Development of polyoxadiazole nanocomposites for high temperature polymer electrolyte membrane fuel cells

Cation-Exchange Membrane with Low Frictional Coefficient and High Limiting Current Density for Energy-Efficient Water Desalination

A sulfonated poly(ether ether ketone) (SPEEK) and phosphorylated graphene oxide (PGO) composite of a cation-exchange membrane with low frictional coefficient and high limiting current density has been reported for water desalination by rapid electrodialysis. The incorporation of PGO in the membrane matrix showed a significant impact on the macroscopic properties, counterion frictional coefficient, and performance of the membrane. A well-optimized SPEEK/PGO-8 (8% PGO content, w/w) membrane showed improved conductivity (4.15 × 10^-2 S cm^-1) and permselectivity (87%), and excellent stabilities (thermal, mechanical, and chemical) because of cherished polymer-PGO (filler) interaction via H-bonding. The efficiency of the SPEEK/PGO-8 membrane was also evaluated for the desalination of brackish water near limiting current density (I _lim). Ion concentration polarization (ICP) was assessed by i-V curves, and below I _lim, water splitting or change in product water pH was ruled out. While above I _lim (10.5 mA cm^-2), ICP was significant and could be finally tuned with applied current density for producing desalinated water with a desired pH. Furthermore, improved I _lim, high current efficiency (82.9%), and low energy consumption (7.9 kWh kg^-1 of the salt removed) of the SPEEK/PGO-8 membrane during electrodialysis provide a broad current window for efficient and rapid water desalination/purification.

Proton Conduction in Sulfonated Organic-Inorganic Hybrid Monoliths with Hierarchical Pore Structure

Porous organic-inorganic hybrid monoliths with hierarchical porosity exhibiting macro- and mesopores are prepared via sol-gel process under variation of the mesopore size. Organic moieties in the pore walls are incorporated by substituting up to 10% of the silicon precursor tetramethylorthosilicate with bisilylated benzene molecules. After functionalization with sulfonic acid groups, the resulting sulfonated hybrid monoliths featuring a bimodal pore structure are investigated regarding proton conduction depending on temperature and relative humidity. The hierarchical pore system and controlled mesopore design turn out to be crucial for sulfonation and proton conduction. These sulfonated hybrid hierarchical monoliths containing only 10% organic precursor exhibit higher proton conduction at different relative humidities than sulfonated periodic mesoporous organosilica made of 100% bisilylated precursors exhibiting solely mesopores, even with a lower concentration of sulfonic acid groups.

In situ growth of biocidal AgCl crystals in the top layer of asymmetric polytriazole membranes

Scalable fabrication strategies to concentrate biocidal materials in only the surface of membranes are highly desirable.

Crosslinked copolyazoles with a zwitterionic structure for organic solvent resistant membranes

Cross-linking of hydroxyl modified polytriazoles.

Proton transport in functionalised additives for PEM fuel cells: contributions from atomistic simulations

The conventional polymer electrolyte membrane (PEM) materials for fuel cell applications strongly rely on temperature and pressure conditions for optimal performance. In order to expand the range of operating conditions of these conventional PEM materials, mesoporous functionalised SiO(2) additives are developed. It has been demonstrated that these additives themselves achieve proton conductivities approaching those of conventional materials. However, the proton conduction mechanisms and especially factors influencing charge carrier mobility under different hydration conditions are not well known and difficult to separate from concentration effects in experiments. This tutorial review highlights contributions of atomistic computer simulations to the basic understanding and eventual design of these materials. Some basic introduction to the theoretical and computational framework is provided to introduce the reader to the field, the techniques are in principle applicable to a wide range of other situations as well. Simulation results are directly compared to experimental data as far as possible.

Detection of homogeneous distribution of functional groups in mesoporous silica by small angle neutron scattering and in situ adsorption of nitrogen or water

The distribution of SO(3)H-functional groups attached to the ordered inner pore walls of mesoporous Si-MCM-41 materials based on SiO(2) was investigated by gas adsorption combined with in situ small angle neutron scattering (SANS). The functionalization was performed by two different methods, (i) grafting and (ii) co-condensation. The adsorbates N(2) at 77 K or a H(2)O/D(2)O mixture of 42:58 at 298 K possess neutron scattering length densities (SLD) similar to that of SiO(2) and therefore quench the diffraction signals of the nonmodified silica. SANS measurements show that N(2) matches completely not only with the pristine mesoporous Si-MCM-41 but also with Si-MCM-41-SO(3)H functionalized by grafting. Thus, full access of adsorbate into the entire length of the pores is proven. For the analysis of the distribution of functional groups within the pores in dependence on the used functionalization method, grafting or co-condensation, however, the more specific adsorbate H(2)O/D(2)O (42:58) is necessary, because it reacts more sensitively toward small changes in the SLD of the host material. For grafted Si-MCM-41-SO(3)H materials, an incomplete quenching was observed, indicating that only some regions, probably the pore mouths, have been modified. For a sample functionalized by co-condensation, almost no quenching of the neutron diffraction was found, indicating a very homogeneous distribution of the functional groups along the entire pores.

Nanoparticles of mesoporous SO3H-functionalized Si-MCM-41 with superior proton conductivity

Nanometer-sized mesoporous silica particles of around 100-nm diameter functionalized with a large amount of sulfonic acid groups are prepared using a simple and fast in situ co-condensation procedure. A highly ordered hexagonal pore structure is established by applying a pre-hydrolysis step in a high-dilution synthesis approach, followed by adding the functionalization agent to the reaction mixture. The high-dilution approach is advantageous for the in situ functionalization since no secondary reagents for an effective particle and framework formation are needed. Structural data are determined via electron microscopy, nitrogen adsorption, and X-ray diffraction, proton conductivity values of the functionalized samples are measured via impedance spectroscopy. The obtained mesoporous SO(3)H-MCM-41 nanoparticles demonstrate superior proton conductivity than their equally loaded micrometer-sized counterparts, up to 5 x 10(-2) S cm(-1). The mesoporosity of the particles turns out to be very important for effective proton transport since non-porous silica nanoparticles exhibit worse efficient proton transport, and the obtained particle size dependence might open up a new route in rational design of highly proton conductive materials.