Electrode polarization measurements in the Fe|SrCe0.95Yb0.05O2.975|Au proton conducting solid electrolyte cell

The effect of hydrogen partial pressure (1.3-5.8 kPa) and cell temperature (600-800 °C) on the kinetics and mechanism of the charge transfer electrode reaction taking place at the three phase boundary H2-Fe-SCY (SCY = SrCe0.95Yb0.05O2.975), was thoroughly examined by performing electrode polarization measurements. A three electrode single chamber proton conducting solid electrolyte cell of the type Fe-SCY-Au, was used in order to conduct the electrode kinetic studies. The steady-state current-overpotential characteristics were analysed with the high field approximations of the Butler-Volmer equation, by taking into account the presence of limiting currents. Both, apparent exchange current density, Io, and anodic/cathodic charge transfer coefficients (αa / αc), were calculated. Limiting currents, Il, were observed in all reaction conditions. The apparent reaction order, q, was found in most cases, within experimental error, close to 0.5 suggesting a possible reaction model, where a competition exists between charge transfer and mass transport of hydrogen ad-atoms or protons along the electrode/solid electrolyte interface.