The combined experimental approach for in-situ Raman spectroscopy of the inner "anode I electrolyte" interfaces in solid oxide fuel cells under current load was examined in a case study centered on the behavior of gadoliniadoped ceria (GDC) interlayers between cermet anodes and stabilized zirconia membrane. The Raman spectra of ceria at 850 degrees C were found sensitive enough with respect to the variations of anodic current and fuel gas mixture composition, which induce oxygen nonstoichiometry changes in GDC. Linear dependence of the Raman peak area on the open-circuit voltage makes it possible to estimate local overpotentials at the GDC interlayer 'electrolyte interface under current load. The calculated local overpotentials exhibit a Tafel-like dependence on the current density, and are essentially independent on the hydrogen and water vapor partial pressures within the limits of experimental uncertainties. The relevant rate-determining mechanism may be associated with ion transfer via the GDC Izirconia interface, whilst the contributions of exchange-related processes involving gaseous phase are less significant in this interfacial zone.