Use In Energy Conversion Devices Research Articles

Multiple defect states engineering towards high thermoelectric performance in GeTe-based materials

GeTe is a promising material for thermoelectric (TE) applications. However, its low Seebeck coefficient and high thermal conductivity in the mid-temperature range of 298–550 K have hindered its widespread use in TE devices. In this work, we show that a combination of band engineering, Fermi level tuning, and miscibility gap exploration can significantly improve the energy conversion performance of GeTe. Bi provides the optimized carrier concentration and induces band convergence, while Ga possibly forms a resonant state. The synergistic effects of Bi and Ga significantly improve the Seebeck coefficient from 38 µVK−1 for undoped GeTe to over 120 µVK−1 for Bi and Ga-containing materials at 298 K and provide a high power factor over a wide temperature range. Phonon scattering is strengthened by optimizing the microstructure through Pb-induced spinodal decomposition and enhanced point defect scattering due to increased dopant solubility, resulting in a very low lattice thermal conductivity of about 0.5 Wm-1K−1 at 600 K for the triple-doped samples. The maximum thermoelectric figure of merit ZT was significantly increased to 2.1 at 600 K for the Ge0.87Pb0.05Bi0.06Ga0.02Te sample due to the improved power factor and reduced lattice thermal conductivity. Additionally, the average figure of merit ZTave for this sample achieved a very high value of 1.4 for Ge0.87Pb0.05Bi0.06Ga0.02Te at a temperature gradient of 475 K (Tc = 298 K). The developed material shows great potential for use in energy conversion devices, with an estimated energy conversion efficiency exceeding 17 %.

Influence of plasmonic resonant wavelength on energy transfer from an InGaN quantum well to quantum dots

We demonstrated the enhanced nonradiative resonant energy transfer (NRET) process by localized surface plasmon (LSP) in the hybrid InGaN quantum well (QW) and CdSe/ZnS quantum dot (QD) structures. The LSP resonant wavelengths could be adjusted by silver (Ag) nanoparticle (NP) arrays annealed from different thicknesses of Ag films. The LSP resonant wavelengths that are close to the peak QD emission helped to enhance the NRET between the QW and QDs. Compared to the original NRET in the absence of Ag NPs, the LSP-enhanced NRET rate was improved by 6.9 times at the resonant wavelength of 600 nm. The calculated efficiency of the LSP-enhanced NRET was 73.1%, which was almost twice that of the original efficiency. Although Ag NPs exhibited a quenching effect, the LSP-enhanced NRET at the resonant wavelength of 465 nm enhanced QD luminescence, which demonstrated their potential use in energy conversion devices.

Distribution of Characteristic Times: A High-Resolution Spectrum Approach for Visualizing Chemical Relaxation and Resolving Kinetic Parameters of Ionic-Electronic Conducting Ceramic Oxides

Surface exchange coefficient (k) and bulk diffusion coefficient (D) are important properties to evaluate the performance of mixed ionic-electronic conducting (MIEC) ceramic oxides for use in energy conversion devices, such as solid oxide fuel cells. The values of k and D are usually estimated by a non-linear curve fitting procedure based on electrical conductivity relaxation (ECR) measurement. However, the rate-limiting mechanism (or the availability of k and D) and the experimental imperfections (such as flush delay for gaseous composition change, τf) are not reflected explicitly in the time–domain ECR data, and the accuracy of k and D demands a careful sensitivity analysis of the fitting error. Here, the distribution of characteristic times (DCT) converted from time–domain ECR data is proposed to overcome the above challenges. It is demonstrated that, from the DCT spectrum, the rate-limiting mechanism and the effect of τf are easily recognized, and the values of k, D and τf can be determined conjunctly. A strong robustness of determination of k and D is verified using noise-containing ECR data. The DCT spectrum opens up a way towards visible and credible determination of kinetic parameters of MIEC ceramic oxides.

PREPARACIÓN Y CARACTERIZACIÓN DE MEMBRANAS DE PVDF/PES/NAFION®117 CON APLICACIÓN POTENCIAL EN BATERÍAS DE FLUJO DE VANADIO

In this work the preparation of dense composite membranes, from blends of poly(vinylidene fluoride) (PVDF), poly(ether sulfone) (PES) and Nafion® 117, with possible applications in vanadium reduction flow battery is reported. The composite Nafion® 117 membranes where prepared by the phase inversion method in controlled air atmosphere, and were characterized to determine their potential for use in energy conversion devices, as a lower cost alternative to the use of the commercial Nafion® membrane. The effect of the thickness on its morphological and cation exchange properties was evaluated, as well as the effect of the chemical composition of the membranes. The characterization of the membranes was carried out using analytical techniques: water uptake, thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), surface charge density (SCD), proton conductivity, as well as in the permeability of vanadium ions. From the six composite Nafion® 117 membranes prepared, five exhibited higher rejection of vanadium ions than commercial membrane and all prepared membranes showed a lower proton conductivity, ranging from 1 to 3 magnitude order.

In English

On the base of graphene/metal type systems there are high-content capacitors, electrodic and magnetic materials of different applications are created with use of nickel, cobalt, and iron. The catalytic activity of systems with bimetal inclusions was studied, moreover the special synergies of the properties of bimetallic particles and fundamental difference between systems containing individual metals were highlighted. The system GNP/(Ni-Co) was synthesized by co-precipitation from a solution of hydrazine-hydrate. The presence of phase GNP, nickel, cobalt was shown by method of X-ray diffraction analysis of crystallites of the size of 15÷20 nm. The image of transmission electron microscope shows that the size of metal particles is 20 nm, and that of their agglomerates in composite is 200 nm. The nanocomposites are sensitive to vapors of acetone, ammonia, ethyl alcohol. The process of adsorption in acetone and ammonia vapors happens with the irreversible loss of properties, which is due to the oxidation of metals on the GNP surface. Sensory properties of composites GNP/(Ni-Co) are stable over many cycles using ethanol vapors. The electrophysical studies indicate a significant difference between the properties at low frequencies of Ni-Co and GNP/(Ni-Co). In the area of ultra-high frequency the characteristics have similar values, which are due to the relaxation phenomena. The resulting nanocomposites can be promising for use in energy conversion devices, catalysis, gas sensor, screening, and magnetic devices.

Electrokinetic Power Generation from Liquid Water Microjets

Although electrokinetic effects are not new, only recently have they been investigated for possible use in energy conversion devices. We recently reported the electrokinetic generation of molecular hydrogen from rapidly flowing liquid water microjets [Duffin et al. J. Phys. Chem. C 2007, 111, 12031]. Here, we describe the use of liquid water microjets for direct conversion of electrokinetic energy to electrical power. Previous studies of electrokinetic power production have reported low efficiencies (∼3%), limited by back conduction of ions at the surface and in the bulk liquid. Liquid microjets eliminate energy dissipation due to back conduction and, measuring only at the jet target, yield conversion efficiencies exceeding 10%.

Magnetic properties of Fe–Zn ferrite substituted ferrofluids

In the present paper Zn x Fe 1− x Fe 2O 4 nanoparticles were synthesized to achieve a low Curie temperature magnetic fluid with moderately high value of magnetization for use in energy conversion devices. Certain structural and magnetic properties of these ferrites are studied and discussed in detail.