This study presents the development of sub-micro porous ultra-thin polymer membranes for the simultaneous purification of hydrogen (H₂) and capture of carbon dioxide (CO₂) under industrial conditions. The membranes, with a thickness of 13–30 nm, were created by transforming amine-linked polymer (ALP) films into benzimidazole-and-amine-linked polymer (BIALP) layers through interfacial polymerization (IP) and thermal treatment. The BIALP membranes exhibit unprecedented H₂/CO₂ selectivity of 120 with a H₂ permeance of 315 GPU, along with high pressure (up to 11 bar) and thermal (up to 300 °C) resistance. The design and synthesis of these membranes involve creating narrow intrinsic and transient pores by combining rigid and flexible polymer segments, which enhance the molecular sieving ability for small gas pairs. The fabrication process, structural properties, and performance of the membranes are detailed, demonstrating their potential for precise molecular discrimination in industrial applications.This study presents the development of sub-micro porous ultra-thin polymer membranes for the simultaneous purification of hydrogen (H₂) and capture of carbon dioxide (CO₂) under industrial conditions. The membranes, with a thickness of 13–30 nm, were created by transforming amine-linked polymer (ALP) films into benzimidazole-and-amine-linked polymer (BIALP) layers through interfacial polymerization (IP) and thermal treatment. The BIALP membranes exhibit unprecedented H₂/CO₂ selectivity of 120 with a H₂ permeance of 315 GPU, along with high pressure (up to 11 bar) and thermal (up to 300 °C) resistance. The design and synthesis of these membranes involve creating narrow intrinsic and transient pores by combining rigid and flexible polymer segments, which enhance the molecular sieving ability for small gas pairs. The fabrication process, structural properties, and performance of the membranes are detailed, demonstrating their potential for precise molecular discrimination in industrial applications.