Understanding structure-function relationship in hybrid Co3O4-Fe2O3/C lithium-ion battery electrodes

A range of high-capacity Li-ion anode materials (conversion reactions with lithium) suffer from poor cycling stability and limited high-rate performance. These issues can be addressed through hybridization of multiple nanostructured components in an electrode. Using a Co3O4-Fe2O3/C system as an example, we demonstrate that the cycling stability and rate performance are improved in a hybrid electrode. The hybrid Co3O4-Fe2O3/C electrode exhibits long-term cycling stability (300 cycles) at a moderate current rate with a retained capacity of approximately 700 mAh g(-1). The reversible capacity of the Co3O4-Fe2O3/C electrode is still about 400 mAh g(-1) (above the theoretical capacity of graphite) at a high current rate of ca. 3 A g(-1), whereas Co3O4-Fe2O3, Fe2O3/C, and Co3O4/C electrodes (used as controls) are unable to operate as effectively under identical testing conditions. To understand the structure-function relationship in the hybrid electrode and the reasons for the enhanced cycling stability, we employed a combination of ex situ and in situ techniques. Our results indicate that the improvements in the hybrid electrode originate from the combination of sequential electrochemical activity of the transition metal oxides with an enhanced electronic conductivity provided by percolating carbon chains.

Performance analysis of a field-effect-transistor based aptasensor

Prostate cancer is one of the most diagnosed cancers which leads to a considerable number of deaths due to the lack of early and sensitive detection. This paper presents an aptamer functionalized field effect (FET) based biosensor for the detection of prostate cancer. Prostate specific antigen (PSA) is considered as the biomarker for prostate cancer whose detection is confirmed by attaching aptamers onto the sensor surface. Through the modelling and numerical simulation, the paper aims to evaluate and predict the performance parameters such as sensitivity, settling time, and limit of detection (LOD) of a label-free FET based electronic biosensor. Various sensor parameters such as structure (i.e., geometry), type of the FET (e.g., nanowire FET, spherical FET, ion-selective FET, and magnetic particle) radius of the FET channel and incubation time are optimized and analyzed. In addition, concentration of analyte biomolecules, diffusion coefficients and affinity to the receptor molecules are also investigated to determine the optimize performance parameters.

Redox voltammetry of sub-parts per billion levels of Cu2+ at polyaspartate-modified gold electrodes

An electrochemical sensor for the detection of Cu2+ is reported which incorporates poly-l-aspartic acid (PLAsp) with 32–96 aspartate units as a selective ligand for the metal ion. PLAsp is covalently attached to a gold electrode modified with a monolayer of 3-mercaptopropionic acid using carbodiimide coupling via an N-hydroxysuccinimide (NHS) ester intermediate. The acid side groups and deprotonated peptide nitrogens on two aspartate moieties are thought to be primarily responsible for chelation of Cu2+, which remains bound when reduced to Cu+. A consequence of the multiple binding points that are available with a polypeptide is the low detection limit. The lowest concentration detected was 3 nM (0.2 ppb) achieved with Osteryoung square wave voltammetry. This detection limit compares favourably with that of ICP-OES and previously reported cysteine-modified electrodes. Analysis of tap and lake water samples using the PLAsp-modified electrode agreed well with ICP-OES analysis of the same samples.

Exploring the use of the tripeptide Gly–Gly–His as a selective recognition element for the fabrication of electrochemical copper sensors

The modification of electrodes with the tripeptide Gly–Gly–His for the detection of copper in water samples is described in detail. The tripeptide modified electrode was prepared by first self-assembling 3-mercaptopropionic acid (MPA) onto the gold electrode followed by covalent attachment of the tripeptide to the self-assembled monolayer using carbodiimide coupling. The electrodes were characterized using electrochemistry, a newly developed mass-spectrometry method and quantum mechanical calculations. The mass spectrometry confirmed the modification to proceed as expected with peptide bonds formed between the carboxylic acids of the MPA and the terminal amine of the peptide. Electrochemical measurements indicated that approximately half the MPA molecules in a SAM are modified with the peptide. The peptide modified electrodes exhibited high sensitivity to copper which is attributed to the stable 4N coordinate complex the peptide formed around the metal ion to give copper the preferred tetragonal coordination. The formation of a 4 coordinate complex was predicted using quantum mechanical calculation and confirmed using mass spectrometry. The adsorption of the copper to the peptide modified electrode was consistent with a Langmuir isotherm with a binding constant of (8.1 ± 0.4) 1010 M−1 at 25 °C.

Preparation of composite electrodes with carbon nanotubes for lithium-ion batteries by low-energy ball milling

Some of the prospective electrode materials for lithium-ion batteries are known to have electronic transport limitations preventing them from being used in the electrodes directly. In many cases, however, these materials may become practical if they are applied in the form of nanocomposites with a carbon component, e.g. via incorporating nanoparticles of the phase of interest into a conducting network of carbon nanotubes. A simple way to prepare oxide-carbon nanotube composites suitable for the electrodes of lithium-ion batteries is presented in this paper. The method is based on low-energy ball milling. An electrochemically active but insulating phase of LiFeTiO4 is used as a test material. It is demonstrated that the LiFeTiO4-carbon nanotube composite is not only capable of having significantly higher capacity (∼105-120 mA h g-1vs. the capacity of ∼65-70 mA h g -1 for the LiFeTiO4 nanoparticles) at a slow current rate but may also operate at reasonably high current rates. © the Partner Organisations 2014.

Graphene nanodots-encaged porous gold electrode fabricated via ion beam sputtering deposition for electrochemical analysis of heavy metal ions

All rights reserved. A graphene nanodots-encaged porous gold electrode via ion beam sputtering deposition (IBSD) for electrochemical sensing is presented. The electrodes were fabricated using Au target, and a composite target of Al and graphene, which were simultaneously sputtered onto glass substrates by Ar ion beam, followed with hydrochloric acid corrosion. The as-prepared graphene nanodots-encaged porous gold electrodes were then used for the analysis of heavy metal ions, e.g. Cu2+ and Pb2+ by Osteryoung square wave voltammetry (OSWV). These porous electrodes exhibited enhanced detection range for the heavy metal ions due to the entrapped graphene nanodots in 3-D porous structure. In addition, it was also found that when the thickness of porous electrode reached 40 nm the detection sensitivity came into saturation. The linear detection range is 0.009-4 μM for Cu2+ and 0.006-2.5 μM for Pb2+. Good reusability and repeatability were also observed. The formation mechanism and 3-D structure of the porous electrode were also investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectra (XPS). This graphene entrapped 3-D porous structure may envision promising applications in sensing devices.

Lithium-ion capacitors with 2D Nb2CTx (MXene) - carbon nanotube electrodes

There is a growing interest to hybrid energy storage devices, such as lithium-ion capacitors, in which battery-type electrodes are combined with capacitor-type ones. It is anticipated that the energy density (either gravimetric or volumetric) of lithium-ion capacitors is improved if pseudocapacitive or fast insertion materials are used instead of conventional activated carbon (AC) in the capacitor-type electrode. MXenes, a new family of two-dimensional transition metal carbides, demonstrate metallic conductivity and fast charge-discharge behavior that make them suitable for this application. In this study, we move beyond single electrodes, half-cell studies and demonstrate three types of hybrid cells using Nb2CTx-carbon nanotube (CNT) films. It is shown that lithiated graphite/Nb2CTx-CNT, Nb2CTx-CNT/LiFePO4 and lithiated Nb2CTx-CNT/Nb2CTx-CNT cells are all able to operate within 3 V voltage windows and deliver capacities of 43, 24 and 36 mAh/g (per total weight of two electrodes), respectively. Moreover, the polarity of the electrodes can be reversed in the symmetric Nb2CTx-CNT cells from providing a positive potential between 0 and 3 V to a negative one from -3 to 0 V. It is shown that the volumetric energy density (50-70 Wh/L) of our first-generation devices with MXene electrodes exceeds that of a lithium titanate/AC capacitor.

Focused ion beam milling as a universal template technique for patterned growth of carbon nanotubes

Focused ion beam (FIB) milling system has been used to create nanosized patterns as the template for patterned growth of carbon nanotubes on Si substrate surface without predeposition of metal catalysts. Carbon nanotubes only nucleate and grow on the template under controlled pyrolysis of iron phthalocyanine at 1000 °C. The size, growth direction, and density of the patterned nanotubes can be controlled under different growth conditions and template sizes. Atomic force microscopy and electron microscopy analyses reveal that the selective growth on the FIB template is due to its special surface morphology and crystalline structure.

Composite cell components for elevated temperature all-solid-state Li-ion batteries

Application of Li-ion batteries with liquid electrolytes at elevated temperatures (above 60°C) is limited due to the decomposition of the electrolyte. Stable solid state electrolytes can solve this problem, but the conductivity of these electrolytes are relatively low, the interfacial contacts with the electrodes are poor, and the charge transfer kinetics in the electrodes are limited. Solutions for these problems by using composite electrodes and electrolytes have been investigated and the results are described. A new concept for making all-solid-state Li-ion batteries that can be applied in the temperature range between room temperature and about 150°C will be presented.

Room-temperature molten salts based on the quaternary ammonium ion

The properties of a family of novel quaternary ammonium salts based on the bis(trifluoromethylsulfonyl)imide and triflate anions are reported. Binary phase diagrams for some of their mixtures and their electrochemical windows of stability are also reported. The highest conductivity observed in the pure salt systems at 25 °C was 7 × 10^-4 S cm^-1. An electrochemical window of stability of up to 5 V was measured on graphite electrodes. The effect of salt structure and solvent on conductivity of the salts is also discussed.

An investigation into transition metal ion binding properties of silk fibers and particles using radioisotopes

Silk is a structural protein fiber that is stable over a wide pH range making it attractive for use in medical and environmental applications. Variation in amino acid composition has the potential for selective binding for ions under varying conditions. Here we report on the metal ion separation potential of Mulberry and Eri silk fibers and powders over a range of pH. Highly sensitive radiotracer probes, ⁶⁴Cu²⁺, ¹⁰⁹Cd²⁺, and ⁵⁷Co²⁺ were used to study the absorption of their respective stable metal ions Cu²⁺, Cd²⁺, and Co²⁺ into and from the silk sorbents. The total amount of each metal ion absorbed and time taken to reach equilibrium occurred in the following order: Cu²⁺ > Cd²⁺ > Co ²⁺. In all cases the silk powders absorbed metal ions faster than their respective silk fibers. Intensive degumming of the fibers and powders significantly reduced the time to absorb respective metal ions and the time to reach equilibrium was reduced from hours to 5-15 min at pH 8. Once bound, 45-100% of the metal ions were released from the sorbents after exposure to pH 3 buffer for 30 min. The transition metal ion loading capacity for the silk sorbents was considerably higher than that found for commercial ion exchange resins (AG MP-50 and AG 50W-X2) under similar conditions. Interestingly, total Cu²⁺ bound was found to be higher than theoretically predicted values based on known specific Cu²⁺ binding sites (AHGGYSGY), suggesting that additional (new) sites for transition metal ion binding sites are present in silk fibers.

Sub-ppt detection limits for copper ions with Gly-Gly-His modified electrodes

An electrochemical metal ion sensor has been developed with a detection limit of less than 0.2 ppt by the covalent attachment of the tripeptide Gly-Gly-His as a recognition element to a 3-mercaptopropionic acid modified gold electrode.

Electrochemical metal ion sensors. Exploiting amino acids and peptides as recognition elements

Amino acids and peptides are known to bind metal ions, in some cases very strongly. There are only a few examples of exploiting this binding in sensors. The review covers the current literature on the interaction of peptides and metals and the electrochemistry of bound metal ions. Peptides may be covalently attached to surfaces. Of particular interest is the attachment to gold via sulfur linkages. Sulfur-containing peptides (eg cysteine) may be adsorbed directly, while any amino group can be covalently attached to a carboxylic acid-terminated thiol. Once at a surface, the possibility for using the attached peptide as a sensor for metal ions becomes realised. Results from the authors’ laboratory and elsewhere have shown the potential for selective monitoring of metal ions at ppt levels. Examples of the use of poly-aspartic acid and the copper binding peptide Gly-Gly-His for detecting copper ions are given.

MoO3 nanoparticles dispersed uniformly in carbon matrix : a high capacity composite anode for Li-ion batteries

A MoO₃-carbon nanocomposite was synthesized from a mixture of MoO₃ and graphite by a controlled ball milling procedure. The as-prepared product consists of nanosized MoO₃ particles (2-180 nm) homogeneously distributed in carbon matrix. The nanocomposite acts as a high capacity anode material for lithium-ion batteries and exhibits good cyclic behavior. Its initial capacity exceeds the theoretical capacity of 745 mA h g^-1 in a mixture of MoO₃ and graphite (1:1 by weight), and the stable capacity of 700 mA h g^-1 (94% of the theoretical capacity) is still retained after 120 cycles. The electrode performance is linked with the unique nanoarchitecture of the composite and is compared with the performance of MoO₃-based anode materials reported in the literature previously (nanoparticles, ball milled powders, and carbon-coated nanobelts). The high value of capacity and good cyclic stability of MoO₃-carbon nanocomposite are attractive in respect to those of the reported MoO₃ electrodes.