Construction of unimpeded proton-conducting pathways in solution-processed nanoporous polymer membranes

Developing proton-conducting membranes with three-dimensional conductivity and expedited interfacial contact is requested in the field of fuel cells. Here, we present a design strategy by combining solution processing and material flexibility into amorphous and porous polymers. We design a nanoporous polymer whose skeleton contains dihydrophenazine as a proton-accepting site, and subsequently protonate these sites to produce abundant charges on the polymer skeletons, which enables ionic polymers to be well dispersed in organic solvents and guarantees that they can be fabricated into uniform and amorphous membranes in a solution-processed manner. Importantly, after protonation, the dihydrophenazines change to proton-donating sites, which exhibit dynamic local motions that assist proton exchange on the polymer skeletons and thus construct three-dimensional and unimpeded proton-conduction pathways, with a striking proton conductivity of 0.30 S cm^-1 (298 K and 90% relative humidity), a low resistance of 3.02 Ω, and a H⁺ transport number of 0.98 that was very close to the upper limitation of 1.0.

Missing metal-linker connectivities in a 3-D robust sulfonate-based metal–organic framework for enhanced proton conductivity

We demonstrate the first example of proton conductivity control with the missing metal–ligand connectivities within a rare 3-D porous sulfonate-based MOF.

Proton Conductivities of Lamellae-Forming Bioinspired Block Copolymer Thin Films Containing Silver Nanoparticles

Size-controlled metal nanoparticles (NPs) were spontaneously formed when the amphiphilic diblock copolymers consisting of poly(vinyl catechol) and polystyrene (PVCa-b-PSt) were used as reductants and templates for NPs. In the present study, the proton conductivity of well-aligned lamellae structured PVCa-b-PSt films with Ag NPs was evaluated. We found that the proton conductivity of PVCa-b-PSt film was increased 10-fold by the addition of Ag NPs into the proton conduction channels filled with catechol moieties. In addition, the effect of humidity and the origin of proton conductivity enhancement was investigated.

1000-fold enhancement in proton conductivity of a MOF using post-synthetically anchored proton transporters

Pyridinol, a coordinating zwitter-ionic species serves as stoichiometrically loadable and non-leachable proton carrier. The partial replacement of the pyridinol by stronger hydrogen bonding, coordinating guest, ethylene glycol (EG), offers 1000-fold enhancement in conductivity (10⁻⁶ to 10⁻³ Scm⁻¹) with record low activation energy (0.11 eV). Atomic modeling coupled with ¹³C-SSNMR provides insights into the potential proton conduction pathway functionalized with post-synthetically anchored dynamic proton transporting EG moieties.

High proton conductivity and spectroscopic investigations of metal-organic framework materials impregnated by strong acids

Strong toluenesulfonic and triflic acids were incorporated into a MIL-101 chromium(III) terephthalate coordination framework, producing hybrid proton-conducting solid electrolytes. These acid@MIL hybrid materials possess stable crystalline structures that do not deteriorate during multiple measurements or prolonged heating. Particularly, the triflic-containing compound demonstrates the highest 0.08 S cm(-1) proton conductivity at 15% relative humidity and a temperature of 60 °C, exceeding any of today's commercial materials for proton-exchange membranes. The structure of the proton-conducting media, as well as the long-range proton-transfer mechanics, was unveiled, in a certain respect, by Fourier transform infrared and (1)H NMR spectroscopy investigations. The acidic media presumably constitutes large separated droplets, coexisting in the MIL nanocages. One component of proton transfer appears to be related to the facile relay (Grotthuss) mechanism through extensive hydrogen-bonding interactions within such droplets. The second component occurs during continuous reorganization of the droplets, thus ensuring long-range proton transfer along the porous structure of the material.