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Ferricyanide/ferrocyanide/guanidinium-based thermoelectrochemical cells have been investigated under different loading conditions in this work. Compared with ferricyanide/ferrocyanide-based devices, the device with guanidinium-added electrolytes shows higher power and energy densities. We observed that the enhanced performance is not due to the ionic Seebeck effect of guanidinium but because of the configuration entropy change resulting from the selective binding of Gdm

With the aid of large Seebeck coefficients, over 1 mV K−1, redox-free ionic conductors have the potential to be used as a component of thermally chargeable supercapacitors and/or thermopiles. To date, most ionic conductors reported exhibit p-type polarity; therefore, it is challenging to develop thermoelectric (TE) supercapacitor modules comprising both p- and n-type TE legs due to the lack of n-type ionic conductors. Herein, we found that the intrinsically p-type polarity of alkylmethylimidazolium chloride (Rmim:Cl)-based ionic hydrogels could be converted into n-type, using poly(3,3-ethylenedioxythiophene):poly(styrenesulfonyl) (PEDOT:PSS)-conducting polymer electrodes. Complementary characterization of the TE voltage response and absorption spectroscopy suggests that “negative” interfacial polarization is induced under asymmetric heating. This results from the ion exchange between PEDOT:PSS and Rmim:Cl upon creating the interfaces and the high affinity of Rmim:PSS compared with PEDOT:Cl, which results in the n-type TE response. Our findings offer a useful method for tuning the polarity of TE supercapacitors by tailoring the ion/electrode interactions despite the use of an identical electrolyte.

This paper shows how protonated 3,4-ethylene dioxythiophene moieties can be used as an end group to make organic conductors. An organic semiconductor 2,5-bis(5-(2,3-dihydrothieno[3,4

The feasibility of using organic thermoelectric devices to power sensors for different applications is a critical area of interest for researchers. Organic semiconductors possess lower thermoelectric performance than their inorganic counterparts, however, this can be compensated for by certain advantages, such as their light weight, low fabrication costs, and low fabrication temperatures. For practical applications, they face competition with Li-ion batteries, which are known for their high energy densities and long lifetimes. Thus, in addition to having a suitable corresponding power output, ideal organic thermoelectric devices require excellent stability. In this study, such a perspective was examined via primarily focusing on recent studies of organic thermoelectric devices and, particularly, their practical applications. The impact of contact resistance on device performance has been discussed, together with suggestions of certain promising device structures for organic thermoelectric devices. Experimentally, it was confirmed that light and compact organic thermoelectric devices with a size of ∼10 cm2 should be sufficiently suitable to power sensors. Moreover, these devices were confirmed to operate under natural cooling conditions without a heat sink, thus showing excellent stability for >70 days under continuous working conditions at 100 °C.

Maximizing the power outputs of devices using benchmark materials is critical for the application of organic thermoelectrics. We report the fabrication of thermoelectric devices using poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) with a Ni foil and polyimide film. The shape of the Ni foil was designed to match the thermal and electrical resistance of the poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) film. Due to the low thermal conductivity of the organic materials, a stable temperature difference of 50 K was achieved under natural cooling conditions without a heat sink at 100 °C. As a result, the device exhibited a power density of 40 μW/cm2, nearly double that of the unoptimized device.

The conventional thermoelectric figure of merit and the power factor are not sufficient as a measure of thin film quality of thermoelectric materials, where the power conversion efficiency depends on the film dimensions. By considering the film size, the effective thermoelectric figure of merit and effective Seebeck coefficient are introduced to guarantee that the maximum energy conversion efficiency increases as the effective thermoelectric figure of merit increases. Similarly, the effective power factor is defined. By introducing typical material properties for Bi$_2$Te$_3$ and PEDOT, we study the thickness dependence of the effective figure of merit and the effective power factor., 4 figures

Thermoelectric properties of organic semiconductors have recently attracted attention owing to their remarkable electrical conductivity, power factor, and figure of merit. Herein, the authors first simply introduce the history of the organic thermoelectric materials; then, they summarize the recent efforts toward improving the thermoelectric properties of p- and n-type organic semiconductors. The p-type semiconductors have been divided into two groups: poly(3,4-ethylenedioxythiophene)-based materials, doped during the polymerization, and the others, which are typically nonconductive and can be molecularly doped after film formation. A couple of examples of n-type organic thermoelectric materials are also presented. Finally, the anisotropic thermoelectric properties and their measurements are discussed.

Thermoelectric power generation from waste heat is an important component of future sustainable development. Ion-conducting materials are promising candidates because of their high Seebeck coefficients. This study demonstrates that ionic hydrogels based on imidazolium chloride salts exhibit outstanding Seebeck coefficients of up to 10 mV K

The contact resistance at conducting polymer-electrode junctions could substantially affect device performance because electrical currents or signals generated in the polymer devices must be transferred in their final form through the junctions to the connected load or devices. We report here the specific contact resistance between the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and a metal electrode as measured by a transmission line technique. Toward developing printed electronics that do not require vacuum processes, we focus on the specific contact-resistance, rc, between PEDOT:PSS films and metal pastes. Addition of a second solvent such as ethylene glycol (EG), poly-ethylene glycol (PEG), and dimethyl sulfoxide (DMSO) to PEDOT:PSS solution for film formation induced a significant reduction of rc together with an enhancement of electrical conductivity. A surface treatment using EG or DMSO on electrode areas of the film also decreased rc at the PEDOT:PSS-Ag paste junction to the value at the PEDOT:PSS-Ag junction formed by electron-beam evaporation. The mechanism of reduction of rc is discussed based on morphology of the PEDOT:PSS film.

Recently, the electrical conductivity of conducting polymers has been significantly improved. Unfortunately, there are nearly no reports on the carrier mobility and carrier density measurements at this stage because traditional measurement approaches are difficult to apply in highly doped disordered systems. In this study, we developed a method to extract the carrier mobility in a highly doped disordered system using a solid state photoinduced charge transfer reaction. Combining the number of the charges transferred from photobase generators to the conducting polymers, the carrier mobility can be extracted from the conductivity change. This approach was successfully applied to conducting polymers with different conductivities. Potentially, this method could also be used to measure the carrier mobility of other disordered systems such as p-type and n-type carbon nanotube films.

In this study, we demonstrate that conducting polymers could be ideal materials for continuously managing humidity in a wide range of enclosed spaces. We demonstrate a simple battery-driven humidity control unit to manage the humidity in a closed environment and studied humidity-responsive nanocapsules using Zn-coordinated lipid nanovesicles. This study not only promises new applications for conducting polymers but also provides an easy approach for fabricating chambers with a controlled environment, which are often used by physicists, chemists, and biologists.

This study reports a thermo-electrochemical cell based on ionic liquids 1-buty1-3-methylimidazolium chloride·FeCl3 and 1-buty1-3-methylimidazolium chloride·FeCl2. This system showed a high ion conductivity of ca.7 S m−1, a low charge transfer resistance of 0.9 Ω cm2 on a Pt electrode, and a thermopower of 0.26 mV K−1. Because the oxidized form of 1-buty1-3-methylimidazolium chloride·FeCl3 is paramagnetic, the diffusion was controllable under a magnetic field. When a magnet was touched to one of the electrodes of the thermo-electrochemical cell, a potential difference of several mV was generated. The unique properties of the magnetic ionic liquid redox couple suggest new possibilities for simultaneously harvesting thermal and mechanical energies.

We evaluated the effect of an amide compound bearing methyl groups on the properties of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) cast films. The spontaneous electron transfer between N , N -dimethylacetamide (DMA) and the TCNQ complex is expected to change the casting condition. Then, we obtained a higher density of nanofibers in TTF-TCNQ films using DMA. The electrical conduction of TTF-TCNQ films using DMA was 58.0 S/cm, which is twice that of previously reported polycrystalline films. We measured the Seebeck coefficients of the films for their future possible use as thermoelectric materials. The Seebeck coefficient and power factor of the films prepared with DMA were 32.3 μV/K and 6.05 μW/mK 2 , respectively.

The thermoelectric properties of organic materials have been greatly improved very recently, but studies of organic thermoelectric device fabrication are still very limited. In this work, we report proof-of-concept studies of organic thermoelectric devices fabricated by thermal lamination at 100 °C using the benchmark p-type material poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate). A 1.54 cm 2 device shows a power output of 37 μW at a temperature difference of 50 K (a power density of 24 μW/cm 2 ), which is one of the highest values when compared with previous studies. This approach potentially enables the fabrication of high-performance, large-area organic thermoelectric devices via roll-to-roll processing at a low temperature.

We report the transport properties of nonwoven fabric-composite thermoelectric (TE) elements impregnated with the polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The porous structure formed in the fabric after the solvent evaporation of the PEDOT:PSS solution resulted in a high thermal resistance. In addition, the polymer films covering the surface of the fibers in the fabric connected the fibers to form electrical conduction paths, resulting in isotropic electrical conductivity at high PEDOT:PSS concentrations. These two factors provided the optimum PEDOT:PSS concentration for the TE power density per PEDOT:PSS content. Optimizing the TE power density per polymer content could contribute to the low-cost fabrication of TE modules from conducting polymers. We also demonstrated that the flexible TE module fabricated from the nonwoven fabric-composite achieved a power output sufficient to power a light-emitting diode. Contact electrical resistance at polymer-electrode junctions was greatly reduced by the increase in contact area arising from the wavy surface of the fabric composite.

We show that conducting polymer Poly (3,4-ethylene dioxythiophene)/poly (styrene sulfonate) film could be an ideal electrode in thermo-electrochemical cells, which shows a low charge transfer resistance. Using ferricyanide/ferrocyanide as an electrolyte, the Poly (3,4-ethylene dioxythiophene)/poly (styrene sulfonate) based thermo-electrochemical cell could be used to drive light-emitting diodes array. The conducting polymers also show the advantage of hybrid insoluble redox couples such as Prussian blue analog materials, making it easy to measure the temperature-dependent redox potential. By a combination of proper redox couples, the thermally regenerative electrochemical cells could realize. The power could generate during the environmental temperature change.

Measuring and understanding the interfacial resistance between the electrode and electrolyte are critically important for fabricating high-performance thermoelectrochemical cells. Although the charge transfer resistance and other resistance, such as the mass transfer resistance, may measure via electrochemical impedance spectroscopy, the resolution of the charge transfer semicircle in the Cole–Cole plot can decrease if these resistance values are smaller than the solution resistances. Moreover, a small dataset at a very low frequency can affect the analysis results. In this study, the transmission line measurement was applied, which is used in semiconductor physics to determine the contact resistance between a metal and a semiconductor, to thermoelectrochemical cells for simultaneously determining the interfacial and solution resistances. This method was used to quantify the direct-current interfacial and solution resistances, which are directly linked to the power output of cells under different temperatures. Because of a wide applicable concentration range, the interfacial reaction rate constant at high electrolyte concentration could be calculated from the transmission line measurement. Through a comparison with electrochemical impedance spectroscopy results, we concluded that the interfacial resistance is dominated not by the charge transfer resistance but by the mass transfer resistance, which could be dependent on the surface energy of the electrodes.

Single-walled carbon nanotubes (SWCNTs) have the potential for application in thermoelectric energy generators owing to their advantages, such as good charge-carrier transport properties, mechanical flexibility and robustness, and tunability of polarity. However, the fabrication of SWCNTs still remains a problem due to its complexity and high cost. In this paper, we propose an approach for the direct formation of free-standing SWCNT films from as-grown SWCNT mats without any dispersion or separation processes. We used this approach to develop high-performance SWCNT-based thermoelectric leg materials. The as-grown SWCNT mats were synthesized by an enhanced direct injection pyrolytic synthesis (eDIPS) method. The selectivity of the tube diameter for the eDIPS method clarified the dependence of the thermoelectric performance of the free-standing SWCNT films on the tube diameter. The Seebeck coefficients and thermal conductivities were found to correlate with the tube diameter and agreed with the theoretical predictions. Owing to the dispersion-free film formation, our SWCNT films afforded large thermoelectric power factors. In particular, a power factor of 350 μW/(m K2) was obtained for the mean tube diameter of 1.7 nm without any semiconductor extraction or doping treatments. Our approach allowed the fabrication of thermoelectric legs with an arbitrary size; thus, it offers a useful strategy for the simpler, cheaper, and low-waste manufacturing of high-performance organic thermoelectric devices.

The through-plane conductivity of a film sample is critically important because it largely affects the performance of batteries, capacitors, and thermoelectric devices. In this study, we developed a modified four-probe through-plane electrical conductivity measurement method using a coaxial structure. This method is general and works for free-standing film samples. We studied different samples including a steel sheet, highly oriented pyrolytic graphite, and conducting polymers. We confirmed metallic transportation in the steel sheet and hopping transportation in graphite in the through-plane direction by conducting low temperature measurements at 100 K. In the case of a conducting polymer poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate, the conductivity anisotropic ratio decreases with increasing in-plane conductivity. Temperature dependent measurements show two distinct activation energy regimes in the through-plane direction in PEDOT/PSS but almost no change in the in-plane electrical conductivity activation energy. This could be due to additional carrier paths that occur through the more disordered region (the PSS-rich region) in the through-plane direction. We also examined the Meyer–Neldel rule in PEDOT/PSS and concluded that PEDOT/PSS follows the anti-Meyer–Neldel rule, likely due to the high carrier density in the film.

Graphene has been widely used as an electrode material for supercapacitors. However, parallelly-stacked graphene layers often result in inefficient ion diffusion and electron transfers that usually reduce the rate capability of a supercapacitor. In this study, reduced graphene oxide (rGO) and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) composite films were prepared by a solvent evaporation method using PEDOT:PSS as the binder to fix aligned graphene for its good conductivity and strong π-π stacking interactions with the graphene sheets. Analyses using scanning electron microscopy (SEM), nitrogen adsorption-desorption, and small-angle X-ray scattering show that the graphene sheets were well aligned when a magnetic field was applied, though they were oriented randomly without the magnetic field. As a capacitor electrode material, the aligned rGO shows a specific capacitance of 169 F g−1 with a capacitance retention of about 70% at a current density of 50 A g−1 and its cyclic voltammetry (CV) loops maintained a rectangular shape at a voltage scan rate of 2 V s−1. The aligned rGO electrode can help break through the limitations of traditional supercapacitors and increase significantly their charge/discharge rate and power density.

Imidazolium chloride salt was demonstrated as a novel water-processable, strong base-free electron dopant for single-walled carbon nanotubes (SWCNTs). By thermoelectric evaluation and various photoelectron spectroscopy analyses associated with the comparison of the redox potentials, the valence change of the anion (Cl-/Cl3-) was presented as a possible mechanism for electron injection into the nanotube conduction band. The obtained n-type SWCNT films presented good thermoelectric power factor exceeding 100 μW m−1 K−2, nearly identical to that of the original p-type film.

Charge-carrier mobility is an important and crucial performance criterion for organic semiconductors and nanocarbon materials such as carbon nanotubes (CNTs). Although high conductivity has been achieved in highly doped organic semiconductors and CNT networks, reliable measurements of charge-carrier mobility in such disordered materials remain a challenge. Here, we developed and extended a new mobility measurement method, referred to as photoinduced charge transfer, from conducting polymers to nanocarbon materials. We apply this method to examine the carrier mobility of graphene, where the carrier mobility can be extracted using a Hall-effect measurement. By comparing the mobility values obtained using these two methods, we can understand the potential errors in the mobility values extracted using photoinduced dedoping reactions. We further extend this approach to disordered CNT networks and determine the relationship among CNT structure, defects, and carrier mobility.

A novel conducting polymer, Poly(3-methoxythiophene-2,5-diyl-co-3,4-ethylenedioxythiophene-2,5-diyl]/tosylate (P1/tos), was synthesized by oxidative in situ polymerization using Fe(tos) 3 as an oxidant. Compared with poly(3,4-ethylenedioxythiophene) (PEDOT), P1 has a deeper HOMO level and a wider energy gap as observed by ultraviolet–visible spectroscopy and photoelectron yield spectroscopy. P1/tos showed electrical conductivity of 10 S/cm and a carrier mobility of about 0.6 cm 2 /(V s), which was extracted by using ion-gel thin film transistors. The calculated carrier concentration was on the order of 10 20 cm −3 , which is lower than that of PEDOT/tos. The Seebeck coefficient of P1/tos was higher than that of PEDOT/tos.

Large anisotropy of thermal and electric conductions of the carbon nanotubes (CNTs) paper between in-plane and through-plane direction due to the one-dimensional fibrous structure of CNTs is problematic when the temperature gradient are required for applications such as thermoelectric conversion using Seebeck effect. To control the orientation of the CNT direction, polymer particles are introduced upon paper formation via vacuum filtration method. Thermal and electric conductivity in in-plane direction are decreased as increase the amount of the polymer particles used for the paper formation, while those in through-plane direction are increased. Heat diffusion in the paper are monitored by IR camera and it is found that the larger temperature gradient are observed for the CNT paper with anisotropy control compared to the original paper without anisotropy control.

We report organic thermoelectric modules screen-printed on paper by using conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and silver paste. Our large-area devices provided sufficient power to illuminate light-emitting diodes. This is the first example of thermoelectric modules containing conducting polymers being used to power practical devices. The stability of this proof-of-concept module was tested at 100 °C for over 100 h without any encapsulation. We showed that the decrease in device performance was caused not by the deterioration of the materials but by degradation of the interface between the conducting polymers and silver paste. These results suggest that organic thermoelectric modules could be used to harvest heat energy at low temperature, although the stability of the interface must be improved.

We developed a procedure for the fabrication of sub 1 nm gap Au electrodes via electromigration. Self-aligned nanogap formation was achieved by applying a bias voltage, which causes electromigration during metal evaporation. We also demonstrated the application of this method for the formation of nanogaps as small as 1 nm in width, and we found that the gap size can be controlled by changing the magnitude of the applied voltage. On the basis of the electric conductance and surface-enhanced Raman scattering (SERS) measurements, the fabricated gap size was estimated to be nearly equal to the molecular length of 1,4-benzenedithiol (BDT). Compared with existing electromigration methods, the new method provides two advantages: the process currents are clearly suppressed and parallel or large area production is possible. This simple method for the fabrication of a sub 1 nm gap electrode is useful for single-molecule-sized electronics and opens the door to future research on integrated sub 1 nm sized nanogap devices.

Hydrogen permeation flux is generally described by the square-root law, but deviation from the law has been widely reported. For more precise description, pressure-dependent permeability has been proposed. Based on this approach, the hydrogen diffusion coefficient in palladium was evaluated as a continuous function of equilibrium hydrogen pressure. Results showed a decreasing diffusion coefficient with pressure, in contrast to increasing permeability and solution coefficient. The pre-exponential factor and activation energy for the diffusion coefficient in the dilute limit, i.e., intrinsic diffusion coefficient, were, respectively, 2.40×10 −7 m 2 /s and 21.1 kJ/mol H. This study did not assume constant hydrogen mobility, differently from most studies, but evaluated the mobility as a function of pressure. This precise analysis revealed slightly increasing mobility with pressure, because of less deep hydrogen potential at higher hydrogen concentrations. Finally, a guideline to develop membrane materials was provided. Materials with large deviation from Sieverts' law possibly have high permeability at practical pressures for permeation, i.e., atmospheric pressure or higher, even if the mobility in the dilute limit is low.

Self-supported Pd membranes were prepared by an electroless plating method, where the membranes were separated from substrate without any damage by introducing Pd-containing sacrificial layer followed by Pd nanoparticles activation, plating and mild removal. The thickness of the obtained membranes was less than 10 μm. The area was wider than 48 cm2. Hydrogen permeation test was carried out for effective area of 2.98 cm2. No other gas except hydrogen was detected in the permeation side by a gas chromatograph when gas mixture including H2, CO and CO2 was introduced into the feed side. The permeability of an obtained membrane was the same as the value of bulk Pd.

Some dense metal membranes are permeable only to hydrogen, useful to produce and purify hydrogen. Conventionally, hydrogen permeation flux through metal membranes is described as the square-root law. The permeability defined in the law is commonly used as a measure of membrane material. However, deviation from the law has been widely reported. We have extended the definition of permeability for precise description. This study applied it to a thick palladium membrane down to 0.01 MPa in absolute pressure. Experimental results showed that hydrogen permeation flux through the palladium membrane 200 μm thick did not obey the square-root law completely. From the permeation behavior, pressure-dependent permeability was evaluated. The resultant permeability was found to decrease and become a constant value, or intrinsic permeability, as pressure approached vacuum.

Hydrogen permeability of metal membranes is generally defined by the square-root law, as the proportional coefficient of permeation flux to the square-root difference of the pressures on both sides of the membrane. However, deviation from the law has been widely reported for palladium, niobium, etc. Although n-th power instead of the square root has often been employed to determine permeability for these membranes, it has no theoretical base. These approaches do not consider concentration dependency of hydrogen diffusivity in the membrane. This study theoretically extended the definition of permeability by taking it into account, where square root of pressure was used throughout. The resultant permeability depended on pressure. This approach had the following four characteristics. First, the permeability could be qualitatively linked with pressure-dependent solution and diffusion coefficients. For this purpose, the solution coefficient was also extended from Sieverts' law. Second, the permeability could be easily evaluated from permeation flux dependent on feed-side pressure, usually measured in membrane study. Third, this approach enabled comparison of permeation ability irrespective of obeying permeation law. Fourth, permeation flux could be estimated for any pressure conditions visually and analytically. Thus, analytically estimated values were more precise than those using the conventional square-root law. These characteristics are successfully demonstrated using experimental results obtained not only for a palladium membrane in this study but also for palladium and niobium membranes in the literature.

Nickel–zirconium-based amorphous alloys are promising hydrogen-selective membrane materials. These membranes can potentially be combined with a suitable water–gas-shift catalyst to form a catalytic membrane reactor, which can produce high-purity H2 and CO2 streams from coal-derived syngas at elevated temperatures. One shortcoming of amorphous alloys is that their temperature of operation is limited by the onset of crystallization, which in many cases occurs at a temperature below that demanded by typical WGS catalysts. It is hypothesized that the substitution of zirconium with other elements of higher bond valance will increase the crystallization temperature of these amorphous alloys. Systematic substitutions (M = Ti, Nb, Mo, Hf, Ta and W) have been made to the eutectic alloy Ni64Zr36−XMX. Results have shown that niobium, hafnium and tantalum increase the crystallization temperature of these alloys, while Ti decreases the crystallization temperature. Mo and W are problematic in that they have limited solubility, and lead to brittle alloys that are unsuitable for the gas separation application. Of the alloys studied, those from the Ni–Nb–Zr system are most prospective for use in a hydrogen-selective catalytic membrane reactor. Hydrogen permeability studies of three alloys showed that partial substitution of Zr with Nb reduced permeability but improved the thermal stability. An increase in thermal stability not only increases the resistance to crystallization, but also reduces interdiffusion between the membrane and Pd catalyst. Thus, the operating temperature of Ni64Zr36 membranes can be increased through partial substitution of zirconium with niobium.

Amorphous alloy membranes are anticipated as substitutes for expensive palladium membranes. Hydrogen separation modules consisting of four amorphous Zr36Ni64 membranes have been developed to demonstrate their practical usefulness. First, surface investigation showed that 50-mm-wide membranes are smoother on the surface and are therefore expected to be better in terms of sealing than 20-mm-wide membranes. A four-membrane module was assembled without leakage for 0.92 MPa inside to the atmospheric outside. Using this module, pure hydrogen was obtained as effluent from the permeation side. The 82.7% recovery and 31.7 mL (STP)/min were attained in separation from CO and CO2 containing a gas mixture simulating methanol reformed gas. Therefore, the practical availability of amorphous alloy membranes was demonstrated.

Amorphous alloys are anticipated as new membrane materials for high purity hydrogen production, as substitutes for expensive palladium alloys. For amorphous Zr–Ni-based alloys reported to date, hydrogen permeability increases with Zr content. Hydrogen solution properties in a series of amorphous Zr–Hf–Ni ternary alloys were measured carefully using the Sieverts method and residual hydrogen measurements to investigate the reason. Results indicate that hydrogen solubility in the ternary alloys increases with increasing Zr to improve hydrogen permeability, not because of the geometrical atomic structure but because of higher hydrogen affinity of Zr than that of Hf. Increased permeability with Zr in other amorphous Zr–Ni-based alloys is also expected to be attributable to the same reason. Additionally, hydrogen was found with low mobility, and was not removable even after 10 h evacuation at 573 K; the importance of decreasing low mobility hydrogen as a countermeasure against hydrogen embrittlement was pointed out. Equilibrium hydrogen concentration was found not to obey Sieverts’ law with respect to hydrogen pressure. Rather, it was linear roughly to the quarter power. Parameters to reproduce pressure–composition isotherms were determined using Kirchheim's theory.

Exploring the various applications of conjugated polymers requires systematic studies of their physical properties as a function of the doping density, which, consequently, calls for precise control of their doping density. In this study, we report a novel solid-state photoinduced charge-transfer reaction that dedopes highly conductive polyelectrolyte complexes such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate). Varying the UV-irradiation time of this material allows the carrier density inside the film to be precisely controlled over more than 3 orders of magnitude. We extract the carrier density, carrier mobility, and Seebeck coefficient at different doping levels to obtain a clear image of carrier-transport mechanisms. This approach not only leads to a better understanding of the physical properties of the conducting polymer but also is useful for developing applications requiring patterned, large-area conducting polymers.

In order to explore n -type borides-based thermoelectric materials, Seebeck coefficients of Fe–Co–B and Ni–Co–B materials were measured between 430 and 960 K. X-ray diffraction (XRD) patterns of Fe x Co 1– x B( x ⩽0.5) showed that FeB and CoB form solid solutions but their Seebeck coefficients were negative only at x =0 (i.e. CoB) or 0.01. As for Ni–Co–B, XRD patterns of Ni 2 B were observed in Ni x Co 1– x B( x ⩾0.02) other than that of CoB. Seebeck coefficients of Ni x Co 1– x B ( x =0.02−0.07) showed more negative values than pure CoB.

The theoretical relationships between the terminal voltage ( V ) and external current ( I ) of a solid-oxide thermocell using oxide ion–electron mixed conductors were derived based on Wagner's theory. The electrical transport parameters of Y 2 Ti 2 O 7 were used to calculate the theoretical V – I characteristics. A mixed discharge region, where the partial currents of the oxide ions and electronic carriers flow in the same direction, appeared under an air atmosphere.

In order to understand thermoelectric properties of B–Si alloys (β-rhombohedral boron (β-B), BnSi, B6Si and B3Si or B4Si), band-calculations have been attempted using a first-principle pseudopotential method within the local density approximation. For β-B, consideration of the partial occupancy of interstitial sites would be required to explain the generation of the localized levels between the gap of the conduction band and the valence band. The semiconducting nature of B3Si (or B4Si) could be predicted. However, B6Si with the hypothetical fixed configuration of boron and silicon atoms has definite density of states at its Fermi level. The localization of the wavefunction by disordered arrangement of the atoms seems to play an essential role for its electronic properties. For BnSi, it was properly predicted that Si occupies the A1 site interstitially and also substitutes boron atoms in B(1) sites of pure β-boron framework.

The electrical transport and thermoelectric property of boron carbide nanowires synthesized by a carbothermal method are reported. It is demonstrated that the nanowires achieve a higher Seebeck coefficient and power factor than those of the bulk samples. The conduction mechanism of the nanowires at low temperatures below 300 K is different from that of the sintered-polycrystalline and single-crystal bulk samples. In a temperature range of 200-450 K, there is a crossover between electrical conduction by variable-range hopping and phonon-assisted hopping. The inhomogeneous carbon concentration and planar defects, such as twins and stacking faults, in the nanowires are thought to modify the bonding nature and electronic structure of the boron carbide crystal substantially, causing differences in the electrical conductivity and Seebeck coefficient. The effect of boundary scattering of phonon at nanostructured surface on the thermal conductivity reduction is discussed.

Theoretical formulae for the thermoelectric power of titanate and ferrite with cubic perovskite structures were presented as the carrier-localized system. The formula for titanate was derived from the configurational entropy of the electrons in the t 2g states of the unoccupied Ti 3d states, whereas the formula for ferrite was derived from the entropy of the holes in the e g states of the occupied Fe 3d states. Both formulae were developed for a simple electron system. Assuming that the electrons and holes in the subbands are strongly localized at the Ti and Fe ions and that only Ti 4+ and Ti 3+ or Fe 3+ and Fe 4+ ions exist in the crystal, the formulae of the thermoelectric power are equivalent to the Heikes formula even though the orbitals in the subbands are triply and doubly degenerated.