Lin Haiqing (Orcid ID: 0000-0001-8042-154X) Molecularly Engineering Polymeric Membranes for H 2 /CO 2 Separation at 100 ℃ – 300 ℃ Leiqing Hu, Sankhajit Pal, Hien Nguyen, Vinh Bui, HaiGIG qing Lin Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA Correspondence to: Haiqing Lin (Email: haiqingl@buffalo.edu) AUTHOR BIOGRAPHIES Dr. Leiqing Hu received his B.Eng. in Thermal and Power Engineering from Shandong University in 2013 and his Ph.D. in Thermal Engineering from Zhejiang University in 2018 in China. He joined University at Buffalo (UB) as a postdoctoral associate in 2019. His research focuses on advanced membranes for gas separation and CO 2 capture. ABSTRACT Over the last two decades, polymers with superior H 2 /CO 2 separation properties at 100 ℃ – 300 ℃ have gathered significant interest for H 2 purification and CO 2 capture. This timely review presents various strategies adopted to molecularly engineer polymers for this application. We first elucidate the Robeson’s upper bound at elevated temperatures for H 2 /CO 2 separation and the advantages of high- temperature operation (such as improved solubility selectivity and absence of CO 2 plasticization), compared with conventional membrane gas separations at ~35 ℃. Second, we describe commercially relevant membranes for the separation and highlight materials with free volumes tuned to discriminate H 2 and CO 2 , including functional polymers (such as polybenzimidazole) and engineered polymers by cross-linking, blending, thermal treatment, thermal rearrangement, and carbonization. Thirdly, we succinctly discuss mixed matrix materials containing size-sieving or H 2 -sorptive nano-fillers with attractive H 2 /CO 2 separation properties. KEYWORDS: Polymeric membranes; H 2 /CO 2 separation; high temperatures; carbon capture This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/pol.29749