Two low equivalent weight perfluorosulfonic acid (PFSA) polymers (825 EW and 733 EW) were success... more Two low equivalent weight perfluorosulfonic acid (PFSA) polymers (825 EW and 733 EW) were successfully electrospun into nanofibers by adding as little as 0.3 wt% of high molecular weight poly(ethylene oxide) as a carrier polymer. The electrospun fiber morphology transitioned from cylindrical filaments to flat ribbons as the total concentration of PFSA + carrier in solution increased from 5 wt% to 30 wt%. PFSA nanofiber mats were transformed into defect-free dense membranes using a four-step procedure: (i) annealing the PFSA polymer during which time intersecting fibers were welded to one another at cross points (ii) mechanically compacting the mats to increase the volume fraction of nanofibers to $75%, (iii) imbibing an inert polymer, Norland Optical Adhesive (NOA) 63, into the mats (to fill entirely the void space between nanofibers) and then crosslinking the NOA with UV light, and (iv) removing the poly(ethylene oxide) carrier polymer by boiling the membrane in 1.0 M H 2 SO 4 and then in deionized water. The resulting membranes exhibited higher proton conductivities than that of commercial Nafion 212 membrane (0.16 S/cm at 80 C and 80% relative humidity and 0.048 S/cm at 80 C and 50% relative humidity for a membrane with 733 EW nanofibers), with low water swelling (liquid water swelling of 18% for membrane with high conductivity). The proton conductivity of both EW nanofiber composite membranes increased linearly with the PFSA nanofiber volume fraction, whereas gravimetric water swelling was less than expected, based on the volume fraction of ionomer. There was a significantly improvement in the mechanical properties of the nanofiber composite membranes, as compared to recast homogeneous PFSA films.
A fuel cell is an electrochemical device that converts the chemical energy of a fuel and oxidant ... more A fuel cell is an electrochemical device that converts the chemical energy of a fuel and oxidant into electricity. Cation-exchange and anion-exchange membranes play an important role in hydrogen fed proton-exchange membrane (PEM) and anion-exchange membrane (AEM) fuel cells, respectively. Over the past 10 years, there has been growing interest in using nanofiber electrospinning to fabricate fuel cell PEMs and AEMs with improved properties, e.g., a high ion conductivity with low in-plane water swelling and good mechanical strength under wet and dry conditions. Electrospinning is used to create either reinforcing scaffolds that can be pore-filled with an ionomer or precursor mats of interwoven ionomer and reinforcing polymers, which after suitable processing (densification) form a functional membrane. In this review paper, methods of nanofiber composite PEMs and AEMs fabrication are reviewed and the properties of these membranes are discussed and contrasted with the properties of fuel...
New technologies are required to electrocatalytically convert carbon dioxide (CO 2) into fuels an... more New technologies are required to electrocatalytically convert carbon dioxide (CO 2) into fuels and chemicals at near-ambient temperatures and pressures more effectively. One particular challenge is mediating the electrochemical CO 2 reduction reaction (CO 2 RR) at low cell voltages while maintaining high conversion efficiencies. Anion exchange membranes (AEMs) in zero-gap reactors offer promise in this direction; however, there remain substantial obstacles to be overcome in tailoring the membranes and other cell components to the requirements of CO 2 RR systems. Here we review recent advances, and remaining challenges, in AEM materials and devices for CO 2 RR. We discuss the principles underpinning AEM operation and the properties desired for CO 2 RR, in addition to reviewing state-of-the-art AEMs in CO 2 electrolysers. We close with future design strategies to minimize product crossover, improve mechanical and chemical stability, and overcome the energy losses associated with the use of AEMs for CO 2 RR systems.
Electrospinning was employed to fabricate composite membranes containing perfluorosulfonic acid (... more Electrospinning was employed to fabricate composite membranes containing perfluorosulfonic acid (PFSA) ionomer, poly(vinylidene fluoride) (PVDF) reinforcement and a sulfonated silica network, where the latter was incorporated either in the PFSA matrix or in the PVDF fibers. The best membrane, in terms of proton conductivity, was made by incorporating the sulfonated silica network in PFSA fibers (Type-A) while the lowest conductivity membrane was obtained when sulfonated silica was incorporated into the reinforcing PVDF fibers (Type-B). A Type-A membrane containing 65 wt.% PFSA with an embedded sulfonated silica network (at 15 wt.%) and with 20 wt.% PVDF reinforcing fibers proved superior to the pristine PFSA membrane in terms of both the proton conductivity in the 30–90% RH at 80 °C (a 25–35% increase) and lateral swelling (a 68% reduction). In addition, it was demonstrated that a Type-A membrane was superior to that of a neat 660 EW perfluoroimide acid (PFIA, from 3M Co.) films wit...
Current water electrolysis technology is limited to operation at a single pH through the use of i... more Current water electrolysis technology is limited to operation at a single pH through the use of ion exchange membranes or traditional liquid alkaline systems. Using a bipolar membrane, comprised of both a cation and anion exchange membrane, operation across a pH gradient may be achieved, with the hydrogen and oxygen evolution reactions occurring in acidic and basic media, respectively. In this work, we focus on the characterization of hydrocarbon bipolar membranes for electrolytic water splitting based on two emerging classes of hydrocarbon Page 1 of 38 ACS Paragon Plus Environment ACS Applied Energy Materials 2 ion-conducting polymers. The influence of the cation and anion exchange membrane interface on the efficiency of water dissociation is explored using two types of 3D, dual-fiber electrospun junctions. The results support the view that both high interfacial surface area and inclusion of Al(OH) 3 enhance water dissociation under high current densities, and affect the rate of ion leakage under open circuit potential. While dual-fiber electrospun interfacial layers were found to provide high junction surface areas, poor adhesion of some hydrocarbon-based polymers is observed due to their relatively high glass transition temperature, Tg. This restricts the formation of a strong interfacial layer, as the different polymers are unable to properly entangle while in the glass phase.
Novel absorbents for the removal of Cu 2+ and Ni 2+ ions from aqueous solutions were prepared fro... more Novel absorbents for the removal of Cu 2+ and Ni 2+ ions from aqueous solutions were prepared from solution cast sulfated chitosan/polyvinyl alcohol membranes (SCS/PVA) and their properties were investigated. FTIR, SEM, XRD and TGA analyses were used to determine membrane structure. The effect of environmental parameters on absorption was studied, including pH, contact time, temperature and the initial concentration of Ni 2+ and Cu 2+ ions. Freundlich and Langmuir absorption isotherms were fitted to experimental data and a pseudo-second order rate equation was employed to model the kinetics of uptake for several copper and nickel ion concentrations. The results indicate that the affinity of a SCS/PVA membrane for Cu 2+ ions was higher than that for Ni 2+ ions. The study demonstrated that the SCS/PVA system can be utilized as highly efficient sorbents, to extract Ni 2+ and Cu 2+ from aqueous feed solutions.
Particle/polymer electrospinning was used to prepare fiber mat cathodes containing LiCoO 2 nanopa... more Particle/polymer electrospinning was used to prepare fiber mat cathodes containing LiCoO 2 nanoparticles, carbon powder, and poly(vinylidene fluoride) for Li-ion batteries. The fibers had a high LiCoO 2 particle content (70 wt%) which allowed for a high gravimetric capacity of 90 mAh g-1 (corresponding to 128 mAh g-1 LiCoO2) at 0.1C. Cathode performance was stable in a half cell with 78% capacity retention over 200 cycles at 0.5C. Unlike previous work on electrospun LiCoO 2 nanofibers prepared using sol-gel chemistry and high temperature processing, the particle/polymer fiber mat cathodes reported here were made thick with a high fiber volume fraction for high areal and volumetric capacities at fast charge/discharge rates (e.g., 0.81 mAh cm-2 and 62 mAh cm-3 at 2C) which were much greater than that of a slurry cast cathode of the same composition (0.004 mAh cm-2 and 0.30 mAh cm-3 at 2C). Full cells containing a LiCoO 2 /C/PVDF fiber mat cathode and C/PVDF fiber mat anode were also prepared and characterized. These electrospun batteries exhibited a high energy density of 144 Wh kg-1 at 0.1C and an areal capacity of 1.03 mAh cm-2 at 1C. The excellent performance of the electrospun particle/polymer cathodes and anodes is attributed to electrolyte penetration throughout the 3D fiber electrode mats, a large electrode/electrolyte interfacial area, and short Li + transport pathways between the electrolyte and active material nanoparticles in the radial fiber direction.
The regenerative H 2 /Br 2-HBr fuel cell, utilizing an oxidant solution of Br 2 in aqueous HBr, s... more The regenerative H 2 /Br 2-HBr fuel cell, utilizing an oxidant solution of Br 2 in aqueous HBr, shows a number of benefits for grid-scale electricity storage. The membrane-electrode assembly, a key component of a fuel cell, contains a proton-conducting membrane, typically based on the perfluorosulfonic acid (PFSA) ionomer. Unfortunately, the high cost of PFSA membranes and their relatively high bromine crossover are serious drawbacks. Nanofiber composite membranes can overcome these limitations. In this work, composite membranes were prepared from electrospun dual-fiber mats containing Nafion ® PFSA ionomer for facile proton transport and an uncharged polymer, polyphenylsulfone (PPSU), for mechanical reinforcement, and swelling control. After electrospinning, Nafion/PPSU mats were converted into composite membranes by softening the PPSU fibers, through exposure to chloroform vapor, thus filling the voids between ionomer nanofibers. It was demonstrated that the relative membrane selectivity, referenced to Nafion ® 115, increased with increasing PPSU content, e.g., a selectivity of 11 at 25 vol% of Nafion fibers. H 2-Br 2 fuel cell power output with a 65 µm thick membrane containing 55 vol% Nafion fibers was somewhat better than that of a 150 µm Nafion ® 115 reference, but its cost advantage due to a four-fold decrease in PFSA content and a lower bromine species crossover make it an attractive candidate for use in H 2 /Br 2-HBr systems.
Membrane-electrode-assemblies (MEAs) with electrospun nanofiber mat electrodes (0.10 mg/cm 2 Pt l... more Membrane-electrode-assemblies (MEAs) with electrospun nanofiber mat electrodes (0.10 mg/cm 2 Pt loading) and a Nafion 211 membrane were prepared and tested in a H 2 /air fuel cell at 100% and 40% relative humidity. The cathode binder was either neat poly(vinylidene fluoride) (PVDF) or a Nafion/PVDF blend (20 to 80 wt% Nafion) and the anode binder was Nafion with poly(acrylic acid). Polarization curves were recorded at 80 • C and ambient pressure before, intermittently, and after a carbon corrosion voltage cycling experiment. The Nafion/PVDF cathode MEA with the smallest amount of PVDF (80/20 Nafion/PVDF weight ratio) produced the highest maximum power at beginning-of-life (BoL), 545 mW/cm 2 at 100% RH, which was 35% greater than that for a conventional MEA with a neat Nafion binder. Carbon corrosion scaled inversely with cathode PVDF content, with a 33/67 Nafion/PVDF cathode binder MEA producing the highest end-of-life (EoL) power (330 mW/cm 2). MEAs with < 50 wt% PVDF in the cathode binder exhibited a power density decline during carbon corrosion, whereas the power increased during/after carbon corrosion for nanofiber cathodes with binders containing > 50 wt% PVDF due to favorable increases in the hydrophilicity of the carbon support and Pt mass activity, coupled with a lower carbon loss.
A series of electrospun nanofiber mat electrodes with two different commercial Pt/C catalysts and... more A series of electrospun nanofiber mat electrodes with two different commercial Pt/C catalysts and a binder of Nafion and poly(acrylic acid) were fabricated and evaluated. The electrodes were assembled into membrane-electrode-assemblies (MEAs) using Nafion 211 as the membrane. Variations in catalyst type, nanofiber composition (the ratio of Pt/C to Nafion), and fiber diameter had little or no impact on hydrogen/air fuel cell power output. 25 cm 2 nanofiber and sprayed gas diffusion electrode MEAs were compared in terms of beginning of life (BoL) and end of life (EoL) performance after automotive-specific load cycling (Pt dissolution) and start-stop cycling (carbon corrosion) cathode durability protocols. Nanofiber electrode MEAs (0.10 mg/cm 2 Pt loading for the anode and cathode) were clearly superior to sprayed MEAs; they produced more power at BoL and maintained a higher percentage of their power after the carbon corrosion durability protocol, resulting in much higher EoL fuel cell performance. On the other hand, there was no effect of electrode morphology on MEA durability for the Pt dissolution test. The higher MEA power output after carbon corrosion with electrospun electrodes is attributed to better oxygen and water transport within the nanofiber electrode and a higher electrochemical surface area for the fiber cathode.
Polyphosphazenes possess numerous properties that are attractive for PEM fuel-cell applications, ... more Polyphosphazenes possess numerous properties that are attractive for PEM fuel-cell applications, including thermal and chemical stability and the unlimited possibility for side-group functionalization. There are some impressive results in the literature, in particular ...
Nanofiber composite proton exchange membranes were fabricated and their properties measured, for ... more Nanofiber composite proton exchange membranes were fabricated and their properties measured, for possible use in a regenerative hydrogen/bromine fuel cell. The membranes were prepared from dual nanofiber mats, composed of Nafion ® perfluorosulfonic acid (PFSA) ionomer for proton transport and polyvinylidene fluoride (PVDF) for mechanical reinforcement. Two composite membranes structures containing Nafion volume fractions ranging from 0.30 to 0.65 were investigated: (1) Nafion nanofibers embedded in a PVDF matrix (N(fibers)/PVDF) and (2) PVDF nanofibers embedded in a Nafion matrix (N/PVDF(fibers)). The in-plane conductivity for films equilibrated in water and 2.0 M HBr scaled linearly with Nafion volume fraction for both morphologies. The through-plane proton conductivity of N(fibers)
PEM Fuel Cell Properties of Pre-Stretched Recast Nafion®
ECS Transactions, 2008
Pre-stretched recast Nafion is a new membrane material with many desirable properties for PEM fue... more Pre-stretched recast Nafion is a new membrane material with many desirable properties for PEM fuel cells. It was previously shown that the proton conductivity of this membrane in room temperature water was identical to that of commercial Nafion but its permeability to methanol was significantly reduced. Consequently, the power output from a direct methanol fuel cell with pre-stretched recast Nafion (draw ratio of 4) was 50% higher than that with Nafion 117. In an effort to better characterize pre-stretched recast Nafion, additional property measurements were made and compared to those for commercial Nafion. There was a substantial increase in the polymer crystallinity with increasing draw ratio which translated into improved membrane mechanical properties (a higher storage modulus and ultimate tensile strength). There was also a modest increase in the α-transition temperature when the membrane was elongated, as determined from dynamic mechanical analysis. Preliminary results indicat...
New Membrane Nano-Morphologies for Improved Fuel Cell Operation
Presented on February 4, 2009, from 4-5 pm in room G011 of the Molecular Science and Engineering ... more Presented on February 4, 2009, from 4-5 pm in room G011 of the Molecular Science and Engineering Building on the Georgia Tech Campus.
Two low equivalent weight perfluorosulfonic acid (PFSA) polymers (825 EW and 733 EW) were success... more Two low equivalent weight perfluorosulfonic acid (PFSA) polymers (825 EW and 733 EW) were successfully electrospun into nanofibers by adding as little as 0.3 wt% of high molecular weight poly(ethylene oxide) as a carrier polymer. The electrospun fiber morphology transitioned from cylindrical filaments to flat ribbons as the total concentration of PFSA + carrier in solution increased from 5 wt% to 30 wt%. PFSA nanofiber mats were transformed into defect-free dense membranes using a four-step procedure: (i) annealing the PFSA polymer during which time intersecting fibers were welded to one another at cross points (ii) mechanically compacting the mats to increase the volume fraction of nanofibers to $75%, (iii) imbibing an inert polymer, Norland Optical Adhesive (NOA) 63, into the mats (to fill entirely the void space between nanofibers) and then crosslinking the NOA with UV light, and (iv) removing the poly(ethylene oxide) carrier polymer by boiling the membrane in 1.0 M H 2 SO 4 and then in deionized water. The resulting membranes exhibited higher proton conductivities than that of commercial Nafion 212 membrane (0.16 S/cm at 80 C and 80% relative humidity and 0.048 S/cm at 80 C and 50% relative humidity for a membrane with 733 EW nanofibers), with low water swelling (liquid water swelling of 18% for membrane with high conductivity). The proton conductivity of both EW nanofiber composite membranes increased linearly with the PFSA nanofiber volume fraction, whereas gravimetric water swelling was less than expected, based on the volume fraction of ionomer. There was a significantly improvement in the mechanical properties of the nanofiber composite membranes, as compared to recast homogeneous PFSA films.
A fuel cell is an electrochemical device that converts the chemical energy of a fuel and oxidant ... more A fuel cell is an electrochemical device that converts the chemical energy of a fuel and oxidant into electricity. Cation-exchange and anion-exchange membranes play an important role in hydrogen fed proton-exchange membrane (PEM) and anion-exchange membrane (AEM) fuel cells, respectively. Over the past 10 years, there has been growing interest in using nanofiber electrospinning to fabricate fuel cell PEMs and AEMs with improved properties, e.g., a high ion conductivity with low in-plane water swelling and good mechanical strength under wet and dry conditions. Electrospinning is used to create either reinforcing scaffolds that can be pore-filled with an ionomer or precursor mats of interwoven ionomer and reinforcing polymers, which after suitable processing (densification) form a functional membrane. In this review paper, methods of nanofiber composite PEMs and AEMs fabrication are reviewed and the properties of these membranes are discussed and contrasted with the properties of fuel...
New technologies are required to electrocatalytically convert carbon dioxide (CO 2) into fuels an... more New technologies are required to electrocatalytically convert carbon dioxide (CO 2) into fuels and chemicals at near-ambient temperatures and pressures more effectively. One particular challenge is mediating the electrochemical CO 2 reduction reaction (CO 2 RR) at low cell voltages while maintaining high conversion efficiencies. Anion exchange membranes (AEMs) in zero-gap reactors offer promise in this direction; however, there remain substantial obstacles to be overcome in tailoring the membranes and other cell components to the requirements of CO 2 RR systems. Here we review recent advances, and remaining challenges, in AEM materials and devices for CO 2 RR. We discuss the principles underpinning AEM operation and the properties desired for CO 2 RR, in addition to reviewing state-of-the-art AEMs in CO 2 electrolysers. We close with future design strategies to minimize product crossover, improve mechanical and chemical stability, and overcome the energy losses associated with the use of AEMs for CO 2 RR systems.
Electrospinning was employed to fabricate composite membranes containing perfluorosulfonic acid (... more Electrospinning was employed to fabricate composite membranes containing perfluorosulfonic acid (PFSA) ionomer, poly(vinylidene fluoride) (PVDF) reinforcement and a sulfonated silica network, where the latter was incorporated either in the PFSA matrix or in the PVDF fibers. The best membrane, in terms of proton conductivity, was made by incorporating the sulfonated silica network in PFSA fibers (Type-A) while the lowest conductivity membrane was obtained when sulfonated silica was incorporated into the reinforcing PVDF fibers (Type-B). A Type-A membrane containing 65 wt.% PFSA with an embedded sulfonated silica network (at 15 wt.%) and with 20 wt.% PVDF reinforcing fibers proved superior to the pristine PFSA membrane in terms of both the proton conductivity in the 30–90% RH at 80 °C (a 25–35% increase) and lateral swelling (a 68% reduction). In addition, it was demonstrated that a Type-A membrane was superior to that of a neat 660 EW perfluoroimide acid (PFIA, from 3M Co.) films wit...
Current water electrolysis technology is limited to operation at a single pH through the use of i... more Current water electrolysis technology is limited to operation at a single pH through the use of ion exchange membranes or traditional liquid alkaline systems. Using a bipolar membrane, comprised of both a cation and anion exchange membrane, operation across a pH gradient may be achieved, with the hydrogen and oxygen evolution reactions occurring in acidic and basic media, respectively. In this work, we focus on the characterization of hydrocarbon bipolar membranes for electrolytic water splitting based on two emerging classes of hydrocarbon Page 1 of 38 ACS Paragon Plus Environment ACS Applied Energy Materials 2 ion-conducting polymers. The influence of the cation and anion exchange membrane interface on the efficiency of water dissociation is explored using two types of 3D, dual-fiber electrospun junctions. The results support the view that both high interfacial surface area and inclusion of Al(OH) 3 enhance water dissociation under high current densities, and affect the rate of ion leakage under open circuit potential. While dual-fiber electrospun interfacial layers were found to provide high junction surface areas, poor adhesion of some hydrocarbon-based polymers is observed due to their relatively high glass transition temperature, Tg. This restricts the formation of a strong interfacial layer, as the different polymers are unable to properly entangle while in the glass phase.
Novel absorbents for the removal of Cu 2+ and Ni 2+ ions from aqueous solutions were prepared fro... more Novel absorbents for the removal of Cu 2+ and Ni 2+ ions from aqueous solutions were prepared from solution cast sulfated chitosan/polyvinyl alcohol membranes (SCS/PVA) and their properties were investigated. FTIR, SEM, XRD and TGA analyses were used to determine membrane structure. The effect of environmental parameters on absorption was studied, including pH, contact time, temperature and the initial concentration of Ni 2+ and Cu 2+ ions. Freundlich and Langmuir absorption isotherms were fitted to experimental data and a pseudo-second order rate equation was employed to model the kinetics of uptake for several copper and nickel ion concentrations. The results indicate that the affinity of a SCS/PVA membrane for Cu 2+ ions was higher than that for Ni 2+ ions. The study demonstrated that the SCS/PVA system can be utilized as highly efficient sorbents, to extract Ni 2+ and Cu 2+ from aqueous feed solutions.
Particle/polymer electrospinning was used to prepare fiber mat cathodes containing LiCoO 2 nanopa... more Particle/polymer electrospinning was used to prepare fiber mat cathodes containing LiCoO 2 nanoparticles, carbon powder, and poly(vinylidene fluoride) for Li-ion batteries. The fibers had a high LiCoO 2 particle content (70 wt%) which allowed for a high gravimetric capacity of 90 mAh g-1 (corresponding to 128 mAh g-1 LiCoO2) at 0.1C. Cathode performance was stable in a half cell with 78% capacity retention over 200 cycles at 0.5C. Unlike previous work on electrospun LiCoO 2 nanofibers prepared using sol-gel chemistry and high temperature processing, the particle/polymer fiber mat cathodes reported here were made thick with a high fiber volume fraction for high areal and volumetric capacities at fast charge/discharge rates (e.g., 0.81 mAh cm-2 and 62 mAh cm-3 at 2C) which were much greater than that of a slurry cast cathode of the same composition (0.004 mAh cm-2 and 0.30 mAh cm-3 at 2C). Full cells containing a LiCoO 2 /C/PVDF fiber mat cathode and C/PVDF fiber mat anode were also prepared and characterized. These electrospun batteries exhibited a high energy density of 144 Wh kg-1 at 0.1C and an areal capacity of 1.03 mAh cm-2 at 1C. The excellent performance of the electrospun particle/polymer cathodes and anodes is attributed to electrolyte penetration throughout the 3D fiber electrode mats, a large electrode/electrolyte interfacial area, and short Li + transport pathways between the electrolyte and active material nanoparticles in the radial fiber direction.
The regenerative H 2 /Br 2-HBr fuel cell, utilizing an oxidant solution of Br 2 in aqueous HBr, s... more The regenerative H 2 /Br 2-HBr fuel cell, utilizing an oxidant solution of Br 2 in aqueous HBr, shows a number of benefits for grid-scale electricity storage. The membrane-electrode assembly, a key component of a fuel cell, contains a proton-conducting membrane, typically based on the perfluorosulfonic acid (PFSA) ionomer. Unfortunately, the high cost of PFSA membranes and their relatively high bromine crossover are serious drawbacks. Nanofiber composite membranes can overcome these limitations. In this work, composite membranes were prepared from electrospun dual-fiber mats containing Nafion ® PFSA ionomer for facile proton transport and an uncharged polymer, polyphenylsulfone (PPSU), for mechanical reinforcement, and swelling control. After electrospinning, Nafion/PPSU mats were converted into composite membranes by softening the PPSU fibers, through exposure to chloroform vapor, thus filling the voids between ionomer nanofibers. It was demonstrated that the relative membrane selectivity, referenced to Nafion ® 115, increased with increasing PPSU content, e.g., a selectivity of 11 at 25 vol% of Nafion fibers. H 2-Br 2 fuel cell power output with a 65 µm thick membrane containing 55 vol% Nafion fibers was somewhat better than that of a 150 µm Nafion ® 115 reference, but its cost advantage due to a four-fold decrease in PFSA content and a lower bromine species crossover make it an attractive candidate for use in H 2 /Br 2-HBr systems.
Membrane-electrode-assemblies (MEAs) with electrospun nanofiber mat electrodes (0.10 mg/cm 2 Pt l... more Membrane-electrode-assemblies (MEAs) with electrospun nanofiber mat electrodes (0.10 mg/cm 2 Pt loading) and a Nafion 211 membrane were prepared and tested in a H 2 /air fuel cell at 100% and 40% relative humidity. The cathode binder was either neat poly(vinylidene fluoride) (PVDF) or a Nafion/PVDF blend (20 to 80 wt% Nafion) and the anode binder was Nafion with poly(acrylic acid). Polarization curves were recorded at 80 • C and ambient pressure before, intermittently, and after a carbon corrosion voltage cycling experiment. The Nafion/PVDF cathode MEA with the smallest amount of PVDF (80/20 Nafion/PVDF weight ratio) produced the highest maximum power at beginning-of-life (BoL), 545 mW/cm 2 at 100% RH, which was 35% greater than that for a conventional MEA with a neat Nafion binder. Carbon corrosion scaled inversely with cathode PVDF content, with a 33/67 Nafion/PVDF cathode binder MEA producing the highest end-of-life (EoL) power (330 mW/cm 2). MEAs with < 50 wt% PVDF in the cathode binder exhibited a power density decline during carbon corrosion, whereas the power increased during/after carbon corrosion for nanofiber cathodes with binders containing > 50 wt% PVDF due to favorable increases in the hydrophilicity of the carbon support and Pt mass activity, coupled with a lower carbon loss.
A series of electrospun nanofiber mat electrodes with two different commercial Pt/C catalysts and... more A series of electrospun nanofiber mat electrodes with two different commercial Pt/C catalysts and a binder of Nafion and poly(acrylic acid) were fabricated and evaluated. The electrodes were assembled into membrane-electrode-assemblies (MEAs) using Nafion 211 as the membrane. Variations in catalyst type, nanofiber composition (the ratio of Pt/C to Nafion), and fiber diameter had little or no impact on hydrogen/air fuel cell power output. 25 cm 2 nanofiber and sprayed gas diffusion electrode MEAs were compared in terms of beginning of life (BoL) and end of life (EoL) performance after automotive-specific load cycling (Pt dissolution) and start-stop cycling (carbon corrosion) cathode durability protocols. Nanofiber electrode MEAs (0.10 mg/cm 2 Pt loading for the anode and cathode) were clearly superior to sprayed MEAs; they produced more power at BoL and maintained a higher percentage of their power after the carbon corrosion durability protocol, resulting in much higher EoL fuel cell performance. On the other hand, there was no effect of electrode morphology on MEA durability for the Pt dissolution test. The higher MEA power output after carbon corrosion with electrospun electrodes is attributed to better oxygen and water transport within the nanofiber electrode and a higher electrochemical surface area for the fiber cathode.
Polyphosphazenes possess numerous properties that are attractive for PEM fuel-cell applications, ... more Polyphosphazenes possess numerous properties that are attractive for PEM fuel-cell applications, including thermal and chemical stability and the unlimited possibility for side-group functionalization. There are some impressive results in the literature, in particular ...
Nanofiber composite proton exchange membranes were fabricated and their properties measured, for ... more Nanofiber composite proton exchange membranes were fabricated and their properties measured, for possible use in a regenerative hydrogen/bromine fuel cell. The membranes were prepared from dual nanofiber mats, composed of Nafion ® perfluorosulfonic acid (PFSA) ionomer for proton transport and polyvinylidene fluoride (PVDF) for mechanical reinforcement. Two composite membranes structures containing Nafion volume fractions ranging from 0.30 to 0.65 were investigated: (1) Nafion nanofibers embedded in a PVDF matrix (N(fibers)/PVDF) and (2) PVDF nanofibers embedded in a Nafion matrix (N/PVDF(fibers)). The in-plane conductivity for films equilibrated in water and 2.0 M HBr scaled linearly with Nafion volume fraction for both morphologies. The through-plane proton conductivity of N(fibers)
PEM Fuel Cell Properties of Pre-Stretched Recast Nafion®
ECS Transactions, 2008
Pre-stretched recast Nafion is a new membrane material with many desirable properties for PEM fue... more Pre-stretched recast Nafion is a new membrane material with many desirable properties for PEM fuel cells. It was previously shown that the proton conductivity of this membrane in room temperature water was identical to that of commercial Nafion but its permeability to methanol was significantly reduced. Consequently, the power output from a direct methanol fuel cell with pre-stretched recast Nafion (draw ratio of 4) was 50% higher than that with Nafion 117. In an effort to better characterize pre-stretched recast Nafion, additional property measurements were made and compared to those for commercial Nafion. There was a substantial increase in the polymer crystallinity with increasing draw ratio which translated into improved membrane mechanical properties (a higher storage modulus and ultimate tensile strength). There was also a modest increase in the α-transition temperature when the membrane was elongated, as determined from dynamic mechanical analysis. Preliminary results indicat...
New Membrane Nano-Morphologies for Improved Fuel Cell Operation
Presented on February 4, 2009, from 4-5 pm in room G011 of the Molecular Science and Engineering ... more Presented on February 4, 2009, from 4-5 pm in room G011 of the Molecular Science and Engineering Building on the Georgia Tech Campus.
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