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@PHDTHESIS{Liu:822403,
      author       = {Liu, Chang},
      othercontributors = {Lehnert, Werner and Singheiser, Lorenz},
      title        = {{N}oble metal coated porous transport layers for polymer
                      electrolyte membrane water electrolysis},
      school       = {Rheinisch-Westfälische Technische Hochschule Aachen},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {RWTH-2021-06712},
      pages        = {1 Online-Ressource : Illustrationen},
      year         = {2021},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University; Dissertation, Rheinisch-Westfälische Technische
                      Hochschule Aachen, 2021},
      abstract     = {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.},
      cin          = {420520},
      ddc          = {620},
      cid          = {$I:(DE-82)420520_20140620$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2021-06712},
      url          = {https://publications.rwth-aachen.de/record/822403},
}