A parameter for defining the energetic efficiency of the cathodic process at high temperature,high current density electrolysis of steam

The electrocatalytic activity for the cathodic reduction of steam at high temperature on metals and oxides at the interface with zirconia base electrolytes have been comparatively analysed. Except the case of the urania-yttria solid solution at temperatures higher than 1273 K, all the cathodic layers investigated up to now showed two different behaviours depending on the current density. At low current density the polarization curves follow Tafel's law. Above certain values of the c.d., which depend on temperature, the applied potential showed a linear relationship with a slope corresponding to the a.c. impedance, thus indicating in such conditions the overall cathodic reaction takes place without any additional overvoltage. This behaviour suggests the introduction of a simple parameter defining the highest possible energetic yield that can be obtained by any individual cathodic material under high current density conditions.