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, 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. INTRODUCTION The difficulty in replicating the Pons/Fleischmann type electrolytic excess heat generation [1],[2] during electrolysis of heavy water has caused strong criticism on their experiments, and the reality of the so-called cold fusion has been questioned. However, to date very few studies have been reported on the fundamental factors controlling the deuterium loading ratio in the palladium cathode which has been believed to be the key factor to control the excess heat generation. The NCFI final report [3] contains some data on the loading ratio under various conditions but they are too preliminary to suggest important factors controlling the loading ratio. Will et al. [4] reported loading ratio higher than 0.85 as key factor for tritium production, while McKubre et al. [5],[6] reported the critical loading ratio around 0.9 to give rise to the excess heat generation. The loading ratio was determined by conducting the electrolysis in a closed cell utilizing a fuel cell anode by Will et al. and by monitoring the electrical resistance by McKubre et al. Electrolysis in a closed cell utilizing a fuel cell anode offers a direct method to determine the loading ratio by monitoring the deuterium pressure during electrolysis while measurement of the electrical resistance is an indirect one which relies on the resistivity data as a function of loading ratio observed in gas phase[7].The structure of the electrolysis cell utilizing fuel cell anode proposed by Will[4] is difficult to conduct calorimetry and to carry out long term electrolysis. The purpose of the present study is firstly to develop a novel new electrolysis cell utilizing a fuel cell anode which allows us simultaneously to carry out calorimetry and to conduct in-situ determination of loading ratio; secondly to examine the factors controlling the loading ratio; and thirdly to investigate the relation between the excess heat generation and the loading ratio. EXPERIMENTALS Determination of hydrogen/deuterium loading ratio in a palladium cathode was done first in a closed cell developed in our laboratory which is shown schematically in Fig. 1. The pressure vessel made from SUS316 filled with deuterium gas of 5 10 atm has an electrolyte container made from PTFE or glass with four windows at which gas diffusion electrodes are attached with their reaction layers in contact with electrolyte solution. A platinized platinum electrode (PVPt) was placed in the electrolyte and acted as a reference electrode (RHE) to measure hydrogen overvoltage at the palladium cathode. The cathode and anode reactions in alkaline solutions are given respectively by,