How Stable Are Spherical Platinum Nanoparticles Applied to Fuel Cells?

International audienc

Molecular dynamics study of ionomer and water adsorption at carbon support materials

Molecular dynamics simulations were applied to unravel the microscopic structure of Nafion ionomer and water adsorbed at graphitized carbon sheets. The considered molecular model resembles microscopic interfaces at which current generation proceeds in catalyst layers of polymer electrolyte fuel cells. The analysis of equilibrated interfacial configurations shows that Nafion ionomer forms a thin adhesive film on the graphite sheet. At low water content, water molecules form clusters around sulfonic acid groups. At high water content, a continuous water film wets the ionomer surface. The structural analysis of this model did not provide any evidence for interconnected water clusters existing inside the ionomer film, which implies that hydronium ion transport will occur mainly along hydrated ionomer surfaces.Des simulations de dynamique mol\ue9culaire ont \ue9t\ue9 appliqu\ue9es pour \ue9lucider la structure microscopique de l\u2019ionom\ue8re Nafion et de l\u2019eau adsorb\ue9s \ue0 la surface de feuillets de graph\ue8ne. Le mod\ue8le mol\ue9culaire \ue0 l'\ue9tude ressemble \ue0 des interfaces microscopiques o\uf9 se d\ue9roule la g\ue9n\ue9ration de courant dans les couches catalytiques des piles \ue0 combustible \ue0 membrane \ue9changeuse de protons. L\u2019analyse des configurations \ue9quilibr\ue9es des interfaces montre que l\u2019ionom\ue8re Nafion forme une couche adh\ue9sive mince sur le graph\ue8ne. \uc0 une teneur en eau faible, les mol\ue9cules d\u2019eau forment des agr\ue9gats autour des groupes d\u2019acide sulfonique. \uc0 une teneur en eau \ue9lev\ue9e, une couche uniforme d\u2019eau mouille la surface de l\u2019ionom\ue8re. L\u2019analyse structurale de ce mod\ue8le n\u2019a pas permis de prouver l\u2019existence d\u2019une interconnexion entre les agr\ue9gats de mol\ue9cules d\u2019eau \ue0 l\u2019int\ue9rieur de la couche d\u2019ionom\ue8re, ce qui laisse entendre que le transport des ions oxonium se produira principalement \ue0 la surface des ionom\ue8res hydrat\ue9s.Peer reviewed: YesNRC publication: Ye

Oxidation and Corrosion of Platinum–Nickel and Platinum–Cobalt Nanoparticles in an Aqueous Acidic Medium

International audienc

Nafion Ionomer aggregation and its influence on proton conduction and mass transport in fuel cell catalyst layers.

NRC publication: Ye

Oxidation-Resistant and Elastic Mesoporous Carbon with Single-Layer Graphene Walls

An oxidation-resistant and elastic mesoporous carbon, graphene mesosponge (GMS), is prepared. GMS has a sponge-like mesoporous framework (mean pore size is 5.8 nm) consisting mostly of single-layer graphene walls, which realizes a high electric conductivity and a large surface area (1940 m2 g−1). Moreover, the graphene-based framework includes only a very small amount of edge sites, thereby achieving much higher stability against oxidation than conventional porous carbons such as carbon blacks and activated carbons. Thus, GMS can simultaneously possess seemingly incompatible properties; the advantages of graphitized carbon materials (high conductivity and high oxidation resistance) and porous carbons (large surface area). These unique features allow GMS to exhibit a sufficient capacitance (125 F g−1), wide potential window (4 V), and good rate capability as an electrode material for electric double-layer capacitors utilizing an organic electrolyte. Hence, GMS achieves a high energy density of 59.3 Wh kg−1 (material mass base), which is more than twice that of commercial materials. Moreover, the continuous graphene framework makes GMS mechanically tough and extremely elastic, and its mean pore size (5.8 nm) can be reversibly compressed down to 0.7 nm by simply applying mechanical force. The sponge-like elastic property enables an advanced force-induced adsorption control.This work was supported by PRESTO, JST (H.N.); a Grant-in-Aid for Scientific Research (A), 15H01999 (T.K.); the Nano-Macro Materials, Devices and System Research Alliance; and the Network Joint Research Center for Materials and Devices