Compared with reported polycrystalline MOF films synthesized via emerging deposition techniques (Fig. and Supplementary Table ), the Zn2(bim)4 film can be uniquely synthesized with thickness down to that of just two unit-cells. Among the array of MOF membrane synthesis methods for H2/CO2 separation, this approach is the only method which yields film thickness below 10 nm. This enhances the potential for achieving high performance in H2/CO2 separation.