Membranes with high selectivity and permeance are needed to reduce energy consumption in hydrogen purification and pre-combustion CO ₂ capture. Polybenzimidazole (PBI) is one of the leading membrane materials for this separation. In this study, we present superior novel supported PBI (poly(p-phenylene benzobisimidazole), PBDI) membranes prepared by a facile interfacial polymerization (IP) method. The effect of IP reaction duration, operating temperature and pressure on membrane separation performance was systematically investigated. The best performance was achieved for membranes prepared in a 2 h reaction time. The resulting membranes display an ultrahigh mixed-gas H ₂ /CO ₂ selectivity of 23 at 423 K together with an excellent H ₂ permeance of 241 GPU, surpassing the membrane performance of conventional polymers (the 2008 Robeson upper bound). These separation results, together with the facile manufacture, pressure resistance, long-term thermostability (>200 h) and economic analysis, recommend the PBDI membranes for industrial use in H ₂ purification and pre-combustion CO ₂ capture. Besides, PBDI membranes possess high selectivities towards H ₂ /N ₂ (up to 60) and H ₂ /CH ₄ (up to 48) mixtures, indicating their potential applications in ammonia synthesis and syngas production.