Microstructures of Directionally Solidified Nb₁₅Ti₅₅Fe₃₀ Alloy and Its Hydrogen Permeation Properties in the Presence of H₂S

Currently, the main limitations of Pd-coated Nb-TiFe dual-phase alloys include insufficient hydrogen permeability, susceptibility to hydrogen embrittlement (HE), and poor tolerance of H₂S poisoning. To address these issues, this study proposes a series of improvements. First, a novel Nb₁₅Ti₅₅Fe₃₀ alloy composed of a well-aligned Nb-TiFe eutectic was successfully prepared using directional solidification (DS) technology. After deposition with a Pd catalytic layer, this alloy exhibits high hydrogen permeability of 3.71 × 10^-8 mol H₂ m^-1 s^-1 Pa^-1/2 at 673 K, which is 1.4 times greater than that of the as-cast counterpart. Second, to improve the H₂S corrosion resistance, a new Pd₈₈Au₁₂ catalytic layer was deposited on the surface using a multi-target magnetic control sputtering system. Upon testing in a 100 ppm H₂/H₂S mixture, this membrane exhibited better resistance to bulk sulfidation and a higher permeance recovery (ca. 58%) compared to pure Pd-coated membrane. This improvement is primarily due to the lower adsorption energies of the former with H₂S, which hinders the formation of bulk Pd₄S. Finally, the composition region of the Pd-Au catalytic membrane with high comprehensive performance was determined for the first time, revealing that optimal performance occurs at around 12-18 at.% Au. This finding explains how this composition maintains a balance between high H₂ permeability and excellent sulfur resistance. The significance of this study lies in its practical solutions for simultaneously improving hydrogen permeability and resistance to H₂S poisoning in Nb-based composite membranes.