16 research outputs found
Ultrafast Proton Conduction in an Aqueous Electrolyte Confined in Adamantane-like Micropores of a Sulfonated, Aromatic Framework
Preparation and Study of Sulfonated Co-Polynaphthoyleneimide Proton-Exchange Membrane for a H2/Air Fuel Cell
The sulfonated polynaphthoyleneimide polymer (co-PNIS70/30) was prepared by copolymerization
of 4,40
-diaminodiphenyl ether-2,20
-disulfonic acid (ODAS) and 4,4’-methylenebisanthranilic acid
(MDAC) with ODAS/MDAC molar ratio 0.7/0.3. High molecular weight co-PNIS70/30 polymers
were synthesized either in phenol or in DMSO by catalytic polyheterocyclization in the presence of
benzoic acid and triethylamine. The titration reveals the ion-exchange capacity of the polymer equal
to 2.13 meq/g. The membrane films were prepared by casting polymer solution. Conductivities of
the polymer films were determined using both in- and through-plane geometries and reached ~96
and ~60 mS/cm, respectively. The anisotropy of the conductivity is ascribed to high hydration of the
surface layer compared to the bulk. SFG NMR diffusometry shows that, in the temperature range from
213 to 353 K, the 1H self-diffusion coefficient of the co-PNIS70/30 membrane is about one third of the
diffusion coefficient of Nafion® at the same humidity. However, temperature dependences of proton
conductivities of Nafion® and of co-PNIS70/30 membranes are nearly identical. Membrane–electrode
assemblies (MEAs) based on co-PNIS70/30 were fabricated by different procedures. The optimal MEAs
with co-PNIS70/30 membranes are characterized by maximum output power of ~370 mW/cm² at
80 °C. It allows considering sulfonated co-PNIS70/30 polynaphthoyleneimides membrane attractive
for practical applications
Combining 7Li NMR field-cycling relaxometry and stimulated-echo experiments: A powerful approach to lithium ion dynamics in solid-state electrolytes
One Dimensional Magnetic Resonance Microscopy with Micrometer Resolution in Static Field Gradients : secondary data
Evaporation of Sessile Binary Mixture Droplets: Time Dependence of Droplet Shape and Concentration Profile from One-Dimensional Magnetic Resonance Microscopy
Many technological applications like inkjet printing, coating, or cooling processes rely on the evaporation of sessile droplets. Regarding liquid mixtures, the understanding of the underlying physics is still incomplete and process optimization requires trial and error. Our main goal is to establish a novel method in this field, one-dimensional magnetic resonance microscopy, to investigate the evaporation of sessile binary mixture droplets in the microliter range. It allows us not only to determine the droplet volume and shape, including contact angle, but also to measure concentration profiles with a spatial resolution of a few micrometers. These capabilities are demonstrated for a mixture of 1-octanol (OCT) and pentadecafluoro-1-octanol (F-OCT) by combining spatially resolved 1H and 19F nuclear magnetic resonance measurements. We clearly observe three evaporation regimes for the OCT/F-OCT mixture. The first and second regimes are characterized by the predominant evaporation of F-OCT and are separated by a depinning event. The third regime starts when no F-OCT is left and, thus, features the evaporation of a pure OCT droplet. During all stages, concentration gradients perpendicular to the substrate are weak in the studied binary droplet
Self-diffusion micromechanism in Nafion studied by 2H NMR relaxation dispersion
Field Cycling (FC) 2H nuclear magnetic resonance (NMR) relaxometry was applied to study dynamics in Nafion NR 212 in the temperature range from 300 K to 190 K and water content of λ = 8.2. The sensitive time window of FC was extended up to eight decades using the temperature–frequency superposition principle and master curve. The rotational correlation times obtained from 2H FC NMR coincide with translational correlation times gained from static field 2H NMR diffusometry in the temperature range applied. This fact means that a long-range mass transport in Nafion is coupled to molecular rotations. It is assumed that confined water in Nafion has more ordered oxygen sublattices as compared with bulk water, on a short range is similar to ice. We discuss the possible role of D and L defects, typical for the ordered ice structure and using this concept to describe the processes of self-diffusion of confined water in Nafion, as well as the similarity of temperature and humidity dependence of self-diffusion and proton conductivity