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@INPROCEEDINGS{Korte:1024852,
      author       = {Korte, Carsten and Suo, Yanpeng and Wippermann, Klaus and
                      Rodenbücher, Christian},
      title        = {{I}nfluence of {A}cidity, {W}ater and {T}emperature on the
                      {D}ouble {L}ayer {P}roperties of {P}rotic {I}onic {L}iquids
                      for {F}uture {F}uel {C}ell {A}pplications},
      issn         = {2151-2043},
      reportid     = {FZJ-2024-02518},
      year         = {2023},
      abstract     = {Polymer electrolyte membrane fuel cells (PEMFC) are a
                      viable alternative to combustion engines and rechargeable
                      batteries for automotive applications. However, the
                      operating temperature of PEMFCs using sulfonated
                      fluoropolymers, e.g. NAFION®, is limited below 80 °C
                      (ambient pressure), because the proton conduction relies on
                      the presence of water. A PEMFC operating above 100 °C would
                      allow a much more simplified system setup for water and heat
                      management. This requires novel non-aqueous protic
                      electrolytes. Proton conducting ionic liquids (PIL) are
                      promising candidates. [1,2]. However, the fuel cell relevant
                      electrode reactions—oxygen reduction and hydrogen
                      oxidation reaction (ORR/HOR)—are not as well understood as
                      in aqueous electrolytes.In this study, we employed
                      electrochemical impedance spectroscopy (EIS),
                      cyclovoltammetry (CV), chronoamperomery (CA) and steady
                      state current measurements to elucidate the double layer
                      properties of the platinum electrode/PIL interface, the
                      kinetics and possible mechanism of the ORR. Three PILs with
                      different cation acidities with an Brønsted-acidic cation
                      [HA+][X−] are compared, [Dema][TfO], [1-EIm][TfO] and
                      [2-Sema][TfO].Comparing the PILs with different cation
                      acidity strongly suggest that the first reduction step
                      including the proton transfer to the (catalytic) active
                      sites on the electrode is mainly determining the ORR rate.
                      The presence of residual water, unavoidable also at fuel
                      cell operation >100 °C, is another important parameter. H2O
                      modifies the ordered structure of the electrochemical double
                      layer. Its protolysis equilibrium with an acidic PIL cation
                      results in the formation of H3O+ that serves as a proton
                      donor in the rate determining step and thus influences the
                      ORR kinetics. Highly acidic PIL cations serve as a proton
                      donor as well, particularly at low H2O concentrations,
                      whereas the role of H3O+ as proton donor in the ORR becomes
                      more prominent at higher water concentrations [3]. In low
                      acidic PILs, H3O+ is the predominant proton donor and the
                      ORR rate is significantly smaller resulting in considerably
                      higher overpotentials. Thus, the onset potential of the ORR
                      in a PIL based fuel cell will depend on both the
                      concentration of residual water and the PIL cation
                      acidity.Plots of the potential-dependent data from EIS
                      measurements in the complex capacitance plane (CCP) show
                      that at least two differential double layer capacitances are
                      present, depending on the cell potential U (vs. RHE), water
                      concentration c(H2O) and temperature T. The double layer
                      properties of the highly acidic [2-Sema][TfO] are
                      significantly different compared to the less acidic PILs
                      [1-EIm][TfO] and [Dema][TfO]. The potential dependent
                      capacitance curves were discussed by taking a mean field
                      model, the presence of water and short range correlations of
                      ions into account. [4, 5] The combined electrochemical
                      kinetics and double layer measurements provide a deeper
                      insight into the double layer structure at the Pt
                      electrode/PIL interface to reveal the rate limiting
                      parameters of the ORR and its mechanism.[1] K. Wippermann,
                      J. Giffin, S. Kuhri, W. Lehnert and C. Korte, Phys. Chem.
                      Chem. Phys. 19, 24706 (2017)[2] K. Wippermann, Y. Suo and C.
                      Korte, J. Phys. Chem. C 125(8), 8 (2021)[3] H. Hou, H. M.
                      Schütz, J. Giffin, K. Wippermann, X. Gao, A. Mariani, S.
                      Passerini and C. Korte, ACS Appl. Mater. Interfaces 13, 8370
                      (2021)[4] Z. A. H. Goodwin, G. Feng and A. A. Kornyshev,
                      Electrochim. Acta 225, 190 (2017)[5] J. Friedl, I. I. E.
                      Markovits, M. Herpich, G. Feng, A. A. Kornyshev and U.
                      Stimming, ChemElectroChem 4, 216 (2017)},
      month         = {May},
      date          = {2023-05-28},
      organization  = {243rd ECS Meeting, Boston (USA), 28
                       May 2023 - 2 Jun 2023},
      cin          = {IEK-14},
      ddc          = {540},
      cid          = {I:(DE-Juel1)IEK-14-20191129},
      pnm          = {1231 - Electrochemistry for Hydrogen (POF4-123)},
      pid          = {G:(DE-HGF)POF4-1231},
      typ          = {PUB:(DE-HGF)1},
      doi          = {10.1149/MA2023-02562719mtgabs},
      url          = {https://juser.fz-juelich.de/record/1024852},
}