Apparent activation energy for hydrogen permeation and its relation to the composition of homogeneous PdAu alloy thin-film membranes

作者：Patki Neil S; Lundin Sean Thomas B; Way J Douglas^*

来源：Separation and Purification Technology, 2018, 191: 370-374.

DOI：10.1016/j.seppur.2017.09.047

• PdAu composite membrane
• In situ parameter to judge homogenization
• Apparent activation energy for hydrogen permeation
• High-pressure hydrogen anneal
• Electroless plating/deposition

PdAu alloy composite membranes are often fabricated by sequential electroless plating of Pd and Au, but this forms a layered structure that must be annealed to form a homogenous alloy. Using ex situ analysis techniques such as X-ray diffraction (XRD) or energy dispersive X-ray spectroscopy (EDS) to judge the extent of homogenization can be time-consuming as the composite membranes must be cooled to ambient temperatures prior to analysis. However, an in situ alternative is to use the apparent activation energy for H-2 permeation (E-act). In this work, 27 - 41 wt% Au films were fabricated to expand upon a range of 0 - 21 wt% that has been previously reported. Homogenization (confirmed by XRD and EDS) was achieved by heat treatment in 3 MPa H2 at 550 degrees C for up to 120 h. The apparent E-act was found to initially decrease with increasing Au composition from 12.2 kJ mol(-1) (pure Pd) to 7.5 kJ mol(-1) (21 wt% Au) after which it slowly increased to 9.0 kJ mol(-1) (41 wt% Au). The two distinct regimes can be explained using the relation E-act = Delta H-H + E-D, wherein E-act is the sum of the partial enthalpy of solution of H into the PdAu alloy (Delta H-H) and the activation energy for diffusion of H in the alloy (E-D). Essentially, the two components of E-act have opposite signs that counteract each other and cause a non-linear trend with increasing Au compositions.

• 出版日期2018-1-31