High temperature water electrolysis: cathodic behaviour of Pt/Yttria Stabilized Zirconia interface

The electrolysis of steam using a solid state cell fed by mixtures of hydrogen and water has been carried out at temperatures ranging 700 to 1000°C. The kinetics of the cathodic reduction of water at Pt/YSZ interface has been investigated. Two different processes seem rate determining depending upon the current densities. The transition between each other was found to depend on the temperature but not on the hydrogen vs. water ratio of the feeding mixtures. At low current densities the over-voltage shows a typical Tafel behaviour; the activation enthalpy of the cathodic process was evaluated around 14 Kcal/mole. At high current densities the straight line relationship between total applied voltage and current density suggests the process to occur without apparent overvoltage. This behaviour has been explained in terms of formation of large amounts of complex defects acting as charge exchange sites for the water reduction. The faradic yield of the electrolysis has been proved to be 100%. © 1982.