Intrinsically proton-conducting poly(1-vinyl-1,2,4-triazole)/triflic acid blends

In the present work, proton conductivity in a polymer blend comprising proton solvating heterocycles was examined. Poly(1-vinyl-1,2,4-triazole), PVTri was produced by free radical polymerization of 1-vinyl-1,2,4-triazole and then proton-conducting polymer electrolytes were obtained by blending of PVTri with trifluoromethanesulfonic acid, triflic acid (TA). To promote the intrinsic proton conductivity the percent blending ratio was changed from 25% to 150% with respect to polymer repeat unit. The protonation of aromatic heterocyclic rings was proved with Fourier-transform infrared spectroscopy (FT-IR). Thermogravimetry (TG) analysis showed that the samples are thermally stable up to approximately 300 °C. Differential scanning calorimetry (DSC) results illustrated that the samples are homogeneous and their glass transition temperatures are located within 130-160 °C. The surface morphology of the materials were characterized by scanning electron microscopy (SEM). The proton conductivity of the blends increased with triflic acid concentration and the temperature. In the anhydrous state, the proton conductivity of PVTriTA100 is 2.2 × 10⁻⁴ S/cm at 150 °C and that of PVTriTA150 is approximately 0.012 S/cm at 80 °C which is similar to that of hydrated Nafion^®.     

Anhydrous proton conducting polymer electrolytes based on poly(vinylphosphonic acid)-heterocycle composite material

The development of anhydrous proton conducting membrane is important for the operation of polymer electrolyte membrane fuel cell (PEMFC) at intermediate temperature (100-200 °C). In this study, we have investigated the acid-base hybrid materials by mixing of strong phosphonic acid polymer of poly(vinylphosphonic acid) (PVPA) with the high proton-exchange capacity and organic base of heterocycle, such as imidazole (Im), pyrazole (Py), or 1-methylimidazole (MeIm). As a result, PVPA-heterocycle composite material showed the high proton conductivity of approximately 10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. In particular, PVPA-89 mol% Im composite material showed the highest proton conductivity of 7×10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. Additionally, the fuel cell test of PVPA-89 mol% Im composite material using a dry H₂/O₂ showed the power density of approximately 10 mW cm⁻² at 80 °C under anhydrous conditions. These acid-base anhydrous proton conducting materials without the existence of water molecules might be possibly used for a polymer electrolyte membrane at intermediate temperature operations under anhydrous or extremely low humidity conditions.     

New highly proton-conducting membrane poly(vinylpyrrolidone)(PVP) modified poly(vinyl alcohol)/2-acrylamido-2-methyl-1-propanesulfonic acid (PVA-PAMPS) for low temperature direct methanol fuel cells (DMFCs)

A new type of chemically cross-linked polymer blend membranes consisting of poly(vinyl alcohol) (PVA), 2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) and poly(vinylpyrrolidone) (PVP) have been prepared and evaluated as proton conducting polymer electrolytes. The proton conductivity (σ) of the membranes was investigated as a function of cross-linking time, blending composition, water content and ion exchange capacity (IEC). Membranes were also characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), and the differential scanning calorimetry (DSC). Membrane swelling decreased with cross-linking time, accompanied by an improvement in mechanical properties and a small decrease in proton conductivity due to the reduced water absorption. The membranes attained 0.088 S cm⁻¹ of the proton conductivity and 1.63 mequiv g⁻¹ of IEC at 25±2 °C for a polymer composition PVA-PAMPS-PVP being 1:1:0.5 in mass, and a methanol permeability of 6.1×10⁻⁷ cm² s⁻¹, which showed a comparable proton conductivity to Nafion 117, but only one third of Nafion 117 methanol permeability under the same measuring conditions. The membranes displayed a relatively high oxidative durability without weight loss of the membranes (e.g. 100 h in 3% H₂O₂ solution and 20 h in 10% H₂O₂ solution at 60 °C). PVP, as a modifier, was found to play a crucial role in improving the above membrane performances.     

Proton conducting membranes based on semi-interpenetrating polymer network of Nafion and polybenzimidazole

A new strategy to prepare the reinforced composite membranes for polymer electrolyte membrane fuel cells (PEMFCs), which can work both in humidified and anhydrous state, was proposed via constructing semi-interpenetrating polymer network (semi-IPN) structure from polybenzimidazole (PBI) and Nafion^®212, with N-vinylimidazole as the crosslinker. The crosslinkable PBI was synthesized from poly(2,2′-(m-phenylene)-5,5′-bibenzimidazole) and p-vinylbenzyl chloride. The semi-IPN structure was formed during the membrane preparation. The composite membranes exhibit excellent thermal stability, high-dimensional stability, and significantly improved mechanical properties compared with Nafion^®212. The proton transport in the hydrated composite membranes is mainly contributed by the vehicle mechanism, with proton conductivity from ∼10⁻² S/cm to ∼10⁻¹ S/cm. When the temperature exceeds 100 °C, the proton conductivity of the semi-IPN membranes decreases quickly due to the dehydration of the membranes. Under anhydrous condition, the proton conductivity of the membranes will drop to ∼10⁻⁴ S/cm, which is also useful for intermediate temperature (100-200 °C) PEMFCs. The benzimidazole structure of PBI and the acidic component of Nafion^® provide the possibility for the proton mobility via structure diffusion involving proton transfer between the heterocycles with a corresponding reorganization of the hydrogen bonded network.     

Novel triazole functional sol-gel derived inorganic-organic hybrid networks as anhydrous proton conducting membranes

In this work, novel inorganic-organic hybrid networks were prepared to obtain anhydrous proton conducting membranes for fuel cells. 3-glycidoxypropyl trimethoxy silane (GPTMS) was functionalized with 1H-1,2,4-triazole (Tri) and 3-aminotriazole (ATri) via ring opening of the epoxide ring and then sol-gel polymerization was performed to produce triazole containing silane networks abbreviated as Si-Tri and Si-ATri. In addition during sol-gel process trifluoromethane sulfonic acid (TA) was introduced into the matrix with several stoichometric ratios. Fourier transform infrared spectroscopy (FT-IR) confirmed the tethering of the Tri and ATri into the silane compound and the sol-gel reaction. Thermogravimetry analysis (TGA) showed that the membranes are thermally stable up to 200 °C. Differential scanning calorimeter (DSC) verified the softening effect of the dopant. The morphology of the membranes was analyzed with SEM images. The proton conductivity of these novel silane networks were studied by dielectric-impedance spectroscopy. Although proton conductivity of these membrane electrolytes depends on the acid ratio, the membrane without dopant produced a proton conductivity of 8.7 × 10⁻⁵ S/cm at 150 °C in dry state. The conductivity isotherms show Vogel-Tamman-Fulcher (VTF) behavior which implies the coupling of the charge carriers with the segmental motion of the polymer chains. A maximum proton conductivity of 8.9 × 10⁻⁴ S/cm was obtained for the sample Si-TriTA1 in the anhydrous condition.     

Synthesis and NMR studies of the polymer membranes based on poly(4-vinylbenzylboronic acid) and phosphoric acid

Proton conduction in novel anhydrous membranes based on host polymer, poly(4-vinylbenzylboronic acid), (P4VBBA) and phosphoric acid, (H₃PO₄) as proton solvent was studied. The materials were prepared by the insertion of the proton solvent into P4VBBA at different stoichiometric ratios to get P4VBBA·xH₃PO₄ composite electrolytes. Homopolymer and the composite materials were characterized by FT-IR, ¹¹B MAS NMR and ³¹P MAS NMR. ¹¹B MAS NMR results suggested that acid doping favors or leads to a four-coordinated boron arrangement. ³¹P MAS NMR results illustrated the immobilization of phosphoric acid to the polymer through condensation with boron functional groups (B-O-P and/or B-O-P-O-B). Thermogravimetric analysis (TGA) showed that the condensation of composite materials starts approximately at 140 °C. An exponential weight loss above this temperature was attributed to intermolecular condensation of acidic units forming cross-linked polymer. The insertion of phosphoric acid into the matrix softened the materials shifting T_g to lower temperatures. The temperature dependence of the proton conductivity was modeled with Arrhenius relation. P4VBBA·2H₃PO₄ has a maximum proton conductivity of 0.0013 S/cm at RT and 0.005 S/cm at 80 °C.     

A proton-conducting composite membrane: Sn0.95Al0.05P2O7 and polystyrene-b-poly(ethylene/propylene)-b-polystyrene

An anhydrous proton conductor, Sn_0.95Al_0.05P₂O₇ (SAPO), composed of polystyrene-b-poly(ethylene/propylene)-b-polystyrene (SEPS), was developed and characterized using morphological, structural, and electrochemical analyses. In the composite membrane with 20 wt% SEPS, a homogeneous distribution of SAPO particles in the matrix was obtained in the thickness range of 65-90 μm, yielding a proton conductivity of 3.4 × 10⁻³ S cm⁻¹ at 200 °C, tensile strength of 4.6 MPa and an elongation at break of 711.0% at room temperature. Fuel cell tests verified that the open-circuit voltage was maintained at a constant value of approximately 1 V between 100 and 250 °C. The peak power densities achieved with unhumidified H₂ and air were 77.0 mW cm⁻² at 100 °C, 121.0 mW cm⁻² at 150 °C, and 163.1 mW cm⁻² at 225 °C.     

Inorganic-organic hybrid membranes with anhydrous proton conduction prepared from tetramethoxysilane/methyl-trimethoxysilane/trimethylphosphate and 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide for H2/O2 fuel cells

Anhydrous proton-conducting inorganic-organic hybrid membranes were prepared by sol-gel process with tetramethoxysilane/methyl-trimethoxysilane/trimethylphosphate and 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide [EMI][TFSI] ionic liquid as precursors. These hybrid membranes were studied with respect to their structural, thermal, proton conductivity, and hydrogen permeability properties. The Fourier transform infrared spectroscopy (FT-IR) and ³¹P, ¹H, and ¹³C nuclear magnetic resonance (NMR) measurements have shown good chemical stability, and complexation of PO(OCH₃)₃ with [EMI][TFSI] ionic liquid in the studied hybrid membranes. Thermal analysis including TG and DTA confirmed that the membranes were thermally stable up to 330 °C. Thermal stability of the hybrid membranes was significantly enhanced by the presence of inorganic SiO₂ framework and high stability of [TFSI] anion. The effect of [EMI][TFSI] ionic liquid addition on the microstructure of the membranes was studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) micrographs and no phase separation at the surfaces of the prepared membranes was observed and also homogeneous distribution of all elements was confirmed. Proton conductivity of all the prepared membranes was measured from −20 °C to 150 °C, and high conductivity of 5.4 × 10⁻³ S/cm was obtained for 40 wt% [EMI][TFSI] doped 40TMOS-50MTMOS-10PO(OCH₃)₃ (mol%) hybrid membrane, at 150 °C under anhydrous conditions. The hydrogen permeability was found to decrease from 1.61 × 10⁻¹¹ to 1.39 × 10⁻¹² mol/cm s Pa for 40 wt% [EMI][TFSI] doped hybrid membrane as the temperature increases from 20 °C to 150 °C. For 40 wt% [EMI][TFSI] doped hybrid membrane, membrane electrode assemblies were prepared and a maximum power density value of 0.22 mW/cm² at 0.47 mA/cm² as well as a current density of 0.76 mA/cm² were obtained at 150 °C under non-humidified conditions when utilized in a H₂/O₂ fuel cell.     

Alginic acid-imidazole composite material as anhydrous proton conducting membrane

Recently, membranes with high anhydrous proton conducting have been attracted remarkable interest for the application to the polymer electrolyte membrane fuel cell (PEFC). In this paper, we have investigated the anhydrous proton conductor consisting of alginic acid (AA), one of the acidic biopolymers, and imidazole (Im). This AA-Im composite material showed the proton conductivity of 2×10⁻³ S cm⁻¹ at 130 °C under anhydrous conditions. Additionally, these AA-Im composite materials have the highly mechanical property and thermal stability. Furthermore, the biological products, such as biopolymer, are cheap, non-hazardous, and environmentally benign. The proton conductive biopolymer composite material may have the potential for its superior ion conducting properties, in particular, under anhydrous (water-free) or extremely low humidity conditions.     

A new anhydrous proton conductor based on polybenzimidazole and tridecyl phosphate

Most of the anhydrous proton conducting membranes are based on inorganic or partially inorganic materials, like SrCeO₃ membranes or polybenzimidazole (PBI)/H₃PO₄ composite membranes. In present work, a new kind of anhydrous proton conducting membrane based on fully organic components of PBI and tridecyl phosphate (TP) was prepared. The interaction between PBI and TP is discussed. The temperature dependence of the proton conductivity of the composite membranes can be modeled by an Arrhenius relation. Thermogravimetric analysis (TGA) illustrates that these composite membranes are chemically stable up to 145 °C. The weight loss appearing at 145 °C is attributed to the selfcondensation of phosphate, which results in the proton conductivity drop of the membranes occurring at the same temperature. The DC conductivity of the composite membranes can reach ∼10⁻⁴ S/cm for PBI/1.8TP at 140 °C and increases with increasing TP content. The proton conductivity of PBI/TP and PBI/H₃PO₄ composite membranes is compared. The former have higher proton conductivity, however, the proton conductivity of the PBI/H₃PO₄ membranes increases with temperature more significantly. Compared with PBI/H₃PO₄ membranes, the migration stability of TP in PBI/TP membranes is improved significantly.     

Nearly stoichiometric BN fiber by curing and thermolysis of a novel poly[(alkylamino)borazine]

Boron nitride (BN) fiber with a composition of BN_1.09 was fabricated by curing and thermolysis of a novel poly[(alkylamino)borazine]. The processes have been studied by a combination of gel-content test, TGA, elemental analysis, IR, XPS, XRD, SEM and TEM. The results show that curing made polymer fiber infusible and resulted in a significant improvement of ceramic yield from 53.2 wt% to 73.8 wt% at 1000 °C. Moreover, pyrolysis in NH₃ at 1200 °C generated a nearly stoichiometric BN without carbonaceous impurities while in Ar led to a BNC material with carbon content of 6.13 wt%. The obtained amorphous BN fiber with a diameter of 13 μm displayed a tensile strength of approximately 600 MPa. Furthermore, the BN fiber illustrated good oxidation resistance in air.     

Synthesis of organosiloxane-based inorganic/organic hybrid membranes with chemically bound phosphonic acid for proton-conductors

Proton conductive inorganic-organic hybrid membranes were synthesized from 3-glycidoxypropyltrimethoxysilane (GPTMS) and phosphonoacetic acid (PA) with various ratios by a sol-gel process. Self-standing, homogeneous, highly transparent membranes were synthesized. TG-DTA analyses indicated that these membranes were thermally stable up to 200 °C. The results of FT-IR and ¹³C NMR revealed that phosphonic acid groups of PA were chemically bound to organosiloxane network as a result of reaction between PA and GPTMS. The leach out of phosphonic acid groups from GPTMS-PA to water was reduced compared with phosphoric acid groups from GPTMS-H₃PO_4. The proton conductivity of the hybrid membranes increased with phosphonic acid content. The conductivity of GPTMS/PA with a 1/1.05 ratio at 130 °C was 8.7 × 10⁻² S cm⁻¹ at 100% relative humidity (RH).     

Acetic acid-doped poly(ethylene oxide)-modified poly(methacrylate): a new proton conducting polymeric gel electrolyte

A proton conducting polymeric gel membrane was first developed from poly(ethylene oxide)-modified poly(methacrylate) (PEO-PMA) containing poly(ethylene glycol) dimethylether (PEGDE). Acetic acid (HAc) was doped by immersing the polymeric film directly in the aqueous solution of HAc. Characterization by FT-IR, XRD and AC conductivity measurements were carried out on the film electrolytes consisting of different gel compositions. The ionic conductivity of the membrane showed a sensitive variation with the immersion time and concentration of the acid in the doping solution through the changes in the contents of acid and water in the gel. The ionic conductivity also depended on the PEGDE content in the polymer. The proton conductivity was 6.2×10⁻⁴ S cm⁻¹ at 20 °C and 1.0×10⁻³ S cm⁻¹ at 80 °C for the gel prepared from HAc concentration of 3.0 mol l⁻¹. The temperature dependence of the conductivity was found to be consistent with Arrhenius-type relationship at a temperature range from 20 to 80 °C, except for the films with low PEGDE contents. The apparent activation energy for the proton conduction was in the range of 5-30 kJ mol⁻¹, depending on the HAc concentration and the polymer matrix composition. The FT-IR spectra of the polymeric membranes showed that HAc does not protonate the carbonyl or ester groups of the polymer matrix, but interacts with them by the hydrogen bonding interaction or weak molecular interactions.     

Boron nitride by pyrolysis of the melt-processable poly[tris(methylamino)borane]: Structure, composition and oxidation resistance

Evolution of structure and composition of the melt-processable poly[tris(methylamino)borane] (PTMB) during its conversion to ceramics was studied by TGA, FTIR, Raman, XRD, XPS and elemental analysis (EA). The results show that the ceramic yield was greatly improved from 60.22 to 74.4 wt% at 900 °C by curing in NH₃ prior to pyrolysis. The carbon impurity in the precursor can be removed effectively in NH₃ whereas no similar result occurred in N₂. In NH₃, 93 wt% of carbon was removed at 600 °C and the carbon content in the pyrolyzed product at 900 °C was only 0.37 wt%. At the same time, the conversion from polymer to ceramics was almost completed at 900 °C. Moreover, the sample acquired at 900 °C was amorphous boron nitride (BN), while that of further annealing at 1600 °C showed characteristic of turbostratic BN (t-BN). Additionally, the BN with nearly stoichiometric composition exhibited good oxidation resistance even up to 900 °C in air.     

Anhydrous proton conductive membrane consisting of chitosan

We have investigated a low production cost anhydrous proton conductor consisting of a composite of chitosan, one of the world's discarded materials, and methanediphosphonic acid (MP) having a high proton exchange capacity. This chitosan-200 wt.% MP composite material showed the high proton conductivity of 5 × 10⁻³ S cm⁻¹ at 150 °C under anhydrous conditions. Additionally, the proton conducting mechanism of the chitosan-MP composite material was due to proton transfer to the proton defect site without the assistance of diffusible vehicle molecules. The utilization of a biopolymer, such as chitosan, for PEMFC technologies is novel and challenging where biological products are usually considered as waste, non-hazardous, and environmentally benign. Especially, the low production cost of the biopolymer is an attractive feature. Anhydrous proton conducting biopolymer composite membranes may have potential not only for PEMFCs operated under anhydrous conditions, but also for bio-electrochemical devices including an implantable battery, bio-sensors, etc.     

Synthesis and electrochemical properties of lithium methacrylate-based self-doped gel polymer electrolytes

In this study, a strategy for synthesizing lithium methacrylate (LiMA)-based self-doped gel polymer electrolytes was described and the electrochemical properties were investigated by impedance spectroscopy and linear sweep voltammetry. LiMA was found to dissolve in ethylene carbonate (EC)/diethyl carbonate (DEC) (3/7, v/v) solvent after complexing with boron trifluoride (BF₃). This was achieved by lowering the ionic interactions between the methacrylic anion and lithium cation. As a result, gel polymer electrolytes consisting of BF₃-LiMA complexes and poly(ethylene glycol) diacrylate were successfully synthesized by radical polymerization in an EC/DEC liquid electrolyte. The FT-IR and AC impedance measurements revealed that the incorporation of BF₃ into the gel polymer electrolytes increases the solubility of LiMA and the ionic conductivity by enhancing the ion disassociations. Despite the self-doped nature of the LiMA salt, an ionic conductivity value of 3.0 × 10⁻⁵ S cm⁻¹ was achieved at 25 °C in the gel polymer electrolyte with 49 wt% of polymer content. Furthermore, linear sweep voltammetry measurements showed that the electrochemical stability of the gel polymer electrolyte was around 5.0 V at 25 °C.     

A polymer electrolyte membrane for high temperature fuel cells to fit vehicle applications

Poly(tetrafluoroethylene) PTFE/PBI composite membranes doped with H₃PO₄ were fabricated to improve the performance of high temperature polymer electrolyte membrane fuel cells (HT-PEMFC). The composite membranes were fabricated by immobilising polybenzimidazole (PBI) solution into a hydrophobic porous PTFE membrane. The mechanical strength of the membrane was good exhibiting a maximum load of 35.19 MPa. After doping with the phosphoric acid, the composite membrane had a larger proton conductivity than that of PBI doped with phosphoric acid. The PTFE/PBI membrane conductivity was greater than 0.3 S cm⁻¹ at a relative humidity 8.4% and temperature of 180 °C with a 300% H₃PO₄ doping level. Use of the membrane in a fuel cell with oxygen, at 1 bar overpressure gave a peak power density of 1.2 W cm⁻² at cell voltages >0.4 V and current densities of 3.0 A cm⁻². The PTFE/PBI/H₃PO₄ composite membrane did not exhibit significant degradation after 50 h of intermittent operation at 150 °C. These results indicate that the composite membrane is a promising material for vehicles driven by high temperature PEMFCs.     

Polybenzimidazole containing benzimidazole side groups for high-temperature fuel cell applications

A polybenzimidazole (PBI) containing bulky basic benzimidazole side groups, poly[2,2′-(2-benzimidazole-p-phenylene)-5,5′-bibenzimidazole] (BIpPBI), was prepared via the condensation polymerization of 3,3′-diaminobenzidine tetrahydrochloride dihydrate with 2-benzimidazole terephthalic acid in PPA. BIpPBI was found to be soluble in aprotic polar solvents without the addition of inorganic salts, such as lithium chloride, and the BIpPBI film also showed very good acid retention capability as well as very high proton conductivity. The maximum acid content of the BIpPBI film was approximately 81 wt.% and the proton conductivity value of the acid-doped BIpPBI membrane was 0.16 S cm⁻¹ at 180 °C and a 0% relative humidity. For comparison, the maximum proton conductivity of the most commonly used polymer for the high-temperature fuel cell membrane, poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (mPBI) membrane, is approximately 0.06 S·cm⁻¹ at 180 °C under anhydrous conditions at a 65 wt.% acid content, which is the maximum acid content that a mPBI membrane can have.     

Hybrid proton-conducting membranes for polymer electrolyte fuel cells: Phosphomolybdic acid doped poly(2,5-benzimidazole)—(ABPBI-H3PMo12O40)

The synthesis and characterization of a novel hybrid organic-inorganic material formed by phosphomolybdic acid H₃PMo₁₂O₄₀ (PMo₁₂) and poly(2,5-benzimidazole) (ABPBI) is reported. This material, composed of two proton-conducting components, can be cast in the form of membranes from methanesulfonic acid (MSA) solutions. Upon impregnation with phosphoric acid, the hybrid membranes present higher conductivity than the best ABPBI polymer membranes impregnated in the same conditions. These electrolyte membranes are stable up to 200 °C, and have a proton conductivity of 3 × 10⁻² S cm⁻¹ at 185 °C without humidification. These properties make them very good candidates as membranes for polymer electrolyte membrane fuel cells (PEMFC) at temperatures of 100-200 °C.     

Synthesis and characterization of proton conducting inorganic-organic hybrid nanocomposite membranes based on tetraethoxysilane/trimethylphosphate/3-glycidoxypropyltrimethoxysilane/heteropoly acids

A series of novel proton conductive inorganic-organic nanocomposite hybrid membranes doped with phosphotungstic acid (PWA)/phosphomolybdic acid (PMA) and trimethylphosphate PO(OCH₃)₃ have been prepared by sol-gel process with 3-glycidoxypropyltrimethoxysilane (GPTMS), and tetraethoxysilane (TEOS) as precursors. The hybrid membranes were studied with respect to their structural and thermal properties, elastic moduli and proton conductivity. Thermal analysis including TG and DTA confirmed that the membranes were thermally stable up to 200 °C. Thermal stability of membranes was significantly enhanced by the presence of SiO₂ framework. Proton conductivity of 1.59 × 10⁻² S/cm with composition of 50TEOS-5PO(OCH₃)₃-35GPTMS-10PWA was obtained (1.15 × 10⁻² S/cm for 10 mol% PMA) at 90 °C under 90% relative humidity. The proton conductivity of the nanocomposite membranes is due to the proton-conducting path through the GPTMS-derived “pseudopolyethylene oxide (pseudo-PEO)” networks in which the trapped solid acid (PWA/PMA) as a proton donor is contained. The molecular water absorbed in the polymer matrix is also presumed to provide high proton mobility, resulting in an increase of proton conductivity with increasing relative humidity.