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The degradation mechanisms and phenomena of membrane electrode assembly (MEA) for proton exchange membrane fuel cell (PEMFC under low humidity operation were investigated by means of several on-line electrochemical methods and transmission electron microscopy (TEM). Electrochemical active surface area (ECSA) of catalyst and hydrogen crossover of MEA were evaluated by cyclic voltagram (CV) and linear sweep voltagram (LSV), respectively. The decrease of catalytic active site and degradation of membrane were evident by ECSA loss and hydrogen crossover rate increase after long-term discharging test. Membrane degradation played the major role for MEAs failure under low humidity operation in this study. The Pt clusters were also observed in the membrane, formed by Pt ions migration and reduction in the membrane, which can react with the crossover gases to produce free radicals that attack membrane and ionomers in the catalyst layer.Those phenomena will drive membrane to rupture and cause a short circuit in MEA. By AST experiments and fluoride release rate results, the MEA with Pt-alloy/C catalyst can show better performance and durability due to its high selectivity on ORR to depress the free radicals formation. [ABSTRACT FROM AUTHOR]

Abstract: Here we report a novel electrophoretic deposition technology for assembling surface-roughened inorganic nanoplatelets into ordered multilayers that mimic the brick-and-mortar nanostructure found in the nacreous layer of mollusk shells. A thin layer of sol–gel silica is coated on smooth gibbsite nanoplatelets in order to increase the surface roughness to mimic the asperity of aragonite platelets found in nacres. To avoid the severe cracking caused by the shrinkage of sol–gel silica during drying, polyelectrolyte polyethyleneimine is used to reverse the surface charge of silica-coated-gibbsite nanoplatelets and increase the adherence and strength of the electrodeposited films. Polymer nanocomposites can then be made by infiltrating the interstitials of the aligned nanoplatelet multilayers with photocurable monomer followed by photopolymerization. The resulting self-standing films are highly transparent and exhibit nearly three times higher tensile strength and one-order-of-magnitude higher toughness than those of pure polymer. The measured tensile strength agrees with that predicted by a simple shear lag model. [Copyright &y& Elsevier]

Abstract: Bio-inspired assembly of platelet particles and polyelectrolytes into ordered layered composites is of great technological importance in developing light-weight reinforced materials, separation membranes, and gas-barrier coatings. Unfortunately, the broadly applied layer-by-layer self-assembly technology is tedious in generating thick multilayered coatings. Here, we report a rapid and scalable cathodic electrophoretic co-deposition technology that enables simultaneous assembly of positively charged gibbsite nanoplatelets and cationic polyelectrolytes into ordered multilayers in a single step. The resulting nanocomposites have similar organic/inorganic weight ratio and ordered brick-and-mortar nanostructure as natural nacres. Nanoindentation tests show that the electrodeposited nanocomposites exhibit similar hardness and reduced modulus as those of pure gibbsite coatings. [Copyright &y& Elsevier]

Abstract: We report a simple and rapid electrophoretic deposition technology for assembling gibbsite (Al(OH)3) nanoplatelets/polyvinyl alcohol nanocomposites in a single step. The single-crystalline gibbsite nanoplatelets with high-aspect ratio are preferentially oriented with their crystallographic c-axis perpendicular to the electrode surface, mimicking the ordered brick-and-mortar nanostructure found in the nacreous layer of mollusk shells. The electrodeposited inorganic–organic nanocomposite films are optically transparent and flexible, even though the weight fraction of the brittle inorganic phase is higher than 80%. The current bottom-up technology enables scalable production of large-area nanocomposites with ordered layered structure that have potential applications ranging from gas-barrier films for optoelectronic devices to light-weight reinforced materials. [Copyright &y& Elsevier]