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@BOOK{Suo:1021557,
      author       = {Suo, Yanpeng and Korte, Carsten},
      title        = {{I}nvestigation of the influence of cation acidity in
                      proton-conducting ionic liquids for the application as
                      electrolyte in a future intermediate-temperature fuel cell},
      address      = {online},
      publisher    = {RWTHpublications},
      reportid     = {FZJ-2024-00831},
      pages        = {pages 1 Online-Ressource : Illustrationen, Diagramme},
      year         = {2023},
      abstract     = {The operation of a Polymer electrolyte membrane fuel cells
                      in an intermediate temperature range between 100–140 °C
                      (IT-PEMFCs) would allow a significant simplified setup for
                      system (no water management, more efficient cooling), and
                      thus a cost cut. The use of proton-conducting ionic liquids
                      (PILs) as electrolytes for future IT-PEMFCs is a promising
                      approach, because of their unique properties. As water is
                      produced during fuel cell operation, the bulk properties of
                      PILs and the properties of the catalyst/PIL interface,
                      including the ORR kinetics, are significantly affected. It
                      is therefore crucial to investigate thoroughly the interface
                      structure and properties of binary PIL/H2O systems. In this
                      thesis, three PILs with different cation acidities were
                      selected to investigate the influence of the cation
                      acidities on the physicochemical and electrochemical
                      properties of PILs: 2-sulfoethylmethylammonium triflate
                      [2-Sema][TfO] ([2-Sema]+: pKa = 0.94), 1-Ethylimidazolium
                      triflate [EIm][TfO] ([EIm]+: pKa = 7.70) and
                      Diethylmethylammonium triflate [Dema][TfO] ([Dema]+: pKa =
                      10.55). PILs with higher pKa exhibit better thermal
                      stability due to a complete proton transfer to the cation.
                      All three PILs are thermally stable at 120 °C. The
                      conductivity of PILs depends strongly on their cation
                      acidities and the interaction between cations and anions.
                      All three PILs have 3–40 times higher values of the
                      product of oxygen diffusivity and solubility (DO2 ∙ cO2)
                      compared to the common electrolyte H3PO4 for high
                      temperature (HT-)PEMFCs, which is beneficial especially for
                      the mass transport in the ORR. The analysis of polarization
                      curves and cyclic voltammograms show that the ORR on
                      platinum electrodes takes place via an associative mechanism
                      with molecular adsorbed oxygen, where the first electron and
                      proton transfer to the oxygen molecules is rate determining.
                      It turned out, that only [2-Sema][TfO] with the highly
                      acidic [2-Sema]+ cation provides sufficient current
                      densities in the potential range relevant for fuel cell
                      application. Hence, a high acidity of the PIL cation is
                      crucial. Moreover, only the [2-Sema]+ cation participates in
                      the proton transfer to the oxygen molecules. On the other
                      hand, the significantly higher DO2 ∙ cO2 value and ORR
                      limiting current of the low acidic PILs suggests combining
                      favorable kinetic and bulk properties by mixing PILs with
                      highly and low acidic cations. For a future improvement of
                      the ORR, a detailed knowledge of the structure and
                      properties of the catalyst/PIL interface, such as the double
                      layer capacitance, is mandatory. The impedance analysis
                      revealed high and low frequency capacitances, C1 and C2,
                      assigned to (fast) ion transport and (slow)
                      pseudo-capacitive processes. The PILs exhibit significant
                      differences in the capacitance C1, which are attributed to a
                      higher compacity of the ions in the double layer in case of
                      [2-Sema][TfO] compared to the low acidic PILs. The increase
                      of peaks of C1 and C2 in the HUPD (hydrogen underpotential
                      deposition) and Pt oxidation region correlate well with the
                      corresponding effects in cyclic voltammograms. By addition
                      of water, C1 tends to increase. This is explained by a
                      change in the dielectric properties and the structure of the
                      double layer, including a lower stiffness of the ion layers,
                      a higher permittivity and a lower thickness.},
      keywords     = {Hochschulschrift (Other) / fuel cells ; protic ionic
                      liquids ; oxygen reduction reaction (ORR) ; electrode
                      kinetics ; double layer capacitance ; Brennstoffzellen ;
                      protische ionische Flüssigkeiten ;
                      Sauerstoffreduktionsreaktion ; Elektrodenkinetik ;
                      Doppelschichtskapazität (Other)},
      cin          = {IEK-14},
      cid          = {I:(DE-Juel1)IEK-14-20191129},
      pnm          = {1231 - Electrochemistry for Hydrogen (POF4-123)},
      pid          = {G:(DE-HGF)POF4-1231},
      typ          = {PUB:(DE-HGF)3},
      doi          = {10.18154/RWTH-2023-08372},
      url          = {https://juser.fz-juelich.de/record/1021557},
}