Surface Charge Transfer Resistance Research Articles

Performance Comparison between AB5 and Superlattice Metal Hydride Alloys in Sealed Cells

High-power cylindrical nickel metal/hydride batteries using a misch metal-based Al-free superlattice alloy with a composition of La11.3Pr1.7Nd5.1Mg4.5Ni63.6Co13.6Zr0.2 were fabricated and evaluated against those using a standard AB5 metal hydride alloy. At room temperature, cells made with the superlattice alloy showed a 40% lower internal resistance and a 59% lower surface charge-transfer resistance compared to cells made with the AB5 alloy. At a low temperature (−10 °C), cells made with the superlattice alloy demonstrated an 18% lower internal resistance and a 60% lower surface charge-transfer resistance compared to cells made with the AB5 alloy. Cells made with the superlattice alloy exhibited a better charge retention at −10 °C. A cycle life comparison in a regular cell configuration indicated that the Al-free superlattice alloy contributes to a shorter cycle life as a result of the pulverization from the lattice expansion of the main phase.

Fe-Substitution for Ni in Misch Metal-Based Superlattice Hydrogen Absorbing Alloys—Part 1. Structural, Hydrogen Storage, and Electrochemical Properties

The effects of Fe partially replacing Ni in a misch metal-based superlattice hydrogen absorbing alloy (HAA) were studied. Addition of Fe increases the lattice constants and abundance of the main Ce2Ni7 phase, decreases the NdNi3 phase abundance, and increases the CaCu5 phase when the Fe content is above 2.3 at%. For the gaseous phase hydrogen storage (H-storage), Fe incorporation does not change the storage capacity or equilibrium pressure, but it does decrease the change in both entropy and enthalpy. With regard to electrochemistry, >2.3 at% Fe decreases both the full and high-rate discharge capacities due to the deterioration in both bulk transport (caused by decreased secondary phase abundance and consequent lower synergetic effect) and surface electrochemical reaction (caused by the lower volume of the surface metallic Ni inclusions). In a low-temperature environment (−40 °C), although Fe increases the reactive surface area, it also severely hinders the ability of the surface catalytic, leading to a net increase in surface charge-transfer resistance. Even though Fe increases the abundance of the beneficial Ce2Ni7 phase with a trade-off for the relatively unfavorable NdNi3 phase, it also deteriorates the electrochemical performance due to a less active surface. Therefore, further surface treatment methods that are able to increase the surface catalytic ability in Fe-containing superlattice alloys and potentially reveal the positive contributions that Fe provides structurally are worth investigating in the future.

The power of Nb-substituted TiO2 in Li-ion batteries: Morphology transformation induced by high concentration substitution

This study aims to investigate the power potential of Li-ion batteries using a hydrothermal process to synthesize nanoscale Nb–TiO2 with high surface area. By substituting Nb into anatase TiO2, the rate capability of Li-ion batteries is improved with the formation of nanoplate Nb–TiO2 containing (001) facets and NbOx species. In addition, the high solubility of Nb promotes the transformation of TiO2 from hollow-like to plate-like morphology, accelerating the Li-ion surface transportation over a large contact area. With respect to rate capability, Nb–TiO2 displays a high capacity of 220 mAh g−1 at 0.5C and retains 127 mAh g−1 at 10C. Additionally, the cyclability test exhibits less degradation after 10,000 cycles. In order to investigate the mechanisms of capability improvement, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) are applied to measure the Li-ion diffusivity and surface charge-transfer resistance. The results demonstrate that both Li-ion diffusivity and surface charge-transfer ability are enhanced, leading to pseudocapacitance. Thus, it can be concluded that nanoplate Nb–TiO2 exhibits superior rate capability by the improvement of pseudocapacitance. This study derives a novel process to synthesize nanoplate TiO2 and should provide a potential approach for industrial fabrication of high power Li-ion batteries.

Surface modification of Li(Li0.17Ni0.2Co0.05Mn0.58)O2 with CeO2 as cathode material for Li-ion batteries

Li-rich layered oxides are of great importance as cathode materials for advanced lithium ion batteries. In this work, Li-rich layered Li(Li0.17Ni0.2Co0.05Mn0.58)O2 oxide is synthesized by a spray-drying method, and modified subsequently with CeO2 nanoparticles. It is demonstrated that the surface of the Li(Li0.17Ni0.2Co0.05Mn0.58)O2 oxide is modified with CeO2 nanocrystallites, which exist as isolated nano-particles or a thick CeO2 layer with increasing CeO2 content. After the surface modification with CeO2 nanoparticles, Li(Li0.17Ni0.2Co0.05Mn0.58)O2 oxide presents lower surface charge transfer resistance, larger discharge capacity and higher initial coulombic efficiency. In particular, the modified sample with 1wt % CeO2 shows the optimized cycle stability and high-rate discharge capability. In addition, the thermal stability of the cathode at delithiated state is improved to a certain extent by the surface modification with CeO2 nanoparticles, which is attributed to that the oxygen generated from the initial charge can be absorbed and stored in CeO2 nanoparticles on the surface of Li(Li0.17Ni0.2Co0.05Mn0.58)O2.

Enhanced electrochemical performance of LiMnPO4 by Li+-conductive Li3VO4 surface coatings

By a simple wet ball-milling method, Li3VO4-coated LiMnPO4 samples were prepared successfully for the first time. The thin Li3VO4 coating layer with a three-dimensional Li+-ion transport path and high mobility of Li+-ion strongly adhered to the LiMnPO4 material reduces Mn dissolution and increases the Li+ flux through the surface of the LiMnPO4 itself by preventing formation of phases on the surface that would normally block Li+ as well as Li+-ion permeation into the surface of the LiMnPO4 electrode and therefore improve the rate capability as well as the cycling stability of LiMnPO4 materials. The electrochemical testing shows that the 5% Li3VO4-coated LiMnPO4 sample shows a clear voltage plateau in the charge curves and a much higher reversible capacity at different discharge rates compared with the pristine LiMnPO4. EIS results also show that the surface charge transfer resistance and Warburg impedance of the Li3VO4-coated LiMnPO4 samples significantly decreased. The surface charge transfer resistance and Warburg impedance for the pristine LiMnPO4 are 955.1Ω and 400.3Ω, respectively. While, for the 5% Li3VO4-coated LiMnPO4, the value are only 400.2Ω and 283.6Ω, respectively. The surface charge transfer resistance decreases more than half. All of the improved performance will be favorable for application of the LiMnPO4 in high-power lithium ion batteries.

DNA detection and cell adhesion on plasma‐polymerized pyrrole

This study investigates the application of Plasma-polymerized pyrrole (ppPY) as bioactive platform for DNA immobilization and cell adhesion based on the fundamental properties of ppPY, such as chemical structure, electrochemical property, and protein adsorption. Variations in electrochemical properties of the ppPY film deposited under different plasma conditions before and after DNA immobilization were measured using electrochemical impedance spectroscopy (EIS). The equilibrium concentration of the probe DNA immobilized on the ppPY surface was deduced by detecting the variations in the surface charge transfer resistance (Rct ) of the ppPY films after DNA immobilization with different concentrations. In addition, the detection limit of the target DNA hybridization with probe DNA, the association constant, Ka , and the dissociation constant were deduced from Langmuir isotherm equations simulated using the experimental data collected by EIS. Moreover, inverted microscope was used to observe the cell adhesions onto the surface of the ppPY films prepared under different plasma conditions. Different adhesive behaviors of cells were observed, demonstrating that ppPY films could be an alternative biomaterial used as the sensitive layer for DNA sensor or cell adhesion.

Derivation of the diffusion impedance of multi-layer cylinders. Application to the electrochemical permeation of hydrogen through Pd and PdAg hollow cylinders

The purpose of this research paper is to report on the diffusion impedance of multi-layer cylinders. Analytical expressions of the diffusion impedance in multi-layer solid cylinders (sorption/desorption experiments) and through multi-layer hollow cylinders (permeation experiments) have been obtained by integration of Fick's diffusion equation in cylindrical coordinates. The resulting impedances are expressed as a function of the characteristics of individual active layers (layer thickness, diffusion coefficient and solubility of diffusing species in each layer). These impedance expressions can be used to characterize a large variety of experimental systems. In this work, model impedances have been used to fit experimental impedances of hydrogen permeation through Pd and Pd77Ag23/Pd mono- and bi-layer hollow cylinders, yielding the values of microscopic rate parameters (surface charge transfer resistances, diffusion coefficient). Analytical expressions of low frequency limits (stationary conditions of flow) have been derived. Practical conditions required for the separation of the contributions of the different layers are analyzed. Some limitations and perspectives offered by this work are discussed.

Label-Free Detection of Hemoglobin Using MWNT-Embedded Screen-Printed Electrode

The synthesis of a network of cross-linked multiwalled carbon nanotubes (MWNTs) on a cysteamine-functionalized screen-printed gold electrode (MWNT/Au-SPE) and its use as a sensor for hemoglobin (Hb) determination is reported. It is proved to be a ready-to-use platform for routine clinical analysis in the blood after the separation of red blood cells. The study shows direct electron transfer between Hb-FeIII and Hb-FeII on applying a potential difference which is beneficial in detecting the presence of Hb in solution. The characterization of MWNT-embedded electrode was accomplished through Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy (EIS), Raman spectroscopy, optical profiling, and cyclic voltammetry. EIS studies show a reduction in the value of surface charge transfer resistance (Rct) from MWNT/Au-SPE (−2.72 kΩ) to bare Au-SPE (−24.38 kΩ), respectively. MWNT/Au-SPE showed better electrochemical characteristics, and kinetic studies revealed the heterogeneous rate transfer constant (ks) of 1.26 s−1. The electrochemically active surface area was also increased 100 times from bare Au-SPE (2.41 × 10−6 cm2) to MWNT/Au-SPE (2.052 × 10−4 cm2). The sensitivity of the sensor for Hb determination was found to be 20.50 μA g−1 dl in the linear range of 9–15 g dl−1 for lyophilized Hb. It is also found to be extremely sensitive for Hb determination in blood samples with 38.75 μA g−1 dl sensitivity in the same linear range.

Nylon Fibers as Template for the Controlled Growth of Highly Oriented Single Crystalline ZnO Nanowires

This article reports the first controlled synthesis of large scale continuous arrays of single-crystalline ZnO nanowires with tunable size and properties on nylon fibers using a two-step low-temperature hydrothermal growth strategy. This process involves seed treatment of the substrate with ZnO nanocrystals that will form nucleation sites for subsequent epitaxial growth of single crystalline ZnO nanowires. Well-defined, vertically oriented, highly dense, and uniform ZnO nanowires of the wurtzite crystal structure covering the entirety of the fibers were achieved. In order to study the size and shape-dependent optical and electrochemical properties of the nanowires, the seed-to-growth solution concentration ratio was varied, resulting in hexagonal flat-ended (nanorods) and tapered (nanoneedles) morphologies. The amount of ZnO nanorods and nanoneedles grown on nylon fibers were determined as 30.1 ± 0.5% and 11.4 ± 0.7% ZnO by weight, respectively. In comparison to nanorods, ZnO nanoneedles demonstrated enhanced crystallinity, better orientation along the c-axis, and widened band gap. A similar trend was observed in the UV–vis absorption of nanorods and nanoneedles, the absorption-edge of the latter exhibiting a blue-shift that correlates with the widening of the band gap with nanoneedle formation. Moreover, the surface charge transport properties showed strong dependence on the ZnO morphology in which ZnO nanorods exhibited lower surface charge transfer resistance.

Atomic layer deposition of Al2O3 on V2O5 xerogel film for enhanced lithium-ion intercalation stability

V2O5 xerogel films were fabricated by casting V2O5 sols onto fluorine-doped tin oxide glass substrates at room temperature. Five, ten and twenty atomic layers of Al2O3 were grown onto as-fabricated films respectively. The bare film and Al2O3-deposited films all exhibited hydrous V2O5 phase only. Electrochemical impedance spectroscopy study revealed increased surface charge-transfer resistance of V2O5 films as more Al2O3 atomic layers were deposited. Lithium-ion intercalation tests at 600 mAg−1 showed that bare V2O5 xerogel film possessed high initial discharge capacity of 219 mAhg−1 but suffered from severe capacity degradation, i.e., having only 136 mAhg−1 after 50 cycles. After deposition of ten atomic layers of Al2O3, the initial discharge capacity was 195 mAhg−1 but increased over cycles before stabilizing; after 50 cycles, the discharge capacity was as high as 225 mAhg−1. The noticeably improved cyclic stability of Al2O3-deposited V2O5 xerogel film could be attributed to the improved surface chemistry and enhanced mechanical strength. During repeated lithium-ion intercalation/de-intercalation, atomic layers of Al2O3 which were coated onto V2O5 surface could prevent V2O5 electrode dissolution into electrolyte by reducing direct contact between active electrode and electrolyte while at the same time acting as binder to maintain good mechanical contact between nanoparticles inside the film.

Human haptoglobin phenotypes and concentration determination by nanogold-enhancedelectrochemical impedance spectroscopy

Haptoglobin (Hp) is an acute phase protein that binds free hemoglobin (Hb), preventingHb-induced oxidative damage in the vascular system. There are three phenotypes in humanHp, whose heterogeneous polymorphic structures and varying concentrations in plasmahave been attributed to the cause of diseases and outcome of clinical treatments.Different phenotypes of Hp may be composed of the same subunits but different copynumbers, rendering their determination difficult by a single procedure. In this study,we have developed a simple, fast, reliable and sensitive method, using label-freenanogold-modified bioprobes coupled with self-development electrochemical impedancespectroscopy (EIS). By this method, probe surface charge transfer resistance isdetected. The relative charge transfer resistance ratios for Hp 1-1, Hp 2-1 and Hp2-2 were characterized. We were able to determine protein size difference within3 nm, and the linear region of the calibration curve for Hp levels in the range of90 pg ml − 1 and90 µg ml − 1 (∼1 fM to 1 pM). We surmise that similar approaches can be used to investigate proteinpolymorphism and altered protein–protein interaction associated with diseases.

Ion pairing and acid dissociation constants in poly(vinyl chloride)‐based ion‐selective electrode membranes

AbstractIon pairing and acid dissociation constants, as well as limiting conductances, have been estimated in ion‐selective electrode membranes based on a 33 wt% poly(vinyl chloride) (PVC), 66 wt% dioctyladipate matrix using the Fuoss equation of conductance for weakly dissociable species. Dissociation constants of 1.66, 3.51, and 0.69 × 10−5 were determined for NaClO4, C6H5COOK (KBz), and benzoic acid (HBz), respectively, in a membrane matrix with 1% valinomycin and 0.01% KB(C6H5)4 present as additives. The first two values are consistent with tight ion pairing in a low dielectric solvent and indicate no special role for PVC in ion solvation. The weak acid dissociation is 4 to 5 orders of magnitude higher than expected; HBz also shows unusual interactions with the membrane matrix at low added concentrations. The effect of HBz and methylbenzoate (MeBz) on surface charge transfer resistance and membrane bulk resistance shows that HBz is dissociating to form ions, and a possible mechanism for the unusual interactions has been deduced. MeBz caused a significant increase in surface charge transfer resistance, indicating a mechanism by which membrane permeation by lipophilic, neutral components of biological samples could degrade sensor performance.