A Dye-Sensitized Solar Cell Using a Composite of PEDOT:PSS and Carbon Derived from Human Hair for a Counter Electrode

Carbon derived from hair is interesting because it has good electrocatalytic activity due to the existence of innate heteroatom dopants especially nitrogen and sulfur. In this study, a carbon catalyst containing high nitrogen contents (9.47 at.%) was fabricated without using any harsh chemicals. Moreover, the carbonization temperature was only 700°C. Carbonized hair/PEDOT:PSS composites (CxP) with varied carbon contents from x = 0.2 to 0.8 g were tested as a counter electrode (CE) for a dye-sensitized solar cell (DSSC). This type of DSSC CE has scarcely been investigated. A DSSC with a C0.6P CE provides the best efficiency (6.54 ± 0.11%) among all composite CEs because it has a high fill factor (FF) and a high short-circuit current density (Jsc). The efficiency of DSSC with C0.6P CE is lower than Pt’s (7.29 ± 0.01%) since the Pt-based DSSC has higher FF and Jsc values. However, C0.6P is still promising as a DSSC CE since it is more cost-effective than Pt

Topological Line Defects around Graphene Nanopores for DNA Sequencing

Topological line defects in graphene represent an ideal way to produce highly controlled structures with reduced dimensionality that can be used in electronic devices. In this work we propose using extended line defects in graphene to improve nucleobase selectivity in nanopore-based DNA sequencing devices. We use a combination of QM/MM and non-equilibrium Green's functions methods to investigate the conductance modulation, fully accounting for solvent effects. By sampling over a large number of different orientations generated from molecular dynamics simulations, we theoretically demonstrate that distinguishing between the four nucleobases using line defects in a graphene-based electronic device appears possible. The changes in conductance are associated with transport across specific molecular states near the Fermi level and their coupling to the pore. Through the application of a specifically tuned gate voltage, such a device would be able to discriminate the four types of nucleobases more reliably than that of graphene sensors without topological line defects.Comment: 6 figures and 6 page

DEVELOPMENT OF COMPOSITE ELECTRODES CONTAINING GEOPOLYMER BINDER FOR ELECTROCHEMICAL APPLICATIONS

The requirements for electrode materials are high electronic conductivity, fast kinetics, high mechanical stability, and high chemical stability under oxidative and reductive environment. In this work, composite electrodes have been prepared containing geopolymer (made from Fly Ash (FA)), zinc, and Multiwalled Carbon Nanotubes (MWCNT) or graphite deposited on a nickel foam with different compositions (FA:Zn:MWCNT or FA:Zn:Graphite, mass ratio = 12:6:1 or 6:6:1). While the commercial zinc plate demonstrated clear oxidation and reduction reactions during cyclic voltammetry, no electrochemical reactions of zinc were observed with the composite electrodes. The composite electrodes suffered from high resistance, which could not be overcome even with reduced geopolymer content. The FE-SEM images indicated that the composite electrodes containing MWCNT were better dispersed than those containing graphite. Moreover, the composite electrode containing FA:Zn:MWCNT = 6:6:1 showed a lower overpotential for Oxygen Evolution Reaction (OER) compared to those with FA:Zn:Graphite at the same mass ratio. The surface morphology, homogeneity and chemical compositions lead to the change of the electrocatalyst activity towards OER. The electrode containing MWCNT may be attractive as anode for alkaline water electrolysis for hydrogen production. Further experiments should focus on optimization of the electrode composition to enhance its conductivity, activity and stability

Electrochemically Deposited Polypyrrole for Dye-Sensitized Solar Cell Counter Electrodes

Polypyrrole films were coated on conductive glass by electrochemical deposition (alternative current or direct current process). They were then used as the dye-sensitized solar cell counter electrodes. Scanning electron microscopy revealed that polypyrrole forms a nanoparticle-like structure on the conductive glass. The amount of deposited polypyrrole (or film thickness) increased with the deposition duration, and the performance of polypyrrole based-dye-sensitized solar cells is dependant upon polymer thickness. The highest efficiency of alternative current and direct current polypyrrole based-dye-sensitized solar cells (DSSCs) is 4.72% and 4.02%, respectively. Electrochemical impedance spectroscopy suggests that the superior performance of alternative current polypyrrole solar cells is due to their lower charge-transfer resistance between counter electrode and electrolyte. The large charge-transfer resistance of direct current solar cells is attributed to the formation of unbounded polypyrrole chains minimizing the I3 − reduction rate

The quantum confined Stark effect in N-doped ZnO/ZnO/N-doped ZnO nanostructures for infrared and terahertz applications

The terahertz (THz) frequency range is very important in various practical applications, such as terahertz imaging, chemical sensing, biological sensing, high-speed telecommunications, security, and medical applications. Based on the density functional theory (DFT), this work presents electronic and optical properties of N-doped ZnO/ZnO/N-doped ZnO quantum well and quantum wire nanostructures. The density of states (DOS), the band structures, effective masses, and the band offsets of ZnO and N-doped ZnO were calculated as the input parameters for the subsequent modeling of the ZnO/N-doped ZnO heterojunctions. The results show that the energy gaps of the component materials are different, and the conduction and valence band offsets at the ZnO/N-doped ZnO heterojunction give type-II alignment. Furthermore, the optical characteristics of N-doped ZnO/ZnO/N-doped ZnO quantum well were studied by calculating the absorption coefficient from transitions between the confined states in the conduction band under the applied electric field (Stark effect). The results indicate that N-doped ZnO/ZnO/ N-doped ZnO quantum wells, quantum wires, and quantum cascade structures could offer the absorption spectrum tunable in the THz range by varying the electric field and the quantum system size. Therefore, our work indicates the possibility of using ZnO as a promising candidate for infrared and terahertz applications

Finite-difference calculation of the electronic structure of artificial graphene, the 2D hexagonal AlwGa1-wAs/GaAs structure with tunable interactions

The energy dispersion relation of two dimensional hexagonal lattice of GaAs quantum wires embedded in AlwGa1-wAs matrix, called artificial graphene, was calculated by the finite difference method with periodic boundary conditions. The validity of the finite difference based code was checked by comparing the bound state energies of various two dimensional systems with appropriate boundary conditions with analytic solutions or the results obtained by COMSOL software, which uses the finite element method, and a very good agreement was found. The energy dispersion relation calculated for artificial graphene structure shows massless Dirac particles, characteristic for real graphene. Therefore, artificial graphene-like structures have properties similar to those of real graphene, and are tailorable by appropriate structure engineering

Magnetic and Cytotoxicity Properties of La1−xSrxMnO3(0 ≤ x ≤ 0.5) Nanoparticles Prepared by a Simple Thermal Hydro-Decomposition

This study reports the magnetic and cytotoxicity properties of magnetic nanoparticles of La1−xSrxMnO3(LSMO) withx = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 by a simple thermal decomposition method by using acetate salts of La, Sr, and Mn as starting materials in aqueous solution. To obtain the LSMO nanoparticles, thermal decomposition of the precursor was carried out at the temperatures of 600, 700, 800, and 900 °C for 6 h. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM, and SEM. Structural characterization shows that the prepared particles consist of two phases of LaMnO3(LMO) and LSMO with crystallite sizes ranging from 20 nm to 87 nm. All the prepared samples have a perovskite structure with transformation from cubic to rhombohedral at thermal decomposition temperature higher than 900 °C in LSMO samples ofx ≤ 0.3. Basic magnetic characteristics such as saturated magnetization (MS) and coercive field (HC) were evaluated by vibrating sample magnetometry at room temperature (20 °C). The samples show paramagnetic behavior for all the samples withx = 0 or LMO, and a superparamagnetic behavior for the other samples havingMSvalues of ~20–47 emu/g and theHCvalues of ~10–40 Oe, depending on the crystallite size and thermal decomposition temperature. Cytotoxicity of the synthesized LSMO nanoparticles was also evaluated with NIH 3T3 cells and the result shows that the synthesized nanoparticles were not toxic to the cells as determined from cell viability in response to the liquid extract of LSMO nanoparticles

A substoichiometric tungsten oxide catalyst provides a sustainable and efficient counter electrode for dye-sensitized solar cells

Development of Pt-free catalyst materials for the counter electrode (CE) in dye-sensitized solar cells (DSSCs) has been regarded as one of the crucial steps to improving energy conversion efficiency and cost effectiveness of DSSCs. In this work, low cost tungsten oxide (WO3-x) counter electrodes, prepared by annealing tungsten metal sheets under an Ar and low O2atmosphere, exhibited high catalytic activity and energy conversion efficiency. The highest efficiency achieved here for DSSCs with WO3-xcounter electrodes, was 5.25%, obtained from a 500 °C annealed tungsten sheet. TEM and XPS analysis suggested the formation of sub-stoichiometric tungsten oxide layer (∼WO2.6) with the presence of W6+, W5+and W4+oxidation states at the tungsten metal surface after the 500 °C annealing. Only W6+and W5+oxidation states were detected after a 600 °C annealing indicating the formation of a more stoichiometric tungsten oxide layer (∼WO2.8) and resulting in a drop in efficiency of the DSSC. We suggest that mixed valence tungsten states account for the excellent catalytic activity and good electrical conductivity as evidenced by the highest cyclic voltammetry response of 0.76 mA/cm2and the lowest impedance value of 44.33 Ω, respectively

Electronic Properties of h-BCN/Blue Phosphorene van der Waals Heterostructures

Van der Waals heterostructures (vdWHs), a new class of materials made of a vertically selective assembly of various 2D monolayers held together by vdW forces, have attracted a great deal of attention due to their premise to design novel electronic and optoelectronic properties which is not achievable by individual 2D crystals. Using the density functional theory (DFT), we have revealed that vdWH composed of monolayers of h-BN and the latest blue phosphorus (blue phosphorene, BlueP) forms straddling type-I band offset where the band edges exclusively belong to BlueP. This feature enables h-BN to be a protective coating material of BlueP to beneficially resolve its so-called air-instability. Furthermore, substitutional doping of C to h-BN at a suitable concentration provokes h-BCN/BlueP into staggered type-II band offset. The type-II band alignment triggered by the intensified built-in electric field across the sheets implies the improved carrier mobility and the suppressed recombination of photogenerated hole-pairs. These major benefits can pave the way for the potential functionality of h-BCN/BlueP for efficient photovoltaic devices

Eco-Friendly Triboelectric Material Based on Natural Rubber and Activated Carbon from Human Hair

The triboelectric nanogenerator (TENG) has emerged as a novel energy technology that converts mechanical energy from surrounding environments to electricity. The TENG fabricated from environmentally friendly materials would encourage the development of next-generation energy technologies that are green and sustainable. In the present work, a green triboelectric material has been fabricated from natural rubber (NR) filled with activated carbon (AC) derived from human hair. It is found that the TENG fabricated from an NR-AC composite as a tribopositive material and a poly-tetrafluoroethylene (PTFE) sheet as a tribonegative one generates the highest peak-to-peak output voltage of 89.6 V, highest peak-to-peak output current of 6.9 µA, and can deliver the maximum power density of 242 mW/m2. The finding of this work presents a potential solution for the development of a green and sustainable energy source