Thermodynamics of hydrogen dissolved in palladium/rhodium and palladium/platinum alloys

Abstract

Partial thermodynamic parameters have been determined for the solution of hydrogen in Pd/Pt and Pd/Rh alloys. The partial excess entropies of absorption of hydrogen at infinite dilution decrease regularly with atom fraction platinum but not with atom fraction rhodium. This suggests that interstices are not excluded for hydrogen occupation by rhodium atoms neighbouring the interstices but are excluded by the platinum nearest neighbours. Other thermodynamic parameters for hydrogen absorption have been determined and are compared for these alloys. These results are discussed in terms of the observation that rhodium will absorb hydrogen at high pressures of hydrogen when situated within the palladium lattice whereas platinum will not.