are prepared by the linear sweep voltammetry (LSV) etching of copper from the electroless Ni-Cu-P and Ni-Cu alloy coatings, respectively. The results of X-ray diffraction (XRD) analysis show that the nanoporous Ni-Cu-P alloy is amorphous structure. The scanning electron microscopy (SEM) analysis demonstrates the NP-NiCuP shows a 3-D bi-continuous porous structure with the pore size of 150–200nm and the ligament size of around 100nm. Electrochemical performances are measured by cyclic voltammetry (CV) and chronoamperometry (CA). The results prove that the NP-NiCuP electrode exhibits higher the proton diffusion coefficient (D0) of Ni(OH)2 and surface coverage (Γ*) of the redox species than those on smooth electroless Ni-Cu-P amorphous alloy (S-NiCuP) and NP-NiCu electrodes in alkaline solution obviously. Moreover, electro-oxidation of methanol suggests that the NP-NiCuP electrode holds higher anodic current density and lower onset potential than the S-NiCuP and NP-NiCu electrodes. Finally, the NP-NiCuP electrode has stable redox behavior and superior catalytic stability for methanol oxidation.

Electrochemical hydrogen storage properties of TixV65−xNi35 (x=45, 55) alloys produced by rapid-quenching

Electrochemical discharge performances of TixV65−xNi35 (x=45, 55) alloy are measured by electrochemical measurements at galvanostatic conditions, and alloy ribbon is prepared by rapid-quenching under argon atmosphere. XRD analysis of TixV65−xNi35 (x=45) alloy shows that the Ti45V20Ni35 (x=45) is mostly the amorphous phase, V-based solid solution phase with BCC structure phase and a negligible amount of (Ni, V) phase. While x=55, namely the Ti55V10Ni35 alloy, mainly consists of the icosahedral quasicrystal (I-phase), face centered cubic (FCC) phase with Ti2Ni-type structure and V-based solid solution phase with BCC structure phase. In the electrochemical tests, the maximum discharge capacity of Ti45V20Ni35 is about 150.4mAh/g at a current density of 30mA/g. However, Ti55V10Ni35 alloy shows that the best discharge capacity is 221.8mAh/g under the same condition. In addition, it exhibits extraordinary cycling stability of 87.2% at 30 charge–discharge cycles. It can be found that the discharge capacity of the amorphous electrode is lower than those of the I-phase ones under the similar composition levels.

Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

All-solid-state sodium batteries using amorphous TiS3 electrode with high capacity

All-solid-state sodium cells (Na15Sn4/Na3PS4 glass-ceramic/a-TiS3) showed a high capacity of over 300 mAh per gram of TiS3 at the 1st discharge–charge cycle. The capacity was gradually decreased to 100 mAh g−1 at the 10th cycle. Nyquist plots of the cell showed that the resistance of the a-TiS3 composite electrode became larger with the discharge–charge cycles. The XRD patterns of the a-TiS3 composite electrode before and after the 1st cycle indicated that the a-TiS3 was still amorphous during discharge–charge process. The Raman bands attributable to a-TiS3 were also observed after the 1st cycle. The SEM images and EDX mapping indicated that the a-TiS3 particles aggregated in the electrode after the 10th cycle. The all-solid-state sodium cell using a-TiS3 composite electrode with acetylene black as a conductive additive showed the high capacity of over 300 mAh g−1 for 5 cycles.

Reversible Lithium Storage at Highly Populated Vacant Sites in an Amorphous Vanadium Pentoxide Electrode

A vanadium pentoxide electrode is prepared in the amorphous form (a-V2O5), and its electrode performances are compared to those for its crystalline counterpart (c-V2O5). The a-V2O5 electrode outperforms c-V2O5 in several ways. First, it is free from irreversible phase transitions and Li trapping, which evolve in c-V2O5, probably due to the lack of interactions between the inserted Li+ ions/electrons and V2O5 matrix. Second, the absence of Li trapping allows a reversible capacity amounting to >600 mA h g–1, which is larger than that given by c-V2O5. Third, it shows an excellent rate property. The notably high reversible capacity and rate capability seem to be due to Li storage at vacant sites that are ill-defined but numerous in a-V2O5, which Li+ ions can easily access. However, irreversible capacity of a-V2O5 is appreciable in the first cycle due to a parasitic Li reaction with surface hydroxyl groups. Treatment with n-butyllithium can suppress the irreversible capacity by removing the surface hydroxyl gr...

Amorphous iron phosphate: potential host for various charge carrier ions

Unlike crystalline electrodes wherein ion insertion is crucially dependent on the presence of energetically equivalent sites, nanostructured amorphous iron(III) phosphate hosts prepared by room temperature strategies and possessing porous properties facilitate the insertion of alkali ions with different sizes and also higher charge carriers including divalent cations (Mg2+−0.72A, Zn2+-0.74 A) or trivalent cations (Al3+−0.53 A). This versatile cathode stores electrical energy by a reversible amorphous to crystalline reconstitutive reaction that occurs during electrochemical reaction with monovalent sodium, potassium and lithium. The study presents opportunities to develop amorphous electrodes with similar phase behavior for energy storage applications.

Ferroelectric properties of vinylidene fluoride–trifluoroethylene copolymer thin films fabricated on amorphous alloy electrode

We have investigated the structure and ferroelectric properties of vinylidene fluoride–trifluoroethylene (VDF–TrFE) copolymer thin films fabricated on amorphous alloy electrodes. Thin films of amorphous Pd–Cu–Si alloys with various compositions were successfully prepared by sputtering deposition. An atomically flat surface resulting from a fully amorphous structure of Pd–Cu–Si was obtained upon achieving a uniform surface of a spin-coated VDF–TrFE copolymer thin film. X-ray diffraction (XRD) measurements revealed that the crystalline structure of the VDF–TrFE copolymer thin films was of ferroelectric β-phase, being independent of the composition and crystalline state of the Pd–Cu–Si alloy. The clearly observed D–E hysteresis loops showed a remanent polarization of 0.075 C/m2 and a coercive field of 90 MV/m at a measurement frequency of 10 Hz for a 50-nm-thick film, which is almost consistent with the results obtained with Pt electrode samples. We also observed the thinning-induced reduction of remanent polarization, which was explained by the depolarization field induced by the surface dead layer in VDF–TrFE copolymer rather than the oxidized layer in Pd–Cu–Si alloy electrode.

로이 응용을 위한 비정질 In-Si-O 다층구조 특성 평가

Transparent amorphous In-Si-O (ISO)/Ag/In-Si-O (ISO) has been reported for low emissivity (low-e) applications. Effective Si doping into the In2O3 matrix led to a completely amorphous ISO film as well as a low resistivity and a high optical transmittance. The optical and electrical performances were examined by measuring transmittance with a UV-VIS spectrophotometer and resistivity with a Hall effect measurement. Consequently, low-e glass with ISO/Ag/ISO showed a high transparency in the visible region and low emissivity in the infrared region, indicating that ISO is a promising amorphous transparent electrode for low-e glass.

Amorphous Columnar Silicon Anodes with Excellent Cycling Stability for Advanced High Voltage Lithium Ion Full Cells: Dominant Factors Governing Cycling Performance

An excellent cycling stability of monolithic amorphous columnar silicon electrodes with the loqading of 1.3 mg/cm2 in fluoroethylene carbonate (FEC)-based electrolyte solutions was demonstrated. The effect of the electrolyte solution composition and the cycling protocol on the long-term cycling performance and surface chemistry of amorphous silicon electrodes was investigated using electrochemical tools, XPS, SEM and EDS. It relates to the ability of FEC to form polyenes, as well as to a high rate of HF formation in its water contaminated LiPF6 solutions, measured by 19F NMR spectroscopy. We found that excellent passivation in FEC solutions related to a low content of oxygen containing moieties species (e.g. organic and inorganic carbonates, alkoxides, oxygen-containing organic polymers) in surface films. Galvanostatic tests and spectroscopic analyses revealed also a strong dependence of the composition and properties of the surface films on amorphous Si electrodes on the cycling procedure. Charge limited galvanostatic cycling procedure including repeated deep discharge of Si electrodes down to 10 mV vs. Li/Li+in every cycle from the very beginning of the electrodes life, ensures the formation of thin and highly passivating surface films on their surface and good cycling performance. To the contrary, when a limited portion of the capacity of Si electrodes during cycling relates to the higher potential range (discharge limited protocol), surface films enriched with oxygen containing species are formed. Their passivating properties are less effective compared to the other composition discussed above (polyenes + LiF).Cycling stability of Si electrodes in LiPF6solutions decreases in the following order FEC/DMC > 3,4-trans-difluoroethylene carbonate (DFEC)/DMC > ethylene carbonate (EC)/DMC > propylene carbonate (PC).Amorphous columnar silicon electrodes were combined with high voltage LiNi0.5Mn1.5O4 spinel and LiCoPO4/C composite cathodes and high specific capacity xLi2MnO3 .(1-x)LiNiyMnzCo1-y-zO2 cathodes. These batteries demonstrated excellent performance in term of cycle life, charge-discharge efficiency and good rate capability.