Quantitative Evaluations of Hydrogen Diffusivity in V-X (X = Cr, Al, Pd) Alloy Membranes Based on Hydrogen Chemical Potential.

Asuka Suzuki,Hiroshi Yukawa

doi:10.3390/membranes11010067

Abstract

Vanadium (V) has higher hydrogen permeability than Pd-based alloy membranes but exhibits poor resistance to hydrogen-induced embrittlement. The alloy elements are added to reduce hydrogen solubility and prevent hydrogen-induced embrittlement. To enhance hydrogen permeability, the alloy elements which improve hydrogen diffusivity in V are more suitable. In the present study, hydrogen diffusivity in V-Cr, V-Al, and V-Pd alloy membranes was investigated in view of the hydrogen chemical potential and compared with the previously reported results of V-Fe alloy membranes. The additions of Cr and Fe to V improved the mobility of hydrogen atoms. In contrast, those of Al and Pd decreased hydrogen diffusivity. The first principle calculations revealed that the hydrogen atoms cannot occupy the first-nearest neighbor T sites (T1 sites) of Al and Pd in the V crystal lattice. These blocking effects will be a dominant contributor to decreasing hydrogen diffusivity by the additions of Al and Pd. For V-based alloy membranes, Fe and Cr are more suitable alloy elements compared with Al and Pd in view of hydrogen diffusivity.

Highlights

Hydrogen energy needs to be utilized effectively to realize a decarbonized society [1].Since hydrogen does not exist as a simple substance in nature, it needs to be manufactured industrially
Hydrogen solubility decreased with increasing temperature, indicatin7gotfh2a3t dissolutions of hydrogen into V-Cr alloys were exothermic reactions
The results for V-Pd alloys are located below the broken line. These results indicate that the hydrogen diffusivity in V-Al and V-Pd alloys is lower than that in V-Fe and V-Cr alloys

Summary

Introduction

Hydrogen energy needs to be utilized effectively to realize a decarbonized society [1].Since hydrogen does not exist as a simple substance in nature, it needs to be manufactured industrially. Hydrogen gas with high purity is obtained by separation and purification through hydrogen-permeable dense metallic membranes [3]. Pd-based alloy membranes are the most representative metallic membranes used for the purification of hydrogen gas [4,5]. Group 5 metals have high hydrogen solubility and become significantly brittle under hydrogen atmosphere (hydrogen-induced embrittlement) [7,8]. The presence of the ductile-to-brittle transition hydrogen concentration (DBTC) has been found by small punch testing under hydrogen atmospheres at elevated temperatures [8,9]. Hydrogen solubility needs to be optimized so that the hydrogen concentration does not exceed 0.2 (H/M) under operating pressure and temperature conditions of metal membranes. The elements with low affinity for hydrogen are usually added to control hydrogen solubility

Methods

Results

Conclusion