Book/Dissertation / PhD Thesis

FZJ-2017-07238

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Poröse Transportschichten für die Polymerelektrolytmembran-Wasserelektrolyse

Höh, M. (Corresponding author)FZJ*

2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-262-7

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Please use a persistent id in citations: http://hdl.handle.net/2128/16205

Abstract: Water electrolysis uses electrical energy to split up water into oxygen and hydrogen. Hydrogenis relevant for future energy systems, among others it can serve as a storage medium for electrical energy from renewable energy converters like photovoltaic or wind energy systems. The polymer electrolye membrane water electrolyzer is considered to be especially suitable for this kind of application. In polymer electrolyte membrane water electrolyzers, water is fed through the so-called porous transport layer to the catalyst layer, where the water splitting takes place. These porous transport layers have to ensure the transport of water to the catalyst layer, the removal ofthe produced gas as well as the electrical contacting of the electrode. Therefore they influence the mass transport and the corresponding overvoltages and consequently the efficiency of the water electrolysis process. The goal of this work was to compare different porous transport layers with respect to their mass transport properties. This was done by comparing different kinds of porous transport layers, partly manufactured as part of this work and partly sourced from suppliers. These materials were electrochemically characterized in cell operation and compared with respect to their mass transport properties. By means of radiography methods (synchrotron and neutron radiation), the local mass transport in the electrolysis cells and within the porous transport layers was examined. A pore network model was used to simulate the mass transport within the porous transport layer and the simulation results were correlated with experimental results. This allowed to obtain the following findings: • The porous transport layers manufactured using tape casting yielded pore structure dependent cell efficiencies and mass transport overvoltages, with porosities of 27−30% (sintering temperatures of 800−850°C) showing the best cell efficiencies. • Analyzing the gas bubble discharge from the water saturated porous transport layer using synchrotron radiography enabled the observation of a current density dependent number of selective transport pathways for the produced gas. Characterizing the local gas- and water distribution using neutron radiography allowed to explain the globally observed und porosity dependent mass transport overvoltages. • Leveraging simulations of the gas and water transport within the porous transport layers, the limiting current densities for a continuous operation of electrolyzer cells could be derived. These were more than an order of magnitude smaller for materials with a porosity of 13% compared to materials with a porosity of greater or equal 27%.

Note: RWTH Aachen, Diss., 2017

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Contributing Institute(s):

1. Elektrochemische Verfahrenstechnik (IEK-3)

Research Program(s):

1. 135 - Fuel Cells (POF3-135) (POF3-135)

Appears in the scientific report 2017

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