Proton Conductivity Of Composites Research Articles

Synthesis and Characterization of Proton-Conducting Composites Prepared by Introducing Imidazole or 1,2,4-Triazole into AlPO-5 and SAPO-5 Molecular Sieves.

The present work concerns proton-conducting composites obtained by replacing the water molecules present in aluminophosphate and silicoaluminophosphate AFI-type molecular sieves (AlPO-5 and SAPO-5) with azole molecules (imidazole or 1,2,4-triazole). Both the introduction of azoles and the generation of Brønsted acid centers by isomorphous substitution in aluminophosphate materials were aimed at improving the proton conductivity of the materials and its stability. In the presented study, AlPO-5 and several SAPO-5 materials differing in silicon content were synthesized. The obtained porous matrices were studied using PXRD, low-temperature nitrogen sorption, TPD-NH3, FTIR, and SEM. The proton conductivity of composites was measured using impedance spectroscopy. The results show that the increase in silicon content of the porous matrices is accompanied by an increase in their acidity. However, this does not translate into an increase in the conductivity of the azole composites. Triazole composites show lower conductivity and significantly higher activation energies than imidazole composites; however, most triazole composites show much higher stability. The different conductivity values for imidazole and triazole composites may be due to differences in chemical properties of the azoles.

Novel Highly Dispersed Additive for Proton-Conducting Composites

The proton conductivity and structural properties of (1–x)CsH2PO4–xZnSnO3 composites with compositions of x = 0.2–0.8 were studied. Zinc stannate ZnSnO3 was prepared by the thermal decomposition of zinc hydroxostannate ZnSn(OH)6, which was synthesized by hydrolytic codeposition. To optimize the microstructure of ZnSnO3, thermal decomposition products of ZnSn(OH)6 were characterized by thermal analysis and X-ray diffraction, Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, and electron microscopy. The study reveals that the thermolysis of ZnSn(OH)6 at temperatures of 300–520 °C formed an X-ray amorphous zinc stannate with a high surface area of 85 m2/g possessing increased water retention, which was used as a matrix for the formation of the composite electrolytes CsH2PO4–ZnSnO3. The CsH2PO4 crystal structure remained in the composite systems, but dispersion and partial salt amorphization were observed due to the interface interaction with the ZnSnO3 matrix. It was shown that the proton conductivity of composites in the low-temperature region increased up to 2.5 orders of magnitude, went through a smooth maximum at x = 0.2, and then decreased due to the percolation effect. The measurement of the proton conductivity of the ZnSnO3–CsH2PO4 composites revealed that zinc stannate can be used as a heterogeneous additive in other composite solid electrolytes. Therefore, such materials can be applied in hydrogen production membrane reactors.

Frontispiece: Designable Guest‐Molecule Encapsulation in Metal–Organic Frameworks for Proton Conductivity

By encapsulating various designable molecules in metal organic frameworks (MOFs), the proton conductivity of composites can be improved. Here we classify these designable molecules into four types, and discuss the effect of their introduction on the improvement of the proton conductivity of MOFs. We hope to provide some feasible guidance for the design and development of future composite proton-conducting materials for MOFs encapsulating guest molecules. For more details, see the Review by C.-X. Zhang, Q.-L. Wang, et al. (DOI: 10.1002/chem.202103732).

Anhydrous proton conductive xCHS-(1-x)WSiA composites prepared via liquid-phase shaking

High proton conductive xCsHSO4-(1-x)H4SiW12O40(CHS-WSiA) composites were successfully prepared via a new liquid-phase shaking method. N,N‑Dimethylacetamide (DMAc) and zirconium balls were used as a solvent/dispersing medium and a collision medium, respectively. X-ray diffraction characterization confirmed that the liquid-phase shaking treatment induced an ion-exchange reaction between Cs+ ions in CHS and H+ ions in WSiA to form new composite materials. The proton conductivities of these composites were significantly improved over their precursor materials, especially at low temperatures, below the superprotic phase-transition temperature of CHS. The 0.9CHS-0.1WSiA (in mole ratio) composite, for instance, showed the highest proton conductivities of 1.38 × 10−4 to 2.42 × 10−3 S cm−1 from 50 °C to 170 °C under dry conditions of nitrogen atmosphere. The enhanced anhydrous proton conductivities of the Cs-substituted WSiA composites were also corroborated with shortening of the hydrogen bonding distance in these composites for fast proton hopping transport mechanism via 1H NMR evaluation.

Nafion-based composite solid electrolytes containing water-soluble fullerene C60 derivatives

Nafion-based composite solid polyelectrolytes containing fullerene C60 and its water-soluble derivatives fullerenol-C60 and tris-malonate-C60 were studied by the impedance spectroscopy method. It was found that introduction of these dopants in Nafion leads to a substantial increase in proton conductivity of the composites in the region of low relative humidity. The reasons for the influence of dopants on proton conductivity of composites were discussed.

Highly Efficient Synthesis of Strongly Coupled Reduced Graphene Oxide/Nafion Nanocomposites with Enhanced Mixed Proton and Electron Conduction

Hydrogen fuel production from solar water splitting using an artificial photosynthetic device is the Holy Grail for sustainable energy generation. In the design of such a device, the development of new functional materials with high simultaneous transport of protons and electrons is an important quota of the work for an efficient energy system. In here, reduced graphene oxide (RGO)-Nafion nanocomposite membrane with both high proton and electron conductivity was successfully synthesized using a simple solution casting method followed by a hot press thermal reduction process at a temperature higher than the thermal stability of Nafion. Interestingly, in the hybrid material, the strong-coupling effects, exerted by the electron withdrawing groups of Nafion and the functional groups of RGO, have played an important role in the improvement of both electron and proton conductivity. The strong coupling interaction phenomena are proved by IR, Raman and X-ray photoelectron spectroscopy. The proton conductivity of the material increased by two order of magnitude (~30 times), from 7.30x10-3 for recast Nafion to 2.20x10-1 S cm-1 while the electron conductivity reached 2.20x10-2 S cm-1 with 5 wt.% of RGO/Nafion nanocomposite in wet condition. The electron conductivity of this same nanocomposite increased 5 times, from 4.40x10-3 for RGO to 2.15x10-2 S cm-1 at ambient condition. The presence of RGO in Nafion increases the water uptake by left oxygen-containing functional groups. The electron withdrawing groups of Nafion (-CF2 &-SO3H) are responsible for the increased electron conductivity of RGO. The proton conductivity of composite is further enhanced by the alignment or morphological change of the membrane’s proton channels during hot press thermal reduction. The proposed synthesis is a simple, environmentally benign and scalable process to produce Nafion/RGO nanocomposites without complex dispersion or chemical reduction processes.

Proton conductivity of composites based on Nafion and silica matrices with a chemically modified surface

The surface of aerosilogel and macroporous and microporous glasses was modified with aromatic sulfo groups (≡Si(CH2)2-C6H4-SO3H) by the chemical assembly method. Composite solid electrolytes containing Nafion were prepared from the silica matrices with a chemically modified surface. The proton conductivity of the materials was studied by impedance spectroscopy. Composite materials based on Nafion and aerosilogel matrices and macroporous glasses with grafted ≡Si(CH2)2-C6H4-SO3H groups showed the highest proton conductivity.

Highly efficient synthesis of reduced graphene oxide–Nafion nanocomposites with strong coupling for enhanced proton and electron conduction

The synthesis of a reduced graphene oxide (RGO)–Nafion nanocomposite membrane with both high electron and proton conductivity was successfully achieved using a simple solution casting method followed by a hot press thermal reduction process. Interestingly, in the hybrid material, the strong-coupling effects, exerted by the functional groups of RGO and the electron withdrawing groups of Nafion, have played a significant role in the enhancement of both proton and electron conductivity. The strong coupling interaction phenomena are evidenced by Raman and X-ray photoelectron spectroscopy (XPS). The proton conductivity of the composite increased by around 30 times, from 7.30 × 10−3 for recast Nafion to 2.20 × 10−1 S cm−1 while the electron conductivity reached 2.20 × 10−2 S cm−1 with 5 wt% of RGO–Nafion nanocomposite in wet condition. The electron conductivity of this same nanocomposite increased 5 times, from 4.40 × 10−3 for RGO to 2.15 × 10−2 S cm−1 at ambient conditions. The presence of RGO in Nafion increases the water uptake by left oxygen-containing functional groups. The electron withdrawing groups of Nafion (–CF2 & –SO3H) are responsible for the increased RGO's electron conductivity. The proton conductivity of composite is further enhanced by the alignment or morphological change of the membrane's proton channels during hot press thermal reduction. The proposed synthesis is a simple, environmentally benign and scalable process to produce Nafion–RGO nanocomposites without complex dispersion or chemical reduction processes.

Effects of SiO2 and P2O5 on structural, thermal and conductivity properties of inorganic materials doped with PVDF

Poly(vinylidene fluoride) (PVDF) doped hybrid glass membranes were prepared with various concentrations of tetraethoxysilane (TEOS), trimethylphosphate and PVDF. The proton conductivities of composites were measured at room temperature under dry conditions. The significant properties of these membranes were their thermal stability, up to 350 °C, and mechanical stability. These properties are adequate for the usage of the membranes in low and intermediate fuel cells. The objective of this work was to improve the conductivity and stability of a class of hybrid composites through optimization of the inorganic compounds and PVDF. The composites were examined using various analytical techniques: XRD, FTIR, ATR, TGA, DSC, proton conductivity and SEM. The H2/O2 fuel cells with the hybrid glass membrane show a maximum current density of about 320 mA cm−2 under the conditions of 60 and 80 °C with a relative humidity of 100%. The results were discussed and compared with the commercially available membranes for fuel cells.

SPSEBS/H3PO4 composite electrolyte membranes for application in PEMFC and DMFC

High proton conducting composite electrolyte membranes based on Sulfonated Poly Styrene Ethylene Butylene Poly Styrene (SPSEBS)/Phosphoric acid (2, 4, 6, 8 and 10 % H3PO4) composites were prepared. Their water and alcohol absorption increased with increase in H3PO4 content. The membranes were stable to aging in boiling water for 8 h. Their thermal stability was also improved. The ion-exchange capacity as well as the proton conductivity of composites increased significantly with the increase in the content of H3PO4. The proton conductivity of the membranes with 10% H3PO4 was in the order of 10−2 S/cm which is appreciable for an electrolyte membrane for application in fuel cell. The composite membrane was also tested for its performance in PEMFC and DMFC units of 25 cm2 area designed in our lab. The maximum power density of PEMFC with composite membranes (2 and 10% phosphoric acid) was 77.5 and 84 mW/cm2 respectively, and that of DMFC 38 and 44 mW/cm2.

Composite Membranes with Sulfonic and Phosphonic Functionalized Inorganics for Reduced Relative Humidity PEM Fuel Cells

Nafion/inorganic (inorganic = S-ZrO2, SiO2-SO3H, SBA-15-SO3H, MCM-41-SO3H, and P-Si gels) composite membranes were synthesized with the goal of increasing the proton exchange membrane (PEM) fuel cell performance at elevated temperatures up to 120°C and reduced relative humidity (RH) down to 25%. Inorganic materials were incorporated within the Nafion by three different techniques. The conductivity of composite membranes with sulfonated inorganic materials was not higher than the conductivity of the recast Nafion in the whole range of inorganic loading. Conductivity of the Nafion/P-Si gel membranes was affected by the surface of inorganic powders and was higher for membranes prepared by in situ formation techniques. At 120°C and 70% RH, the conductivity of some composite membranes reached 100 mS cm−1. Effect of the inorganic phase on the membrane performance in a fuel cell was much stronger than on its conductivity probably due to substantial improvement in membrane water retention properties. At 120°C and 50% RH, the cell resistance of the P-Si composite membrane was found to be 40% lower than that of Nafion. By applying the modified rule of mixtures, the composite proton conductivity was calculated and compared with experimental data.

Heterogeneous Doping of a Weak Covalent Electrolyte: Proton Conductivity Enhancement of Imidazole by Admixture of Oxide Particles

The proton conductivity of composites comprising dispersions of various types of nanometer-sized oxide particles in pure imidazole is investigated. The composite materials show significantly enhanced (up to a maximum of ten times in the case of sZrO2) ionic conductivity compared to pure imidazole. The reason is the formation of a space–charge layer on the oxide surface, as a consequence of adsorptive interaction.

Intermediate-temperature composite proton electrolyte CsH 5(PO 4) 2/SiO 2: Transport properties versus oxide characteristic

Composite solid electrolytes (1 − x)CsH 5(PO 4) 2/ xSiO 2 ( x = 0–0.75) based on silica with different specific surface areas have been studied by the complex impedance, DSC, and X-ray diffraction methods. The proton conductivity of composites is shown to depend on the silica's specific surface area: the higher the specific surface area the stronger influence on the transport properties of composites. The maximal composite conductivity was 2.3 mS∙cm − 1 at T = 140 °C, which exceeded the conductivity of pure CsH 5(PO 4) 2 by more than one order of magnitude. The drastic changes in the transport properties of composites are governed by the salt dispersion and/or amorphisation, which are confirmed by the changes in thermodynamic parameters. An H 2/air fuel cell based on CsH 5(PO 4) 2/SiO 2 demonstrates a maximum power density of 8 mW/cm 2 at U = 0.3 V and a current density up to 80 mA/cm 2 at a short circuit.

Synthesis and characterization of silicotungstic acid based organic–inorganic nanocomposite membrane

Organic–inorganic composites consisting of silicotungstic acid and poly(vinyl alcohol) were prepared by a sol–gel method. The advantage of this strategy is that it is to manipulate the desired properties such as thermal stability, conductivity. The silicotungstic acid present in the composite acts as acid catalyst to hydrolyze/condense the silica precursor that leads to isotropic composite. The composite is structurally characterized with various techniques such as IR, UV–vis, TGA, SEM, TEM and CV measurements. The proton conductivity of composites is measured using impedance spectroscopy. The conductivity is found to increase with increase in temperature. The activation energy for the proton migration in the composite film was calculated to be 10 kJ/mol.