Membranes for Hydrogen Purification: An Important Step toward a Hydrogen-Based Economy

Abstract

Production of pure molecular hydrogen is essential to the realization of the proposed “hydrogen economy” that could ultimately provide hydrogen as a clean, renewable source of energy; eliminate the industrialized world's dependence on petroleum; and reduce the generation of greenhouse gases linked to global warming. A crucial step in obtaining pure hydrogen is separating it from other gaseous compounds—mainly CO2—that often accompany hydrogen in industrial chemical reactions. Advanced membrane technology may prove to be the key to the successful, economical production of molecular hydrogen.Size-sieving glassy polymer membranes can separate H2 on the basis of its small size. Alternatively, reverse-selective rubbery polymers can expedite the passage and, hence, removal of CO2 due to its relatively high solubility in such membranes alone or in conjunction with dissociative chemical reactions. Transition-metal membranes and their alloys can adsorb H2 molecules, dissociate the molecules into H atoms for transport through interstitial sites, and subsequently recombine the H atoms to form molecular H2 again on the opposite membrane side. Microporous amorphous silica and zeolite membranes comprising thin films on a multilayer porous support exhibit good sorption selectivity and high diffusion mobilities for H2, leading to high H2 fluxes. Finally, carbon-based membranes, including carbon nanotubes, may be viable for H2 separation on the basis of selective surface flow and molecular sieving. A wide variety of materials challenges exist in hydrogen purification, and the objective of this issue of MRS Bulletin is to address those challenges and their potential solutions from basic principles.

The Hydrogen Fuel Alternative

“…The challenges are discovering and developing the thermodynamics of chemical cycles that split water and finding materials that can withstand the high temperatures and often corrosive environments required by these processes. 19 …”

Multilayer Amorphous‐Si‐B‐C‐N/γ‐Al2O3/α‐Al2O3 Membranes for Hydrogen Purification

“…Zeolite membranes show relatively low hydrogen permeances and their thickness should be significantly reduced to achieve acceptable H 2 fluxes/permeances. [4] The application of amorphous, sol-gel derived, silica membranes is limited due to their instability under hydrothermal conditions. [6] In comparison to sol-gel membranes the stability of turbostratic carbon structures is much higher but nevertheless limited to 300-400 8C.…”

Supported Molten Metal Membranes for Hydrogen Separation

“…This is a key reason for seeking alternate H 2 separation technologies, particularly via dense metal membranes. The most promising current membranes involve Pd and its alloys with Ag and Cu, either as thin foils or as thin membranes supported on porous ceramic or metal supports (Paglieri and Way, 2002;Fukai, 2005;Sholl and Ma, 2006;Nenoff et al, 2006;Adhikari and Fernando, 2006;Ockwig and Nenoff, 2007;Yun and Oyama, 2011). However, these membranes still fall short of the desired cost, chemical and mechanical robustness, and durability targets (Table 1).…”