Membrane electrode assembly

About: Membrane electrode assembly is a research topic. Over the lifetime, 7134 publications have been published within this topic receiving 98472 citations.

Instability of Pt ∕ C Electrocatalysts in Proton Exchange Membrane Fuel Cells A Mechanistic Investigation

Abstract: Equilibrium concentrations of dissolved platinum species from a Pt/C electrocatalyst sample in 0.5 M H2SO4 at 80°C were found to increase with applied potential from 0.9 to 1.1 V vs reversible hydrogen electrode. In addition, platinum surface area loss for a short-stack of proton exchange membrane fuel cells PEMFCs operated at open-circuit voltage 0.95 V was shown to be higher than another operated under load 0.75 V. Both findings suggest that the formation of soluble platinum species such as Pt 2+ plays an important role in platinum surface loss in PEMFC electrodes. As accelerated platinum surface area loss in the cathode from 63 to 23 m 2 /gPt in 100 h was observed upon potential cycling, a cycled membrane electrode assembly MEA cathode was examined in detail by incidence angle X-ray diffraction and transmission electron microscopy TEM to reveal processes responsible for observed platinum loss. In this study, TEM data and analyses of Pt/C catalyst and cross-sectional MEA cathode samples unambiguously confirmed that coarsening of platinum particles occurred via two different processes: i Ostwald ripening on carbon at the nanometer scale, which is responsible for platinum particle coarsening from 3t o6 nm on carbon, and ii migration of soluble platinum species in the ionomer phase at the micrometer scale, chemical reduction of these species by crossover H2 molecules, and precipitation of platinum particles in the cathode ionomer phase, which reduces the weight of platinum on carbon. It was estimated that each process contributed to 50% of the overall platinum area loss of the potential cycled electrode.

Anhydrous proton conduction at 150 °C in a crystalline metal–organic framework

Abstract: Metal organic frameworks (MOFs) are particularly exciting materials that couple porosity, diversity and crystallinity. But although they have been investigated for a wide range of applications, MOF chemistry focuses almost exclusively on properties intrinsic to the empty frameworks; the use of guest molecules to control functions has been essentially unexamined. Here we report Na(3)(2,4,6-trihydroxy-1,3,5-benzenetrisulfonate) (named β-PCMOF2), a MOF that conducts protons in regular one-dimensional pores lined with sulfonate groups. Proton conduction in β-PCMOF2 was modulated by the controlled loading of 1H-1,2,4-triazole (Tz) guests within the pores and reached 5 × 10(-4) S cm(-1) at 150 °C in anhydrous H(2), as confirmed by electrical measurements in H(2) and D(2), and by solid-state NMR spectroscopy. To confirm its potential as a gas separator membrane, the partially loaded MOF (β-PCMOF2(Tz)(0.45)) was also incorporated into a H(2)/air membrane electrode assembly. The resulting membrane proved to be gas tight, and gave an open circuit voltage of 1.18 V at 100 °C.