High-performance polymeric materials are essential to enable energy-efficient membrane technology in hydrogen purification and carbon capture. However, polymers face the permeability/selectivity trade-off, and they can be incorporated with inorganic fillers to improve gas transport properties; however, the two distinctive phases often have interfacial incompatibility, making them difficult to fabricate into defect-free submicron thin-film composite (TFC) membranes. In this study, we demonstrate macrophase-separated polymer blends with superior H
2/CO
2 separation properties by dispersing a highly permeable and non-selective polyimide (6FDA-DAM, PI) phase in a highly selective but moderately permeable continuous polybenzimidazole (PBI) phase. At loadings of 10-40 wt%, PI forms a macroscopic discontinuous phase in the blends, as confirmed by scanning electron microscope (SEM) images, two distinct d-spacings from WAXD patterns, and two glass transition temperatures in DSC curves. The effect of the PI loading on H
2 permeability can be satisfactorily described using the Maxwell model. For instance, adding 40 mass% PI in PBI increases H
2 permeability from 27 to 120 Barrer with H
2/CO
2 selectivity of 10 at 150 °C, breaking the traditional trade-off and surpassing the upper bound. More importantly, the blends can be fabricated into TFC membranes while retaining their macrophase separation, leading to a significant increase in H
2 permeance compared to PBI-based membranes. For example, adding 30% PI increases H
2 permeance by 250%, from 18 to 63 GPU, while slightly decreasing H
2/CO
2 selectivity from 10 to 8.4 at 140 ℃. This facile and elegant approach of polymer blending provides a new platform for designing high-performance membranes for gas and liquid separations with great manufacturability.
