Tomohiro Yasuda

Nonhumidified Intermediate Temperature Fuel Cells Using Protic Ionic Liquids

In this paper, the characterization of a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), as a proton conductor for a fuel cell and the fabrication of a membrane-type fuel cell system using [dema][TfO] under nonhumidified conditions at intermediate temperatures are described in detail. In terms of physicochemical and electrochemical properties, [dema][TfO] exhibits high activity for fuel cell electrode reactions (i.e., the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR)) at a Pt electrode, and the open circuit voltage (OCV) of a liquid fuel cell is 1.03 V at 150 degrees C, as has reported in ref 27. However, diethylmethylammonium bis(trifluoromethane sulfonyl)amide ([dema][NTf(2)]) has relatively low HOR and ORR activity, and thus, the OCV is ca. 0.7 V, although [dema][NTf(2)] and [dema][TfO] have an identical cation ([dema]) and similar thermal and bulk-transport properties. Proton conduction occurs mainly via the vehicle mechanism in [dema][TfO] and the proton transference number (t(+)) is 0.5-0.6. This relatively low t(+) appears to be more disadvantageous for a proton conductor than for other electrolytes such as hydrated sulfonated polymer electrolyte membranes (t(+) = 1.0). However, fast proton-exchange reactions occur between ammonium cations and amines in a model compound. This indicates that the proton-exchange mechanism contributes to the fuel cell system under operation, where deprotonated amines are continuously generated by the cathodic reaction, and that polarization of the cell is avoided. Six-membered sulfonated polyimides in the diethylmethylammonium form exhibit excellent compatibility with [dema][TfO]. The composite membranes can be obtained up to a [dema][TfO] content of 80 wt % and exhibit good thermal stability, high ionic conductivity, and mechanical strength and gas permeation comparable to those of hydrated Nafion. H(2)/O(2) fuel cells prepared using the composite membranes can successfully operate at temperatures from 30 to 140 degrees C under nonhumidified conditions, and a current density of 250 mA cm(-2) is achieved at 120 degrees C. The protic ionic liquid and its composite membrane are a possible candidate for an electrolyte of a H(2)/O(2) fuel cell that operates under nonhumidified conditions.

Physicochemical properties determined by ΔpKa for protic ionic liquids based on an organic super-strong base with various Brønsted acids.

Neutralization of an organic super-strong base, 1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU), with different Brønsted acids affords a novel series of protic ionic liquids (PILs) with wide variations in the ΔpK(a) of the constituent amine and acids. The physicochemical properties of these PILs, such as thermal properties, density, conductivity, viscosity, self-diffusion coefficient, vibrational stretching frequency, and (1)H-chemical shifts of the N-H bond, have been studied in detail. The generated PILs have melting temperatures below 100 °C, and six are liquids at ambient temperatures. Thermogravimetric analyses (TGA) conducted under isothermal and programmed heating conditions have shown that PILs with ΔpK(a)≥ 15 exhibit good thermal stability similar to aprotic ionic liquids. For instance, PILs with ΔpK(a) > 20 show remarkably high short-term thermal stability up to ca. 450 °C under a nitrogen atmosphere. The viscosity, ionic conductivity, and molar conductivity of the PILs fit well with the Vogel-Fulcher-Tamman equation for their dependencies on temperature. The relative cationic and anionic self-diffusion coefficients of the PILs estimated by the pulsed-field gradient spin-echo (PGSE) NMR method appear to be dependent on the structure and strength of the Brønsted acids. Evaluation of the ionicity based on both the Walden plot and PGSE-NMR revealed that it increases until ΔpK(a) becomes 15 for the PILs.

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties become unique (i.e., not easily achieved by other materials) must be explored. Thus, through strong demands for research and consideration of ILs unique properties, we will be able to identify indispensable applications for ILs.

Muscle activation during low-intensity muscle contractions with restricted blood flow

Abstract We examined muscle activation during low-intensity muscle contractions with a moderate restriction of blood flow and complete occlusion of blood flow. Unilateral elbow flexion muscle contractions (20% of 1-RM) were performed in Experiment 1 (30 contractions), Experiment 2 (3 sets × 10 contractions), and Experiment 3 (30 repetitive contractions followed by 3 sets × 15 contractions) with moderate restriction, complete occlusion of blood flow or unrestricted blood flow (control). Electromyography (EMG) was recorded from surface electrodes placed on the biceps brachii muscle and the integrated EMG (iEMG) and mean power frequency (MPF) obtained. During Experiments 1 and 2, muscle activation was progressively increased in complete occlusion and moderate restriction of blood flow to levels greater than in the control. The decline in maximal voluntary isometric contraction (MVC) following the bout of contractions was greater with complete occlusion (39–48%) than moderate restriction of blood flow (16–19%); control MVC did not change. In Experiment 3, changes in MVC, iEMG, and MPF were greater with moderate restriction of blood flow than in the control but comparable with complete occlusion of blood flow where less total work was performed. In conclusion, moderate restriction of blood flow results in similar neural manifestations in muscle as complete occlusion of blood flow but without the apparent contractile/metabolic impairment observed with complete occlusion. Thus, low-intensity muscle contractions, with moderate restriction of blood flow, leads to more intense activation of the muscle relative to the external load.

Hydrogen bonds in protic ionic liquids and their correlation with physicochemical properties

The temperature dependence of the N-H proton chemical shift in protic ionic liquids (PILs) and FT-IR spectra of the N-H bonds indicated the presence of strong hydrogen bonds between the protonated cation and the anion, depending on the ΔpK(a) of the constituent acid and base, and their successive breaking with temperature, which may explain the characteristic properties of PILs such as relatively low ionicity and its decrease with temperature.

Effects of polymer structure on properties of sulfonated polyimide/protic ionic liquid composite membranes for nonhumidified fuel cell applications.

To investigate the effects of polymer structure on the properties of composite membranes including a protic ionic liquid, [dema][TfO] (diethylmethylammonium trifluoromethanesulfonate), for nonhumidified fuel cell applications, we synthesized sulfonated polyimides (SPIs) with different structures as matrix polymers, which have different magnitudes of ion-exchange capacities (IECs), different sequence distributions of ionic groups, and positions of sulfonate groups in the main chain or side chain. Despite having similar IECs, multiblock copolymer SPI and random copolymer SPI having sulfonate groups in the side chain exhibit higher ionic conductivity than random copolymer SPI having sulfonate groups in the main chain, indicating that the flexibility of sulfonic acid groups and the sequence distribution of ionic groups greatly affect the ion conduction. Atomic force microscopy observation revealed that the multiblock copolymer SPI forms more developed phase separation than the others. These results indicate that the flexibility of sulfonic acid groups and the connectivity of the ion conduction channel, which greatly depends on the sequence distribution, affect the ion conduction.

Printable Polymer Actuators from Ionic Liquid, Soluble Polyimide, and Ubiquitous Carbon Materials

We present here printable high-performance polymer actuators comprising ionic liquid (IL), soluble polyimide, and ubiquitous carbon materials. Polymer electrolytes with high ionic conductivity and reliable mechanical strength are required for high-performance polymer actuators. The developed polymer electrolytes comprised a soluble sulfonated polyimide (SPI) and IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]), and they exhibited acceptable ionic conductivity up to 1 × 10(-3) S cm(-1) and favorable mechanical properties (elastic modulus >1 × 10(7) Pa). Polymer actuators based on SPI/[C2mim][NTf2] electrolytes were prepared using inexpensive activated carbon (AC) together with highly electron-conducting carbon such as acetylene black (AB), vapor grown carbon fiber (VGCF), and Ketjen black (KB). The resulting polymer actuators have a trilaminar electric double-layer capacitor structure, consisting of a polymer electrolyte layer sandwiched between carbon electrode layers. Displacement, response speed, and durability of the actuators depended on the combination of carbons. Especially the actuators with mixed AC/KB carbon electrodes exhibited relatively large displacement and high-speed response, and they kept 80% of the initial displacement even after more than 5000 cycles. The generated force of the actuators correlated with the elastic modulus of SPI/[C2mim][NTf2] electrolytes. The displacement of the actuators was proportional to the accumulated electric charge in the electrodes, regardless of carbon materials, and agreed well with the previously proposed displacement model.

Interactions in ion pairs of protic ionic liquids: Comparison with aprotic ionic liquids

The stabilization energies for the formation (E(form)) of 11 ion pairs of protic and aprotic ionic liquids were studied by MP2/6-311G** level ab initio calculations to elucidate the difference between the interactions of ions in protic ionic liquids and those in aprotic ionic liquids. The interactions in the ion pairs of protic ionic liquids (diethylmethylammonium [dema] and dimethylpropylammonium [dmpa] based ionic liquids) are stronger than those of aprotic ionic liquids (ethyltrimethylammonium [etma] based ionic liquids). The E(form) for the [dema][CF3SO3] and [dmpa][CF3SO3] complexes (-95.6 and -96.4 kcal/mol, respectively) are significantly larger (more negative) than that for the [etma][CF3SO3] complex (-81.0 kcal/mol). The same trend was observed for the calculations of ion pairs of the three cations with the Cl(-), BF4(-), TFSA(-) anions. The anion has contact with the N-H bond of the dema(+) or dmpa(+) cations in the most stable geometries of the dema(+) and dmpa(+) complexes. The optimized geometries, in which the anions locate on the counter side of the cations, are 11.0-18.0 kcal/mol less stable, which shows that the interactions in the ions pairs of protic ionic liquids have strong directionality. The E(form) for the less stable geometries for the dema(+) and dmpa(+) complexes are close to those for the most stable etma(+) complexes. The electrostatic interaction, which is the major source of the attraction in the ion pairs, is responsible for the directionality of the interactions and determining the magnitude of the interaction energy. Molecular dynamic simulations of the [dema][TFSA] and [dmpa][TFSA] ionic liquids show that the N-H bonds of the cations have contact with the negatively charged (oxygen and nitrogen) atoms of TFSA(-) anion, while the strong directionality of the interactions was not suggested from the simulation of the [etma][CF3SO3] ionic liquid.

Solubility of Poly(methyl methacrylate) in Ionic Liquids in Relation to Solvent Parameters

The solubility of poly(methyl methacrylate) (PMMA) in 1-alkyl-3-methylimidazolium ionic liquids (ILs) with different anionic structures has been explored. Nearly monodisperse PMMA-grafted silica nanoparticles (PMMA-g-NPs) were used as a measurement probe for evaluating the PMMA solubility in ILs. The hydrodynamic radius (Rh) of PMMA-g-NPs was measured in the ILs by dynamic light scattering (DLS). Changes in Rh and colloidal stability, that is, the PMMA-solubility change in the ILs, were observed depending on the ionic structures of the ILs. The solubility was mainly affected by the anionic structures of the ILs rather than by the alkyl chain length of the cationic structure. Solvent parameters, including Lewis basicity, solubility parameters, and a hydrophobicity parameter, were used to discuss the change in the PMMA solubility in ILs with different ionic structures. By considering the PMMA solubility in the ILs using these parameters, it was found that there is a good correlation between the PMMA solubility and the hydrophobicity parameter of the anions. Although the change in the PMMA solubility with different cationic structures was not remarkable, the hydrophobicity of the cations also played a role in the solvation of PMMA by providing a low-polarity environment adequate to dissolve PMMA.

Development of nonexercise prediction models of maximal oxygen uptake in healthy Japanese young men

The present study developed nonexercise models for predicting maximal oxygen uptake