Research Progress on the Preparation of Palladium and Its Alloy Membranes

Research Progress on the Preparation of Palladium and Its Alloy Membranes

I. Research Background

II. Preparation Methods

1. Electroless Plating
• Electroless Plating (ELP): Palladium membranes are deposited on porous supports through chemical reactions. This method is simple to operate but can easily produce defects on the membrane surface.
• Vacuum Electroless Plating (VELP): Combining vacuum operations with a continuous flow system can reduce pinholes and other defects during the palladium deposition process, resulting in more uniform and strongly adherent dense thin palladium membranes.
• Electroless Plating with Pore Permeation (ELP-PP): The palladium source and reducing agent are fed from the opposite sides of the porous support, allowing the reaction to occur within the pores. This ensures that palladium particles accurately fill the pores of the support, reducing defects in the palladium membrane.
2. Composite Membrane Preparation
• Surface Modification of Porous Supports: Refractory oxides, zeolites, natural minerals, and polymers are used to modify the surface of porous supports, significantly improving the thermal and chemical stability of the palladium membrane.
• High-Pressure PdCl₂ Solution Permeation: PdCl₂ reacts with Fe, Cr, and Ni in stainless steel support tubes to form a "hook-like" palladium layer at defect sites. This increases the specific surface area of the palladium membrane, significantly enhancing membrane stability and hydrogen purity.

III. Research Progress on Alloy Membranes

1. Binary Alloy Membranes
• Pd-Ag Alloy Membranes: Hydrogen solubility increases with the addition of Ag, but hydrogen diffusion decreases. At low temperatures, Pd-Ag alloys exhibit higher hydrogen permeability and resistance to hydrogen embrittlement, but they have lower tolerance to hydrogen sulfide.
• Pd-Cu Alloy Membranes: These can form both bcc and fcc crystal structures, and their hydrogen permeability and sulfur resistance depend on the alloy composition and temperature.
• Pd-Au Alloy Membranes: The addition of Au enhances both hydrogen permeability and sulfur resistance, showing excellent sulfur resistance in high-concentration H₂S environments.
2. Ternary Alloy Membranes
• Pd-Ag-Au Alloy Membranes: These membranes exhibit higher hydrogen selective permeability and sulfur resistance. Studies have shown that they perform excellently in hydrogen permeability and sulfur resistance at low temperatures.

IV. Application Status

1. Hydrogen Purification
• Palladium and its alloy membranes perform exceptionally well in hydrogen purification, capable of increasing hydrogen purity to over 99.99%, meeting the high-purity hydrogen requirements of fuel cells.
• Stainless steel-supported palladium membranes have been commercialized and can operate stably for more than 19,000 hours, meeting the requirements for rapid temperature cycling.
2. Industrial Applications
• The "self-healing" technology for palladium composite membrane defects has been successfully applied in industrial hydrogen purification, increasing hydrogen purity from 75% to 99.99% and maintaining stable operation for 300 hours.

V. Future Development Directions

1. Cost Reduction
• By optimizing preparation processes and material selection, the production cost of palladium and its alloy membranes can be reduced to enable large-scale industrial applications.
2. Enhanced Durability
• Further research on the durability of alloy membranes in complex environments, especially their tolerance to impurities such as hydrogen sulfide, is needed.
3. Expanded Application Fields
• Exploring the potential applications of palladium and its alloy membranes in emerging fields such as new energy, electronics, and medical industries.