Proton Conductive Inorganic Organic Hybrid Membranes Research Articles

One-pot synthesis of proton-conductive inorganic–organic hybrid membranes from organoalkoxysilane and phosphonic acid derivatives

Inorganic–organic hybrid membranes consisting of an aliphatic main-chain polymer and Si–O linkages were synthesized via a simple one-pot process from an alkoxysilane derivative, methyl-substituted phenylvinylphosphonic acid, and phosphonic acid acrylate. (Methyldimethoxysilylmethyl)styrene (MDMSMS) was copolymerized with 3-methylphenylvinylphosphonic acid (CH3C6H4VPA, or MPVPA), and 2-hydroxyethyl methacrylate acid phosphate (HEMAP), and then hydrolyzed, yielding inorganic–organic hybrid composites. The formation of the inorganic–organic hybrid structure was confirmed by IR, 13C, and 29Si NMR spectroscopy. The membranes exhibited good thermal stability up to 180°C. The combination of aliphatic chains of the methacrylate derivative and Si–O networks in the hybrid membranes improved the mechanical properties of the membranes, enabling the construction of a membrane electrode assembly. The tensile modulus of the MDMSMS/MPVPA/HEMAP membrane with a composition of 1:1:5 was 688MPa. The conductivity of the 1:1:5 membranes was 4.1×10−2Scm−1 at 130°C and 100% relative humidity (RH), while it was 4.7×10−4Scm−1 at 130°C and 19.3% RH. The peak power of the 1:1:5 membrane was 4.8mW/cm2 at 140°C and 30% RH. The cell utilizing the hybrid membrane was operated at 120°C and 30% RH for 24h without any drop in cell voltage.

Proton-conductive inorganic–organic hybrid membranes synthesized from a trimethoxysilylmethylstyrene–fluorophenylvinyl acid copolymer

Inorganic–organic hybrid membranes composed of Si–O networks and an aliphatic main-chain polymer backbone were synthesized from an alkoxysilane derivative and an F-substituted phenylvinylphosphonic acid via copolymerization and sol–gel reaction. Thus, (trimethoxysilylmethyl)styrene (TMSMS) was copolymerized with 3-fluorophenyl- vinylphosphonic acid (FC6H4VPA), and the product was hydrolyzed to afford an inorganic–organic hybrid composite. Spectroscopic analysis revealed that the inorganic–organic hybrid structure was constructed via the polymerization of TMSMS and FC6H4VPA and the condensation of methoxy-Si bonds. The membranes showed good thermal stability up to 180°C, and it was found that the aliphatic chains bound to the F-substituted aromatic rings and the Si–O linkages in the hybrid membranes improved their mechanical properties. In addition, the proton conductivity of the membranes depended on the P/Si ratio of the product and increased as the P content increased. Notably, the conductivity at 130°C for the hybrid membrane synthesized with a TMSMS/FC6H4VPA ratio of 1/6 was 1.6×10−3Scm−1 and 6.4×10−2Scm−1 at low and 100% relative humidity (RH), respectively, while its power density at 140°C and 30% RH was 3.0mW/cm2.

Preparation conditions of inorganic–organic hybrid membranes synthesized from Epoxycyclohexylethyltrimethoxysilane and 1-hydroxyethane-1, 1-diphosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from Epoxycyclohexylethyltrimethoxysilane (EHTMS) and 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) by the sol–gel method. In this paper, the effect of gel temperature, membrane-forming temperature and Si/P on hybrid membranes performance were discussed. FT-IR studies revealed the phosphonic acid was chemically bonded to the siloxane network. When the membrane-forming temperature is 150 °C, thermal analysis including TG and DTG confirmed that the hybrid membranes were thermally stability up to 250 °C and SEM images showed that the membranes surface smooth and dense, eliminating the phase separation phenomenon. The hybrid membranes with a molar ratio of Si/P = 6/1 possess better thermal stability and preferable flexibility.

Proton conductive inorganic–organic hybrid membranes functionalized with phosphonic acid for polymer electrolyte fuel cell

Proton conductive sol–gel derived hybrid membranes were synthesized from aromatic derivatives of methoxysilanes and ethyl 2-[3-(dihydroxyphosphoryl)-2-oxapropyl]acrylate (EPA). Two aromatic derivatives of methoxysilanes with different number of methoxy groups were used as the starting materials. Hybrid membranes from difunctional (methyldimethoxysilylmethyl)styrene (MDMSMS(D))/EPA revealed a higher chemical stability and mechanical properties than those from monofunctional (dimethylmethoxysilylmethyl)styrene (DMMSMS(M))/EPA. The membrane–electrode assembly (MEA) using the hybrid membranes as electrolytes worked as a fuel cell at 100 °C under saturated humidity. The DMMSMS(M)/EPA membrane-based MEA showed a larger current density than that from MDMSMS(D)/EPA. On the other hand, the MDMSMS(D)/EPA membrane-based MEA exhibited higher open circuit voltages than the DMMSMS(M)/EPA-based MEA, and was stable during fuel cell operation at 80 °C at least for 48 h.

Synthesis of proton conductive membranes based on inorganic–organic hybrid structure bound with phosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from styrene derivatives of alkoxysilane and ethyl 2-[3-(dihydroxyphosphonyl)-2-oxopropyl] acrylate (EPA) through copolymerization followed by sol–gel reaction. Self-standing, homogeneous and transparent hybrid membranes with chemically bound phosphonic acid groups were synthesized. FT-IR analysis exhibited the hybrid membranes included phosphonic acid groups. 13C and 29Si NMR studies indicated that alkoxysilyl functionalized styrene derivatives were not only copolymerized with EPA but also condensed yielding Si–O–Si linkages by sol–gel reaction. TG–DTA analysis revealed that these membranes were thermally stable up to 200 °C in dry O 2. The proton conductivities of the hybrid membranes increased with phosphonic acid content and temperature. The P/Si ratio of the membrane was dependent on the number of alkoxy group in the starting alkoxysilane. The hybrid membrane from (dimethylmethoxysilylmethyl)styrene (DMMSMS(M))/EPA = 1/6 revealed proton conductivities of 6.3 × 10 −3 and 2.4 × 10 −4 S cm −1 at 68.0% relative humidity and 18.8% relative humidity, respectively, at 140 °C.

Proton-Conductive Inorganic–Organic Hybrid Membrane Prepared from 3-(2-Aminoethylaminopropyl)triethoxysilane and Sulfuric Acid by the Sol-Gel Method

Proton conductive inorganic–organic hybrid membranes were prepared from 3-(2-aminoethylaminopropyl)triethoxysilane (AEAPTES) and by the sol-gel method. Differential thermal analysis–thermogravimetry measurements revealed that the resulting membranes were thermally stable up to . From the IR spectra, formation of acid-base pairs by protonation of the amino groups with was confirmed. X-ray diffraction patterns of the membranes showed diffraction peaks corresponding to d-spacings of hexagonal structure, probably indicating that stacking of rodlike polysiloxanes with the acid-base pairs extruded outside. The conductivity of the membrane with the molar ratio of was at under dry Ar atmosphere.

Synthesis of proton conductive inorganic–organic hybrid membranes from organoalkoxysilane and hydroxyalkylphosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from 3-glycidyloxypropyltrimethoxysiane (GPTMS), phenyltriethoxysilane (PhTES) and hydroxyalkylphosphonic acid. Two kinds of hydroxyalkylphosphonic acids, 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) and hydroxyethanephosphonic acid (HEPA), were incorporated into the membranes as functional molecules for proton conduction. FT-IR and Raman studies revealed the presence of phosphonic acid groups in the hybrid membranes. 13C and 29Si NMR confirmed that a three-dimensional siloxane network was formed in the prepared hybrid membrane by hydrolysis and condensation reactions. DTA-TG analysis showed that these membranes were thermally stable up to 200 °C. The HEDPA-based system was found to have higher proton conductivities than the HEPA-based one. The proton conductivities of the hybrid membranes increased with the phosphonic acid content and temperature up to 130 °C. The conductivities of the HEDPA/GPTMS/PhTES membranes = 1/1.6/0.4 were 1.0 × 10 −1 and 4.5 × 10 −4 S cm −1 at 100% relative humidity and non-humidified conditions, respectively, at 130 °C.

Proton conductive inorganic–organic hybrid membranes prepared from 3-aminopropyltriethoxysilane and phosphoric acid by the sol–gel method

Proton conductive inorganic–organic hybrid membranes with acid–base pairs have been prepared from 3-aminopropyltriethoxysilane and phosphoric acid by the sol–gel method. The self-standing membranes obtained are represented as poly(3-aminopropylsilsesquioxane)-H 3PO 4 (PAPS–H 3PO 4) membranes. Infrared absorption spectra of the PAPS–H 3PO 4 films showed that amino groups of PAPS were protonated by phosphoric acid, indicating the formation of acid–base pairs. X-ray diffraction patterns of the PAPS–H 3PO 4 membranes showed diffraction peaks attributed to hexagonal structure, which is probably formed by stacking of rodlike polysiloxane with the acid–base pairs extruded outside. The conductivities of the PAPS–H 3PO 4 membranes with a molar ratio of H 3PO 4/APTES = 1.0 was 4 × 10 − 4 S cm − 1 at 150 °C under dry condition.

Synthesis of proton conductive inorganic–organic hybrid membranes through copolymerization of dimethylethoxyvinylsilane with vinylphosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from dimethylethoxyvinylsilane (DMEVS), vinylphosphonic acid (VPA) and 3-glycidoxypropyltrimethoxysilane (GPTMS) through copolymerization followed by sol–gel process. The ratio of phosphorus to silicon in the copolymer almost corresponded to the charged molar ratio of VPA to DMEVS when the ratio of VPA to DMEVS was below 1/2. Self-standing, homogeneous, highly transparent membranes were synthesized from DMEVS–VPA copolymer and GPTMS via sol–gel condensation. Differential thermal analysis-thermogravimetry analyses indicated that these membranes were thermally stable up to 200 °C. The results of Fourier transform infrared and 13C NMR revealed that phosphonic acid groups of VPA were chemically bound to organosiloxane network. The copolymerization and condensation of (DMEVS–VPA)/GPTMS were confirmed by 31P and 29Si NMR spectra. The proton conductivity of the hybrid membranes increased with phosphonic acid content. The membrane of (DMEVS–VPA)/GPTMS showed a remarkable conductivity of 6.3 × 10−2 S cm−1 at 130 °C and 100% relative humidity.

Proton-conductive sol–gel membranes from phenylvinylphosphonic acid and organoalkoxysilanes with different functionalities

Novel proton-conductive inorganic–organic hybrid membranes were synthesized from styryl-substituted alkoxysilanes containing different numbers of methoxy groups and phenylvinylphosphonic acid (PhVPA) through the use of radical copolymerization followed by sol–gel process. The substituted alkoxysilanes were copolymerized with phenylvinylphosphonic acid yielding copolymers that were chemically bound with phosphonic acid groups. The mechanical properties and flexibility of these membranes reflected the type of Si–O–Si linkages, which were controlled through the number of alkoxy groups on the Si atoms in the starting organosiloxane compounds. The proton conductivity of the hybrid membranes increased with increasing phosphonic acid content and with decreasing inorganic Si–O cross-linking. The membrane from difunctional methyl (dimethoxy)silylmethylstyrene/PhVPA = 1/4 exhibited a conductivity of 3.4 × 10 −3 S cm −1 under about 19.2% R.H. at 130 °C.

Synthesis of proton-conductive sol–gel membranes from trimethoxysilylmethylstyrene and phenylvinylphosphonic acid

Novel proton-conductive inorganic–organic hybrid membranes were synthesized from (trimethoxysilylmethyl)styrene (TMSMS) and phenylvinylphosphonic acid (PhVPA) mixed at various ratios using radical copolymerization followed by the sol–gel process. Self-standing, homogeneous, highly transparent membranes were synthesized. TG-DTA analysis indicated that these membranes were thermally stable up to 180 °C. FT-IR and 13C NMR revealed that the functionalized alkoxysilane was copolymerized with phenylvinylphosphonic acid. The phosphonic acid groups of the TMSMS/PhVPA copolymer were chemically bound to the organosiloxane network formed via the hydrolysis and polycondensation reaction between the silanol groups of TMSMS. The proton conductivity of the hybrid membranes increased with the phosphonic acid content. The TMSMS/PhVPA membrane of a 1/4 ratio revealed conductivities of 3.7 × 10 −2 S cm −1 under 100% R.H. at 130 °C and 9.5 × 10 −4 S cm −1 under about 19.2% R.H. at 130 °C.

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–H 3PO 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).

Preparation and Characterization of Proton Conductive Phosphosilicate Membranes Based on Inorganic-Organic Hybrid Materials

A series of proton conductive inorganic-organic hybrid membranes doped with phosphoric acid (<TEX>$H_3PO_4$</TEX>) and/or triethylphosphate (PO(OEt)<TEX>$_3$</TEX>) have been prepared by sol-gel process with 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) as precursors. High proton conductivity of 3.0 <TEX>${\times}$</TEX> <TEX>$10^{-3}$</TEX> S/cm with composition of 50TEOS-30GPTMS-20APTES-50<TEX>$H_3PO_4$</TEX> was obtained at 120 <TEX>${^{\circ}C}$</TEX> under 50% relative humidity. Thermal stability of membrane was significantly enhanced by the presence of SiO<TEX>$_2$</TEX> framework up to 250 <TEX>${^{\circ}C}$</TEX>. XRD revealed that the gels are amorphous. IR spectra showed a good complexation of <TEX>$H_3PO_4$</TEX> in the matrix. The conductivity under 75% relative humidity was significantly improved by addition of APTES due to the increase in concentration of defected site in hybrid matrix. The effect of PO(OEt)<TEX>$_3$</TEX>, humidifying time, and heat-treatment were also investigated. PO(OEt)<TEX>$_3$</TEX> had no improvement on conductivity and conductivity increased with humidifying time, however, decreased with heating temperature.

Utilization of glass paper as a support of proton conductive inorganic–organic hybrid membranes based on 3-glycidoxypropyltrimethoxysilane

Proton conductive inorganic–organic membranes supported by glass paper were prepared from 3-glycidoxypropyltrimethoxysilane, tetraethoxysilane and orthophosphoric acid. Hybrid membranes with a thickness of 80 μm were obtained by using 40 μm-thick glass papers. Support of the hybrid membrane by the glass paper enables the formation of the membrane with small thickness and high mechanical strength. The open circuit voltage of the test cell using the membrane supported by the glass paper was 0.75 V and a power density of about 85 mW cm −2 was obtained with current density of 300 mA cm −2 at cell temperature of 130 °C and 7% relative humidity.