抄録
Hydrogen permeable membranes with a cylindrical shape are used in membrane reactors. Systematic investigations have been conducted on hydrogen diffusion coefficients in palladium (Pd) and its alloys. Currently, Pd and its alloys are widely used as hydrogen permeable membranes. Pd-Ag alloy membranes have been reported to exhibit higher permeability and durability than those of Pd. In this work, a cylindrical Pd cell system was constructed, with the inside filled with a pressure-controllable gas and the outside in contact with an electrolyte of an electrochemical cell. Using this system, the hydrogen permeation behavior was evaluated at various temperatures by controlling the temperature of the electrolyte in contact with the entire cylinder. By applying a time-lag method on hydrogen permeation, the hydrogen diffusion coefficient in Pd cylinder at 300.15 K was calculated to be D = 1.7 × 10 -10m2/s , which is considered to be a diffusion coefficient in Pd hydride phase. An additional assessment of hydrogen diffusion coefficients in Pd and Pd-Ag alloy plate specimens was conducted using an electrochemical double-cell equipment also by the time-lag method. In the hydrogen solid solution phase the hydrogen diffusion coefficients of Pd and Pd-Ag alloy plate at 300.15 K were calculated to be D = 1.96 × 10-11 m2/s and D = 1.75 × 10-11 m2/s, respectively. Comparative analysis with previous studies indicates that the hydride formation mechanism significantly influences both hydrogen diffusion kinetics and overall permeation behavior.
