The influence of modifying nanoflower and nanostar type Pd coatings on low temperature hydrogen permeability through Pd-containing membranes

Abstract

Methodsof modifying the surface of Pd–23%Ag alloy films have been developed in order to increase the rate of hydrogen permeability and to produce palladium-containing nanostar and nanoflower type coatings. Modifying coatings have been synthesized by electrolytic deposition at a reduced current density compared to classical methods. Low current densities affect the formation of pentagonally structured surface modifiers. The low deposition rate of Pd and Ag particles on a thin palladium-silver film allows them to line up in clearly defined structures, probably due to the properties of the surfactant used. The methods developed for modifying palladium-containing membranes makes it possible to create palladium nanostructures not only with a well-defined surface structure, but also with morphologies that have never been achieved by other approaches. Modification of the membrane surface makes it possible to measure the permeability in the temperature range up to 100°С. Membranes modified with nanoflower and nanostar type pentagonally branched crystallites show a hydrogen flux of up to 0.008 mol s−1 m−2 and up to 0.01 mol s−1 m−2 at a pressure of 0.3 MPa in the low temperature range (<100 °C). The hydrogen flux for membranes modified by such coatings is twice as much as the flux of hydrogen through membranes modified by the classical palladium black method, despite the fact that the latter is slightly more developed. The results obtained during the experiment may indicate that the contribution to the increase in activity and consequently the increase in the hydrogen permeability rate through the membrane that is in a stage of surface limitation by surface effects is made not only by the increased surface area but also by the structural organization characteristics of the membrane modifying layer.