Deuterium loading ratio and excess heat generation during electrolysis of heavy water by a palladium cathode in a closed cell using a partially immersed fuel cell anode

We have developed a novel electrolytic cell pressurized by D2 in which deuterium loading ratio in a palladium cathode can be determined in-situ during the calorimetric measurements of excess heat. A gas diffusion type fuel cell anode is partially immersed in the electrolyte solution to act as a counter electrode, at which electrochemical oxidation of deuterium gas molecules to deuterium ions takes place instead of electrolytic decomposition of water molecules to generate oxygen gas. Factors controlling the loading ratio such as electrolyte composition, hydrogen overvoltage at the palladium cathode, current density and isotope effect have been examined. Dependence of the excess heat generation at the palladium cathode on the loading ratio as well as on the current density shows that the critical loading ratio and the current density to generate excess heat are ca. 0.83 and 100mA/cm 2, respectively. The maximum D/Pd of 0.89 has been achieved in the present study, at which excess heat generation of ca. 35 % with respect to the input electrolytic power has been observed.