(383al) Polyorganosilica Membranes Structure Tightening and Hydrothermal Stabilization Via Few Cycle Atomic Layer Deposition for Hydrogen Purification Process

Polyorganosilica (POSi) membranes with excellent H₂ separation properties can be rapidly prepared via 2-minute oxygen plasma treatment of polydimethylsiloxane (PDMS)-based thin-film composite (TFC) membranes. However, POSi membranes are subject to hydrothermal instability, decreasing H₂ permeance and H₂/CO₂ selectivity. In this study, we employ few-cycle atomic layer deposition (ALD) of aluminum oxide to induce metal-siloxane covalent linkage, which can simultaneously stabilize POSi networks and tighten porous structures to improve H₂/CO₂ separation performance. First, oxygen plasma treatment induces an ultrathin (<10 nm) POSi top layer with abundant silanol (Si-OH) groups, as confirmed by XPS and SEM images. Second, the hydroxide groups enable the ALD process, where exposure to trimethylaluminum (TMA) forms Al-O-Si covalent linkages. The effect of the ALD parameters on the POSi network structure, gas transport properties at 150^oC, and hydrothermal stability are thoroughly examined. For example, exposing POSi membranes to 3-cycle ALD improves H₂/CO₂ selectivity from 67 to 110 but decreases H₂ permeance from 380 to 240 GPU. When challenged with roughly 0.6 mol% water vapor, the pristine POSi membrane exhibits an irreversible drop of H₂/CO₂ selectivity to 55 while a 3-cycle of ALD retains the selectivity, suggesting improved hydrothermal stability with the ALD treatment. The superior H₂/CO₂ separation properties and robust hydrothermal stability coupled with the facile fabrication processes demonstrate the potential of the POSi membranes for practical H₂ purification and CO₂ capture.