We tested the gas separation performance of the millimeter-scale membranes using a custom-built permeation setup. During the tests, we maintained the pressure on the feed side between 1-6 bar, while the permeate side was kept at 1 bar. All measurements were conducted after reaching a steady state, with argon used as the sweep gas. The membranes were carefully sealed using a stainless-steel gasket to ensure accurate results. For analyzing the composition of the permeate, we employed an online Hiden Analytical HPR-20 mass spectrometer. The permeances Ji of gas i was calculated as follows: