SOI-Supported Microdevice for Hydrogen Purification Using Palladium–Silver Membranes

Abstract

High-purity hydrogen continues to receive attention as a promising energy source for fuel cells in portable power applications. On-demand hydrogen generation via fuel reforming offers a convenient alternative to hydrogen storage, but the concomitant CO generation is deleterious to the fuel cell catalyst. Of the possible hydrogen purification options, palladium membranes allow a compact design suitable for portable applications. We present a micromembrane device built in silicon-on-insulator wafers for hydrogen purification. The design imparts structural stability to a submicrometer-thick palladium–silver membrane, enabling hydrogen purification at higher pressures than were tolerated by previous devices with supported thin palladium membranes. The devices are manufactured using bulk micromachining techniques including photolithography, plasma, and wet etching. They are operated at pressures up to 2 atm with a correspondingly enhanced hydrogen flux. In particular, thin (200 nm) palladium–silver membrane yield high permeation rates of up to 50 mol/m²/s at 350 ◦C. The different transport resistances controlling hydrogen permeation in the micromembrane system are evaluated.