A comprehensive review on PEM water electrolysis

The flow of homogeneous fluids through porous media: analogies with other physical problems

In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics. Although quite well investigated for decades, PFSA ionomers’ complex behavior, along with their key role in many emerging technologies, have presented significant scientific challenges but also helped create a unique cross-disciplinary research field to overcome such challenges. Research and progress on PFSAs, especially when considered with their applications, are at the forefront of bridging electrochemistry and polymer (physics), which have also opened up development of state-of-the-art in situ characterization techniques as well as multiphysics computation models. Topics reviewed stem from correlating the various physical (e.g., mechanical) and transport properties with morphology and structure across time and length scales. In addition, topics of recent interest such as structure/transport correlations and modeling, composite PFSA membranes, degradat...

New Insights into Perfluorinated Sulfonic-Acid Ionomers

Due to the excellent proton conductivity of Nafion membranes in polymer electrolyte membrane fuel cells (PEMFCs), Nafion has been applied also in microbial fuel cells (MFCs). In literature, however, application of Nafion in MFCs has been associated with operational problems. Nafion transports cation species other than protons as well, and in MFCs concentrations of other cation species (Na+, K+, NH4+, Ca2+, and Mg2+) are typically 10(5) times higher than the proton concentration. The objective of this study, therefore, was to quantify membrane cation transport in an operating MFC and to evaluate the consequences of this transport for MFC application on wastewaters. We observed that during operation of an MFC mainly cation species other than protons were responsible for the transport of positive charge through the membrane, which resulted in accumulation of these cations and in increased conductivity in the cathode chamber. Furthermore, protons are consumed in the cathode reaction and, consequently, transport of cation species other than protons resulted in an increased pH in the cathode chamber and a decreased MFC performance. Membrane cation transport, therefore, needs to be considered in the development of future MFC systems.

Effects of membrane cation transport on pH and microbial fuel cell performance.

Lattice Boltzmann methods for multiphase flow and phase-change heat transfer

The proton conductivity of a series of extruded Nafion membranes @of equivalent weight ~EW! of 1100 and nominal dry thickness of 51, 89, 127, and 178 mm# has been studied. Measurements were made in 1 M H2SO4 at 298 K using a four-electrode, dc technique. The membrane area resistance increases with thickness, as expected, from 0.07 to 0.16 V cm2 for Nafion 112 and Nafion 117, respectively. However, in contrast to the published literature, after correcting for the membrane thickness, the conductivity of the membranes decreases with decreasing membrane thickness. For example, values of 0.083 and 0.16 S cm21 were obtained for Nafion 112 and 117 membranes, respectively. In situ current-interrupt measurements in a proton exchange membrane fuel cell confirmed the relatively poor conductivity of the membrane electrode assemblies ~MEAs! based on the thinner membranes. While a high contact resistance to the electrodes may have contributed to the in situ MEA resistance, water balance measurements over the MEA showed that the high resistance was not due to a low water content or to an uneven water distribution in the MEAs. The implications of the findings for the understanding of the membrane properties are discussed.

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Ionic Conductivity of an Extruded Nafion 1100 EW Series of Membranes

A polymer-electrolyte membrane fuel cell model that incorporates chemical degradation in perlfluorinated sulfonic acid membranes is developed. The model is based on conservation principles and includes a detailed description of the transport phenomena. A degradation sub-model describes the formation of hydrogen peroxide \/\it via\/ distinct mechanisms in the cathode and anode, together with the subsequent formation of radicals \/\it via\/ Fenton reactions involving metal-ion impurities. The radicals participate in the decomposition of reactive end groups to form carboxylic acid, hydrogen fluoride and CO_2. Degradation proceeds through unzipping of the polymer backbone and cleavage of the side chains. Simulations are presented and the numerical code is shown to be extremely time efficient. Known trends with respect to operating conditions are qualitatively captured and the exhibited behaviour is shown to be robust to changes in the rate constants. The feasibility of a chemical degradation mechanism based on peroxide and radical formation is discussed.

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Modeling and Simulation of the Degradation of Perfluorinated Ion-Exchange Membranes in PEM Fuel Cells

Recent trends and developments in polymer electrolyte membrane fuel cell modelling

Platinum-coated Nafion 117 structures were characterised using electrochemical measurements of platinum surface area and a number of microscopy techniques. The morphology and composition of the platinum deposits were related to their preparation conditions in terms of platinum salt concentration, electrolyte flow and the surface roughness of Nafion 117. Platinum surface areas achieved were higher than the values predicted for ideal spherical platinum particles of average diameter. This is due to a fine microstructure, which realises much smaller platinum particles than average (down to about 50 nm) allied to the geometry produced by their clustering to form nodules (about 0.1–1.5 µm diameter micro-nodules and about 3–5 µm macro-nodules). Adherent platinum deposits with high surface areas were promoted by using roughened Nafion 117 membranes and enhancing the mass transport of chloroplatinate and tetraborohydrate ions by magnetic stirring of the electrolyte. A flow cell produced much more reproducible platinum-coated Nafion 117 structures. At best, platinum surface areas of 30–50 m2 g–1 Pt were achieved at platinum penetration depths of 5–30 µm into the membrane surface.

T. R. Ralph

Papers

Ionic Conductivity of an Extruded Nafion 1100 EW Series of Membranes

Modeling and Simulation of the Degradation of Perfluorinated Ion-Exchange Membranes in PEM Fuel Cells

Recent trends and developments in polymer electrolyte membrane fuel cell modelling

Electrochemical and microscopic characterisation of platinum-coated perfluorosulfonic acid (Nafion 117) materials

The electrochemistry of l-cystine and l-cysteine part 2 : Electrosynthesis of l-cysteine at solid electrodes