Calorimetry of the palladium-deuterium-heavy water system

Abstract

It is shown that accurate values of the rates of enthalpy generation in the electrolysis of light and heavy water can be obtained from measurements in simple, single compartment Dewar type calorimeter cells. This precise evaluation of the rate of enthalpy generation relies on the non-linear regression fitting of the “black-box” model of the calorimeter to an extensive set of temperature time measurements. The method of data analysis gives a systematic underestimate of the enthalpy output and, in consequence, a slightly negative excess rate of enthalpy generation for an extensive set of blank experiments using both light and heavy water. By contrast, the electrolysis of heavy water at palladium electrodes shows a positive excess rate of enthalpy generation; this rate increases markedly with current density, reaching values of approximately 100 W cm −3 at approximately 1 A cm −2. It is also shown that prolonged polarization of palladium cathodes in heavy water leads to bursts in the rate of enthalpy generation; the thermal output of the cells exceeds the enthalpy input (or the total energy input) to the cells by factors in excess of 40 during these bursts. The total specific energy output during the bursts as well as the total specific energy output of fully charged electrodes subjected to prolonged polarization (5–50 MJ cm −3) is 10 2–10 3 times larger than the enthalpy of reaction of chemical processes.