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%0 Thesis
%A Liu, Chang
%T Noble metal coated porous transport layers for polymer electrolyte membrane water electrolysis
%I Rheinisch-Westfälische Technische Hochschule Aachen
%V Dissertation
%C Aachen
%M RWTH-2021-06712
%P 1 Online-Ressource : Illustrationen
%D 2021
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
%Z Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021
%X Polymer electrolyte membrane (PEM) water electrolyzers are electrochemical energy conversion devices that split water into its constituent elements of hydrogen and oxygen. Titanium-based porous transport layers (PTL) are widely used due to their good bulk conductivity, high corrosion resistivity, and excellent mechanical strength. However, titanium-based PTLs situated at the anode side of PEM electrolyzers are subjected to harsh oxidizing conditions such as high anode overpotential, low pH and oxygen evolution. Under these conditions, titanium (Ti0) changes its oxidation state over time, which induces the formation of a thin but continuously growing layer of passivated titanium (TiOx). Consequently, the contact resistance of titanium PTLs is adversely affected, critically decreasing cell performance and durability. In this thesis, a very simple and scalable method is used to protect the titanium-based PTL from passivation by sputtering very thin layers of noble metal coatings such as Ir, Pt, or Au onto the PTLs. The 20 to 50 nm thick noble metal coatings on the titanium fibers significantly decreased interfacial contact resistance between the PTL and catalyst layer, and improved cell performance. The single cells assembled with Ir- or Pt-coated PTLs delivered higher cell performance than cells with Au-coated PTLs, and nearly identical cell performance as carbon paper, which is prone to carbon corrosion under these operating conditions. The high cost of using noble metal coatings can be decreased by reducing the loading of the noble metals. The loading of Ir as a protective layer on the PTL has an impact on the cell performance. The amount of iridium on one side of the PTL was reduced to 0.025 mgIr∙cm-2 and showed identical cell performance as Ir-coated PTLs with higher iridium loading, which effectively reduced the cost of the Ir. The total amount of iridium is 40 times less compared to what is usually used in an anode catalyst layer, and 20 times less than Au or Pt typically used as protective layers in contemporary and commercial electrolyzers. The critical passivation of the bare titanium-based PTL is also one significant factor that restricts the durability of a PEM water electrolyzer. In order to investigate the durability of noble metal coatings (Ir, Pt, Au) on the PTLs, a series of long-term measurements were performed under 2 V and 80 °C on the single cells assembled with Ir-coated, Pt-coated and Au-coated PTLs, respectively. Compared to the cell without the coatings, the cell assembled with iridium and platinum coatings showed degradation rates close to zero, while the identical cell performance was observed after 4000 hours with a cell voltage of 2 V. These results demonstrate that iridium and platinum coatings on titanium-based PTLs are highly effective at protecting the PTL against passivation, ultimately improving cell performance and durability.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%R 10.18154/RWTH-2021-06712
%U https://publications.rwth-aachen.de/record/822403