Abstract
A proton exchange composite membrane (PECM) and a method of synthesizing the membrane are disclosed. The PECM may include a PBI membrane doped with an acid, an imidazolium-based dicationic ionic liquid, and a mesoporous material. This PECM can be used as an improved high-temperature polymer electrolyte membrane (HT-PEM) fuel cell. The disclosed fuel cell can provide improved proton conductivity, acid uptake, and thermal stability.
Claims
1. A method for synthesizing a proton exchange composite membrane, the method comprising: preparing a PBI solution by dissolving PBI powder in a solvent; adding an imidazolium-based dicationic ionic liquid to the PBI solution to obtain a second solution, the imidazolium-based dicationic ionic liquid comprising two singly charged imidazolium cations linked by an alkyl chain spacer, the singly charged imidazolium cations paired with two singly charged anions, wherein a molar ratio of the PBI to the imidazolium-based dicationic ionic liquid is between 2:1 and 9:1, the molar ratio calculated based on molecular weight of the repeating unit of PBI; dispersing a mesoporous material in the second solution to obtain a third solution, wherein the mesoporous material is present at an amount ranging between 5 and 15 percent of a total weight of the PBI; casting the third solution; removing a solvent from the third solution to obtain a composite membrane; and doping the composite membrane with an acid.
2. The method of claim 1, wherein the imidazolium-based dicationic ionic liquid includes anions selected from the group consisting of CH.sub.3CO.sub.2, CH.sub.3SO.sub.4, C(CF.sub.3SO.sub.2).sub.2, (Tf.sub.2N)N(CF.sub.3SO.sub.2).sub.2, (TfO)CF.sub.3SO.sub.2, BF.sub.4, PF.sub.6, ASF.sub.6, SbF.sub.6, CF.sub.3CO.sub.2, and AlCl.sub.4.
3. The method of claim 1, wherein the imidazolium-based dicationic ionic liquid is selected from the group consisting of 1,3-di(3-methylimidazolium) propane bis (trifluoromethyl sulfonyl) imide, 1,6-di(3-methylimidazolium) hexane bis (hexafluorophosphate), 1,5 bis (3-benzyl-2-methyimidazolium) pentane di-bis (trifloromethanesulfonyl) imide, 1,5 bis (3-methyl-2-phenylimidazolium) pentane di-bis (trifloromethanesulfonyl) imide, 1,5 bis (2,3-dimethylimidazolium) pentane di-bis (trifloromethanesulfonyl) imide, 1,10 bis (2,3-methylimidazolium) decane di-bis (trifluoromethanesulfonyl) imide, 1,10 bis (2,3-dimethylimidazolium) decane di-bis (trifluoromethanesulfonyl) imide and combinations thereof.
4. The method of claim 1, wherein the imidazolium-based dicationic ionic liquid is selected from the group consisting of 1,3-di(3-methylimidazolium) propane bis (trifluoromethylsulfonyl) imide, 1,6-di(3-methylimidazolium) hexane bis (hexafluorophosphate), and combinations thereof.
5. The method of claim 1, wherein the mesoporous material is selected from the group consisting of SBA-15, SBA-16, MCM-41, and MCM-48.
6. The method of claim 1, wherein the mesoporous material is selected from the group consisting of mesoporous SBA-15 silica sulfonic acid and mesoporous SBA-15 silica phenyl sulfonic acid.
7. The method of claim 1, wherein doping the composite membrane includes using a phosphoric acid.
8. The method of claim 7, wherein the composite membrane is doped with phosphoric acid at a concentration of 85 wt % over approximately 5 days.
9. The method of claim 7, wherein the casting the third solution includes casting onto glass plates by a film applicator.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The drawing figures depict one or more implementations in accord with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.
(2) FIG. 1 depicts a method for synthesizing a composite proton exchange membrane according to one or more implementations of the present disclosure;
(3) FIG. 2 illustrates a structure of 1,3-di(3-methylimidazolium) propane bis (trifluoromethylsulfonyl) imide and a structure of 1,6-di(3-methylimidazolium) hexane bis (hexafluorophosphate);
(4) FIG. 3 presents an attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectra of mesoporous SBA-15-Ph-SO.sub.3H and four composite membranes of SBA.sub.11-PDC.sub.34, SBA.sub.9-PDC.sub.64, SBA.sub.9-PMC.sub.63 and SBA.sub.4-PMC.sub.43, according to one or more implementations of the present disclosure;
(5) FIG. 4 is a proton conductivity plot of SBA.sub.y-PPDC.sub.34 and SBA.sub.y-PPMC.sub.63 composite membranes and PA-PBI, PPDC.sub.34 and PPMC.sub.63 composite membranes versus SBA-15-Ph-SO.sub.3H content, according to one implementation of the present disclosure;
(6) FIG. 5 presents scanning electron microscope with energy dispersive X-ray spectroscope (SEM-EDX) images of SBA.sub.11-PDC.sub.34 and SBA.sub.15-PDC.sub.34, according to one implementation of the present disclosure;
(7) FIG. 6 shows SEM-EDX images of SBA.sub.9-PMC.sub.63 and SBA.sub.13-PMC.sub.63, according to one implementation of the present disclosure;
(8) FIG. 7 shows PA.sub.dop versus SBA-15-Ph-SO.sub.3H content plots of SBA.sub.y-PPDC.sub.34, SBA.sub.y-PPMC.sub.63, PA-PBI, PPDC.sub.34, and PPMC.sub.63 composite membranes, according to one or more implementations of the present disclosure;
(9) FIG. 8 is a proton conductivity plot of SBA.sub.y-PPDC.sub.64, SBA.sub.y-PPMC.sub.43, PA-PBI, PPDC.sub.64, and PPMC.sub.43 composite membranes versus SBA-15-Ph-SO.sub.3H content, according to one or more implementations of the present disclosure;
(10) FIG. 9 shows SEM-EDX images of SBA.sub.9-PDC.sub.64 and SBA.sub.13-PDC.sub.64, according to one implementation of the present disclosure;
(11) FIG. 10 shows SEM-EDX images of SBA.sub.7-PMC.sub.43 and SBA.sub.11-PMC.sub.43, according to one implementation of the present disclosure;
(12) FIG. 11 shows PA.sub.dop versus SBA-15-Ph-SO.sub.3H content plots of SBA.sub.y-PPDC.sub.64, SBA.sub.y-PPMC.sub.43, PA-PBI, PPDC.sub.64, and PPMC.sub.43 composite membranes, according to one or more implementations of the present disclosure;
(13) FIG. 12A shows Arrhenius plots of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes, according to one implementation of the present disclosure;
(14) FIG. 12B shows Arrhenius plots of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes, according to one implementation of the present disclosure;
(15) FIG. 13A shows time stability plot of proton conductivity for SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 at 180 C., according to one implementation of the present disclosure;
(16) FIG. 13B shows time stability plot of proton conductivity for SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 at 180 C., according to one implementation of the present disclosure;
(17) FIG. 14A shows mechanical stability plots for SBA.sub.y-PPDC.sub.34 composite membrane, according to one implementation of the present disclosure;
(18) FIG. 14B shows mechanical stability plots for SBA.sub.y-PPMC.sub.63 composite membrane, according to one implementation of the present disclosure;
(19) FIG. 15A shows mechanical stability plots for SBA.sub.y-PPDC.sub.64 composite membrane, according to one implementation of the present disclosure;
(20) FIG. 15B shows mechanical stability plots for SBA.sub.y-PPMC.sub.43 composite membrane, according to one implementation of the present disclosure;
(21) FIGS. 16A-16C show polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes in the temperature range of 80-180 C., according to one implementation of the present disclosure;
(22) FIG. 16D-16F show polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes in the temperature range of 80-180 C., according to one implementation of the present disclosure;
(23) FIG. 17 shows polarization curves for Nafion 117 membrane at 80 C., 90 C., 100 C. and 120 C., according to one implementation of the present disclosure;
(24) FIG. 18A shows power density plots of PPDC.sub.34, PPMC.sub.63, SBA.sub.11-PPDC.sub.34, SBA.sub.9-PPMC.sub.63 composite membranes along with power density plots of Nafion and PA-PBI at 0.5 V, according to one implementation of the present disclosure;
(25) FIG. 18B shows power density plots of PPDC.sub.64, PPMC.sub.43, SBA.sub.9-PPDC.sub.64, SBA.sub.7-PPMC.sub.43 composite membranes along with power density plots of Nafion and PA-PBI at 0.5 V, according to one implementation of the present disclosure;
(26) FIG. 19A shows a life test result of PPDC.sub.34 membrane unit cell operated at 180 C. under a constant current loading of 0.4 A/cm.sup.2, according to one implementation of the present disclosure; and
(27) FIG. 19B shows a life test result of SBA.sub.11-PPDC.sub.34 membrane unit cell operated at 180 C. under a constant current loading of 0.4 A/cm.sup.2, according to one implementation of the present disclosure.
DETAILED DESCRIPTION
(28) The following detailed description is presented to enable a person skilled in the art to make and use the methods and devices disclosed in exemplary embodiments of the present disclosure. For purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required to practice the disclosed exemplary embodiments. Descriptions of specific exemplary embodiments are provided only as representative examples. Various modifications to the exemplary implementations will be readily apparent to one skilled in the art, and the general principles defined herein may be applied to other implementations and applications without departing from the scope of the present disclosure. The present disclosure is not intended to be limited to the implementations shown, but is to be accorded the widest possible scope consistent with the principles and features disclosed herein. In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.
(29) The following disclosure describes a composite proton exchange membrane and a method for preparing the composite proton exchange membrane, where the membrane may include polybenzimidazole (PBI) doped with an acid, a dicationic ionic liquid including imidazolium cations, and a mesoporous material.
(30) In order to provide the reader with an overview, FIG. 1 illustrates a method 100 for synthesizing a composite proton exchange membrane according to one or more implementations of the present disclosure. In one implementation, the method 100 may include a first step 101 of preparing a PBI solution by dissolving PBI powder in a solvent; a second step 102 of adding a dicationic ionic liquid to the PBI solution to obtain a second solution; a third step 103 of dispersing a mesoporous material in the second solution to obtain a third solution; a fourth step 104 of casting the third solution; a fifth step 105 of removing the solvent from the third solution to obtain a composite membrane; and a sixth step 106 of doping the composite membrane with an acid. Additional details regarding these steps are provided below.
(31) With respect to the first step 101, in some implementations, the preparation of the PBI solution may involve dissolving the PBI powder in an organic solvent such as dimethylacetamide (DMAc) under a nitrogen atmosphere at a temperature of approximately 150 C. According to one implementation, the PBI solution may have a concentration of at least 2 wt %.
(32) Furthermore, in some implementations, in the second step 102 of method 100, a dicationic ionic liquid (IL) may be added to the PBI solution to obtain a second solution containing PBI and the dicationic ionic liquid with a PBI to IL molar ratio between 2:1 and 9:1.
(33) According to one implementation, the addition of dicationic IL to the PBI solution may be followed by rigorous stirring at a temperature of approximately 35 C. for a predetermined amount of time, for example 24 h.
(34) With respect to the second step 102, according to some implementations, the dicationic IL may be a dicationic IL that includes imidazolium cations. A dicationic IL that includes imidazolium cations is referred to herein as imidazolium-based dicationic IL. The imidazolium-based dicationic IL may have different anions such as CH.sub.3CO.sub.2, CH.sub.3SO.sub.4, C(CF.sub.3SO.sub.2).sub.2, (Tf.sub.2N) N(CF.sub.3SO.sub.2).sub.2, (TfO) CF.sub.3SO.sub.2, BF.sub.4, PF.sub.6, ASF.sub.6, SbF.sub.6, CF.sub.3CO.sub.2, AlCl.sub.4 and the like. For example, the imidazolium-based IL may be 1,3-di(3-methylimidazolium) propane bis (trifluoromethylsulfonyl) imide, 1,6-di(3-methylimidazolium) hexane bis (hexafluorophosphate), 1,5 bis (3-benzyl-2-methyimidazolium) pentane di-bis (trifloromethanesulfonyl) imide, 1,5 bis (3-methyl-2-phenylimidazolium) pentane di-bis (trifloromethanesulfonyl) imide, 1,5 bis (2,3-dimethylimidazolium) pentane di-bis (trifloromethanesulfonyl) imide, 1,10 bis (2,3-methylimidazolium) decane di-bis (trifluoromethanesulfonyl) imide, 1,10 bis (2,3-dimethylimidazolium) decane di-bis (trifluoromethanesulfonyl) imide or a combination thereof.
(35) In addition, according to some implementations, the third step 103 may involve dispersing a mesoporous material such as mesoporous silica in the second solution to obtain a third solution. For example, a mesoporous silica such as SBA-15, SBA-16, MCM-41, or MCM-48 may be dispersed in the second solution. According to one implementation, functionalized mesoporous silica, such as mesoporous SBA-15 silica sulfonic acid or mesoporous SBA-15 silica phenyl sulfonic acid (SBA-15-Ph-SO.sub.3H) may be dispersed in the second solution with, for example, an ultrasonic probe. According to some implementations, the mesoporous material may be dispersed in the second solution with a weight percent of mesoporous material/PBI between about 5 and 15.
(36) With respect to fourth step 104, in one implementation, the third solution may be cast or otherwise coated on a glass plate using a film applicator to form a thin film of the third solution. In fifth step 105, in some implementations, the solvent in the thin film of the third solution may be removed by heating the film of the third solution and thereby evaporating the solvent. According to one implementation, the thin film of the third solution may be heated at a temperature of approximately 80 C. for about 16 h and then at a temperature of 120 C. for 5 h under vacuum in order to remove the solvent and obtain the composite membrane.
(37) Referring again to FIG. 1, according to one implementation, after removing the solvent from the third solution and obtaining the composite membrane, method 100 may proceed to the sixth step 106. In some implementations, the sixth step 106 may involve doping the composite membrane with an acid such as phosphoric acid for a predetermined amount of time to obtain the composite proton exchange membrane of the present disclosure. According to one implementation, the composite membrane may be doped with phosphoric acid with a concentration of about 85% for around 5 days.
(38) In some implementations, the composite proton exchange membrane that may be synthesized as described in detail in connection with method 100 of FIG. 1 may include PBI doped with phosphoric acid, an imidazolium-based dicationic IL, and a functionalized mesoporous silica. An imidazolium-based dicationic IL includes two singly charged imidazolium cations that are linked by an alkyl chain spacer and are paired with two singly charged anions.
(39) For example, FIG. 2 illustrates a structure 201 of 1,3-di(3-methylimidazolium) propane bis (trifluoromethylsulfonyl) imide (referred to herein as DC.sub.3) and a structure 202 of 1,6-di(3-methylimidazolium) hexane bis (hexafluorophosphate) (referred to herein as DC.sub.6). In FIG. 2, structure 201 includes two singly charged imidazolium cations 204 that are linked by an alkyl chain spacer 205 to compose a doubly charged cation 203. The two singly charged imidazolium cations 204 are paired with two singly charged Bis (trifluoromethanesulfonyl) imide (Tf.sub.2N) anions 206 to form the DC.sub.3 ionic liquid. With further reference to FIG. 2, structure 202 also includes two singly charged imidazolium cations 204 that are linked by an alkyl chain spacer 207 to compose a doubly charged cation 208. The two singly charged imidazolium cations 204 are paired with two singly charged bis (hexafluorophosphate) (PF.sub.6) anions 209 to form the DC.sub.6 ionic liquid. It should be understood that the imidazolium-based dicationic IL may include different anions such as CH.sub.3CO.sub.2, CH.sub.3SO.sub.4, C(CF.sub.3SO.sub.2).sub.2, (Tf.sub.2N) N(CF.sub.3SO.sub.2).sub.2, (TfO) CF.sub.3SO.sub.2, BF.sub.4, PF.sub.6, ASF.sub.6, SbF.sub.6, CF.sub.3CO.sub.2, AlCl.sub.4 and the like.
(40) In some implementations, the composite proton exchange membrane that may be synthesized as described in detail in connection with method 100 of FIG. 1 may have a general formula of SBA.sub.y-(PA-PBI) DCIL.sub.x, where SBA represents the functionalized mesoporous silica. In different implementations, the functionalized mesoporous silica may be for example a mesoporous SBA-15 silica sulfonic acid or a mesoporous SBA-15 silica phenyl sulfonic acid. PA-PBI represents the PBI doped with phosphoric acid and DCIL represents the imidazolium-based dicationic IL. In the formula, y is weight ratio of functionalized mesoporous silica to PBI and x is mole ratio of PBI/IL. According to one implementation, y may have a value between about 5 and 15 and x may have a value between about 2 and 9.
Example
(41) In the following example, four different composite proton exchange membranes were synthesized by the method 100 of FIG. 1. SBA-15-Ph-SO.sub.3H were used as the functionalized mesoporous silica and two types of dicationic ionic liquids DC.sub.3, DC.sub.6, as well as two types of monocationic ionic liquids 1-hexyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (referred to herein as MC.sub.6) and 1-butyl-3-methylimidazolium hexafluorophosphate) (referred to herein as MC.sub.4) were used as the ionic liquid for synthesizing the four different composite proton exchange membranes.
(42) In order to synthesize the composite proton exchange membranes, PBI powder was first dissolved in DMAc under a nitrogen atmosphere at 150 C. to obtain a PBI solution with a concentration of 2 wt %. Then DC.sub.3, DC.sub.6, MC.sub.4, and MC.sub.6 ionic liquids were added to the PBI solutions in four separate containers to obtain four different second solutions. The four second solutions were vigorously stirred for approximately 24 hours at 35 C. Following this step, different amounts of mesoporous SBA-15-Ph-SO.sub.3H were dispersed in the four second solutions using an ultrasonic bath. The obtained solutions were then directly cast onto glass plates by a film applicator. The cast solutions were heated at 80 C. for approximately 16 hours and then at 120 C. for 5 hours under vacuum to remove DMAc solvent to obtain four membranes SBA.sub.y-PDC.sub.3x, SBA.sub.y-PDC.sub.6x, SBA.sub.y-PMC.sub.6x and SBA.sub.y-PMC.sub.4x. The obtained four membranes were then doped with phosphoric acid (PA) with a concentration of 85 wt % for approximately 5 days to obtain doped composite membranes that are referred to herein as SBA.sub.y-PPDC.sub.3x, SBA.sub.y-PPDC.sub.6x, SBA.sub.y-PPMC.sub.6x and SBA.sub.y-PPMC.sub.4x. Here, x represents mole ration of PBI/ionic liquid. In this example, for dicationic ionic liquids DC.sub.3 and DC.sub.6, x is chosen to be 4 and for monocationic ionic liquids MC.sub.4 and MC.sub.6, x is chosen to be 3. Furthermore, y represents weight ratio of PBI/mesoporous SBA-15-Ph-SO.sub.3H. Consequently, the obtained composite membranes before doping with PA are referred to as SBA.sub.11-PDC.sub.34, SBA.sub.9-PDC.sub.64, SBA.sub.9-PMC.sub.63 and SBA.sub.7-PMC.sub.43, and doped composite membranes in this example are referred to as SBA.sub.11-PPDC.sub.34, SBA.sub.9-PPDC.sub.64, SBA.sub.9-PPMC.sub.63 and SBA.sub.7-PPMC.sub.43.
(43) Referring now to FIG. 3, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectra of mesoporous SBA-15-Ph-SO.sub.3H and four composite membranes of SBA.sub.11-PDC.sub.34, SBA.sub.9-PDC.sub.64, SBA.sub.9-PMC.sub.63 and SBA.sub.7-PMC.sub.43 are shown. The presence of sulfonic acid group in the composite membranes may be confirmed by the absorption bands assigned to the sulfonic acid group at 1145 cm.sup.1 (asymmetric OSO stretch), 1030 cm.sup.1 (SO stretch), and 830 cm.sup.1 (SO stretch). The 1050 and 800 cm.sup.1 regions correspond to SiOSi and SiOSi stretching of the silicate network, respectively. The peak at 880-920 cm.sup.1 corresponds to the SiOH stretching vibration of the hydrogen-bonded silanol groups in SBA-15. The peaks of single substituted phenyl group also appear at 740 and 700 cm.sup.1, respectively. The band at 1000-1250 cm-1 may be attributed to the stretching of the Tf.sub.2N anion in composite membranes. The peak around 1445 cm.sup.1 may suggest deformation of benzimidazole Breathing mode of imidazole rings of the PBI membrane. The peak at 1600 cm.sup.1 may be assigned to the CC and CN stretching groups and the peak at 2900 cm.sup.1 may be assigned to the stretching vibration of aromatic CH groups.
(44) The proton conductivities of the composite membranes were evaluated by in-plane measurements using four-point-probe AC impedance spectroscopy. Measurements were carried out with a PGSTAT303N potentiostat/galvanostat (Ecochemie) with a frequency range of 100 Hz to 1 MHz and voltage amplitude of 50 mV. Temperature was controlled using a Globe Tech Computer Cell GT fuel cell test station. It is generally believed that the in-plane conductivity measurements are easier to carry out and provide greater accuracy due to the larger cell constant, L/A, where L is the distance between electrodes, usually several millimeters, and A is the cross-sectional area of the sample. Conductivity measurements of DC.sub.6 and MC.sub.4 ILs in PA solution (Purity: 85%) were carried out using Thermo Fisher Scientific/Eutech Instrument PC700 pH/mV/Conductivity meter.
(45) FIG. 4 is a proton conductivity plot of SBA.sub.y-PPDC.sub.34 and SBA.sub.y-PPMC.sub.63 composite membranes and PA-PBI, PPDC.sub.34 and PPMC.sub.63 composite membranes versus SBA content which is represented by y. PA-PBI is a PBI membrane doped with PA, PPDC.sub.34 and PPDC.sub.63 are composite membranes containing dicationic ionic liquids DC.sub.3 and DC.sub.4 to which no mesoporous silica were added.
(46) As shown in FIG. 4, proton conductivity of PA-PBI membrane was 3.1 mS/cm in 25 C. The SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes displayed a higher proton conductivity compared to the PA-PBI membranes. This improvement may be attributed to the hygroscopic nature and high surface area of mesoporous SBA-15-Ph-SO.sub.3H. Presence of highly hydrophilic mesoporous SBA-15-Ph-SO.sub.3H within the matrix of the composite membranes may increase the PA uptake ability of composite membranes to a higher amount compared to that of PBI membranes. High surface area of SBA-15-Ph-SO.sub.3H mesoporous provides hydrogen bond interactions between mesoporous silica, ionic liquids, PA and PBI in composite membranes. The pore size of SBA-15-Ph-SO.sub.3H mesoporous is 4.8 nm and may play a relatively important role in increasing the proton conductivity of composite membranes. The SBA.sub.y-PPDC.sub.34 composite membranes demonstrated higher conductivity in comparison with SBA.sub.y-PPMC.sub.63 composite membranes. This result may be attributed to high interactions of DC.sub.3 ionic liquid and mesoporous SBA-15-Ph-SO.sub.3H. Mesoporous SBA-15-Ph-SO.sub.3H may make strong and effective hydrogen bond interactions with high charge density of DC.sub.3 ionic liquid. The SBA.sub.11-PPDC.sub.34 composite membrane displayed the highest conductivity (47 mS/cm) in comparison with other composite membranes. Increasing the mesoporous SBA-15-Ph-SO.sub.3H content in SBA.sub.y-PPDC.sub.34 and SBA.sub.y-PPMC.sub.63 composite membranes (a y>1 for SBA.sub.y-PPDC.sub.34 and a y>9 for SBA.sub.y-PPMC.sub.63) decreases the proton conductivity of composite membranes. These results can be attributed to the self-aggregation of the SBA-15-Ph-SO.sub.3H mesoporous inside the composite membranes.
(47) FIG. 5 shows scanning electron microscope with energy dispersive X-ray spectroscope (SEM-EDX) images 501 and 502 of SBA.sub.11-PDC.sub.34 and SEM-EDX images 503 and 504 of SBA.sub.15-PDC.sub.34. Referring to image 502, mesoporous SBA-15-Ph-SO.sub.3H has a homogenous distribution in the cross-section of SBA.sub.11-PDC.sub.34 composite membrane. In contrast, referring to image 504, significant agglomerations of Si particles are noticeably observable in the SBA.sub.15-PDC.sub.34 composite membrane. Thus, it can be understood that images 502 and 504 support that aggregation of the Si nanoparticles happens at high content of mesoporous SBA-15-Ph-SO.sub.3H. The self-aggregate of Si particles leads to a decrease in the active surface area of the SBA-15-Ph-SO.sub.3H, and consequently the proton conductivity of the membrane is decreased.
(48) FIG. 6 shows SEM-EDX images 601 and 602 of SBA.sub.9-PMC.sub.63 and SEM-EDX images 603 and 604 of SBA.sub.13-PMC.sub.63. Referring to image 602, mesoporous SBA-15-Ph-SO.sub.3H has a homogenous distribution in the cross-section of SBA.sub.9-PMC.sub.63 composite membrane. In contrast, referring to image 604, significant agglomerations of Si particles are noticeably observable in the SBA.sub.13-PMC.sub.63 composite membrane. Thus, it can be understood that images 602 and 604 support that aggregation of the Si particles happens at high content of mesoporous SBA-15-Ph-SO.sub.3H. The self-aggregate of Si particles leads to a decrease in the active surface area of the SBA-15-Ph-SO.sub.3H and consequently the proton conductivity is decreased in SBA.sub.13-PMC.sub.63 in comparison with SBA.sub.9-PMC.sub.63.
(49) As mentioned before, the composite membranes SBA.sub.11-PPDC.sub.34, SBA.sub.9-PPDC.sub.64, SBA.sub.9-PPMC.sub.63 and SBA.sub.7-PPMC.sub.43 were doped with PA by immersion in an aqueous PA solution with a concentration of 85 wt % for 5 days. Afterwards, the composite membranes were dried with a blotting paper and finally evacuated at 80 C. for at least 24 h. The PA doping level (designated herein by PA.sub.dop) of membranes was defined as moles of PA obtained for 1 mol of each repeat unit of PBI, and was calculated using equation (1) below:
(50)
(51) Where W.sub.0 is total weight of a dry composite membrane, W.sub.1 is the weight of a PA-PBI membrane, and the values 98 and 308 are the molecular weights of PA and a PBI repeat unit, respectively.
(52) In FIG. 7, PA.sub.dop versus SBA-15-Ph-SO.sub.3H content plots of SBA.sub.y-PPDC.sub.34 and SBA.sub.y-PPMC.sub.63 composite membranes and PA-PBI, PPDC.sub.34 and PPMC.sub.63 composite membranes are shown. Referring to FIG. 7, it can be observed that by incorporation of ILs and mesoporous SBA-15-Ph-SO.sub.3H in composite membranes, the PA.sub.dop of SBA.sub.y-PPDC.sub.34 (up to y=11) and SBA.sub.y-PPMC.sub.63 (up y=9) composite membranes increases. The Ph-SO.sub.3H groups of mesoporous SBA-15-Ph-SO.sub.3H and TF.sub.2N anions of DC.sub.3 IL take part in the mechanism of proton transfer and therefore more PA can be absorbed into the composite membranes. Ordered structure of SBA-15-Ph-SO.sub.3H mesoporous may increase PA absorption of the composite membranes. Pores of SBA-15-Ph-SO.sub.3H mesoporous may adsorb more ionic liquids and PA in the composite membrane structure. The SBA.sub.11-PPDC.sub.34 composite membrane shows the highest PA.sub.dop (13 mol of PA per mole PBI repeat unit) at dry condition. The results may indicate that DC.sub.3 ionic liquid has strong hydrogen bond interactions with mesoporous SBA-15-Ph-SO.sub.3H and PA in SBA.sub.11-PPDC.sub.34 composite membranes which may lead to an increase in PA.sub.dop of the SBA.sub.11-PPDC.sub.34 composite membrane.
(53) FIG. 8 is a proton conductivity plot of SBA.sub.y-PPDC.sub.64 and SBA.sub.y-PPMC.sub.43 composite membranes and PA-PBI, PPDC.sub.64 and PPMC.sub.43 composite membranes versus SBA-15-Ph-SO.sub.3H content which is represented herein by y. The SBA.sub.y-PPDC.sub.64 (up to y=9) and SBA.sub.y-PPMC.sub.43 (up to y=7) composite membranes showed a high proton conductivity compared with PBI membranes. These results may be attributed to high surface area and pores of mesoporous SBA-15-Ph-SO.sub.3H. The SBA.sub.y-PPDC.sub.64 composite membrane reflected higher proton conductivity compared to SBA.sub.y-PPMC.sub.43 composite membrane, due to greater hydrogen bond interaction of DC.sub.6 ionic liquid. The imidazolium cations in DC.sub.6 IL have different positions and numbers of possible hydrogen bonding. The hydrogen bond between the C.sub.2 hydrogen atom (the hydrogen atom attached to the single carbon atom bonded to two nitrogen atoms) of an imidazolium cation and PF.sub.6 anion has been regarded as an important interaction in controlling the structures and physical properties. The nature of this hydrogen bond is considerably different from that of conventional hydrogen bonds. This interaction is significantly stronger than conventional hydrogen bonds. The size of hydrogen bond is determined mainly by the distance between the imidazolium ring and the anion. The PF.sub.6 anions in DC.sub.6 IL would make more hydrogen bond interactions with PA and SBA-15-Ph-SO.sub.3H and so would increase the proton conductivity of SBA.sub.y-PPDC.sub.64 composite membrane in comparison with SBA.sub.y-PPMC.sub.43 composite membranes. SBA.sub.9-PPDC.sub.64 composite membrane showed the highest proton conductivity (39 mS/cm) in comparison with other SBA.sub.y-PPDC.sub.64 and SBA.sub.y-PPMC.sub.43 composite membranes at 25 C.
(54) FIG. 9 shows scanning electron microscope with energy dispersive X-ray spectroscope (SEM-EDX) images 901 and 902 of SBA.sub.9-PDC.sub.64 and SEM-EDX images 903 and 904 of SBA.sub.13-PDC.sub.64. Referring to image 902, mesoporous SBA-15-Ph-SO.sub.3H has a homogenous distribution in the cross-section of SBA.sub.9-PDC.sub.64 composite membrane. In contrast, referring to image 904, significant agglomerations of Si particles are noticeably observable in the SBA.sub.13-PDC.sub.64 composite membrane. Images 902 and 904 show that the aggregation of Si particles happens at high content of mesoporous SBA-15-Ph-SO.sub.3H. The self-aggregate of Si particles leads to a decrease in the active surface area of the SBA-15-Ph-SO.sub.3H and consequently the membrane proton conductivity is decreased.
(55) FIG. 10 shows scanning electron microscope with energy dispersive X-ray spectroscope (SEM-EDX) images 1001 and 1002 of SBA.sub.7-PMC.sub.43 and SEM-EDX images 1003 and 1004 of SBA.sub.11-PMC.sub.43. Referring to image 1002, mesoporous SBA-15-Ph-SO.sub.3H has a homogenous distribution in the cross-section of SBA.sub.7-PMC.sub.43 composite membrane. In contrast, referring to image 1004, significant agglomerations of Si particles are noticeably observable in the SBA.sub.11-PMC.sub.43 composite membrane. Images 1002 and 1004 show that the aggregation of Si particles happens at high content of mesoporous SBA-15-Ph-SO.sub.3H. The self-aggregate of Si particles leads to a decrease in the active surface area of the SBA-15-Ph-SO.sub.3H and consequently the membrane proton conductivity is decreased in SBA.sub.11-PMC.sub.43 in comparison with SBA.sub.7-PMC.sub.43.
(56) FIG. 11 shows PA.sub.dop versus SBA-15-Ph-SO.sub.3H content plots of SBA.sub.y-PPDC.sub.64 and SBA.sub.y-PPMC.sub.43 composite membranes and PA-PBI, PPDC.sub.64 and PPMC.sub.43 composite membranes. SBA.sub.y-PPDC.sub.64 composite membranes showed higher PA.sub.dop compared to SBA.sub.y-PPMC.sub.43 composite membranes. Hydrogen bonds interactions between PA, DC.sub.6 ionic liquid and -Ph-SO.sub.3H groups of SBA-15-Ph-SO.sub.3H mesoporous act as a continuous path for absorption of PA in the SBA.sub.y-PPDC.sub.64 composite membranes. SBA.sub.9-PPDC.sub.64 composite membranes showed the highest PA.sub.dop (11 mol).
(57) FIG. 12A shows Arrhenius plots of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes. The SBA.sub.11-PPDC.sub.34 composite membranes showed higher proton conductivities in different temperatures in comparison with SBA.sub.9-PPMC.sub.63 composite membranes. The proton conductivity of SBA.sub.11-PPDC.sub.34 composite membranes were about 123 mS/cm at 180 C., which may be considered a significant increase in proton conductivity.
(58) FIG. 12B shows Arrhenius plots of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes. The SBA.sub.9-PPDC.sub.64 composite membranes displayed high proton conductivity in deferent temperature compared with SBA.sub.7-PPMC.sub.43 composite membranes. The proton conductivity of composite membranes increases with increasing temperature. An increase in proton conductivity at high temperatures in composite membranes is due to an increase in transfer kinetics with increasing temperature. The lower activation energy for proton transfer can increase proton transfer speed in high-temperature. The pores of SBA-15-Ph-SO.sub.3H mesoporous act as continuous ion channels of protons in high temperatures in the presence of dicationic ionic liquids. The proton conductivity of SBA.sub.9-PPDC.sub.64 composite membranes obtained 90 mS/cm at 180 C.
(59) Referring to FIGS. 12A and 12B, the activation energies (E.sub.a) for the proton transport in composite membranes calculated from the slope of the Arrhenius plots, ln() versus 1000/T (K) are presented. Furthermore, Table 1 below reports activation energies of composite membranes. The activation energy of cationic dicationic composite membranes (SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPDC.sub.64) was less than that of monocationic composite membranes (SBA.sub.9-PPMC.sub.63 and SBA.sub.7-PPMC.sub.43). The results showed that the activation energies for proton transfer in dicationic composite membranes were less than monocationic composite membranes. As a result, proton transfers speeds were more in dicationic composite membranes. According to Table 1, the activation energies were the range of 14-21 kJmol.sup.1 in composite membranes. The results show that the dominant mechanism of composite membranes for proton transfer is the mutation mechanism.
(60) TABLE-US-00001 TABLE 1 Activation energies of dicationic and monocationic composite membranes SBA.sub.11- SBA.sub.9- SBA.sub.9- SBA.sub.7- Membrane PPDC.sub.34 PPMC.sub.63 PPDC.sub.64 PPMC.sub.43 E.sub.a 14.13 18.19 16.56 20.15 (kJ/mol)
(61) FIG. 13A shows time stability plot of proton conductivity for SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 at 180 C. and FIG. 13B shows time stability plot of proton conductivity for SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 at 180 C. The proton conductivity of composite membranes was investigated at 180 C., and it was kept overnight at 150 C. The proton conductivity of composite membranes remained almost constant for the duration of 144 hours and very little reduction was observed. This phenomenon is due to the presence of SBA-15-Ph-SO.sub.3H mesoporous in the structure of composite membranes. The pores of the SBA-15-Ph-SO.sub.3H mesoporous have an important role in the prevention of leaching of ionic liquids in composite membranes. These pores provide high surface to maintain the ionic liquids and PA in the structure of composite membranes. At high temperatures, the presence of SBA-15-Ph-SO.sub.3H mesoporous in composite membranes leads to a significant increase in proton conductivity. The reason for this view is that the SBA-15-Ph-SO.sub.3H mesoporous provides continuous path for proton transfer at high temperatures. The -Ph-SO.sub.3H groups play an important role in the formation of hydrogen bonds in proton transfer process. SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPDC.sub.64 dicationic composite membranes displayed less reduction of proton conductivity compared with SBA.sub.9-PPMC.sub.63 and SBA.sub.7-PPMC.sub.43 monocationic composite membranes. This can be understood to be a result of the effective hydrogen bond interactions of dicationic ionic liquid (DC.sub.3 and DC.sub.6) with SBA-15-Ph-SO.sub.3H mesoporous compared with monocationic ionic liquids (MC.sub.6 and MC.sub.4) in dicationic composite membranes. The presence SBA-15-Ph-SO.sub.3H mesoporous in dicationic composite membranes which have a high charge density, provides high hydrogen bond interactions for maintain PA and ionic liquids.
(62) FIG. 14A shows mechanical stability plots for SBA.sub.y-PPDC.sub.34 composite membrane and FIG. 14B shows mechanical stability plots for SBA.sub.y-PPMC.sub.63 composite membrane. Mechanical stability of SBA.sub.y-PPDC.sub.34 and SBA.sub.y-PPMC.sub.63 composite membranes increased with incorporation of SBA-15-Ph-SO.sub.3H mesoporous. This phenomenon is due to the hydrogen bond interactions of SBA-15-Ph-SO.sub.3H mesoporous with Ils in the membrane matrix. SBA-15-Ph-SO.sub.3H mesoporous with high surface to volume ratio have a greater possibility of interactions with membrane matrix.
(63) Referring to FIGS. 14A and 14B, with the addition of SBA-15-Ph-SO.sub.3H mesoporous in composite membrane, which create hydrogen bonds between the SBA-15-Ph-SO.sub.3H mesoporous, ionic liquids and membrane, the membrane structure became more compact and the mechanical strength and module of the membrane was improved. Improving the mechanical strength of composite membranes by increasing hydrogen bonds decreases the amount of freedom and mobility of polymer chains in the membrane. Decreased mobility of polymer chains in the membranes has a direct impact on the elongation of the membrane. The decreased mobility of polymer chains further causes a reduction of the elongation of the membrane and so the membrane becomes more rigid. The SBA.sub.y-PPDC.sub.34 composite membranes displayed high mechanical stability compared with SBA.sub.y-PPMC.sub.63 composite membranes, which can be understood to result from the high interactions between SBA-15-Ph-SO.sub.3H mesoporous and DC.sub.3 ionic liquid. Uniform dispersion of SBA-15-Ph-SO.sub.3H mesoporous is an important factor in these interactions. Hence SBA.sub.11-PPDC.sub.34 composite membranes due to homogenous dispersion of SBA-15-Ph-SO.sub.3H mesoporous demonstrated high mechanical stability compared with others SBA.sub.y-PPDC.sub.34 composite membranes.
(64) FIG. 15A shows mechanical stability plots for SBA.sub.y-PPDC.sub.64 composite membrane and FIG. 15B shows mechanical stability plots for SBA.sub.y-PPMC.sub.43 composite membrane. SBA.sub.y-PPDC.sub.64 composite membranes because of DC.sub.6 ionic liquid interactions displayed high mechanical stability compared with SBA.sub.y-PPMC.sub.43 composite membranes. SBA.sub.9-PPDC.sub.64 composite membranes due to homogenous dispersion of SBA-15-Ph-SO.sub.3H mesoporous demonstrated high mechanical stability compared with others SBA.sub.y-PPDC.sub.64 composite membranes.
(65) Referring to Table 2 below, the mechanical strengths of dicationic membranes, monocationic membranes, dicationic and monocationic composite membranes are presented. The strong hydrogen bonding between N and NH groups is a key factor controlling the mechanical behavior of the PBI. When ionic liquids are introduced into the PBI structure in dicationic membranes (PPDC.sub.34 and PPDC.sub.64) and monocationic membranes (PPMC.sub.63 and PPMC.sub.43), the molecular cohesion between PBI chains is decreased. However, the hydrogen bonds between nitrogen atoms and DC.sub.3 ionic liquid would increase the cohesion. As a result of these opposite effects, no important change of modulus or tensile strength of the PBI membranes is observed.
(66) TABLE-US-00002 TABLE 2 Mechanical strength of dicationic membranes, monocationic membranes, and dicationic and monocationic composite membranes. Tensile strength Modulus Elongation at break Membranes (MPa) (GPa) (%) PA-PBI 14 0.4 50 PPDC.sub.34 8 0.2 65 SBA.sub.11-PPDC.sub.34 34 0.55 23 PPDC.sub.64 7 0.15 67 SBA.sub.9-PPDC.sub.64 29 0.5 35 PPMC.sub.63 6 0.14 74 SBA.sub.9-PPMC.sub.63 29 0.45 37 PPMC.sub.43 5 0.11 78 SBA.sub.7-PPMC.sub.43 18 0.43 41
(67) Dicationic and monocationic composite membranes displayed high mechanical stability compared with dicationic and monocationic membranes. This result may be attributed to high interface interactions of SBA-15-Ph-SO.sub.3H mesoporous with membranes matrix in composite membranes.
(68) The prepared composite membranes and Nafion 117 were used to prepare MEAs. The catalyst was PtC(E-TEK, 20 wt % Pt) and the Pt loadings of anode and cathode were 0.5 mg/cm.sup.2. The MEA of composite membranes was fabricated according to the literature procedure [41]: PtC/PBI/LiCl/DMAc (3.6/1/0.2/38 by wt) catalyst solution was prepared by ultrasonic disturbing for 1 h. The catalyst ink was painted onto carbon cloth (E-TEK, HT 2500-W) and dried at 190 C. in a conventional oven. Hot-pressing was performed at 130 C. applying a load of 50 kg/cm.sup.2 for 5 min. In this example, the MEA of Nafion 117 membrane was fabricated by following procedure: PtC was mixed with deionized water, isopropyl alcohol (Sigma-Aldrich) and Nafion solution (5 wt % solution, EW1000, Dupont) to form a catalyst ink. The catalyst ink was painted onto carbon cloth (E-TEK, HT 2500-W) and dried at 80 and 120 C. for 40 and 60 min respectively in a conventional oven. The MEA was made by hot-pressing a sandwich of electrodes and a Nafion 117 membrane at 140 C. for 3 min with a pressure of 50 kg/cm.sup.2. Prior to the i-V measurement, the MEAs of composite membranes and Nafion 117 were activated.
(69) FIGS. 16A-16C show polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes in the temperature range of 80-180 C. and FIG. 16D-16F show polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes in the temperature range of 80-180 C.
(70) Referring to FIG. 16A, polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes along with PA-PBI membrane at 80 C. are shown in chart 1601, and polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes along with PA-PBI membrane at 90 C. are shown in chart 1602. In FIG. 16B, polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes along with PA-PBI membrane at 100 C. are shown in chart 1603, and polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes along with PA-PBI membrane at 120 C. are shown in chart 1604. In FIG. 16C polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes along with PA-PBI membrane at 150 C. are shown in chart 1605, and polarization curves of SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPMC.sub.63 composite membranes along with PA-PBI membrane at 180 C. are shown in chart 1606. In this example, the anode and cathode Pt loadings were both 0.5 mg/cm.sup.2. Each MEA with an active area of 2.32.3 cm.sup.2 underwent the fuel cell test with the H.sub.2/O.sub.2 flow rates at 300/500 mL/min under anhydrous condition.
(71) Referring to FIG. 16D, polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes along with PA-PBI membrane at 80 C. are shown in chart 1607, and polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes along with PA-PBI membrane at 90 C. are shown in chart 1608. In FIG. 16E, polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes along with PA-PBI membrane at 100 C. are shown in chart 1609, and polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes along with PA-PBI membrane at 120 C. are shown in chart 1610. In FIG. 16F polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes along with PA-PBI membrane at 150 C. are shown in chart 1611, and polarization curves of SBA.sub.9-PPDC.sub.64 and SBA.sub.7-PPMC.sub.43 composite membranes along with PA-PBI membrane at 180 C. are shown in chart 1612. In this example, the anode and cathode Pt loadings were both 0.5 mg/cm.sup.2. Each MEA with an active area of 2.32.3 cm.sup.2 was performed the fuel cell test with the H.sub.2/O.sub.2 flow rates at 300/500 mL/min under anhydrous condition.
(72) With further reference to FIGS. 16A-16F, SBA.sub.11-PPDC.sub.34 and SBA.sub.9-PPDC.sub.64 composite membranes displayed high fuel cell performance compared with SBA.sub.9-PPMC.sub.63 and SBA.sub.7-PPMC.sub.43 composite membranes due to high proton conductivity. The fuel cell performance of composite membrane increases as the temperature was increased from 80 C. to 180 C. The cause of this phenomenon is high proton conductivity and reaction kinetics of composite membranes at high temperatures. OCV value of composite membranes increased with increasing temperature as a result of confirmation of the applicability of these membranes at high temperatures.
(73) In Table 3 below, fuel cell performance parameters for composite membranes at 180 C. and 0.5 V are presented. The SBA.sub.11-PPDC.sub.34 composite membranes showed the highest fuel cell performance. Several factors can contribute to the high fuel cell performance SBA.sub.11-PPDC.sub.34 composite membranes, such as high proton conductivity, suitable surface roughness, uniform and high level of SBA-15-Ph-SO.sub.3H mesoporous, pores of SBA-15-Ph-SO.sub.3H mesoporous, hydrogen interactions of -Ph-SO.sub.3H groups with ionic liquids and high proton conductivity life time. Current density for SBA.sub.11-PPDC.sub.34 composite membranes at 0.5 V and 80 C. was 0.22 A/cm.sup.2 (chart 1601). This current density was increased to about 1.16 A/cm.sup.2 at 180 C. (chart 1606).
(74) TABLE-US-00003 TABLE 3 Fuel cell parameters of composite membranes at 180 C. and 0.5 V. SBA.sub.7- SBA.sub.9- SBA.sub.9- SBA.sub.11- Membrane PPMC.sub.43 PPDC.sub.64 PPMC.sub.63 PPDC.sub.34 Current density 0.65 0.91 0.72 1.16 (A/cm.sup.2) Power density 0.32 0.45 0.36 0.58 (W/cm.sup.2)
(75) FIG. 17 shows polarization curves for Nafion 117 membrane at 80 C., 90 C., 100 C. and 120 C. The anode and cathode Pt loadings were both 0.5 mg/cm.sup.2. The active area of each MEA was 2.32.3 cm.sup.2. The performance of Nafion 117 is noticeably decreased with increasing temperature from 80 C. to 120 C. This occurs because of the requirement of humidification of Nafion 117 for a good operation. As the relative humidity decreases at higher temperatures, the performance of Nafion 117 MEA would also decrease. FIG. 17 shows that the OCV drops from 0.98 V at 80 C. to a value of only 0.51 V at 120 C. Polarization curves for Nafion 117 at 150 C. and 180 C. could not be obtained due to the absence of moisture. Referring to FIG. 17, the power density of Nafion 117 decreases with increases in temperature due to decreasing relative humidity. However, the power density of PA-PBI, dicationic membranes, monocationic membranes, dicationic and monocationic composite membranes increase with increasing temperature.
(76) FIG. 18A shows power density plots of PPDC.sub.34, PPMC.sub.63, SBA.sub.11-PPDC.sub.34, SBA.sub.9-PPMC.sub.63 composite membranes along with power density plots of Nafion and PA-PBI at 0.5 V. FIG. 18B shows power density plots of PPDC.sub.64, PPMC.sub.43, SBA.sub.9-PPDC.sub.64, SBA.sub.7-PPMC.sub.43 composite membranes along with power density plots of Nafion and PA-PBI at 0.5 V. Referring to FIGS. 18A and 18B, a similar trend of increase in the monocationic composite membranes (SBA.sub.9-PPMC.sub.63 and SBA.sub.7-PPMC.sub.43) compared to monocationic membranes (PPMC.sub.63 and PPMC.sub.43) is observed. This observation is due to the presence of SBA-15-Ph-SO.sub.3H mesoporous in the structure of composite membranes. SBA-15-Ph-SO.sub.3H mesoporous keep ionic liquids and PA in the structure of the composite membranes due to strong and effective hydrogen interaction. In other words SBA-15-Ph-SO.sub.3H mesoporous reduces PA and ionic liquids leaching and to be climbing onto the power density. The SBA.sub.11-PPDC.sub.34 dicationic composite membranes displayed power density of 0.58 W/cm.sup.2 at 180 C. and 0.5 V. These results indicate that the capability of SBA.sub.11-PPDC.sub.34 dicationic composite membranes to provide high fuel cell performance for use in high temperature PEM fuel cells.
(77) FIG. 19A shows a life test result of a PPDC.sub.34 membrane unit cell operated at 180 C. under a constant current loading of 0.4 A/cm.sup.2 and FIG. 19B shows a life test result of a SBA.sub.11-PPDC.sub.34 membrane unit cell operated at 180 C. under a constant current loading of 0.4 A/cm.sup.2. During each 24-hour cycle the life test was interrupted (12 times), including four complete shut downs after each sixty hours after the test started. Under a fixed loading current for a long time fuel cell test, two regions were observed in the output voltage versus testing time curve. The first initial testing period was the activation region in which cell voltage increased with operating time. The improvement of fuel cell performance at the activation region is due to the better contact of membrane with catalyst layers by the pressure of the end plates and expansion of the interface for the electrochemical reaction. Following the activation region was the decline region, in which the cell voltage decreased with operating time. The decline of cell voltage during the latter stage of life test of PPDC.sub.34 membranes was due to the leaching of DC.sub.3 ionic liquid and PA from membrane.
(78) Referring to FIG. 19B, it can be seen that a significant increase was observed in fuel cell life time of SBA.sub.11-PPDC.sub.34 composite membranes compared to PPDC.sub.34 membranes. Due to retention of PA and DC.sub.3 ionic liquid, SBA-15-Ph-SO.sub.3H mesoporous increases fuel cell life time of SBA.sub.11-PPDC.sub.34 composite membranes. OCV value SBA.sub.11-PPDC.sub.34 composite membranes remained relatively constant over 150 hours and did not decrease. These results reflect the successful preparation of SBA.sub.11-PPDC.sub.34 composite membranes with high fuel cell performance which is suitable for applications in high temperature PEM fuel cells.
(79) The well-ordered pores of acid functionalized SBA-15-Ph-SO.sub.3H mesoporous provide a continuous proton transfer pathway which act as diffusional barriers to prevent the dicationic ionic liquid leaching from high temperature PBI composite membranes, thereby providing high fuel cell performance.
(80) While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings.
(81) Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. They are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain.
(82) The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows and to encompass all structural and functional equivalents.
(83) Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirement of Sections 101, 102, or 103 of the Patent Act, nor should they be interpreted in such a way. Any unintended embracement of such subject matter is hereby disclaimed.
(84) Except as stated immediately above, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims.
(85) It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms comprises, comprising, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by a or an does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
(86) The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various implementations. This is for purposes of streamlining the disclosure, and is not to be interpreted as reflecting an intention that the claimed implementations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed implementation. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
(87) While various implementations have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more implementations and implementations are possible that are within the scope of the implementations. Although many possible combinations of features are shown in the accompanying figures and discussed in this detailed description, many other combinations of the disclosed features are possible. Any feature of any implementation may be used in combination with or substituted for any other feature or element in any other implementation unless specifically restricted. Therefore, it will be understood that any of the features shown and/or discussed in the present disclosure may be implemented together in any suitable combination. Accordingly, the implementations are not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.
