Hongtao Li

Jilin University, Yung-chi, Jilin Sheng, China

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Publications (28)63.85 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: With the goal of reducing water swelling and methanol permeability in sulfonated proton exchange membranes (PEM), bromomethylated poly(ether etherketone) was synthesized and used as a macromolecular cross-linker. The cross-linking reaction was performed at 195 °C for 5 h and resulted in cross-linked membranes with high cross-linked density. Compared to the pristine membrane, the cross-linked membranes displayed greatly reduced water uptake and methanol permeability. Other properties of the cross-linked membranes, including proton conductivity, mechanical properties, and oxidative stability, were also investigated and compared with the pristine membrane. All the results indicated that the novel macromolecular cross-linker and the resulting cross-linked membranes are promising for fuelcell applications.
    Journal of Materials Chemistry 03/2011; 21(14):5511-5518. · 5.97 Impact Factor
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    ABSTRACT: Cross-linked polybenzimidazole membranes were obtained by heating at 160 °C, using 4,4′-diglycidyl(3,3′,5,5′-tetramethylbiphenyl) epoxy resin (TMBP) as the cross-linker. The cross-linking reaction temperature was determined by DSC and the successful completion of the cross-linking reaction was shown by FTIR and solubility tests. The cross-linked membranes showed high proton conductivity and strong mechanical properties, as well as low swelling after immersion in 85% phosphoric acid at 90 °C. For instance, the membrane with a cross-linker content weight percent of 20% (PBI-TMBP 20%) with a PA doping level of 4.1 exhibited a proton conductivity of 0.010 S cm−1 and a low swelling volume of 50%. Moreover, the cross-linked membranes showed excellent oxidative stability. The PBI-TMBP 20% cross-linked membrane tested in Fenton's reagent (3% H2O2 solution, 4 ppm Fe2+, 70 °C) kept its shape for more than 480 h and did not break. In particular, the proton conductivity of the PA-PBI-TMBP 20% membrane after Fenton's test (30% H2O2, 20 ppm Fe2+, 85 °C) remained at a high level of 0.009 S cm−1. This investigation proved that cross-linking is a very effective approach for improving the performance of proton exchange membranes.
    Journal of Materials Chemistry 02/2011; 21(7):2187-2193. · 5.97 Impact Factor
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    ABSTRACT: A series of cross-linked membranes based on SPEEK/Nafion have been prepared to improve methanol resistance and dimension stability of SPEEK membrane for the usage in the direct methanol fuel cells (DMFCs). Sulfonated diamine monomer is synthesized and used as cross-linker to improve the dispersion of Nafion in the composite membranes and decrease the negative effect of cross-linking on proton conductivity of membranes. FT-IR analysis shows that the cross-linking reaction is performed successfully. The effects of different contents of Nafion on the properties of cross-linked membranes are investigated in detail. All the cross-linked membranes show lower methanol permeability and better dimensional stability compared with the pristine SPEEK membrane. SPEEK-N30 with the 30 wt % Nafion shows a methanol permeability of 0.73 × 10−6 cm2 s−1 and a water uptake of 24.4% at 25 °C, which are lower than those of the pristine membrane. Meanwhile, the proton conductivity of SPEEK-N30 still remains at 0.041 S cm−1 at 25 °C, which is comparable to that of the pristine SPEEK membrane. All the results indicate that these cross-linked membranes based on SPEEK/Nafion show good prospect for the use as proton exchange membranes.
    Fuel and Energy Abstracts 01/2011; 36(17):11025-11033.
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    ABSTRACT: A series of novel hybrid membranes based on sulfonated poly(arylene ether ketone)s (SNPAEKs), polysiloxane (KH-560) and sulfonated curing agent (BDSA) has been prepared by sol–gel and cross-linking reaction for direct methanol fuel cells (DMFCs). All the hybrid membranes (SKB-xx) show high thermal properties and improved oxidative stability compared with the pristine SNPAEK membrane. The sulfonated cross-linked polysiloxanes networks in the hybrid membranes enhance the mechanical properties and reduce the swelling ratio. The swelling ratio of SKB-20 is 22%, which is much lower than that of the pristine SNPAEK (37%) at 80°C. Meanwhile, SKB-xx membranes with greatly reduced methanol permeabilities show comparative proton conductivities to pristine SNPAEK membranes. Notably, the proton conductivities of SKB-5 and SKB-10 reach to 0.192Scm−1 and 0.179Scm−1 at 80°C, respectively, which are even higher than the 0.175Scm−1 of SNPAEK.
    Lancet. 01/2011; 196(14):5803-5810.
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    ABSTRACT: In order to enhance the ion exchange capacity (IEC) in the proton exchange membrane materials, a novel sulfonated poly(arylene ether ketone) (SQNPAEK) containing tri-side chains in one unit is synthesized by direct polymerization. The SQNPAEK membrane shows excellent proton conductivity up to 0.102 S cm−1 at 80°C, which are superior to previous side-chain-type and main-chain-type sulfonated polymer membranes at similar IEC. Cross-linked membranes are then obtained by a heating reaction at 190°C, using 4,4’-diglycidyl (3,3’,5,5’-tetramethylbiphenyl) epoxy resin (TMBP) as the cross-linker. As expected, the water uptake and the methanol permeability of the cross-linked membranes decrease with increasing the content of TMBP. Compared to Nafion 117, the cross-linked membranes show comparable proton conductivities and much higher selectivities, which are in the range of 5.18×105∼1.46×106 S s−1cm3. Other properties of the cross-linked membranes, such as mechanical properties, thermal properties, are also investigated. All the results indicated that the cross-linked membranes based on SQNPAEKs and TMBP are promising candidate for direct methanol fuel cells.
    Lancet. 01/2011;
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    ABSTRACT: An approach has been proposed to prepare the reinforced phosphoric acid (PA) doped cross-linked polybenzimidazole membranes for high temperature proton exchange membrane fuel cells (HT-PEMFCs), using 1,3-bis(2,3-epoxypropoxy)-2,2-dimethylpropane (NGDE) as the cross-linker. FT-IR measurement and solubility test showed the successful completion of the crosslinking reaction. The resulting cross-linked membranes exhibited improved mechanical strength, making it possible to obtain higher phosphoric acid doping levels and therefore relatively high proton conductivity. Moreover, the oxidative stability of the cross-linked membranes was significantly enhanced. For instance, in Fenton’s reagent (3% H2O2 solution, 4 ppm Fe2+, 70 °C), the cross-linked PBI-NGDE-20% membrane did not break into pieces and kept its shape for more than 480 h and its remaining weight percent was approximately 65%. In addition, the thermal stability was sufficient enough within the operation temperature of PBI-based fuel cells. The cross-linked PBI-NGDE-X% (X is the weight percent of epoxy resin in the cross-linked membranes) membranes displayed relatively high proton conductivity under anhydrous conditions. For instance, PBI-NGDE-5% membrane with acid uptake of 193% exhibited a proton conductivity of 0.017 S cm−1 at 200 °C. All the results indicated that it may be a suitable candidate for applications in HT-PEMFCs.
    Fuel and Energy Abstracts 01/2011; 36(14):8412-8421.
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    ABSTRACT: A novel benzimidazole trimer (alkyl-BI) was synthesized using 3,3′-diaminobenzidine and succinic acid as monomers, and then a series of cross-linked membranes (c-SPEEK-Xs) were prepared by a heating method using the alkyl-BI as the cross-linker. We systematically studied the water uptake and swelling ratio, thermal and chemical stability, mechanical properties, proton conductivity, and methanol permeability of the cross-linked membranes as a function of different loading ratios of the alkyl-BI trimer. All of the properties of the cross-linked membranes were significantly improved over membranes consisting of unmodified SPEEK. In particular, the performance of the c-SPEEK-Xs membranes was compared to that of a cross-linked membrane, c-SPEEK-BI7, which was prepared by using rigid-BI as the cross-linker. The latter cross-linker was synthesized by using 3,3′-diaminobenzidine and isophthalic acid as monomers in order to investigate how cross-linkers with different structures affect the morphology and properties of the membranes. Transmission electron microscopy (TEM) analysis showed that c-SPEEK-BI7 and the c-SPEEK-6.5% possess different hydrophilic/hydrophobic two-phase separation morphologies, which have dramatic effects on the proton conductivity and methanol permeability.
    Fuel and Energy Abstracts 01/2011; 36(3):2197-2206.
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    ABSTRACT: A diamine-terminated polybenzimidazole oligomer (o-PBI) has been synthesized for introducing the benzimidazole groups (BI) into sulfonated poly(ether ether ketone) (SPEEK) membranes. SPEEK/o-PBI/4,4′-diglycidyl(3,3′,5,5′-tetramethylbiphenyl) epoxy resin (TMBP) composite membranes in situ polymerization has been prepared for the purpose of improving the performance of SPEEK with high ion-exchange capacities (IEC) for the usage in the direct methanol fuel cells (DMFCs). The composite membranes with three-dimensional network structure are obtained through a cross-linking reaction between PBI oligomer and TMBP and the acid–base interaction between sulfonic acid groups and benzimidazole groups. Resulting membranes show a significantly increasing of all of the properties, such as high proton conductivity (0.14Scm−1 at 80°C), low methanol permeability (2.38×10−8cm2s−1), low water uptake (25.66% at 80°C) and swelling ratio (4.11% at 80°C), strong thermal and oxidative stability, and mechanical properties. Higher selectivity has been found for the composite membranes in comparison with SPEEK. Therefore, the SPEEK/o-PBI/TMBP composite membranes show a good potential in DMFCs usages.
    Lancet. 01/2011; 196(23):9916-9923.
  • Journal of Polymer Science Part A Polymer Chemistry 10/2010; 48(24):5824 - 5832. · 3.54 Impact Factor
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    ABSTRACT: A series of SPEEK/HPW/Ppy-n composite membranes with a sandwich structure were successfully prepared by surface modification with polypyrrole (Ppy) in order to stabilize phosphotungstic acid (HPW) in poly(ether ether ketone)s (SPEEKs) and reduce the methanol crossover. Ppy coatings with a large number of secondary ammoniumgroups (NH2+) interact with anions of HPW to decrease HPWleaching from the membrane. In addition, the hydrophobic Ppy layers allow for little methanoltransport, which leads to a significant decline in methanol crossover with reasonable levels of proton conductivity. The properties of the membranes were investigated in detail by UV, SEM, ac impedance, and TGA. As observed, Ppy-modified membranes were better at immobilizing HPW and exhibited higher selectivities than previously reported SPEEK/HPW composite membranes. All the results indicate that the SPEEK/HPW/Ppy-n composite membranes are excellent candidates for direct methanolfuelcells.
    Journal of Materials Chemistry 10/2010; 20(41):9239-9245. · 5.97 Impact Factor
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    ABSTRACT: A carboxyl-terminated benzimidazole trimer was synthesized as a crosslinker by controlling the ratio of 3,3′-diaminobenzidine and isophthalic acid. Composite membranes were obtained by mixing the benzimidazole trimer and sulfonated poly(ether ether ketone) (SPEEK) together. Cross-linked membranes were obtained by heating the composite membranes at 160 °C. All of the properties of the cross-linked membranes were significantly increased, including proton conductivity, methanol permeability and water uptake due to the more compact structure compared to the non-cross-linked membranes. The cross-linked SPEEK-BI7 and cross-linked SPEEK-BI11 had excellent proton conductivities (0.22 and 0.19 S cm−1) at 80 °C, which were higher than that of Nafion 117 (0.125 S cm−1). Transmission electron microscopy (TEM) analysis revealed a clear microphase separated structure of cross-linked membranes. Other properties, such as thermal and mechanical stability, required for use as a proton exchange membrane (PEM) have been investigated. The cross-linked membranes showed improved properties over membranes without crosslinking.
    Journal of Materials Chemistry 01/2010; 20(16). · 5.97 Impact Factor
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    ABSTRACT: Proton exchange membranes with high dimensional stabilities and low water uptakes were constructed by incorporating phosphotungstic acid (PWA) into a cross-linked network composed of a crosslinkable sulfonated poly(ether ether ketone) containing dipropenylgroups (SDPEEK) and γ-methacryloxypropyltrimethoxysilane (KH570). The chemical structures of the hybrid membranes were confirmed by FT-IR spectroscopy and scanning electron microscopy (SEM). The results indicated that PWA particles were well dispersed in these membranes. The influences of the dispersed PWA on the properties of membranes such as thermal stability, water uptake, swelling ratio, proton conductivity, methanol permeability and mechanical property were researched. The addition of KH570-5/PWA in the hybrid membranes contributed to the improvement of the dimensional stabilities. And the hybrid membranes with 10–40wt% PWA showed higher proton conductivities than Nafion 117 at 80 °C, while the methanol permeabilities of these membranes were much lower than that of Nafion 117. The membranes also exhibited excellent mechanical properties. These results imply that the SDPEEK/KH570-5/PWA-xmembranes are promising materials in the direct methanolfuelcells (DMFC) applications.
    Journal of Materials Chemistry 01/2010; 20(30). · 5.97 Impact Factor
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    ABSTRACT: Sulfonated poly(arylene ether ketone) bearing pendant carboxylic acid group (C-SPAEK) had been prepared for direct methanol fuel cell applications, and subsequently cross-linked by a thermal curing reaction using hexafluoro-bisphenol-A novolac epoxy resin (HFANER) as a cross-linker. The cross-linked network structure caused significant enhancement in the mechanical properties and oxidative stability. Meanwhile, water uptake, swelling ratio and methanol permeability substantially decreased with increasing the content of cross-linker. Notably, the water uptake of C-SPAEK was 506.9% at 80 °C, but after cross-linking, Cr-SPAEK-17 exhibited a water uptake of 32.3%. Meanwhile, a 12.1% of swelling ratio was obtained which was lower than that of Nafion 117 (17.2%). Although the proton conductivities of the cross-linked membranes were lower than that of the pristine membrane, the higher selectivity defined as the proton conductivity to methanol permeability was obtained for the cross-linked membranes.
    International Journal of Hydrogen Energy. 01/2010;
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    ABSTRACT: A series of cross-linkable sulfonated poly(arylene ether ketone)s bearing carboxylic acid groups (C-SPAEKs) have been prepared for direct methanol fuel cells (DMFCs). The chemical structure of the cross-linkable copolymers was analyzed by 1H NMR and 13C NMR spectra. Cross-linked membranes were obtained by thermal curing cross-linkable copolymers. The cross-linked network structure caused significant enhancement in the mechanical properties and large reduction in water uptake (WU), swelling ratio and methanol permeability of the membranes. The water uptake and methanol permeability of C-SPAEK-50 membrane was 506.9% (80 °C) and 14.83 × 10−7 cm2/s, but after cross-linking they reduced to 75.2% and 1.74 × 10−7 cm2/s, while maintaining proton conductivity of 0.197 S/cm, which was higher than 0.146 S/cm of Nafion 117.
    Journal of Membrane Science. 01/2010;
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    ABSTRACT: A novel poly(ether ether ketone) (PEEK) containing pendant carboxyl groups has been synthesized by a nucleophilic polycondensation reaction. Sulfonated polymers (SPEEKs) with different ion exchange capacity are then obtained by post-sulfonation process. The structures of PEEK and SPEEKs are characterized by both FT-IR and 1H NMR. The properties of SPEEKs as candidates for proton exchange membranes are studied. The cross-linking reaction is performed at 140°C using poly(vinyl alcohol) (PVA) as the cross-linker. In comparison with the non-cross-linked membranes, some properties of the cross-linked membranes are significantly improved, such as water uptake, methanol resistance, mechanical and oxidative stabilities, while the proton conductivity decreases. The effect of PVA content on proton conductivity, water uptake, swelling ratio, and methanol permeability is also investigated. Among all the membranes, SPEEK-C-8 shows the highest selectivity of 50.5×104Sscm−3, which indicates that it is a suitable candidate for applications in direct methanol fuel cells.
    Journal of Power Sources 01/2010; 195(19):6443-6449. · 4.68 Impact Factor
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    ABSTRACT: Sulfonated poly(ether ether ketone) containing hydroxyl groups (SPEEK-OH) has been prepared for use as a proton exchange membrane (PEM) by reducing the carbonyl groups on the main chain of the polymers. With the goal of reducing water uptake and methanol permeability, a facile thermal-cross-linking process is used to obtain the cross-linked membranes. The properties of the cross-linked membranes with different cross-linked density are measured and compared with the pristine membrane. Notably, SPEEK-4 with the highest cross-linked density shows a water uptake of 39% and a methanol permeability of 2.52×10−7cm2s−1, which are much lower than those of the pristine membrane (63.2% and 5.37×10−7cm2s−1, respectively). These results indicate that this simple approach is very effective to prepare cross-linked proton exchange membranes for reducing water uptake and methanol permeability.
    Journal of Power Sources 01/2010; 195(24):8061-8066. · 4.68 Impact Factor
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    ABSTRACT: Poly(ether ether ketone) (PEEK) and sulfonated poly(ether ether ketone) (SPEEK, IEC = 2.07 mequiv.g−1) have been synthesized via nucleophilic aromatic substitution reaction. Bromomethylated poly(ether ether ketone) (PEEK-Br) is then prepared and reacted with 2-benzimidazolethiol to obtain the benzimidazole grafted poly(ether ether ketone) (PEEK-BI). The structures of PEEK-Br and PEEK-BI are characterized by 1H NMR spectra. Composite membranes based on SPEEK and PEEK-BI are prepared and their properties used for fuel cells are studied in detail. The results show that the composite membranes exhibit greatly improved mechanical properties as well as reduced water uptake and methanol permeability compared with the pristine SPEEK membrane. The increased oxidative stability and selectivity indicate that the composite membranes are promising to be used as proton exchange membranes.
    International Journal of Hydrogen Energy. 01/2010;
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    ABSTRACT: To prepare a cross-linked hybrid proton exchange membrane with high mechanical and oxidative stability, a silane monomer, namely 3-glycidoxypropyltrimethoxysilane (KH-560), is first grafted to sulfonated poly(arylene ether ether ketone)s bearing carboxyl groups (SPAEK-C) and hydrolysis–condensation is then performed on the grafted membranes to make them cross-link. 1H NMR measurements and Fourier transform infrared spectroscopy are used to characterize and confirm the structures of SPAEK-Cs and hybrid polymer electrolyte membranes, respectively. The Si–O–Si cross-linking structure enhances the stability of the PEM greatly. The proton conductivities of the hybrid membranes with 5% KH-560 in weight reach 0.155Scm−1 at 80°C which is comparable to that of Nafion® membranes. The ion-exchange capacity, water uptake and swelling, methanol permeability, mechanical properties are investigated to confirm their applicability in fuel cells.
    Journal of Power Sources 01/2010; 195(3):762-768. · 4.68 Impact Factor
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    ABSTRACT: A series of novel side-chain-type sulfonated hydroxynaphthalene poly(aryl ether ketone)s (SHNPAEKs) containing hydroxyl groups was synthesized by post grafted method and the sulfonated degree (Ds) of the polymers could be well controlled. The resulting polymers were characterized by 1H NMR, FT-IR and thermogravimetric analysis (TGA). Meanwhile, the membrane properties for fuel cell applications such as water uptake, proton conductivity and methanol transport have been studied. The influence of pendent structure and inter-/intramolecular H-bonded to the properties of SHNPAEKs has been investigated. The proton conductivities of SHNPAEK membranes showed a range of 0.020–0.197 S/cm and the highest conductivity of 0.197 S/cm was obtained for SHNPAEK-90 (IEC = 2.08 meq./g) at 80 °C. The methanol permeability of SHNPAEK membranes was in the range from 2.65 × 10−7 to 11.9 × 10−7 cm2/s, which was much lower than that of Nafion 117.
    Polymer. 01/2010; 51(14):3047-3053.
  • Journal of Polymer Science Part A Polymer Chemistry 09/2009; 47(21):5772 - 5783. · 3.54 Impact Factor