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@INPROCEEDINGS{Edeh:1049914,
      author       = {Edeh, Obinna and Schäfer, Dominik and Samsun, Remzi Can
                      and Eichel, Rüdiger-A.},
      title        = {{I}mpact of {G}as {C}onversion {R}atios on {I}mpedance
                      {R}esponse and {N}on-{L}inear {B}ehavior of {SOEC}s in
                      {C}o-{E}lectrolysis {M}ode},
      issn         = {2151-2043},
      school       = {RWTH Aachen},
      reportid     = {FZJ-2025-05668},
      year         = {2025},
      abstract     = {High-temperature solid oxide electrolysis cells (SOECs)
                      have emerged as a promising technology to produce green
                      hydrogen and other valuable chemicals like syngas. SOECs
                      offer several advantages over conventional electrolysis
                      methods, including high efficiency, fuel flexibility, and
                      the ability to operate at elevated temperatures, which
                      favors the kinetics of electrochemical
                      reactions.[1,2]However, the widespread adoption of SOEC
                      technology faces challenges, particularly related to
                      performance degradation and the complex interplay of
                      operating parameters[3]. A crucial factor influencing SOEC
                      performance is the gas conversion ratio (CR), which reflects
                      the extent to which reactant gases (CO2 and H2O) are
                      converted into products (CO and H2). While researchers have
                      extensively studied the influence of CR using linear methods
                      like EIS and nonlinear methods like THD in solid oxide fuel
                      cells SOFCs[4], similar studies in SOECs have largely
                      neglected the non-linear techniques. This creates a critical
                      gap in understanding degradation mechanisms in SOECs,
                      particularly those arising from nonlinearities such as mass
                      transport limitations and beginning local
                      reactant-starvation at high CR. By combining EIS and THD in
                      our study, we provide an investigation of these effects in
                      co-electrolysis mode, leveraging the strengths of both
                      techniques to detect early nonlinear behavior and
                      elucidating their impact on SOEC performance and durability
                      at different CR.The study employs a comprehensive approach,
                      utilizing electrochemical impedance spectroscopy (EIS) as
                      the primary method, with distribution of relaxation times
                      (DRT) analysis as a deconvolution tool for evaluating EIS
                      spectra, along with the novel application of total harmonic
                      distortion (THD) as a diagnostic tool.[4]. The findings
                      reveal a strong correlation between increasing CR and
                      significant changes in the impedance response of the SOEC
                      stack. These changes point toward beginning localized
                      reactant-starvation (CR getting close to 100 $\%$ locally)
                      and mass transport limitations, as indicated by trends such
                      as higher impedance values and elevated THD indices at high
                      CR.Furthermore, this research proposes a mechanism linking
                      the observed linear and non-linear behaviors to the dynamics
                      of reactant and product transport within the SOEC. The
                      insights gained from this investigation contribute to a more
                      comprehensive understanding of SOEC operation under
                      different CR, emphasizing the need to optimize operating
                      conditions and electrode designs to mitigate mass transport
                      limitations. This work aims to pave the way for enhancing
                      SOEC performance, durability, and ultimately, the
                      feasibility of large-scale implementation of this promising
                      technology for a sustainable energy future.References[1] S.
                      R. Foit, I. C. Vinke, L. G. J. de Haart, R.-A. Eichel,
                      Angewandte Chemie International Edition 2017, 56,
                      5402–5411.[2] S. Gupta, M. Riegraf, R. Costa, M. P.
                      Heddrich, K. A. Friedrich, Ind. Eng. Chem. Res. 2024, 63,
                      8705–8712.[3] B. Königshofer, M. Höber, G. Nusev, P.
                      Boškoski, C. Hochenauer, V. Subotić, J. Power Sources
                      2022, 523, 230982.[4] H. Moussaoui, G. Hammerschmid, J. Van
                      herle, V. Subotić, Journal of Power Sources 2023, 556,
                      232352.[5] G. Jeanmonod, S. Diethelm, J. Van Herle, J. Phys.
                      Energy 2020, 2, 034002.[6] P. Caliandro, A. Nakajo, S.
                      Diethelm, J. Van herle, Journal of Power Sources 2019, 436,
                      226838.[7] N. J. Steffy, S. V. Selvaganesh, M. Kumar L, A.
                      K. Sahu, Journal of Power Sources 2018, 404, 81–88.[8] S.
                      Thomas, S. C. Lee, A. K. Sahu, S. Park, International
                      Journal of Hydrogen Energy 2014, 39, 4558–4565.},
      month         = {Jul},
      date          = {2025-07-14},
      organization  = {19th International Symposium on Solid
                       Oxide Fuel Cells, Stockholm (Sweden),
                       14 Jul 2025 - 18 Jul 2025},
      subtyp        = {After Call},
      cin          = {IET-1},
      ddc          = {540},
      cid          = {I:(DE-Juel1)IET-1-20110218},
      pnm          = {1231 - Electrochemistry for Hydrogen (POF4-123) / HITEC -
                      Helmholtz Interdisciplinary Doctoral Training in Energy and
                      Climate Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF4-1231 / G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)6},
      doi          = {10.1149/MA2025-031253mtgabs},
      url          = {https://juser.fz-juelich.de/record/1049914},
}