Isotope effects in: a) Catalytic generation of hydrogen from sodium tetrahydridoborate and b) Oxidation of hydrogen in fuel cells

Abstract

We have investigated deuterium/hydrogen (D/H) isotope effects a) during catalytic evolution of hydrogen gas from the water solution of sodium tetrahydridoborate (NaBH4), the sodium borohydride fueled hydrogen generator HGen-E, Fractal Carbon, with the carbon monolith supported platinum reactor was used; b) oxidation of hydrogen in a PEM-type fuel cell to produce electrical energy. We used the E-TEK membrane electrode assemblies with an active area of 4 cm2, assembled in a two fuel cell stack. Both processes are important as possible parts of an energy-hydrogen-energy cycle. Any transfer of energy into hydrogen or vice versa induces a change of the D/H isotope ratio, which can be considered from the isotope separation point of view and possible development of a method to produce heavy water as a by-product of the above cycle. In this way, the separation efficiency can contribute to the overall efficiency of the cycle. This work is an initiative to take the isotope effects into account while cycling energy via some specific processes. We measured the isotope separation factor (a) of the single-stage process, as a basic parameter determining the isotope separation efficiency. The results proved that deuterium migrated to the dense (liquid) phase in both systems. Average values of the obtained separation factors are: ?(a) = 5.4 ?(b)>12. The results obtained could serve for a model for optimization purposes rather than to improve the separation efficiency of a particular unit. To do that it would primarily be necessary to play with a variety of catalysts, which was beyond the main aim of this work.