1. Introduction 46372. Theoretical Methodologies and Simulation Tools 46402.1. Ab Initio Quantum Chemistry 46412.2. Molecular Dynamics 46422.2.1. Classical Molecular Dynamics and MonteCarlo Simulations46432.2.2. Empirical Valence Bond Models 46442.2.3. Ab Initio Molecular Dynamics (AIMD) 46452.3. Poisson−Boltzmann Theory 46452.4. Nonequilibrium Statistical Mechanical IonTransport Modeling46462.5. Dielectric Saturation 46473. Transport Mechanisms 46483.1. Proton Conduction Mechanisms 46483.1.1. Homogeneous Media 46483.1.2. Heterogeneous Systems (ConfinementEffects)46553.2. Mechanisms of Parasitic Transport 46613.2.1. Solvated Acidic Polymers 46613.2.2. Oxides 46654. Phenomenology of Transport inProton-Conducting Materials for Fuel-CellApplications46664.1. Hydrated Acidic Polymers 46664.2. PBI−H

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Transport in proton conductors for fuel-cell applications: simulations, elementary reactions, and phenomenology.

On the development of proton conducting materials for technological applications

The development of anhydrous proton-conductive materials operating at temperatures above 80 degrees C is a challenge that needs to be met for practical applications. Herein, we propose the new idea of encapsulation of a proton-carrier molecule--imidazole in this work--in aluminium porous coordination polymers for the creation of a hybridized proton conductor under anhydrous conditions. Tuning of the host-guest interaction can generate a good proton-conducting path at temperatures above 100 degrees C. The dynamics of the adsorbed imidazole strongly affect the conductivity determined by (2)H solid-state NMR. Isotope measurements of conductivity using imidazole-d4 showed that the proton-hopping mechanism was dominant for the conducting path. This work suggests that the combination of guest molecules and a variety of microporous frameworks would afford highly mobile proton carriers in solids and gives an idea for designing a new type of proton conductor, particularly for high-temperature and anhydrous conditions.

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One-dimensional imidazole aggregate in aluminium porous coordination polymers with high proton conductivity.

A new series of Bronsted acid−base ionic liquids were derived from the controlled combination of a monoprotonic acid with an organic base under solvent-free conditions. Appropriate amounts of solid bis(trifluoromethanesulfonyl)amide (HTFSI) and solid imidazole (Im) were mixed at various molar ratios to have compositions varying from an equimolar salt to HTFSI- or Im-rich conditions. The mixture at equivalent molar ratio formed a protic neutral salt with a melting point of 73 °C, which was thermally stable at temperatures even above 300 °C. The melting points of other compositions were lower than those of the equimolar salt and Im or HTFSI, giving eutectics between the equimolar salt and HTFSI or Im. Some of the compositions with certain molar ratios of Im and HTFSI were liquid at room temperature. For Im excess compositions, the conductivity was found to increase with increasing Im mole fraction, and the 1H NMR chemical shift of the proton attached to the nitrogen atom of Im was shifted to a lower magneti...

Brønsted acid-base ionic liquids as proton-conducting nonaqueous electrolytes

Progress over the past decades in proton-conducting materials has generated a variety of polyelectrolytes and microporous polymers. However, most studies are still based on a preconception that large pores eventually cause simply flow of proton carriers rather than efficient conduction of proton ions, which precludes the exploration of large-pore polymers for proton transport. Here, we demonstrate proton conduction across mesoporous channels in a crystalline covalent organic framework. The frameworks are designed to constitute hexagonally aligned, dense, mesoporous channels that allow for loading of N-heterocyclic proton carriers. The frameworks achieve proton conductivities that are 2-4 orders of magnitude higher than those of microporous and non-porous polymers. Temperature-dependent and isotopic experiments revealed that the proton transport in these channels is controlled by a low-energy-barrier hopping mechanism. Our results reveal a platform based on porous covalent organic frameworks for proton conduction.

Proton conduction in crystalline and porous covalent organic frameworks

Imidazole single crystal has a highly anisotropic conductivity; the ratio of conductivity in the c and a crystallographic directions is ∼103. In the c crystallographic direction, the hydrogen bonded direction, protonic carriers are discharged as hydrogen at the negative electrode. The limiting conduction process is possibly due to L‐defect injection and transport back down the hydrogen bonded chain after the proton is discharged. Conductivity in the a direction is probably electronic and extrinsic.

A. R. Mcghie

Papers

Protonic Conductivity in Imidazole Single Crystal

Protonenleitfaehigkeit von imidazol-einkristallen