Efficient water management of composite membranes operated in polymer electrolyte membrane fuel cells under low relative humidity (original) (raw)
Related papers
ACS Applied Materials & Interfaces, 2014
We describe a facile route to fabricate mesoporous metal oxide (TiO 2 , CeO 2 and ZrO 1.95) nanotubes for efficient water retention and migration in a Nafion membrane operated in polymer electrolyte fuel cell under low relative humidity (RH). Porous TiO 2 nanotubes (TNT), CeO 2 nanotubes (CeNT), and ZrO 1.95 (ZrNT) were synthesized by calcining electrospun polyacrylonitrile nanofibers embedded with metal precursors. The nanofibers were prepared using a conventional single spinneret electrospinning technique under an ambient atmosphere. Their porous tubular morphology was observed by SEM and TEM analyses. HR-TEM results revealed a porous metal oxide wall composed of small particles joined together. The mesoporous structure of the samples was analyzed using BET. The tubular morphology and outstanding water absorption ability of the TNT, CeNT, and ZrNT fillers resulted in the effective enhancement of proton conductivity of Nafion composite membranes under both fully humid and dry conditions. Compared to a commercial membrane (Nafion, NRE-212) operated under 100% RH at 80°C, the Nafion−TNT composite membrane delivered approximately 1.29 times higher current density at 0.6 V. Compared to the Nafion-TiO 2 nanoparticles membrane, the Nafion−TNT membrane also generated higher current density at 0.6 V. Additionally, compared to a NRE-212 membrane operated under 50% RH at 80°C, the Nafion−TNT composite membrane exhibited 3.48 times higher current density at 0.6 V. Under dry conditions (18% RH at 80°C), the Nafion−TNT, Nafion-CeNT, and Nafion-ZrNT composite membranes exhibited 3.4, 2.4, and 2.9 times higher maximum power density, respectively, than the NRE-212 membrane. The remarkably high performance of the Nafion composite membrane was mainly attributed to the reduction of ohmic resistance by the mesoporous hygroscopic metal oxide nanotubes, which can retain water and effectively enhance water diffusion through the membrane.
Journal of Membrane Science, 2015
We report a high performance and durable electrolyte membrane operated in polymer electrolyte membrane fuel cells under low relative humidity (RH). This was accomplished by incorporating water retaining mesoporous zirconium oxide (ZrO 1.95) nanotubes (ZrNT) in a perfluorosulfonic acid (Nafion) membrane. Porous ZrNT with average diameters of 90 nm was synthesized by pyrolysing electrospun zirconium precursor embedded polymer fibers at 600 o C under an air atmosphere. The superior water retention ability and the tubular morphology of the ZrNT fillers resulted in facile water diffusion though the membrane, leading to a significant improvement in membrane proton conductivity under both fully humid and dry conditions. Compared to a commercial membrane (Nafion, NRE-212) operated under 50, and 100 % RH at 80 o C, the Nafion-ZrNT membrane exhibited 2.7, and 1.2 times higher power density at 0.6 V, respectively. Under dry condition (18% RH at 80 o C), the Nafion-ZrNT membrane exhibited 3.1 times higher maximum power density than the NRE-212 membrane. In addition, the Nafion-ZrNT membrane also exhibited durable operation for 200 h under 18% RH at 80 o C. The remarkably high performance of the Nafion-ZrNT composite membrane was mainly attributed to the reduction of ohmic resistance by incorporating the mesoporous hygroscopic ZrO 1.95 nanotubes.
Journal of Power Sources, 2002
Composite polymer electrolyte membranes were prepared by impregnating Nafion solution into the porous expanded PTFE (ePTFE) films as a substrate and their single cell performance, gas permeability, water flux, and water uptake were investigated. Although the nitrogen permeability of the composite membrane was higher than that of Nafion 112, there was not the serious cross-over of gases to diminish cell performance and it was seen that the cell performance could be improved by reduced thickness of the composite membrane. It was also seen that water uptake and water flux of the composite membrane were dependent on the Nafion loading amount on the substrate and, therefore, the thickness of the membrane. The water uptake as well as the water flux of the composite membrane increased as the Nafion loading amount increased and the increase rate of water uptake with temperature for the composite membranes was found to be larger than Nafion 112. #
Nafion–Titanate Nanotube Composite Membranes for PEMFC Operating at High Temperature
Journal of The Electrochemical Society, 2007
Nafion-titanate nanotube composites were investigated as electrolytes for proton exchange membrane fuel cells ͑PEMFCs͒ operating at high temperature T. With the addition of 5-15 wt % of nanotubes to the ionomer, PEMFC performance can be significantly sustained for T up to 130°C. The polarization curves of PEMFCs using the composite electrolytes reflect a competing effect between an increase in water uptake due to the extremely large surface area of the nanotubes and a decrease in proton conductivity of the composites.
ECS Transactions, 2007
Nafion-trititanate nanotubes composites were investigated as electrolytes for proton exchange membrane fuel cells (PEMFC) operating at high temperatures (T). With the addition of 5-15 wt.% of nanotubes to the ionomer, PEMFC performance can be significantly sustained for T up to 130 {degree sign}C. This behavior reflects a competing effect between an increase in water uptake due to the extremely large surface area of the nanotubes and a decrease in proton conductivity of the composites.
Journal of Polymer Science Part B-polymer Physics, 2006
Measurements of the mechanical and electrical properties of Nafion and Nafion/titania composite membranes in constrained environments are reported. The elastic and plastic deformation of Nafion-based materials decreases with both the temperature and water content. Nafion/titania composites have slightly higher elastic moduli. The composite membranes exhibit less strain hardening than Nafion. Composite membranes also show a reduction in the long-time creep of 4040% in comparison with Nafion. Water uptake is faster in Nafion membranes recast from solution in comparison with extruded Nafion. The addition of 3-20 wt % titania particles has minimal effect on the rate of water uptake. Water sorption by Nafion membranes generates a swelling pressure of 400.55 MPa in 125-lm membranes. The resistivity of Nafion increases when the membrane is placed under a load. At 23 8C and 100% relative humidity, the resistivity of Nafion increases by $15% under an applied stress of 7.5 MPa. There is a substantial hysteresis in the membrane resistivity as a function of the applied stress depending on whether the pressure is increasing or decreasing. The results demonstrate how the dynamics of water uptake and loss from membranes are dependent on physical constraints, and these constraints can impact fuel cell performance.
International Journal of Hydrogen Energy, 2012
Nafion Polymer electrolyte membrane fuel cells Dynamical mechanic analyses Vibrational spectroscopy Fabrication and testing of membrane-electrode assemblies a b s t r a c t In this report, three hybrid inorganic-organic proton-conducting membranes based on a novel fluorinated titania labeled TiO 2 F dispersed in Nafion were prepared. The mass fraction of TiO 2 F nanofiller ranged between 0.05 and 0.15. The water uptake and the proton exchange capacity of the membranes were determined; the membranes were further characterized by TG, DMA and FT-IR ATR investigations. Finally, the hybrid membranes were used in the fabrication of membrane-electrode assemblies (MEAs), which were tested in operating conditions as a function of the back pressure and of the hydration degree of the reagents streams. It was demonstrated that, with respect to pristine recast Nafion, at 25%RH the MEA fabricated with the membrane including a mass fraction of TiO 2 F equal to 0.10 yielded a higher maximum power density (0.206 W cm À2 vs. 0.121 W cm À2 ). Finally, it was proposed a coherent structural model of this family of hybrid membranes accounting for both the properties determined from "ex-situ" characterizations and for the performance obtained from measurements in a single fuel cell in operating conditions.
International Journal of Hydrogen Energy, 2017
An innovative membrane-electrode assembly, based on a polyoxometalate (POM)-modified low-Pt loading cathode and a sulphated titania (S-TiO 2)-doped Nafion membrane, is evaluated in a polymer electrolyte membrane fuel cell. The modification of fuel cell cathode with Cs 3 HPMo 11 VO 40 polyoxometalate is performed to enhance particles dispersion and increase active area, allowing low Pt loading while maintaining performance. The POM's high surface acidity favors kinetics of oxygen reduction reaction. The mesoporous features of POM allow the embedding of Pt inside the micro-mesopores, avoiding the Pt aggregation during fuel cell operation and delaying the aging process, with consequent increase of lifetime. On the other hands, commercial Nafion is modified with superacidic sulphated titanium oxide nanoparticles, allowing operation at low relative humidity and controlled polarization of the MEA. Further MEAs, formed by unmodified Nafion membrane and the POM-based cathode, as well as sulphated titanium-added Nafion and commercial Pt-based electrodes, are used as terms of comparison. The cell performances are studied by polarization curves, electrochemical impedance spectroscopy, Tafel plot analysis and high frequency resistance measurements. The dependence of cell performances on relative humidity is also studied. The catalytic and transport properties are improved using the coupled system, despite the reduced Pt loading, thanks to rich proton environment provided by cathode and membrane.
Journal of Power Sources, 2007
A novel Pt/zeolite-Nafion (PZN) polymer electrolyte composite membrane is fabricated for self-humidifying polymer electrolyte membrane fuel cells (PEMFCs). A uniform dispersion of Pt nanoparticles with an average size of 3 nm is achieved by ion-exchange of the zeolite HY. The Pt nanoparticles embedded in the membrane provide the catalytic sites for water generation, whereas the zeolite HY-supported Pt particles absorbs water and make it available for humidification during cell operation at elevated temperature. Compared with the performance of ordinary membranes, the performance of cells with PZN membranes is improved significantly under dry conditions. With dry H 2 and O 2 at 50 • C, the PZN membrane with 0.65 wt.% of Pt/zeolite (0.03 mg Pt cm −2) gives 75% of the performance obtained at 0.6 V with the humidified reactants at 75 • C. Impedance analysis reveales that an increase in charge-transfer resistance is mainly responsible for the cell performance loss operated with dry gases.