Significance Statement
The current collector of a proton exchange membrane electrolyzer consists of a porous structure of titanium such as a sintered disc, foams, felt or expanded meshes. However, the water or gas management faced by micro-structured current collector remains challenging in proton exchange membrane electrolysis.
The interfacial contact resistance between current collector and catalyst layer can be further lowered by use of expensive precious metal group coatings on current collector. This reduction is achieved in proton exchange membrane fuel cells by introducing a backing or micro-porous layer between the catalytic layer and carbon current collector or gas diffusion layer. Its resulting effect has led to reduction in ohmic losses, better transport for various species required for reaction and serves as a backing layer in proton exchange membrane fuel cells, buffering regions between diffusion media and the catalyst layer. Despite the listed improved performance on proton exchange membrane fuel cells, none has been provided in terms of proton exchange membrane electrolyzers.
Researchers from the Institute of Engineering Thermodynamics at the German Aerospace Center developed a macro-porous layer produced by thermal spraying on the current collector of a proton exchange membrane electrolyzer. A new paper describing the research was published in the peer-reviewed journal of Power Sources.
The authors deposited porous titanium coatings by vacuum plasma spraying on 5 x 5 cm2 sintered titanium while only one side of the current collector that is in contact with catalyst layer was coated. Electrochemical tests were performed in 25 cm2 single proton exchange membrane electrolyzer cells using the porous titanium as current collector with and without macro-porous layer.
When several layers were deposited on the current collector in order to check their effects on water or gas management, the first two layers of titanium produced a leakage rate of 480 mbar 1 cm-2 s-1, with addition of two more layers, leakage rate decreased further by two third to 112 mbar 1 cm-2 s-1. Hence, additional increase in layers resulted to lower leakage rate and higher density of coating.
Current-voltage characteristics and Nyquist plots showed that the electrolyzer with macro-porous layer had lower internal ohmic resistance compared to one without macro-porous layer. Moreover, macro-porous layer on current collector had a moderate impact on performance of the electrolyzer when operating at current densities below 1.2 Acm-2 but its effect was discovered to be more profound at higher densities.
The use of thermal spraying for coating the current collector of proton exchange membrane electrolyzers have been shown in this study to provide appropriate structures showing potential for further improvement of the macro-porous layer.
About the author
Philipp Lettenmeier was born in 1988 in Stuttgart (Germany) and studied chemical engineering at the Friedrich – Alexander University of Erlangen – Nuremberg (Germany) and at the Åbo Akademi University of Turku (Finland) and received his Master of Science in 2014. Since April 2014, he works as a scientist in the field of electrochemical energy technology at the Institute of Engineering Thermodynamics at the German Aerospace Center (DLR) in Stuttgart/Germany.
He is currently pursuing his Ph. D. degree at the University of Stuttgart (Germany) on the development and integration of new polymer exchange membrane (PEM) electrolyzer components.
Since January 2015 he is a founder member of H2FLY GmbH, the operator of the world’s first hydrogen fuel cell passenger Aircraft. In 2016, he shared the 2nd place F-Cell award for “Innovative materials and components for PEM electrolysis”.
About the author
Svenja Kolb studied environmental engineering at the University of Applied Science Amberg. She received her B.Eng. in 2013 for the development of an ex-situ-method for determining the condensation rate in gas diffusion media for PEM fuel cells.
Since June 2013, she works in the field of electrochemical energy technology at the Institute of Engineering Thermodynamics at the German Aerospace Center (DLR) in Stuttgart/Germany. She is responsible for setting up and operating test rigs in the field of PEM water electrolysis systems.
Since October 2015 she is studying environmental engineering at the University of Stuttgart and will finish as Master of Science in 2016. Currently she is writing her master thesis about thermally sprayed current collectors for PEM electrolyzers in cooperation with the team of Prof. Aimy Bazylak at the University of Toronto.
About the author
Fabian Burggraf studied chemistry at the University of Freiburg where he received his diploma degree in 2009. In 2012 he received his PhD degree in theoretical chemistry from the University of Freiburg for his research on ground-state charge transfer processes in photosynthesis at the Institute of Physical Chemistry. In 2013 he joined the Electrochemical Energy Technology group of Prof. K.A. Friedrich at the Institute of Engineering Thermodynamic at the German Aerospace Center in Stuttgart where he was in charge of the “Low- temperature fuel cell systems and electrolysis“ team.
His research interests included the durability and degradation of PEM water electrolyzers, power-to- hydrogen applications as well as mobile and stationary applications of low- temperature fuel cell systems.
In 2016, he joined the Climate Partner Upper Rhine Valley in Freiburg as an innovation and cluster manager. He is in charge of the Innovation- and Efficiency Cluster innoEFF with special focus on energy efficiency technologies and the sustainable use of renewable energies in the private, industry and mobility sector.
About the author
Aldo Gago received his doctorate degree in chemistry in 2011, under supervision of Prof. Nicolas Alonso-Vante, from the University of Poitiers, France. He joined the section of Electrochemical Energy Technology of the German Aerospace Center (DLR) in 2013, led by Prof. K. Andreas Friedrich to work on the development of coatings and catalysts for proton exchange membrane (PEM) electrolyzers, filing several patent applications. In addition, he has developed testing protocols and identified degradation mechanisms in PEM electrolyzer stack components, resulting in numerous publications in renowned scientific journals.
In 2016, he and co-workers were awarded with the 2nd place F-Cell prize for their contributions in the field. He is currently responsible for the team of low temperature electrolyzer systems, as well as project leader and laboratory manager.
About the author
Prof. K. Andreas Friedrich is Head of the Section “Electrochemical Energy Technology” at the German Aerospace Center and professor for Mechanical Engineering at the University of Stuttgart. His research area is electrochemical energy conversion and storage, in particular the technologies of polymer electrolyte fuel cells and electrolyzers, solid oxide fuel cells and electrolyzers, system design and optimization and advanced lithium batteries.
Prof. Friedrich has authored and coauthored about 200 papers ranging from fundamental aspects to system integration in applications. He received the Fischer medal (Dechema) in 2009 and the Ertl prize 2014 for his scientific work. His group was recognized with the 2008 F-Cell Award together with Airbus for fuel cell development in aeronautic applications, the Clean Tech Media Award 2012 and the 2nd place F-Cell Award 2016 for “Innovative materials and components for PEM electrolysis”.
Journal Reference
P. Lettenmeier1, S. Kolb1, F. Burggraf1, A.S. Gago1 , K.A. Friedrich1, 2. Towards developing a backing layer for proton exchange membrane electrolyzers, Journal of Power Sources, Volume 311, 2016, Pages 153–158.
[expand title=”Show Affiliations”]
- Institute of Engineering Thermodynamics, German Aerospace Center, Pfaffenwaldring 38-40, Stuttgart 70569, Germany
- Institute of Energy Storage, University of Stuttgart, Keplerstraße 7, Stuttgart 70174, Germany
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Abstract
Current energy policies require the urgent replacement of fossil energy carriers by carbon neutral ones, such as hydrogen. The backing or micro-porous layer plays an important role in the performance of hydrogen proton exchange membrane (PEM) fuel cells, reducing contact resistance and improving reactant/product management. Such carbon-based coating cannot be used in PEM electrolysis since it oxidizes to CO2 at high voltages. A functional titanium macro-porous layer (MPL) on the current collectors of a PEM electrolyzer is developed by thermal spraying. It improves the contact with the catalyst layers by ca. 20 mΩ cm2, increasing significantly the efficiency of the device when operating at high current densities.
Go To Journal of Power Sources
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