Uniform In‐Plane Growth of Large‐Area Ultrathin Zn ₂ (benzimidazole) ₄ Membrane

Ultrathin metal‐organic framework membranes hold immense potential for challenging gas separations. In particular, Zn 2 (benzimidazole) 4 membranes hosting H 2 ‐sieving apertures have shown attractive H 2 /CO 2 separation performance. Nevertheless, the current synthesis routes for Zn 2 (benzimidazole) 4 face challenges that hinder the scalable fabrication of ultrathin MOF membranes. Here, a multicycle, short‐exposure growth strategy using ultradilute precursors is presented that hinders homogeneous nucleation and promotes uniform in‐plane heteroepitaxial growth on graphitic substrates. By reducing substrate roughness and optimizing multicycle deposition parameters, continuous high‐quality uniform 8–50 nm thick Zn 2 (benzimidazole) 4 films are achieved across a large‐area substrate. Time‐resolved dynamic light scattering and X‐ray photoelectron spectroscopy reveal a progressive reduction of grain‐boundary defects over successive cycles. These membranes deliver attractive H 2 /CO 2 selectivity and permeance at elevated temperature with a 100% success rate in fabricating selective membranes. This scalable approach provides a robust pathway to ultrathin, defect‐free MOF membranes for high‐performance gas separations.