Simultaneous Increase Of Conductivity Research Articles

Simultaneous enhancement of conductivity and Seebeck coefficient of PEDOT:PSS by triflic acid treatment for flexible thermoelectric generator

Organic thermoelectric materials are of great interest for development of flexible thermoelectric devices. Two crucial parameters namely conductivity and Seebeck coefficient apparently display a trade-off effect towards optimization of thermoelectric (TE) properties. Dopants normally increase the conductivity of PEDOT:PSS but Seebeck coefficient remains unaffected at around 15–18 µV K −1 . In this work, pre-treatment using triflic acid to PEDOT:PSS solution is employed displaying simultaneous increase in conductivity of 1686 S cm −1 and Seebeck coefficient of 23.6 µV K −1 . Mechanism of improvements are attributed to the increased order of long-range crystal packing as well as hopping between newly generated DOS. HRTEM and XRD data substantiated the improved crystallinity. Acid treatment induced change of conformation from coil like benzoid to linear quinoid structure as observed by Raman spectra, with increasing level of oxidation based on Raman and UV–vis–NIR spectra. The carrier concentration and mobility increased leading to the power factor of 94 µW m −1 K −2 . Flexible thermoelectric generator (TEG) device is developed on PET film which generate thermovoltage of 2.0 mV at temperature difference of 15 K. • Single step treatment of PEDOT:PSS by dopant TFMSA in DI water making the process green and R2R processable. • Simultaneous enhanced conductivity and Seebeck coefficient is observed with maximum power factor of 94 µW m −1 K −2 . • Mechanism of enhanment is attributed to improved in the long-range ordered packing of doped material. • The developed flexible TEG generated thermovoltage of 2.0 mV at temperature difference of 15 K.

The effects of alkaline-earth-metal-element doping on the thermoelectric properties of β-Zn4Sb3

The effects of alkaline-earth metal elements Ca, Sr, and Ba on the electronic structure and thermoelectric properties of β-Zn4Sb3 were investigated by performing self-consistent ab initio electronic structure calculations within density functional theory and solving the Boltzmann transport equations within the relaxation time approximation. The results demonstrate that these alkaline-earth metal elements with s orbitals could introduce giant sharp resonant peaks in the electronic density of states (DOS) near the host valence band maximum in energy. And these deliberately engineered DOS peaks result in a sharp increase of the room-temperature Seebeck coefficient of β-Zn4Sb3 by a factor of nearly 8/9/19, respectively. Additionally, with the simultaneous increase of conductivity and decline of carrier thermal conductivity upon Ca/Sr/Ba doping, potentially, at least, 10/4/2-fold increase in optimizing power factor, and 14/12/8-fold increase in thermoelectric figure of merit of β-Zn4Sb3 at room temperature are achieved. And their corresponding optimal Fermi levels are all located near the host valence band maximum.

Simultaneous increase in conductivity and phonon scattering in a graphene nanosheets/(Bi2Te3)0.2(Sb2Te3)0.8 thermoelectric nanocomposite

Abstract A thermoelectric nanocomposite of Bi 0.4 Sb 1.6 Te 3 (BiSbTe) incorporated with the graphene nanosheets (GNs) has been synthesized and studied. The reduction of the carrier mobility is much less than the increase of the carrier concentration, resulting in the increase in conductivity at a low graphene nanosheets content. Simultaneously, graphene nanosheets causes 20–30% reduction in thermal conductivity (κ) owing to phonons blocking of nanosheets as well as phase boundaries. As a result, high dimensionless figure of merit (ZT) values of up to 1.29 (300 K) and 1.54 (440 K) are obtained in Bi 0.4 Sb 1.6 Te 3 incorporated with only 0.3 vol.% and 0.4 vol.% graphene nanosheets, respectively, demonstrating that the thermoelectric performance of the BiSbTe alloy can be improved effectively through incorporation of GNs.

High temperature thermoelectric properties of co-doped Ca3−xAgxCo3.95Fe0.05O9+δ (0≤x≤0.3)

Abstract We have fabricated a series of co-doped misfit-layered cobaltites Ca 3− x Ag x Co 3.95 Fe 0.05 O 9+ δ with x =0.0, 0.1, 0.2 and 0.3 using conventional solid state reaction. The electrical resistivity and thermopower were measured between 300 and 700 K. For all the samples, the temperature dependence of electrical resistivity exhibits broad maximum. The level-off thermopower behavior of misfit-layered cobaltites in the temperature range of 200 and 300 K is often observed. Instead, the thermopower of Ca 3− x Ag x Co 3.95 Fe 0.05 O 9+ δ increases with increasing temperature up to 700 K, which could be associated with the strong temperature dependence of quasiparticle resonance. Partial substitution of Ag + for Ca 2+ in the Ca 2 CoO 3 sublattice results in simultaneous increase of conductivity and thermopower. Considering that both the sublattices of CoO 2 and Ca 2 CoO 3 could make contribution to the transport properties, it is therefore likely that the conduction behavior of the Ca 2 CoO 3 sublattice is activated type in the framework of two-carrier system. Ca 2.9 Ag 0.2 Co 3.95 Fe 0.05 O 9+ δ exhibits the highest power factor and highest figure of merit (zT) among this series of samples.

Simultaneous increase in conductivity and Seebeck coefficient in a polyaniline/graphene nanosheets thermoelectric nanocomposite

Polyaniline/graphene nanosheets (PANI/GNs) thermoelectric (TE) bulk composite pellets and films have been prepared with PANI to GNs weight ratios ranging from 4:1 to 1:1. Their structure and morphology have been investigated by Raman spectroscopy, thermogravimetric analysis and field emission scanning electron microscopy. The TE properties of the pellets and films were measured at room temperature. As the weight ratio of PANI to GNs decreased from 4:1 to 1:1, both the electrical conductivity and the Seebeck coefficient of pellets and the films increased. This was attributed to a substantial increase in carrier mobility while carrier concentration was not significantly changed. As a result, the power factor of the pellets and films increased from 0.64 to 5.60 and 0.05 to 1.47 μW m−1 K−2, respectively. This is the first time the TE properties of PANI/GNs nanocomposites were reported.

High-Temperature Thermoelectric Properties of Cu-Substituted Bi<sub>2</sub>Sr<sub>2</sub>Co<sub>2</sub>O<sub>Y</sub> Oxides

Bi2Sr2Co2-xCuxOy (x=0.0, 0.2, 0.4) samples were prepared by solid-state reaction method and the effect of Cu substitution on the high-temperature thermoelectric properties was investigated. The presence of Cu element improved the grain size and the thermoelectric properties increased owing to the simultaneous increase of conductivity and Seebeck coefficients. The optimal thermoelectric performance was obtained in x=0.2 sample and the power factor was two times as large as that in Cu-free sample at 923K.

The role of the electric conductivity of carbons in the electrochemical capacitor performance

The interpretation of the performance of electrochemical capacitors based exclusively on the textural features and surface chemistry of carbons can be insufficient, or even misleading, in the case of materials prepared at low temperatures (typically below 800 °C). It is suggested that the gradual improvement of the electrochemical performances of carbon-based capacitors at high current densities, following heat treatments up to 900 °C, is mainly a consequence of the simultaneous increase in conductivity. This is illustrated by a study of carbons based on a mesoporous carbon prepared at 550 °C, which displays poor electrochemical performances and a low conductivity (4.6 × 10−6 S m−1). A first heat treatment at 700 °C leads to major structural, chemical and electrochemical changes, due to the collapse of the smaller mesopores and the formation of a microporous structure with average pore widths around 1.3 nm. One also observes a reduction in the surface oxygen density from 13 to approximately 5 μmol m−2. Further heat treatments at 800 and 900 °C do not modify significantly these characteristics, nor the surface-related capacitances at low current densities (1 mA cm−2) in the aqueous (2 M H2SO4) and organic (1 M (C2H5)4NBF4/CH3CN) electrolytes. On the other hand, one observes increasingly high rate capabilities which may be ascribed to the simultaneous increase in conductivity from 7.3 to 147.8 S m−1 between 700 and 900 °C.

High-Temperature Thermoelectric Properties of Pb- and La-Substituted Bi<sub>2</sub>Sr<sub>2</sub>Co<sub>2</sub>O<sub>y</sub> Misfit Compounds

Pb- and La-substituted (Bi,Pb)2(Sr,La)2Co2Oy samples were prepared by solid-state reaction method and the effect of element substitution on the high-temperature thermoelectric properties was investigated. It was found that the presence of Pb and La elements improved the thermoelectric properties of the Bi2Sr2Co2Oy system owing to the simultaneous increase of conductivity and Seebeck coefficients. The optimal thermoelectric performance was obtained in Pb and La co-substituted samples and the power factor could reach 2.1×10-4Wm-1K-2 at 1000K.

Phase transitions and “nonmetallic” temperature dependence of conduction electron spin resonance line width in quasi-two-dimensional synthetic metal C 15HNO 3

Abstract In the synthetic metal C 15 HNO 3 during and after crystallization of the HNO 3 “guest” molecules, the simultaneous increase of conductivity, conduction electron spin resonance (CESR) line width and spin carriers concentration ( N ) was found and investigated. The increase of N is directly connected with the partial localization of the conduction π-electrons (in terms of graphite intercalation compounds tight binding model). Since the localized electrons are the perturbation centres for the conduction electrons, it has been proposed that the increase of their concentration is the main reason for the decrease of the in-plane spin carriers mobility and the “nonmetallic” increase of the CESR line width observed during and after crystallization of the HNO 3 “guest” layers.

Electrical properties of Bi2S3 thin films prepared by the dip-dry method

Bi2S3 thin films have been prepared by the dip-dry method and their electrical properties such as conductivity, thermoelectric power and spectral response of photoconductivity were investigated. Some uncommon findings, such as a simultaneous increase in conductivity and thermoelectric power with thickness of film, are explained by Seto's model for polycrystalline silicon film duly modified for in homogeneities.