Temperature and humidity dependence of the electrode polarization in intermediate-temperature fuel cells employing CsH2PO4/SiP2O7-based composite electrolytes

The polarization behaviors of platinum electrode were investigated with a single cell employing CsH2PO4/SiP2O7-based composite electrolyte. The electrochemical measurements were conducted in the temperature range of 180–240 °C under various humidity conditions. The cell performance was enhanced during several discharge cycles, and then the steady state was attained. The active triple phase boundary (TPB) appears to be spontaneously formed. The polarization behaviors for both anode and cathode were strongly affected by the electrolyte conductivity due to its humidity dependence. In accordance with this tendency, the maximum performance was achieved at 220 °C in 30% humidified condition whereas the deterioration was observed at 240 °C. Throughout the analysis, however, the performance limitation was mainly due to cathodic polarization at every condition. The cathodic overpotential showed a linear dependence against the log of current density at each temperature, which can be expressed as a Tafel equation. Then, the influence of steam concentration and temperature on the electrochemical kinetics was also discussed.