Performance and durability studies of perfluorosulfonic acid ionomers as binders in PEMFC catalyst layers using Electrochemical Impedance Spectroscopy (original) (raw)
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International Journal of Hydrogen Energy, 2014
We report on polymer electrolyte membrane fuel cells (PEMFCs) that function at high temperature and low humidity conditions based on short-side-chain perfluorosulfonic acid ionomer (SSC-PFSA). The PEMFCs fabricated with both SSC-PFSA membrane and ionomer exhibit higher performances than those with long-side-chain (LSC) PFSA at temperatures higher than 100 C. The SSC-PFSA cell delivers 2.43 times higher current density (0.524 A cm À1) at a potential of 0.6 V than LSC-PFSA cell at 140 C and 20% relative humidity (RH). Such a higher performance at the elevated temperature is confirmed from the better membrane properties that are effective for an operation of high temperature fuel cell. From the characterization technique of TGA, XRD, FT-IR, water uptake and tensile test, we found that the SSC-PFSA membrane shows thermal stability by higher crystallinity, and chemical/mechanical stability than the LSC-PFSA membrane at high temperature. These fine properties are found to be the factor for applying Aquivion™ E87-05S membrane rather than Nafion ® 212 membrane for a high temperature fuel cell.
ACS Applied Materials & Interfaces, 2021
Transport phenomena are key in controlling performance of electrochemical energy-conversion technologies and can be highly complex involving multiple length-scales and materials/phases. Material designs optimized for one reactant species transport however may inhibit other transport processes. We explore such trade-offs in the context of polymer-electrolyte fuel-cell (PEFC) electrodes, where ionomer thin films provide the necessary proton conductivity but retard oxygen transport to the Pt reaction site and cause interfacial resistance due to sulfonate/Pt interactions. We examine electrode overall gas-transport resistance and its components as a function of ionomer content and chemistry. Low equivalent-weight ionomers allow better dissolved-gas and proton transport due to greater water uptake and low crystallinity, but also cause significant interfacial resistance due to high density of sulfonic-acid groups. These effects of equivalent weight are also observed via in-situ ionic conductivity and CO displacement measurements. Of critical importance, the results are supported by ex-situ ellipsometry and x-ray scattering of model thin-film systems, thereby providing direct linkages and applicability of model studies to probe complex heterogeneous structures. Structural and resultant performance changes in the electrode are shown to occur above a threshold sulfonic-group loading highlighting the significance of ink-based interactions. Our findings and methodologies are applicable to a variety of solid-state energy-conversion devices and material designs.
The proton conductive Nafion ® type membranes with perfluorosulfonic acid as basis are compounds of a polymer belonging to the family of the ionomers. The properties of these materials with respect to those of normal polymers are focused on the interaction ion-polymer in the ionomers allowing among others; conductive characteristics, hence its applications are diverse. The membrane Nafion ® is commonly used as an electrolyte in the proton exchanging membrane fuel cell (PEMFC). Different kinetic and transport phenomena (mass, electrons and charges) are producing in this electrochemical device during its operation. Particularly, the electrical resistance on the Nafion surface contributes significantly in the phenomena associated with the transport of electrons between the interfaces carbon -catalyst -electrolyte developing a significant effect on the PEMFC performance. This paper presents the statistical analyses results of an experimental design 2 3 type with central compound for the records of Superficial Electrical Resistance (SER) measured on both sides of a Nafion 115 (N115) activated and other similar non activated. The statistical results show at 95% confiability, the evidence that process activation produce some modifications in the electrical resistance characteristics on the surface of N115, this includes; decrease in the SER average value in 10 times approximately, the formation of areas with different values SER and a randomization of these regions. Finally, the zones with different levels in ohmic losses may affect the PEMFC performance by non homogeneous conversion of chemical energy in electrical energy and increase of the thermal energy generated in the fuel cell.
2019
Rapid improvements in polymer-electrolyte fuel-cell (PEFC) performance have been driven by the development of commercially available ion-conducting polymers (ionomers) that are employed as membranes and catalyst binders in membrane-electrode assemblies. Commercially available ionomers are based on a perfluorinated chemistry comprised of a polytetrafluoroethylene (PTFE) matrix that imparts low gas permeability and high mechanical strength but introduces significant mass-transport losses in the electrodes. These transport losses currently limit PEFC performance, especially for low Pt loadings. In this study, we present a novel ionomer incorporating a glassy amorphous matrix based on a perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone. The novel backbone chemistry induces structural changes in the ionomer, restricting ionomer domain swelling under hydration while disrupting matrix crystallinity. These structural changes slightly reduce proton conductivity while significant...
Journal of Power Sources, 2011
A new Aquivion TM E79-03S short-side chain perfluorosulfonic membrane with a thickness of 30 m (dry form) and an equivalent weight (EW) of 790 g/equiv recently developed by Solvay-Solexis for hightemperature operation was tested in a pressurised (3 bar abs.) polymer electrolyte membrane (PEM) single cell at a temperature of 130 • C. For comparison, a standard Nafion TM membrane (EW 1100 g/equiv) of similar thickness (50 m) was investigated under similar operating conditions. Both membranes were tested for high temperature operation in conjunction with an in-house prepared carbon supported Pt electrocatalyst. The electrocatalyst consisted of nanosized Pt particles (particle size ∼2 nm) dispersed on a high surface area carbon black. The electrochemical tests showed better performance for the Aquivion TM membrane as compared to Nafion TM with promising properties for high temperature PEM fuel cell applications. Beside the higher open circuit voltage and lower ohmic constraints, a higher electrocatalytic activity was observed at high temperature for the electrocatalyst-Aquivion TM ionomer interface indicating a better catalyst utilization.
Electrochimica Acta, 2001
The influence of the Nafion content in polymer electrolyte fuel cell (PEFC) gas diffusion electrodes with intermixed ionomer in the catalyst was evaluated. Electrochemical studies were carried out in a 50 cm 2 single cell in H 2 /air operation at 70°C. Low platinum loading (0.1 mg cm 2 ) electrodes with a Nafion content ranging from 14 to 66 wt% were studied. The performance of PEFC electrodes is affected by the Nafion content and an optimal content of about 33 wt% of ionomer was found. Hg intrusion porosimetry and cyclic voltammetry were carried out to evaluate the pore size distribution and the electrochemical surface area respectively. These data were correlated with single-cell performance. The electrochemical experimental data were analysed using a theoretical equation and the kinetics parameters obtained were related to the catalytic layer structure.
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. #
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.
Clean Technologies
Despite being the most employed polymer electrolyte for proton exchange membrane fuel cells (PEMFCs), Nafion® has several limitations: expensiveness, poor performance when exposed to temperatures higher than 80 °C, and its potential as a source of environmentally persistent and toxic compounds (i.e., per- and polyfluoroalkyl substances, known as PFASs) when disposed of. This work explores the functional and environmental performances of three potential PFAS-free alternatives to Nafion® as electrolytic membranes in PEMFCs: sulfonated graphene oxide (SGO), graphene oxide-naphthalene sulfonate (GONS), and borate-reinforced sulfonated graphene oxide (BSGO). Investigated via ATR-FTIR spectroscopy, TGA, and cross-sectional SEM, the membranes show an effective functionalization of GO and good thermal stability. Functional properties are determined via Ion Exchange Capacity (IEC) evaluation, Electrochemical Impedance Spectroscopy, and tensile tests. In terms of IEC, the innovative materials...