Capacity Optimization Nanotechnologies for Enhanced Energy Storage Systems

Rechargeable lithium-ion battery (LIB) cathodes consist of transition metal oxide material, which reversibly (de)intercalates lithium at a high potential difference versus a carbon anode. Manganese oxide cathode material offers lower cost and toxicity than the normally used cobalt. However, LiMn2O4 suffers from capacity fading, Mn dissolution at high temperatures, and poor high rate capability. Its ultimate performance, however, depends on the morphology and electrochemical properties. In this work, Au alloyed with Fe, Pd, and Pt, respectively, was synthesized and used to improve the microstructure and catalytic activities by functionalizing LiMn2O4 via a coprecipitation calcination method. The pristine LiMn2O4 and modified materials were examined using a combination of spectroscopic and microscopic techniques along with in-detail galvanostatic charge–discharge tests. Microscopic results revealed that the modified composite cathode materials had high phase purity, highly crystallized particles, and more regular morphological structures with narrow size distributions. Galvanostatic charge–discharge testing indicated that the initial discharge capacities of LiMxMn2-xO4 at 0.1 C for M0.02=PtAu, FeAu, and PdAu were 147, 155.5, and 160.2 mAh g−1, respectively. The enhancement of the capacity retention and higher electrode coulombic efficiency of the modified materials were significant, especially at high C rate. At enlarged cycling potential ranges, the Li(M)0.02Mn1.98O4 samples delivered relevant discharge capacities (70, 80, and 90 mAh g-1) compared to LiMn2O4 (45 mAh g-1)

Analysis of Electrochemical and Structurally Enhanced LiMn2O4 Nanowire Cathode System

The performance of the battery cathode depends on the electrode microstructure and morphology, as well as the inherent electrochemical properties of the cathode materials. The spinel LiMn2O4 is the most promising candidate as a cathode material because of its low cost and nontoxicity compared with commercial LiCoO2. However, there is still a challenge to synthesize high-quality single-crystal nanostructured cathode materials. Nanowires offer advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. To enhance the activity and stability, flexible spinel nanowires are synthesized, via α-MnO2 nanowire precursor method. Ultrathin LiMn2O4 nanowires with cubic spinel structure were synthesized by using a solvothermal reaction to produce α-MnO2 nanowire followed by solid-state lithiation. LiMn2O4 nanowires have diameters less than 10 nm and lengths of several micrometers. The LiMn2O4 nanowires are used as stabilizing support during the electrochemical redox processes. The unique nanoporous material effectively accommodates structural transformation during Li+ ion insertion and effectively reduces Li+ diffusion distances, reducing the volumetric changes and lattice stresses during charge and discharge. Galvanostatic battery testing showed that LiMn2O4 nanowires delivered 146 mAh/g in a large potential window. The electrochemical and spectrochemical interrogation techniques demonstrated that LiMn2O4 nanowires are promising cathode materials for lithium ion batteries as apposed to LiMn2O4 powders

Stripping Voltammetric Measurement of Trace Metal Ions at Screen-printed Carbon and Carbon Paste Electrodes

AbstractScreen-printed carbon electrodes (SPCEs) and carbon paste electrodes (CPEs) were prepared as “mercury-free” electrochemical sensors for the determination of trace metal ions in aqueous solutions. SPCEs were coated with conducting polymer layers of either polyaniline (PANI), or polyaniline-poly(2,2′–dithiodianiline) (PANI-PDTDA). Furthermore, CPEs containing electroactive compounds with reactivity towards metal ions were employed to obtain enhanced selectivity. Optimised experimental conditions for Hg2+, Pb2+, Ni2+ and Cd2+ determination included the supporting electrolyte concentration, deposition potential (Ed) and accumulation time (tacc). Initial results showed linearity in the examined concentration range between 1 × 10-9M and 1 × 10-6M for laboratory prepared solution

Actuation behaviour of a derivatized pyrrole accordion type polymer

A monomer (Phenazine-2,3-diimino(pyrrole-2-yl)–PDP) derived from the condensation reaction between 2,3-diaminophenazine and a pyrrole derivative has been synthesized as a hinge molecule in the design of a zig-zag polymer. The monomer was polymerized both chemically and electrochemically in order to produce the polymer material, phenazine-2,3-diimino(pyrrole-2-yl (PPDP). During electrochemical polymerization the system was doped using 1,4-napthaquinone sulphonic acid (NQSA) and polyvinylsulfonic acid (PVSA) respectively, to improve conductivity. Characterization of the materials by Fourier transform infrared spectroscopy (FTIR) confirmed the successful linking of the starting materials to produce the hinge molecule and nuclear magnetic resonance spectroscopy (NMR) supported the FTIR data. The electrochemistry of the polymer in the doped and undoped state was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)

Voltammetric Analysis of Platinum Group Metals Using a Bismuth-Silver Bimetallic Nanoparticles Sensor

This study dealt with the development of a bismuth-silver bimetallic nanosensor for differential pulse adsorptive stripping voltammetry of platinum group metals (PGMs) in environmental samples. The nanosensor was fabricated by drop coating a thin bismuth-silver bimetallic film onto the active area of the screen-printed carbon electrodes. Optimization parameters such as pH, dimethylglyoxime (DMG) concentration, deposition potential and deposition time, stability test and interferences were also studied. In 0.2 M acetate buffer (pH = 4.7) solution and DMG as the chelating agent, the reduction signal for PGMs ranged from 0.2 to 1.0 ng L−1. In the study of possible interferences, the results have shown that Ni(II), Co(II), Fe(III), Na+, SO42−, and PO43− do not interfere with Pd(II), Pt(II), and Rh(III) in the presence of DMG with sodium acetate buffer as the supporting electrolyte solution. The limit of detection for Pd(II), Pt(II), and Rh(III) was found to be 0.07, 0.06 and 0.2 ng L−1, respectively. Good precision for the sensor application was obtained with a reproducibility of 7.58% for Pd(II), 6.31% for Pt(II), and 5.37% for Rh(III) (n = 10)

Influence of quantum dot surface on electrochemical DNA sensing mechanism

Owing to their high surface‐to‐volume ratio, electrocatalytic activity, biocompatibility and novel electron transport properties, quantum dots (QDs) are highly attractive materials for the ultrasensitive detection of biological macromolecules via bioelectronic devices. In this study, a QD‐based genosensor was developed, in which Ga2Te3‐based QDs were synthesized using an aqueous solution approach by mixing 3‐mercaptosuccinic acid (3MSA)‐capped gallium metal precursor with reduced tellurium metal. The results enabled us to reach an original understanding related to the active material involved in the probe DNA sensing mechanism. The morphological and structural characterization of the QDs was performed prior to their utilization in a DNA sensor construction. High‐resolution TEM (HR‐TEM) and atomic force microscopy (AFM) images confirmed the spherical and crystalline nature of the QDs, whereas X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD) analyses were able to confirm the oxidation states and formation of the prepared QDs. UV/Vis was capable of finding the optical band gap energy and the photostability of the QDs. The resultant Ga2Te3 QDs together with metal ions confirmed their use for DNA signal detection through their DNA binding mechanism in the genosensor construction. Genosensing in Cs+ and Li+ ions exhibited high sensitivity (2.74–3.69 μA ng−1 mL) and very low detection limits (0.4 pg mL−1) with a linear dynamic range of 0.1–1 ng mL−1

Quantum dot nanotoxicity investigations using human lung cells and toxor electrochemical enzyme assay methodology

Recent studies have suggested that certain nanomaterials can interfere with optically based cytotoxicity assays resulting in underestimations of nanomaterial toxicity. As a result there has been growing interest in the use of whole cell electrochemical biosensors for nanotoxicity applications. Herein we report application of an electrochemical cytotoxicity assay developed in house (TOXOR) in the evaluation of toxic effects of mercaptosuccinic acid capped cadmium telluride quantum dots (MSA capped CdTe QDs), toward mammalian cells. MSA capped CdTe QDs were synthesized, characterized, and their cytotoxicity toward A549 human lung epithelial cells investigated. The internalization of QDs within cells was scrutinized via confocal microscopy

Graphene Oxide–Antimony Nanocomposite Sensor for Analysis of Platinum Group Metals in Roadside Soil Samples

The present study introduced a very sensitive and low-cost analytical procedure based on voltammetry to study platinum group metals in road dust and roadside soil matrices. Cathodic stripping voltammetry in conjunction with a reduced graphene oxide-antimony nanocomposite sensor and ICP-MS analysis were used to analyse roadside soil and dust samples. The results were processed to evaluate possible pollution in order to map the distribution of the PGMs along specific roads in the Stellenbosch area, outside Cape Town. The results revealed that within each site under investigation, Pd was more abundant than Pt and Rh using both voltammetric and spectroscopic methods. The AdDPCSV results obtained showed concentrations for Pd(II) ranging between 0.92 – 4.0 ng kg–1. For Pt (II), the concentrations ranged between 0.84 – 0.99 ng kg–1. For Rh(III), concentrations ranged between 0.42 – 1.21 ng kg–1. The ICP-MS results showed Pd concentrations ranging between 0.01 – 0.34 µg kg–1. For Pt the concentrations ranged between 0.004 – 0.07 µg kg–1. For Rh, concentrations ranged between 0.002 – 0.26 µg kg–1. The analysis showed significant levels of all PGMs in soil and dust samples analysed. Metal concentration in dust and soil followed the trend Pd > Pt > Rh using both voltammetric and spectroscopic technique

Carcinoembryonic antigen immunosensor developed with organoclay nanogold composite film

Organoclay nanogold composite were prepared using gold nanoparticles and the natural Cameroonian clay grafted with amino organosilane. The functionnalization of clay provided abundant amino group to assemble gold nanoparticles. A label-free electrochemical immunosensor for the sensitive determination of carcinoembryonic antigen (CEA) was fabricated by immobilizing anti-CEA onto organoclay nanogold composite film modified electrode by the cross-linking method using glutaraldehyde. In addition, the preparation procedure of the immunosensor was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimal conditions, the resulting immunosensor displayed a high sensitivity for the detection of CEA, and responded to the CEA concentration in two ranges from 0.05 to 5.0 ng/mL (R = 0.991) and from 5.0 to 120.0 ng/mL (R = 0.998) with a detection limit of 0.01 ng/mL

Hall measurements on carbon nanotube paper modified with electroless deposited platinum

Carbon nanotube paper, sometimes referred to as bucky paper, is a random arrangement of carbon nanotubes meshed into a single robust structure, which can be manipulated with relative ease. Multi-walled carbon nanotubes were used to make the nanotube paper, and were subsequently modified with platinum using an electroless deposition method based on substrate enhanced electroless deposition. This involves the use of a sacrificial metal substrate that undergoes electro-dissolution while the platinum metal deposits out of solution onto the nanotube paper via a galvanic displacement reaction. The samples were characterized using SEM/EDS, and Hall-effect measurements. The SEM/EDS analysis clearly revealed deposits of platinum (Pt) distributed over the nanotube paper surface, and the qualitative elemental analysis revealed co-deposition of other elements from the metal substrates used