Superhydrophobic polycarbosilane membranes for purification of solar hydrogen

Abstract

Superhydrophobic membranes composed of an organic-inorganic hybrid polymer, namely polycarbosilane (PCS) with Mw of 4–8.9 × 103, were formed on a mesoporous γ-Al2O3-modified α-Al2O3 porous support. Under dry condition at 50 °C, the supported PCS membranes exhibited H2 permeance of 1.1–1.6 × 10−6 mol·m−2·s−1·Pa−1 and H2/N2 selectivity of 9.7–12.6 together with unique H2/He selectivity of 1.4–1.6. Even under saturated humidity at 50 °C, H2 permeance remained at 7.7 × 10−8 mol−1 m−2 s−1 Pa−1 with improved H2/N2 selectivity of 26. Moreover, when the measurements were performed using a H2-N2 (2:1) mixed feed gas as a simulated syngas produced by novel solar hydrogen production systems, the H2 permeance almost unchanged, while the N2 permeance was below the limit of detection. These results revealed a great potential of PCSs to develop novel H2-selective membranes for purifying solar hydrogen under high-humidity conditions around 50 °C. Further study on the gas permeation behaviors of He, H2 and N2 suggested that the enhanced H2/N2 selectivity under the high-humidity conditions could be explained by the synergistic effect of preferential H2 permeation through the dense PCS network governed by the solid state diffusion mechanism and blockage of N2 permeation through micropore channels within the PCS network by the permeate H2O-induced plugging at around the hetero interface between the superhydrophobic PCS and highly hydrophilic γ-Al2O3.