Perfluorosulfonic Acid Resin Research Articles

Fabrication of high-performance pervaporation desalination composite membranes with study of its acid-base stability

In the process of industrial production will produce a lot of acid and alkaline waste liquid, how to effectively treat acid and alkali waste liquid is an important topic at present. At present, there are some problems about the treatment of acid and alkali waste liquid, such as large investment, complicated process and low efficiency. Pervaporation has the characteristics of mild operating conditions and no influence of osmotic pressure threshold, so it has great application potential in the concentration, reuse and reduction of acid and alkali waste liquid. However, at present, conventional pervaporation dense membrane materials cannot maintain long-term stability in strong acid and alkali environment, in order to achieve this performance, we use perfluorosulfonic acid resin with good acid and alkali resistance as the dense layer substrate. PFSA/PTFE/PP composite membrane was prepared by spraying process, and the final prepared composite membrane had a pure water flux of 45 ± 1.2 kg/(m2∙h) at 70 ℃. The acid and alkali resistance of the intrinsic membrane and the composite membrane was evaluated, and it was found that the feed liquid was concentrated to 20 wt% after 19 h long concentration operation at 70℃ and starting liquid was 5 wt% H2SO4 and 5 wt% NaOH. The retention rate of acid and alkali can be maintained above 99.9 %. During the concentration of H2SO4 solution, the dense layer structure is affected, and the pure water flux of the composite membrane is reduced, eventually maintaining around 32 kg/(m2∙h). In the process of concentrating NaOH solution, the pure water flux of the composite membrane increased first and then decreased, and the final pure water flux of the membrane remained near 40 kg/(m2∙h).

Highly durable perfluorosulfonic acid proton exchange membrane by combining inorganic free radical scavengers and organic antioxidants

In this work, a new type of complex was constructed by coordinating quercetin (QC) with cerium (Ce) ions. This complex was introduced into perfluorosulfonic acid resin (PFSA) to fabricate a proton exchange membrane. The coordination process prevented the formation of ion cross-links between cerium and sulfonic acid groups in PFSA, thereby keeping proton conductivity and fuel cell performance of membrane samples at a high level. Due to the insolubility of quercetin in water, its coordination with cerium minimized cerium migration, providing long-lasting resistance to free radicals. The effects of additives on PFSA membrane properties were investigated by measuring IEC, water uptake, swelling ratio, and proton conductivity. Fenton degradation experiments and membrane electrode assembly performance tests was conducted simultaneously. The results demonstrated that compared to the addition of quercetin or cerium alone, the use of QC-Ce increased the proton conductivity by 23.70% after 24-h Fenton degradation and lowered fluoride release by 58.29%. Meanwhile, the PFSA/QC-Ce composite membrane samples maintained an open circuit voltage of 0.935 V and a maximum power density of 668.15 mW cm−2 after 96 h of open circuit voltage hold testing.

Benzylation of 1,3‐Dicarbonyl Compounds with Benzyl Alcohols Promoted by Perfluorosulfonic Acid Resin

AbstractThe catalytic performance of Perfluorosulfonic acid resin (PFSA), a solid superacid, was studied in the catalytic benzylation of 1,3‐dicarbonyl compounds with benzylic alcohols. The PFSA‐catalyzed reactions could proceed smoothly to provide the products under solvent‐free conditions or in toluene and dichloromethane, which gave moderate to excellent yields. Due to its high chemical stability, PFSA was quite stable under the reaction conditions and could be recovered at least eight times without significant reduction of its catalytic effect. Moreover, this reaction was investigated at a 20 mmol scale, which indicated the potential applicability of the large‐scale industrial synthesis. Finally, the mechanism of the PFSA‐catalyzed benzylation of 1,3‐dicarbonyl compounds with benzylic alcohols was also investigated.

Improved performance of nafion membranes by blending ultra-high molecular weight polyvinylidene fluoride

Proton exchange membrane (PEM) is developing towards thin thickness and high mechanical strength for extraordinary performance proton exchange membrane fuel cells (PEMFCs). However, the commercial membrane such as Nafion can hardly satisfy the practical application of PEMFCs because of high gas crossover and low mechanical strength when the thickness is less than 20 μm. Here, a reinforced composite membrane (denoted as P110-PFSA) was synthesized by blending poly(vinylidene fluoride)(PVDF) featured with high molecular weight of Mw= 1100000 g mol-1 into perfluorosulfonic acid resin (PFSA). The P110-PFSA with the thickness of 15 μm exhibits tensile strength of over 33 MPa because the PVDF with high molecular weight forms a higher density of hydrogen bonds with PFSA, resulting in a reinforcement of the bonding strength between PVDF and PFSA. H2/O2 fuel cell performance with the P110-PFSA shows more than 1170 mW cm-2 fed with H2 at 70 °C and 100% RH much better than that with Nafion 211. Direct methanol fuel cell power densities of the blent PEM are 92, 61, 50, 28 and 15 mW cm-2 fed with 2, 6, 10,16 and 20 M methanol solution respectively at the anode.

Foams Stabilized by AquivionTM PFSA: Application to Interfacial Catalysis for Cascade Reactions

AbstractFoams are attractive platforms for engineering gas–liquid–solid catalytic microreactors with enhanced triphasic contact. In this study, the foaming properties of surface‐active AquivionTM perfluorosulfonic acid resin (AquivionTM PFSA) are unraveled. Stable aqueous and non‐aqueous foams are prepared driven by hydrogen bond interactions between AquivionTM PFSA and protic solvents (e.g., benzyl alcohol, aniline, water). In light of these unique properties, a catalytic foam system for one‐pot cascade deacetalization–hydrogenation reactions is designed. As proof of concept, benzaldehyde dimethyl acetal is converted into benzyl alcohol with 84% overall yield at room temperature in a foam system in the presence of AquivionTM PFSA and Pd/SiO2 catalysts, whereas the yield is halved in a non‐foam system. The enhanced reaction efficiency is attributed to a marked increase in interfacial area of the foam system and preferential location of catalytic acid centers at the gas–liquid interface.

Direct conversion of fructose to levulinic acid in water medium catalyzed by a reusable perfluorosulfonic acid Aquivion® resin

In this work, we reported an environmental-benign and cost-effective route for the direct conversion of fructose to levulinic acid. A commercial perfluorosulfonic acid resin in a pellet form, that is, Aquivion® P98, was shown as a water-tolerant and reusable solid acid catalyst. The influence of catalyst dosage, reaction temperature and reaction time on the dehydration of fructose was systematically investigated. It was disclosed that fructose was initially dehydrated to 5-hydroxymethylfurfural as the intermediate and it was subsequently hydrolyzed to produce levulinic acid and formic acid over the Brønsted acidic sites provided by Aquivion® P98. Under the optimum reaction conditions, 96% yield to levulinic acid at 100% conversion of fructose was obtained in water at 120 °C after 12 h. Productivity of levulinic acid reached 3.2 mol mol−1H+, an outstanding value reported in literature to date. The Aquivion® P98 catalyst can be regenerated through a simple ion-exchange method, and a stable yield of levulinic acid was maintained after six consecutive reuses. The controlled experiments proved that the acidic products, i.e., formic acid and levulinic acid, allowed working as homogeneous catalysts to accelerate the dehydration of fructose and the subsequent hydrolysis of 5-hydroxymethylfurfural.

Highly selective self-condensation of cyclohexanone: the distinct catalytic behaviour of HRF5015.

HRF5015, a perfluorosulfonic acid resin catalyst with unique pore structures, was investigated in the catalytic self-condensation of cyclohexanone under mild conditions. The morphology of HRF5015 was characterized by transmission electron microscopy (TEM) and atomic force microscope (AFM), and the reaction mechanism was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The effects of reaction time and temperature on the yield of dimer were investigated under the nitrogen atmosphere. The results show that the reaction temperature is low, and especially, the selectivity of the dimer is close to 100%. The apparent activation energy for the dimer formation reaction is 54 kJ mol−1. Synergistic action of cluster structure formed by sulfonic groups and nanopores in HRF5015 may be the key factor of high-efficiency catalytic activity and high selectivity. In situ infrared spectra indicate that the intermediate is stable in the reaction process. HRF5015 is environmentally friendly and re-usable, which shows good potential in a future application.

Poly-hydroxyethylidene-1,1-diphosphonic acid (PHEDP) as a highly effective water-retentive and proton-conductive material for low-humidity proton exchange membranes

To improve the proton conductivity and fuel cell performance of a perfluorosulfonic acid (PFSA) membrane under low-humidity conditions, a series of poly-hydroxyethylidene-1,1-diphosphonic acid (PHEDP) materials are designed and synthesized through a self-polycondensation reaction. Self-humidifying proton exchange membranes are fabricated by combining PHEDP with commercial PFSA resin, then optimized by using various amounts of PHEDP. The experimental results show that the PHEDP/PFSA composite membrane provides a proton conductivity of up to 28.2 mS cm−1 at 30% RH and up to 13.6 mS cm−1 at 10% RH, which are respectively 5.6 and 13.6 times higher than a pristine PFSA membrane, and 4.5 and 6.8 times higher than a commercial Gore 740 membrane. In addition, the PHEDP/PFSA composite membrane exhibits superior fuel cell performance and low ohmic resistance under low relative humidity. The results show that the PHEDP/PFSA composite membrane's superior performance arises from its ability to absorb and retain more water in the membrane, enhance water transport from cathode to anode, and form new proton transport channels, indicating that the PHEDP/PFSA composite membrane has great potential for application in low relative humidity.

Water transport law of fuel cell membranes at different current densities

Proton exchange membrane fuel cell (PEMFC) is considered to be one of the most promising technical for automotive power. Because it has high power density, low operating temperature and environmental friendliness. During the operation of the fuel cell, hydrogen protons accompanying water was transferred from the anode to the cathode by electro-osmotic drag. At the same time, the water will be produced at the cathode, and diffused from the cathode to the anode by a certain concentration difference. When the electro-osmotic drag is greater than the back diffusion, the anode needs to be continuously humidified to prevent the water loss in the membrane. When the back diffusion is greater than the electro-osmotic drag, the water generated in the cathode is continuously transferred to the anode. Therefore, the law of water transfer in the membrane is an important issue in fuel cell research. In the present work, it adapted such thicker homogeneous membranes such as Nafion 117. It was found that at low current densities (0.2 A/cm2), the anode was more likely to be flooded. While at high current densities, they believed that a higher electroosmotic drag will drag the anode water to the cathode, thereby reducing the anode water content. However, the used more and more thin membranes become a trend in fuel cell technology. For example, in the past, DuPont′s most thin membrane Nafion 211 was 25 μm, but now the 15 μm membrane represented by Gore was widely used, and Toyota has used 10 μm membrane. these thin membranes are different from the conventional thick membrane with uniform structure. Generally, the membrane was a sandwich structure with a perfluorosulfonic acid resin on both sides of the porous PTFE reinforced matrix. Therefore, the law of water transport was different from the homogeneous membrane. The water transport flux of the actual situation was tested by designing a dew point meter water balance test to analyze the water transfer law in the fuel cell. At the same time, the three-dimensional PEM fuel cell was simulated by using the fluid dynamics calculation software. The distribution of water content, anode water molar concentration and hydrogen mole fraction in the membrane was obtained. The results of experiment were compared to simulation results. The simulation results show that under the working condition of 75°C, 150 kPa, and cathode non-humidification conditions, the anode moisture of 15 μm membrane below 0.4 A/cm2 decreases with the increase of current. In this case, electroosmosis drags counteract partial back diffusion; The anode water above 0.4 A/cm2 increases with the increase of current, and the back diffusion played a leading role in transferring a large amount of water from cathode to the anode; the higher the current density, the more water was transferred to the anode. The actual test results showed that as the current increases, the more liquid water could be observed by the anode, which was consistent with the simulation results. When the membrane thickness was 15 μm, a thinner membrane increases the amount of water transferred from the cathode to anode. When the current was higher than 3.0 A/cm2, the anode water volume of 25 μm membrane will decrease due to electroosmotic drag. But the anode water of 15 μm membrane will still increase, and the effect of back diffusion will increase with the decrease of membrane thickness.

Etherification of 5‐Hydroxymethylfurfural to Biofuel Additive Catalyzed by Aquivion® PFSA Modified Mesoporous Silica

Catalytic etherification of 5‐hydroxymethylfurfural (HMF) with isobutene (IB) to a biodiesel additive, that is, 5‐(tert‐butoxymethyl)‐furfural (tBMF), is studied on the Aquivion® perfluorosulfonic acid resin (PFSA) modified mesoporous silica (Aquivion®/m‐SiO2) solid acid. Mesoporous silica, composed of amorphous silica‐particle aggregates, is synthesized by the sol–gel method using the amphiphilic Aquivion® PFSA as both the acidic and the template reagent. The silica surface is then modified by the Aquivion® resin, leading to the hybrid Aquivion®/m‐SiO2 solid acid bearing highly accessible sulfonic acid sites and adequate porous structure. The catalytic properties, including composition, thermal stability, acidity, porosity, and morphology, are characterized by FTIR spectroscopy, Raman spectroscopy, solid‐state NMR spectroscopy, XPS, TGA/DTG, elemental analysis, potentiometric titration, N2 physisorption, SEM, and TEM. The influence of different reaction parameters, such as catalyst dosage, reaction time and temperature, reactants composition, and solvent, is investigated. The optimal Aquivion®/m‐SiO2 catalyst (10 wt.‐%), with an accessible acidity of 45 µmolH+ gcatal.–1 demonstrates 78 % conversion of HMF and 66 % yield of tBMF, in the presence of THF, after 3 h at 90 °C, whereas the yield of byproduct 5,5′‐[oxy‐bis(methylene)]bis‐2‐furfural (OBMF), generated by the oligomerization of HMF, is lowered to 4 %. The developed catalyst demonstrates good stability after regeneration for five consecutive cycles.

Nafion/IL Intermediate Temperature Proton Exchange Membranes Improved by Mesoporous Hollow Silica Spheres

AbstractA novel polyelectrolyte composite membrane was designed and prepared for intermediate temperature proton exchange membrane fuel cells (PEMFCs). It was composed of perfluorosulfonic acid resin (Nafion®), protic ionic liquid (IL, [dema][TfO]) and mesoporous hollow silica spheres (MHSi). The morphologies of MHSi and Nafion‐based composite membranes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of MHSi on proton conductivity of the composite membranes versus relative humidity (RH) and temperature (100–140 °C) were investigated. The results indicated, that the Nafion/IL/MHSi composite membranes exhibited excellent proton conductivity even under 30% RH or high temperature (above 100 °C). A high proton conductivity (5.41 mS cm−1) of the composite membrane at 30 °C and 30% RH can be observed from the test result, which was five times higher than that of the pristine Nafion. The N‐IL‐12S composite membrane showed an outstanding proton conductivity, as far as 14.7 mS cm−1 under 140 °C and low RH, which was almost two orders higher than that of the pristine Nafion membrane. Moreover, the unique hollow and mesoporous structure of MHSi improved IL retention rate of the membrane evidently. Together with high thermal stability of the composite membrane confirmed by thermogravimetric analysis (TGA), the Nafion/IL composite membrane improved by MHSi is a potential candidate in intermediate temperature PEMFC.

5-Hydroxymethylfurfural production from dehydration of fructose catalyzed by Aquivion@silica solid acid

5-Hydroxymethylfurfural (HMF) production from catalytic dehydration of fructose was studied over mesoporous silica heterogenized perfluorosulfonic acid resin (Aquivion@silica) catalyst. Amphiphilic Aquivion PFSA was used as both acidic and template agent for the sol–gel synthesis of amorphous mesoporous silica which was found very appropriate to effectively immobilize Aquivion resin by using an impregnation method. Various characterizations including elemental analysis, acid-base titration, XRD, FTIR, Raman, N2 adsorption–desorption, SEM and TEM revealed that Aquivion@silica catalyst presented large surface area, sufficient porosity and afforded highly accessible sulfonic acid groups. Efficient and productive HMF production from the dehydration of fructose was achieved in the polar dimethyl sulfoxide (DMSO) solvent at low temperature of 90 °C, i.e. 85% yield of HMF and 43 molHMF molH+ productivity of HMF. The influence of reaction time, reaction temperature, Aquivion loading, catalyst dosage and solvent on the dehydration process was systematically investigated. The catalyst could be regenerated through a simple ion-exchange method and a stable HMF yield was maintained after being used four times.

Nafion®-Containing Solid Lipid Nanoparticles as a Tool for Anticancer Pt Delivery: Preliminary Studies

Preliminary studies of nanoparticles based on the perfluorosulfonic acid resin Nafion have been carried out with the aim of establishing an ionic connection with the protonable phosphine 1,3,5-triaza-7-phosphaadamantane (PTA), suitable for the coordination of platinum. Nafion-containing nanoparticles (NAF) were produced by homogenization followed by ultrasonication method. After production, NAF were characterized in terms of size, morphology, andin vitrocytotoxicity. The PCS studies showed that theZ-average mean diameter was around 250 nm. Moreover, the polydispersity index showed a monodimensional distribution of nanoparticles. Cryo-TEM analysis showed a uniform and homogenous population of particles, characterized by the presence of both ovoidal and needle-like structures. To evaluate thein vitrocytotoxicity, NAF were tested on human cancer cell lines K562 and A2780. No cytotoxic effect was found on both cell lines. By13P-NMR measures, it is here proved that the strongly acidic sulfonic groups of Nafion-containing nanoparticles (NAF) can act as protonating agents for PTA. The protonation occurs selectively at nitrogen; hence protonated PTA maintains its ability to coordinate platinum via its phosphorus atom.

Polybenzimidazole/poly(tetrafluoro ethylene) composite membranes for high temperature proton exchange membrane fuel cells

A porous poly(tetrafluoro ethylene) (PTFE) thin film (thickness 16 ± 2 μm) is used as a supporting material for polybenzimidazole (PBI) to prepare the PBI/PTFE composite membrane (thickness 38 ± 2 μm). The perfluorosulfonic acid resin (Nafion) is used as a coupling agent at the interface between PTFE and PBI to improve the bonding between PBI and PTFE. The composite membrane, after doping with phosphoric acid, is used to prepare membrane electrode assemblies (MEAs). A 450 h continuous fuel cell life test at 160 °C with a fixed current density i = 200 mA cm−2 and a 20 cycles cell on/off test, in which the fuel cell is operated at 160 °C with i = 200 mA cm−2 for 12 h and then switched off at room temperature in an ambient environment for 12 h per cycle, are performed. Both tests show good fuel cell performances.

Durable perfluorosulfonic polymer electrolyte membranes prepared from alkaline-ion-assisted heat treatment

Perfluorosulfonic acid (PFSA) electrolyte heat-treated at elevated glass transition temperature ( T g, 140–290 °C) with alkaline metal ions as the sulfonic group protector have been used to prepare stable PFSA/polytetrafluoroethylene (ePTFE) polymer electrolyte membrane for fuel cells. Thermal mechanical analysis (TMA) and X-ray diffraction results revealed that the PFSA resin with alkaline metal ions (Li, Na, and K) exhibits a significant increase of T g, as well as an improved crystalline structure after heat treatment at T g. Resin solubility measurement indicated the heat-treated PFSA show a better solvent resistance which favors membrane stability. The effect of ionic modification on PFSA/ePTFE composite PEMs performances, such as gas crossover, shrinkage stress, proton conductivity, and mechanical properties has been investigated in details. In general, the heat-treated PFSA/ePTFE composite PEMs showed lower dissolved fraction in water–alcohol solvents and better dimensional stability. The increased heat-treated temperature also enhanced the membrane performance because of the improved interface compatibility between PFSA resin and PTFE. The PFSA/ePTFE membrane prepared from heat-treated PFSA in Na-form at 290 °C ( T g of Na-form PFSA) increased the performance up to 0.744 V@600 mA cm −2, significantly higher than those of other PEMs because of the T g of Na-PFSA were close to the T g of PTFE.

Recycling of membrane electrode assembly of PEMFC by acid processing

A simple, high efficient and environmentally friendly approach was investigated to recycle the key materials of membrane electrode assembly (MEA) applied in proton exchange membrane fuel cell (PEMFC). The catalyst coated membranes (CCMs) was dipped into sulfuric acid until the formation of transparent solution composed of Pt and perfluorosulfonic acid resin. Wherein, the membrane was dissolved, and the amorphous carbon nanoparticles as catalyst supports in catalyst layers were oxidized. Subsequently, both metal Pt and perfluorosulfonic acid resin were separated by centrifugal separation. Then the resin was recast into a membrane and the single fuel cell performance was tested. As a result, the solution to recycle the key materials of MEAs is promising for recycling MEA materials used in PEMFC.

Enhancement of Electrical Properties of Ferroelectric Polymers by Polyaniline Nanofibers with Controllable Conductivities

AbstractConductive nanofibers are adopted to enhance the electric properties of ferroelectric polymers. Polyaniline (PANI) nanofibers doped by protonic acids have a high dispersion stability in vinylidene fluoride‐trifluoroethylene copolymers [P(VDF‐TrFE)] and lead to percolative nanocomposites with enhanced electric responses. About a 50‐fold rise in the dielectric constant of the ferroelectric polymer matrix has been achieved. Percolation thresholds of the nanocomposites are relevant to doping levels of PANI nanofibers and can be as low as 2.9 wt% for fully doped nanofibers. The interface between the conductive nanofiber and the polymer matrix plays a crucial role in the dielectric enhancement of the nanocomposites in the vicinity of the percolation threshold. Compared with other dopants, perfluorosulfonic acid resin is better at improving the performance of the nanofibers in that it serves as a surface passivation layer for the conductive fillers and suppresses leakage current at low frequency. The nanofibers drastically reduce the electric field strength required to switch spontaneous polarization of P(VDF‐TrFE). The nanocomposites can be utilized for potential applications as high energy density capacitors, thin‐film transistors, and non‐volatile ferroelectric memories.

Fabrication and characterization of PFSI/ePTFE composite proton exchange membranes of polymer electrolyte fuel cells

PFSI/ePTFE composite proton exchange membranes were fabricated by impregnating perfluorosulfonic acid resin (PFSI resin, Nafion) into chemically modified expanded PTFE (ePTFE) matrix. Chemical modification of sodium–naphthalene treatment and N-methylol acrylamide (NMA) grafting decreased the contact angle of the as-received ePTFE from 125 ± 0.5° to 67 ± 0.5°, effectively converting the as-received hydrophobic ePTFE to a hydrophilic ePTFE matrix. The composite membrane fabricated with the hydrophilic ePTFE have higher impregnated PFSI loading, much lower porosity and better PTFE/PFSI interface contact, as compared to the composite membranes with the as-received ePTFE. This leads to much lower gas permeability and significantly improves the durability under an accelerated dry/wet cycle test. The fuel cell made from the PFSI/ePTFE composite membranes with hydrophilic ePTFE showed superior performance as compared to that with the composite membrane made from the as-received ePTFE and Nafion 211 membrane.

Dimerization of α-Methylstyrene (AMS) Catalyzed by Sulfonic Acid Resins: A Quantitative Kinetic Study

The dimerization of α-methylstyrene was examined at 50°C and 1 atm in nonpolar cumene and polarp-cresol solvents, using both soluble liquid acids and resin-based solid acids as catalysts. In particular, the activities of a representative macroporous sulfonic acid resin, Amberlyst-15®, and Nafion® perfluorosulfonic acid resin in three different microstructures, gel-type Nafion® NR-50 resin, a carbon-supported Nafion® resin, and a Nafion® resin/silica composite material, have been compared. The Nafion® resin/silica composites showed, by far, the highest activity. Supported Nafion® resin on carbon and Amberlyst-15® are effective catalysts as well and are all more active than pure Nafion® resin based on catalyst weight. None of the small molecule acids were sufficiently soluble to show significant catalytic action in the nonpolar solvent cumene. On the other hand, in the polarp-cresol media, the homogeneous acids showed relative activities in the same order as theirpKas; and the strongest aqueous acid, triflic acid was more active than any of the resin catalysts on an acid equivalent basis. Among the resin catalysts, only the Nafion® NR50 gel showed significant activity enhancement inp-cresol. In order to gain insight into these relative catalytic activities, the acid capacity and accessibility of acid groups in these solid acid catalysts were studied using temperature programmed desorption/thermogravimetric analysis (TPD/TGA) techniques with isopropanol as probe molecule. The TPD/TGA studies show that the sulfonic acid groups are readily accessible to 2-propanol vapor in the 13 wt% Nafion® resin/SiO2composite but not in gel-type Nafion® resin and Amberlyst-15®.

Perfluoropolymer-supported fits reagents

Perfluoropolymer-supported FITS reagents (FITS-Nafion) were synthesized by treatment of bis(trifluoroacetoxy)iodoperfluoroalkanes with perfluorosulfonic acid resin (Nafion-H) and benzene or fluorobenzene.