Suppression of Hysteresis in Absorption of Hydrogen by a Pd-Au Alloy
Статья (Full article),
Physical Review E
, E-ISSN: 2470-0053
||TOTAL-ENERGY; PALLADIUM; THERMODYNAMICS; SOLUBILITY; TRANSITION; DYNAMICS; GOLD; SIZE
Zhdanov Vladimir P.
Boreskov Institute of Catalysis, Russian Academy of Sciences, Novosibirsk, Russia
Department of Physics, Chalmers University of Technology, Göteborg, Sweden
Информация о финансировании (1)
Федеральное агентство научных организаций России
Hydrogen absorption by Pd exhibits hysteresis loops (provided the temperature is not too high) and represents one of the classical examples of first-order phase transitions in metals. Experiments indicate that addition of even a small amount of Au is able to suppress hysteresis. From this perspective, we analyze the energetics of hydrogen in a Pd-Au alloy by using extensive density-functional-theory (DFT) calculations. The dependence of the hydrogen binding energy on the number (n) of Au atoms forming an adsorption site is found to be appreciably nonlinear. With the DFT input for statistical calculations, we reproduce special features of the hydrogen absorption isotherms and explain the rapid decrease of the corresponding critical temperature with increasing Au fraction. The key factor here is that the phase transition is related primarily to absorption in sites formed only by Pd. With increasing Au amount, the fraction of such sites rapidly decreases, the distance between H atoms located there becomes on average larger, the interaction between them becomes weaker, and accordingly the driving force for the phase transition decreases. It is of interest that all these effects can be illustrated by taking only the configurations with n≤2 into account. This means that in the context under consideration the fine details of the dependence of the hydrogen binding energy on n are in fact not too important.