In this review the phenomenon of proton conductivity in materials and the elements of proton conduction mechanismsproton transfer, structural reorganization and diffusional motion of extended moietiesare discussed with special emphasis on proton chemistry. This is characterized by a strong proton localization within the valence electron density of electronegative species (e.g., oxygen, nitrogen) and self-localization effects due to solvent interactions which allows for significant proton diffusivities only when assisted by the dynamics of the proton environment in Grotthuss and vehicle type mechanisms. In systems with high proton density, proton/proton interactions lead to proton ordering below first-order phase transition rather than to coherent proton transfers along extended hydrogen-bond chains as is frequently suggested in textbooks of physical chemistry. There is no indication for significant proton tunneling in fast proton conduction phenomena for which almost barrierless proton transfer is suggest...

Proton Conductivity: Materials and Applications

The compound CsH2PO4 has emerged as a viable electrolyte for intermediate temperature (200–300 °C) fuel cells. In order to settle the question of the high temperature behavior of this material, conductivity measurements were performed by two-point AC impedance spectroscopy under humidified conditions (p[H2O] = 0.4 atm). A transition to a stable, high conductivity phase was observed at 230 °C, with the conductivity rising to a value of 2.2 × 10−2 S cm−1 at 240 °C and the activation energy of proton transport dropping to 0.42 eV. In the absence of active humidification, dehydration of CsH2PO4 does indeed occur, but, in contradiction to some suggestions in the literature, the dehydration process is not responsible for the high conductivity at this temperature. Electrochemical characterization by galvanostatic current interrupt (GCI) methods and three-point AC impedance spectroscopy (under uniform, humidified gases) of CsH2PO4 based fuel cells, in which a composite mixture of the electrolyte, Pt supported on carbon, Pt black and carbon black served as the electrodes, showed that the overpotential for hydrogen electrooxidation was virtually immeasurable. The overpotential for oxygen electroreduction, however, was found to be on the order of 100 mV at 100 mA cm−2. Thus, for fuel cells in which the supported electrolyte membrane was only 25 μm in thickness and in which a peak power density of 415 mW cm−2 was achieved, the majority of the overpotential was found to be due to the slow rate of oxygen electrocatalysis. While the much faster kinetics at the anode over those at the cathode are not surprising, the result indicates that enhancing power output beyond the present levels will require improving cathode properties rather than further lowering the electrolyte thickness. In addition to the characterization of the transport and electrochemical properties of CsH2PO4, a discussion of the entropy of the superprotonic transition and the implications for proton transport is presented.

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Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes

Intriguing ZnO dendritic nanostructures have been synthesized by a two-step chemical vapor deposition process. Regular nanorods grow uniformly to the presynthesized ZnO nanowires on silicon substrate, the secondary nanorods are single-crystal hexagonal ZnO, and each nanorod grows along the [0001] direction. The relationship between the secondary-grown nanorods and the primary ZnO nanowire is not epitaxial due to the high temperature-increasing rate during the rapid grown process. The size and morphology of branches can be controlled by adjusting the temperature and duration of growth. Room temperature photoluminescence (PL) and mircrowave absorption properties of the ZnO dendritic nanostructures have been investigated in detail. The value of minimum reflection loss for the composite with 50 vol % ZnO dendritic nanostructures is -42 dB at 3.6 GHz with a thickness of 5.0 mm. Hierarchical nanostructures of this type are ideal objects for the fabrication of nanoscale functional devices.

Multistep synthesis, growth mechanism, optical, and microwave absorption properties of ZnO dendritic nanostructures

Charge- and spin-density waves in existing superconductors: competition between Cooper pairing and Peierls or excitonic instabilities

By a simple method, that is, by heating raw materials in a flowing gas at ambient pressure, Si3N4, Ga2O3, and ZnO nanowires, SiC nanocables, and SiO2 amorphous nanowires are synthesized without metal catalysts. The diameters of these one-dimensional nanoscale materials are greatly affected by synthesis temperatures. At suitable synthesis temperatures, their diameters are <100 nm. The growth mechanisms of these nanowires are discussed preliminarily.

A Simple Method To Synthesize Nanowires

FTIR analysis of a-SiC:H films grown by plasma enhanced CVD

In situ measurements and growth kinetics of silicon carbide chemical vapor deposition from methyltrichlorosilane

Growth mechanism of vapor liquid solid (VLS) grown indium tin oxide (ITO) whiskers along the substrate

The dielectric constants along the c ' axis of Cs 3 H(SeO 4 ) 2 and its deuterated crystal were measured in a temperature range from 5 K to 460 K. It was found that Cs 3 H(SeO 4 ) 2 undergoes three phase transitions at 451 K, 364 K and 50 K. The dielectric constant of Cs 3 H(SeO 4 ) 2 shows a small peak at 50 K, and it obeys the Curie-Weiss law above 50 K. The transition temperature (50 K) is increased to 168 K by deuteration, showing a large isotope effect, while other two transition temperatures do not change appreciably.

Dielectric Study of Phase Transitions in Cs3H(SeO4)2 and Its Isotope Effect

The dielectric constants of K 3 H(SeO 4 ) 2 and its partially deuterated crystal were measured from 5 K to 400 K. It was found that K 3 H(SeO 4 ) 2 undergoes a phase transition accompanied with a small peak in the dielectric constant at about 20 K. The peak of the dielectric constant was shifted from 20 K to 73 K by deuteration of about 70%.

Tsutomu Kaneko

Papers

FTIR analysis of a-SiC:H films grown by plasma enhanced CVD

In situ measurements and growth kinetics of silicon carbide chemical vapor deposition from methyltrichlorosilane

Growth mechanism of vapor liquid solid (VLS) grown indium tin oxide (ITO) whiskers along the substrate

Dielectric Study of Phase Transitions in Cs3H(SeO4)2 and Its Isotope Effect

Dielectric Study of the Phase Transition in K3H(SeO4)2 and Isotope Effect