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Metal–organic framework (MOF) incorporated mixed–matrix membranes (MMMs) attract great interest for gas separation applications because they overcome limitations faced by typical polymer membranes, including permeability–selectivity trade‐off, aging effect, and plasticization phenomenon. However, optimal MOF–polymer interface compatibility is the key challenge in fabricating defect‐free high‐performance gas‐separation MMMs. Here, a surface modification strategy of the UiO‐66‐NH2 MOF using a covalently bound PIM‐PI‐oligomer is developed to engineer interface compatibility with the polymer that has an identical chemical structure (PIM‐PI‐1) in the MMMs. A series of MMMs are prepared with different loadings of homogeneously distributed PIM‐PI‐functionalized MOFs (PPM). Significant improvements in CO2/N2 and CO2/CH4 selectivity and permeability are achieved with these MMMs, ranging from 5 to 10 wt% of the PPM loadings. The MMM with 10 wt% loading (PPM‐10@MMM) shows a CO2 permeability of 3827.3 Barrer and a CO2/N2 and CO2/CH4 selectivity of 24 and 13.4, respectively. This surpasses the 2008 Robeson upper bound for CO2/N2 and is very close to the 2008 upper bound for CO2/CH4. The experimental results are further compared using Maxwell's equation for MMMs. The resulting MMMs show a plasticization resistance against CO2 up to 25 atm pressure and anti‐aging performance for 180 h.

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Nafion, as a perfluorosulfonic acid (PFSA)-based polymer, is a key material that contributes to the commercialization of proton exchange membrane fuel cells (PEMFCs). The high dependence on relative humidity (RH) of Nafion or other PFSA membranes for proton conduction, together with its decreased mechanical and dimensional stability and high fuel (H 2 ) crossover at the cell operating temperatures (80 °C or above), however, remain issues that have yet to be solved. In the current work, thin sulfonated poly(arylene ether sulfone) (sPES)-coated Nafion membranes (sPES-c-Nafions) are developed, for the first time, by simply spin-coating the sPES solution onto a Nafion membrane, and the results are compared with the sPES-blended Nafion counterparts. The sPES-c1-Nafion demonstrates a very high proton conductivity of 223.3 mS cm −1 (80 °C) and a very low hydrogen permeability, a 41% reduction compared to that of Nafion-212, together with improved mechanical and dimensional stabilities compared to Nafion-212. The developed membrane also shows excellent cell performance (i.e., with a current density of 1.56 A cm −2 and a peak power density of 1.20 W cm −2 at 0.6 V potential in the actual operating conditions of PEMFCs).