Among various H2 purification technologies, the use of membrane technology has been considered an ecofriendly approach for addressing the increasing hydrogen demand. Although many H2-selective membrane materials have been reported, processing them into hollow fibers or thin-film composites (TFCs) via traditional methods either affects the performance of the materials or renders their further processing into applicable membrane forms infeasible. Herein, we propose a water-casting method for fabricating TFC membranes for hydrogen purification with high permselectivity. The film integrity and thickness were manipulated by controlling the spreadability of the casting solution, and the resultant water-cast TFC membrane that comprised an ∼30 nm selective layer demonstrated high H2 permeance and H2/CH4 selectivity of approximately 190 GPU and 100, respectively, under optimized conditions. We performed a mixed-gas permeation test using a simulated off-gas of steam–methane reforming from natural gas in a single-stage system and obtained hydrogen gas of >99 mol % purity. This indicates not only the suitability of the water-cast membranes for satisfying the demand for pure hydrogen as a fuel and chemical reagent but also the great potential of the water-casting method for high-performance membranes in various industrial and environmental applications.

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