Concentration Of Sulfonic Acid Groups Research Articles

Biomimetic cellulose membrane enables high-performance salinity gradient energy conversion: Coupling surface charge and nanopore structure

Surface charge and nanoscale porous structure of ion-selective membranes have been considered prominent in affecting conversion capability of salinity gradient energy-to-power, while the synergistic contribution of them is conventionally overlooked, thus limiting their further development toward high-performance harvesting of salinity gradient energy. Herein, bioinspired by organisms achieving effective intracellular ion transport through their surface-charged nanochannels, we designed porous-charged cellulose membrane (PCC) by simultaneously engineering surface charge and pore structure, followed by desirably chemical and structural distinctions, such as high zeta potential and sulfonic acid group content of −44 mV and 1.22 mmol/g, large porosity of 84 % and pore volume of 0.01 cm3/g (d ≤ 10 nm), while just −23 mV, 42 %, 0.0036 cm3/g and 0 mmol/g for pristine cellulose. Such distinctions endow PCC with excellent ion transport rate and capability (high t+ of 0.97 and η of 44.18 % in 0.001/0.01 M), correspondingly superhigh power density of 21.6 W/m2 (0.01/5 M), which surpasses that of most membrane materials, including biomass materials, synthesized polymers, and even some composite materials. By a tandem 30 PCC units, the output voltage of the designed PCC device reaches 2.24 V, which successfully powers calculator and light-emitting diode. In addition, our PCC demonstrates excellent stability in various pH system (from 3 to 11) during 30-day testing. The PCC with environmentally friendly, low cost, and large-scale advantages demonstrates strong competitiveness in advanced membrane materials toward high-performance manipulating ion transport.

Introducing sulfonic acid polymers into MOF nanochannels for ultra-high Ba2+ adsorption capacity and proton conductivity

Porous materials with a high concentration of sulfonic acid groups are highly desirable for applications such as radioactive Ba2+ adsorption, catalysis, and proton-conductive materials, but they are also challenging to synthesize. In this work, we introduce polymers containing sulfonic acid groups into the nanochannels of metal–organic frameworks (MOFs) through in-situ synthesis to enhance the sulfonic acid content. We use a alkene with sulfonic acid groups (2)-acrylamido-2-methylpropane sulfonic acid, AMPS) and a crosslinking agent N,N’-methylenebisacrylamide (MBAA) to synthesize two MOF composites, PAMPS@MIL-101 and PAMPS@MIL-101-SO3H, in the ultra-stable MIL-101 series through in-situ polymerization with free radical initiators. The two MOF composites have a high and uniform distribution of sulfonic acid groups in the MOF framework, which results in ultra-high barium ion adsorption capacity. The maximum adsorption amounts are 142.7 and 356.9 mg·g−1 for PAMPS@MIL-101 and PAMPS@MIL-101-SO3H, respectively, which are higher than those of most reported adsorbents. Importantly, the adsorption equilibrium can be achieved within 20 min. Moreover, both MOF composites, PAMPS@MIL-101 and PAMPS@MIL-101-SO3H, exhibit super proton conductivity, with values of 6.43 × 10−2 S·cm−1 and 1.43 × 10−1 S·cm−1 at 85 °C and 98 % RH, respectively. This method offers a new way of modifying MOF nanochannels with high sulfonic acid concentrations, and opens up new opportunities for developing radioactive Ba2+ adsorption materials and proton-conductive materials.

The relationship between chemical structure of perfluorinated sulfonic acid ionomers and their membrane properties for PEMEC application

Polymer electrolyte membrane electrolyzer cells (PEMECs) has been confirmed as a prototype electrochemical system that is effective in converting water into hydrogen and oxygen under the application of electricity. Among the core components of PEMEC, the polymer electrolyte membrane (PEM) determines critically an overall electrochemical performance of the PEMEC. Ideally a PEM system should exhibit a complex transport behavior of small molecules (e.g., gases and ions) while mediating flows of ions in the cell; it should exhibit high proton selectivity while serving as a gas barrier to hydrogen and oxygen to increase current efficiency, which are in turn vital factors in determining an effectiveness when the electric energy is used for water electrolysis. Until now, perfluorinated sulfonic acid (PFSA) ionomers have been extensively used as PEM materials in water electrolysis while in generating hydrogen and oxygen gases simultaneously in high purity. In this study we have examined the chemical structure of PEM membranes derived from various types of PFSA ionomers by employing solid-state 19F MAS NMR. Subsequently, a structure-property-performance correlation was sought in accordance with the chemical structure, the dispersion characteristics, and membrane properties of PFSA ionomers. Furthermore, the effects of the membrane morphology as well as the ionomer packing characteristics on proton conduction and hydrogen transportation were investigated. Lastly, the membrane properties exerted by varying the chemical architectures and equivalent weight (EW) values of PFSA ionomers in PEMEC were confirmed. 3 M 725 membrane, which has the highest concentration of sulfonic acid groups in the hydrated state, has the highest proton conductivity. In addition, it showed the best water electrolytic cell performance via the synergistic effect with low gas permeability obtained as a result from the short side chain structure.

In-situ lignin sulfonation for enhancing enzymatic hydrolysis of poplar using mild organic solvent pretreatment

Biomass pretreatment is an essential strategy to overcome biomass recalcitrance and promote lignocellulosic bioconversion. Here, a reusable organic solvent system (formic acid-methanesulfonic acid) was explored to pretreat poplar under a mild temperature (below 100 °C). The results showed that the co-solvent system could extract basically complete hemicelluloses and part of lignin with original cellulose retained in the pretreated substrates. Meanwhile, sulfonic acid groups were introduced into lignin structure remained in the substrates. The glucose conversion yield of the substrates with a higher concentration of sulfonic acid groups (13.2 mmol/kg) reached 45.9 % by reducing the hydrophobic interaction between lignin and cellulase, showing 89.3 % improvement compared with that of the substrates treated with single formic acid. This progressive study aimed to develop a new strategy to realize sulfonation and promote enzymatic hydrolysis of substrates by using mild organic solvent pretreatment.

Selective synthesis of 5-hydroxymethylfurfural over natural rubber–derived carbon/silica nanocomposites with acid–base bifunctionality

5-Hydroxymethylfurfural (HMF) is an important platform molecule, derived from biomass-based carbohydrates, for the production of renewable fuel additives, liquid hydrocarbon fuels, biopolymers, and specialty chemicals. In this study, a mesoporous carbon/silica (MCS) nanocomposite, as catalyst support, was prepared using a nanocomposite of natural rubber (NR) and hexagonal mesoporous silica (HMS) as a precursor. To obtain a series of acidic, basic, and bifunctional acid-base catalysts, the MCS surface was modified using post-synthesis methods in which the carbon moieties were decorated with sulfonic acid groups, whereas the silica matrix surface was grafted with 3-aminopropyl groups. The resulting materials exhibited high surface area, large pore volume, and contain some oxygen-containing functional groups. Their acid-base properties were tunable by varying the content of sulfonic acid and aminopropyl groups. The HMF was synthesized by catalytic conversion of fructose and glucose in a biphasic medium. Fructose dehydration catalyzed by sulfonated MCS catalyst (MCS-SO3H) at 150 °C for 2 h yields 56% HMF at 81% conversion. For the glucose system, the Brønsted basic sites facilitated the glucose–fructose isomerization, however, it promoted the formation of undesired humins. The acid/base ratio of bifunctional MCS catalysts (MCS-SO3H-NH2) contributes to the HMF yield and selectivity. The HMF yield of 39.4% was obtained over the MCS-SO3H-NH2 catalyst with an acid/base ratio of 0.10 at 190 °C for 1 h. In both systems, the formation of levulinic acid, a byproduct of HMF hydrolysis, was suppressed due to the hydrophobicity of the MCS catalyst. These developed catalysts are promising for the synthesis of HMF from glucose, at high substrate concentration than those reported in the literature.

The transformation and degradation of Nafion® solutions under ultrasonic treatment. The effect on transport and mechanical properties of the resultant membranes

This work addresses the study of the effect of ultrasonic (US) treatment on the properties of alcohol solutions of perfluorinated sulfonic acid polymer Nafion® and cast membranes. The effect of the duration of US treatment on the physico-chemical properties (water uptake, transport and mechanical properties) of the resulted membranes is described for the first time. Upon the US treatment, viscosity of the polymer solutions irreversibly decreases due to deagglomeration and rupture of macromolecular chains. As a result of the US treatment, mechanical properties of the Nafion® membranes are deteriorated. The dependences of water uptake and conductivity of the Nafion® membranes in the proton form on sonication time pass the maximum (at 30–45 min). Due to the sonication of polymer solutions, proton conductivity of the membranes increases by 40–45%. Upon extended sonication, the content of sulfonic acid groups decreases, and carboxyl groups are formed at the ends of macromolecules. Thus, water uptake of the membranes prepared from the polymer solutions after the US treatment for 60 min decreases, and conductivity of the obtained membranes in the H+-form is reduced. However, for the Nafion® membranes in the Na+-form, as the duration of the US treatment is extended, their conductivity and diffusion permeability tend to increase due to the enhanced connectivity of pores and channels as well as due to the participation of carboxyl groups in the ionic transport. Upon extended sonication, selectivity of the cation transfer through the membranes is reduced. The results of this work highlight the importance of the proper selection of favorable conditions of the US treatment of the solutions of perfluorinated sulfonic acid polymers for the preparation of hybrid membranes and for the development of catalytic layers of membrane-electrode assemblies for fuel cells.

Sulfonated silica coated polyvinylidene fluoride electrospun nanofiber-based composite membranes for direct methanol fuel cells

A sulfonated silica coated polyvinylidene fluoride (S-SiO2@PVDF) nanofiber substrate with high strength and ultrahigh surface concentration of sulfonic acid groups was prepared by a three-step simple surface functionalization process. The S-SiO2@PVDF substrate was then used as both mechanical reinforcement support and inter-connected three-dimensional proton transport network for chitosan (CS) to prepare thin composite proton exchange membranes for direct methanol fuel cells (DMFCs). As the mechanical support for CS matrix, the S-SiO2@PVDF nanofiber framework could significantly improve the dimensional stability, tensile strength, elongation and mechanical damage resistance. Meanwhile, as a proton conduction network, the conductivity of the composite membrane was remarkably enhanced to 21.2 mS cm−1 (about 2.8 times than that of pure CS). Moreover, due to the excellent methanol barrier ability of CS matrix itself as well as the limitation role of the nanofibers, the methanol crossover of the composite membrane was as low as 4.2 × 10−7 cm2 s−1 that was only 26% of commercial Nafion 115. DMFC test showed the composite membrane exhibited the maximum power density of 86.3 mW cm−2 (80 °C), and the power density loss was only 5.4% even after operating at a constant current of 0.35A cm−2 for 100 h.

Sulfonation of dialdehyde cellulose extracted from sugarcane bagasse for synergistically enhanced water solubility

Sulfonated cellulose (SC) was successfully derived from microcrystalline cellulose (MCC) extracted from sugarcane bagasse, which is a type of agricultural waste. The obtained MCC was first modified by oxidation using sodium periodate in order to cleave the carbon-carbon bonds at the C2 and C3 of the pyranose ring to form 2,3-dialdehyde cellulose. These activated aldehyde groups significantly facilitated the sulfonation carried out using potassium metabisulfite. The sulfonic acid group contents, surface morphology, and water solubility of the obtained products were characterized by titration, field-emission scanning electron microscopy, UV–vis spectroscopy, and zeta potential. High sulfonic acid group content was achieved for the obtained SC samples (i.e., 305–689 μmol/g). The increase in the sulfonic acid group content resulted in the gradual change in the surface morphology and water solubility of the SC samples. The obtained results imply that sugarcane bagasse is a promising raw material for the production of SC with good water solubility.

Effect of sulfonation treatment concentration on the properties of mulberry chemi-mechanical pulp

Sulfonation chemimechanical pulping (SCMP) of mulberry stalk was studied with different treatment concentrations. The resulting mulberry SCMP pulp contained different content of sulfonic acid groups depending on the concentrations. The brightness, tensile index, and folding resistance of mulberry SCMP pulp increased with the increasing concentration of sulfonation treatment, but the thickness decreased with increasing concentration. There was either a linear or a non-linear relationship between the content of sulfonic groups and the pulp physical properties. The mass average length of mulberry SCMP pulp was 0.66 mm, the fiber width was 16.4 μm, and the content of fine fibers was 20.6%.The mulberry extract and lignin dissolved, and part of soluble lignin may have been deposited on fiber surface in the process of SCMP pretreatment. There were almost no changes to the cellulose crystalline structure.

Highly stable ionic-covalent cross-linked sulfonated poly(ether ether ketone) for direct methanol fuel cells

Abstract A novel ionic cross-linked sulfonated poly(ether ether ketone) containing equal content of sulfonic acid and pendant tertiary amine groups (TA-SPEEK) has been initially synthesized for the application in direct methanol fuel cells (DMFCs). By adjusting the ratio of p-xylene dibromide to tertiary amine groups of TA-SPEEK, a series of ionic-covalent cross-linked membranes (C-SPEEK-x) with tunable degree of cross-linking are prepared. Compared with the pristine membrane, the ionic and ionic-covalent cross-linked proton exchange membranes (PEMs) exhibit reduced methanol permeability and improved mechanical properties, dimensional and oxidative stability. The proton conductivity and methanol selectivity of protonated TA-SPEEK and C-SPEEK-x at 25 °C is up to 0.109 S cm−1 and 3.88 × 105 S s cm−3, respectively, which are higher than that of Nafion 115. The DMFC incorporating C-SPEEK-25 exhibits a maximum power density as high as 35.3 mW cm−2 with 4 M MeOH at 25 °C (31.8 mW cm−2 for Nafion 115). Due to the highly oxidative stability of the membrane, no obvious performance degradation of the DMFC is observed after more than 400 h operation, indicating such cost-effective ionic-covalent cross-linked membranes have substantial potential as alternative PEMs for DMFC applications.

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.

Development of Sulfonated Poly(Arylene Ether Sulfone) Multi-Block Membranes for Low RH PEMFC Operation

Perfluorosulfonic acid (PFSA) polymers are the most promising state-of-the-art materials as proton exchange membranes (PEM) for fuel cells, however, there are some drawbacks such as high production cost and hydrothermal stability. Aromatic membranes based on hydrocarbon polymers have been studied as alternatives. Among them, multi-block copolymers seem to be promising to compete with PFSA resulting high proton conductivity even under low RH conditions.[1, 2] In this report, novel sulfonated poly(arylene ether sulfone)s multi-block copolymer membranes containing highly sulfonated hydrophilic blocks were synthesized.[3] Different local concentration of sulfonic acid in their hydrophilic blocks affected chemical and physical properties of the SPAES. To investigate the effects of chemical composition on their membrane properties, different hydrophilic oligomers sharing same hydrophobic blocks gave us exact comparison of effect of hydrophilic blocks. The higher concentration of sulfonic acid groups resulted in higher proton conductivity under certain relative humidity conditions than that of the state-of-the-art perfluorinated sulfonic acid membrane and showed that the well-developed phase separation of SPAES. Moreover, physical properties of theses SPAES including water behavior, humidity dependence of proton conductivity were investigated along with morphology characterizations by transmission electron microscopy (TEM) for PEMFC application. Two types of oligomers, F-terminated and OH-terminated telechelic oligomers, were synthesized by controlling the feed ratio of dihydroxyl- and difluoro-monomers. Their number of repeating unit (X and Y) was analyzed by GPC and 1H NMR. Copolymerization with F-terminated and OH-terminated telechelic oligomers via nucleophilic aromatic substitution, gave high-molecular-weight multi-block PESs. Each block length was controlled to have different values with X5Y10, X10Y10, X20Y10 and X20Y20. The SPAES X10Y10 membrane showed highest proton conductivity than that of our previous random and block copolymers at wide range of humidity. The best balanced membrane was SPAES X10Y5 membrane with high proton conductivity and lower water uptake. Consequently, the SPAES X10Y5 membrane showed high cell performance under various conditions (510 mA/cm2, 290 mA/cm2 @ 0.6V under 80% and 50 % RH conditions at 80℃, respectively). Systematic approaches for developing alternative block SPES membrane for low RH condition will be discussed.

Preparation and properties of DMFC membranes from polymer-brush nanoparticles

We describe a novel approach for the preparation of proton-conducting membranes using polymer brush nanoparticles (PBNPs). PBNPs can be assembled into the membranes directly, or the membranes can be prepared by first assembling porous scaffolds from unmodified NPs followed by surface modification with polymer brushes. In both cases, proton-conducting channels are formed in the interstitial spaces between the nanoparticles. First, proton-conducting membranes were prepared using silica nanoparticles (SNPs) surface-grafted with 40–400nm sulfonated polymer brushes, poly(3-sulfopropylmethacrylate), pSPM, and poly(4-styrenesulfonic acid), pSSA, grown via surface-initiated atom transfer radical polymerization (SI-ATRP). The membranes prepared from the NPs carrying longer polymer chains possessed polymer-like characteristics, compared to the stiffer membranes made with shorter polymer brushes. All these membranes showed comparable proton conductivities, with a maximum value of ~0.06S/cm at 98°C and 70% R. H. Second, we prepared proton-conducting pore-filled membranes. In this case, nanoporous colloidal crystals were first assembled from unmodified SNPs, followed by filling the pores with pSPM or pSSA brushes covalently attached to the pore surface using SI-ATRP. The membranes could be hydrated almost completely and did not swell. The proton conductivity was similar for both polymer-filled membranes, with a maximum value of ~0.02S/cm achieved at 30°C and 94% R. H. A sigmoidal dependence of the proton conductivity on the amount of sulfonic acid groups was found for pSPM pore-filled membranes. The proton conductivity remained relatively low at low degrees of sulfonation, increased rapidly around 50% sulfonic acid group content, and did not increase significantly after reaching ca. 75% sulfonic acid group content. We found that OCV for DMFC MEAs built using these membranes reached its maximum at 65% sulfonic group and decreased after that. We attribute this effect to the increased methanol cross-over, which was confirmed by methanol uptake measurements for the membranes.

Biomass derived solid acids as effective hydrolysis catalysts

The conversion of cellulose into products with higher added value often includes a depolymerization step to obtain glucose, its fundamental unity. The depolymerization reaction is carried out via hydrolysis of the β-1,4-glycosidic bond. The search for a solid acid catalyst capable of breaking these bonds is gaining increasing prominence in the literature. In this regard, sulfonated carbons have shown promising results.This work evaluated the use of a residue from the extraction of palm oil as raw material for the production of sulfonated carbons. The raw material was carbonized and sulfonated. The obtained solid acids were tested in the hydrolysis of cellobiose, a dimer of glucose often used as a model compound for cellulose. The hydrolysis reaction is the first step in converting renewable carbon sources into chemical products and biofuels.Some aspects were investigated, as the effect of carbonization temperature on the concentration of sulfonic groups, the results showing that the content thereof reached a maximum value at 300°C. Regarding the hydrolysis of cellobiose, it has been identified that there is a relationship between the concentration of sulfonic acid groups and the activity of these catalysts. However, there is a drop in the turnover number as the amount of sulfonic acid sites increases. This was related to a preferred position sulfonation mechanism.Furthermore, sulfonated carbons showed higher activity than the commercial acid resins, indicating that this material may be a good option for the generation of solid acid catalysts.

Comparison of polyflavonoids in bayberry tanning effluent and commercial bayberry tannin: prerequisite information for vegetable tanning effluent recycling

Recycling system is capable to minimize the serious environmental issues in leather making. It also has the advantage of reducing chemical consumption and providing an efficient way to decrease the cost of leather manufacture. High chemical oxygen demand, bio-chemical oxygen demand and microbial toxicity are all considered as the characters of vegetable tanning effluent, however, only a few recycling technologies were developed. In this study, bayberry tanning effluent was obtained with a commercial bayberry tannin through a common vegetable tanning process, then the polyflavonoids in the bayberry tanning effluent and commercial bayberry tannin were characterized with Fourier translation infrared spectrum, matrix-assisted laser desorption/ionization time of flight mass spectrometry, nuclear magnetic resonance, gel permeation chromatography and an elemental analysis. The results showed that the flavanol subunit in the polyflavonoids of the bayberry tanning effluent was the same with the commercial bayberry tannin, however the differences of the polyflavonoids between the bayberry tanning effluent and commercial bayberry tannin were presented in the aspect of stereochemistry, molecular weight as well as the quantity of sulfonic acid group. Polyflavonoid in the bayberry tanning effluent was composed of cis isomers, while both cis and trans stereoisomers were found in the commercial bayberry tannin. Average molecular weight of the bayberry tanning effluent was 1130 Da, in contrast to an obviously higher value in the commercial bayberry tannin (2292 Da). Meanwhile, higher sulfonic acid group content was presented in the bayberry tanning effluent. These structural differences were deduced in accordance with the diversity of collagen binding activities of the polyflavonoids. For the first time, the polyflavonoids in vegetable tanning effluent were characterized, meanwhile, the structural differences between the polyflavonoids in tanning effluent and commercial tannin were found. The results can be applied on the development of the vegetable tanning effluent related recycling technology.

Synthesis and characterization of sulfonated polymers containing triazoles as low-humidity proton exchange membranes

A series of copolymers, sulfonated poly (aryl ether ketone sulfones) containing triazoles (SPAEKST), were synthesized by direct polycondensation reactions. The content of sulfonic acid and triazole groups was controlled by adjusting the molar ratio of feeding. The structures of triazole monomer and SPAEKST copolymers were confirmed by their 1H NMR and FTIR spectral analyses. The performance of membranes such as thermal and oxidative stabilities was clearly improved with increasing content of triazole groups. The morphology of SPAEKST membranes was investigated by TEM analyses, and the results indicate that the sulfonic acid groups were dispersed evenly. No clear phase separation was observed. The contact angle tests showed that the presence of triazoles clearly improved the hydrophilicity of membranes. The water desorption curves showed that the water retention of membranes increased with increasing content of triazole groups. The proton conduction of membranes exhibited a low dependence on relative humidity. At 80 °C, the proton conductivity of SPAEKST-30 % reached to 1.1 mScm−1 under 20 % RH.

Enhancement of proton conductivity of chitosan membrane enabled by sulfonated graphene oxide under both hydrated and anhydrous conditions

In this study, sulfonated graphene oxide (SGO) nanosheets with controllable sulfonic acid group loading are synthesized via the facile distillation–precipitation polymerization, and then incorporated into chitosan (CS) matrix to prepare nanohybrid membranes. The microstructure and physicochemical properties of the resulting membranes are extensively investigated. Compared with CS control and GO-filled membranes, SGO-filled membranes attain enhanced thermal and mechanical stabilities due to the strong electrostatic attractions between –SO3H of SGO and –NH2 of CS, which inhibit the mobility of CS chains. Additionally, the inhibited mobility reduces the area swellings of SGO-filled membranes, reinforcing their structural stabilities. The incorporation of SGO generates acid–base pairs along CS–SGO interface, which work as facile proton-hoping sites and thus construct continuous and wide proton transfer pathways, yielding enhanced proton conductivities under both hydrated and anhydrous conditions. Meanwhile, the conductivity can be elevated by increasing the sulfonic acid group loading and content of SGO. Particularly, incorporating 2.0% S4GO can afford the nanohybrid membrane a 122.5% increase in hydrated conductivity and a 90.7% increase in anhydrous conductivity when compared with CS control membrane. The superior conduction properties then offered a significant enhancement in H2/O2 cell performances to the nanohybrid membranes, guaranteeing them to be promising proton exchange membranes.

The effect of sulfonic acid group content in pore-filled silica colloidal membranes on their proton conductivity and direct methanol fuel cell performance

We prepared mesoporous silica colloidal membranes pore-filled with polymer brushes with different degrees of sulfonation. In these membranes, the assembly of silica colloidal spheres serves as a rigid matrix containing a continuous network of interconnected mesopores and providing mechanical and thermal stability, non-swelling and water retaining properties, while sulfonic acid group-containing polymer brushes grown on the surface of silica provide proton conductivity. We studied the proton conductivity of these membranes as well as open circuit voltage and linear polarization of the fuel cells prepared using these membranes as a function of sulfonic acid group content in the pore-filling polymer brushes. We found a sigmoidal dependence of the proton conductivity on the amount of sulfonic acid groups. We showed that the proton conductivity of the membrane does not increase significantly after reaching ca. 75% sulfonic acid group content. The fuel cell performance, on the other hand, decreased after reaching ca. 65–70% sulfonic acid group content, which was attributed to the increased methanol permeability of the membranes at higher sulfonic acid group content.

Nanostructured bacterial cellulose-poly(4-styrene sulfonic acid) composite membranes with high storage modulus and protonic conductivity.

The present study reports the development of a new generation of bio-based nanocomposite proton exchange membranes based on bacterial cellulose (BC) and poly(4-styrene sulfonic acid) (PSSA), produced by in situ free radical polymerization of sodium 4-styrenesulfonate using poly(ethylene glycol) diacrylate (PEGDA) as cross-linker, followed by conversion of the ensuing polymer into the acidic form. The BC nanofibrilar network endows the composite membranes with excellent mechanical properties at least up to 140 °C, a temperature where either pure PSSA or Nafion are soft, as shown by dynamic mechanical analysis. The large concentration of sulfonic acid groups in PSSA is responsible for the high ionic exchange capacity of the composite membranes, reaching 2.25 mmol g(-1) for a composite with 83 wt % PSSA/PEGDA. The through-plane protonic conductivity of the best membrane is in excess of 0.1 S cm(-1) at 94 °C and 98% relative humidity (RH), decreasing to 0.042 S cm(-1) at 60% RH. These values are comparable or even higher than those of ionomers such as Nafion or polyelectrolytes such as PSSA. This combination of electric and viscoelastic properties with low cost underlines the potential of these nanocomposites as a bio-based alternative to other polymer membranes for application in fuel cells, redox flow batteries, or other devices requiring functional proton conducting elements, such as sensors and actuators.

Sulfonic acid-functionalized aerogels as high resistant to deactivation catalysts for the etherification of glycerol with isobutene

Silica aerogel and lyogel have been successfully sulfonated in one step by a simple post-synthesis method using microwaves as well as conventional heating. The use of microwaves allowed loading higher amounts of sulfonic acid groups in both silicas, according to the higher S/Si atomic ratio determined by XPS, and the higher sulfur content determined by TGA, also exhibiting lower surface area and higher acidity. Sulfonated aerogels showed higher conversion and selectivity to h-GTBE (glycerol di- and tri-ethers) than sulfonated lyogels for the acid-catalyzed etherification of glycerol with isobutene. This was attributed to the higher content of sulfonic acid groups incorporated in aerogel. Microwave-assisted sulfonated aerogel yielded 75% of selectivity to h-GTBE, which can be used as fuel additive, for practically total conversion. Interestingly, larger porosity of aerogel avoided the partial blocking of pores by reaction products observed when other micro- and mesoporous catalysts were tested for this reaction. The combination of high conversion, high selectivity to h-GTBE, practically no formation of undesired di-isobutylenes and very high resistance to catalyst deactivation makes microwave-assisted sulfonic acid functionalized aerogel a promising catalyst for this etherification reaction.