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[Display omitted] • Flexible and defects-free MMMs possess bi-continuous MOFs pathway. • DA promotes heterogeneous nucleation and growth of ZIF-8 on fiber. • In-situ polymerization intensifies interface affinity between ZIF-8 and PEO. • CO 2 permeability and CO 2 /N 2 selectivity surpass 2019 McKeown upper bound. Highly-loaded metal–organic frameworks (MOFs) based mixed matrix membranes (MMMs) are essential for high-efficiency gas separation. However, the continuous distribution of MOFs across the membrane with intensified interface remains challenging. Herein, a flexible and defects-free MMM with a bi-continuous MOFs pathway is constructed by dopamine (DA)-assisted MOFs growth along nanofibers. Nanofibers are used to upload and distribute ZIF-8, which continues to grow via an epitaxial growth strategy to obtain ZIF-8 fibers, achieving ZIF-8 continuous both in long and short range. DA promotes heterogeneous nucleation and growth of ZIF-8 on fiber surface by chelating with Zn2+ through –OH and –NH 2 groups. DA also ensures excellent interfacial compatibility by hydrogen bonding interaction between amino groups of DA and ether-oxygen groups of PEO. Finally, the highly-loaded MMM is constructed by in-situ photopolymerization of Poly (ethylene glycol) diacrylate) to embrace ZIF-8 fibers tightly. The resultant MMM presents ZIF-8 loading as high as 72.41 vol% with Young's modulus of 33.42 MPa, and unchanged morphology and separation performances after bending for 180° over 50 times, revealing outstanding mechanical properties. The CO 2 permeability and CO 2 /N 2 selectivity are 280.3 % and 73.0 % higher than the PEO membrane, surpassing the 2019 McKeown upper bound. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hollow ZIF-8 in micron accumulated continuously across membrane to construct transport highway. • The real CO 2 transport distance was reduced. • In-situ polymerization intensifies the interface affinity between ZIF-8 and PEO. The hollow filler has been verified to effectively enhance the CO 2 permeability of mixed matrix membrane (MMMs) by constructing low-resistance transport pathway. However, the in-continuity of hollow fillers across the membrane results in insufficient CO 2 permeability. In this work, the micron-sized hollow ZIF-8 (Mic-H-ZIF-8) were designed and proposed to accumulate continuously across the membrane to construct the transport highway for CO 2. Importantly, the in-situ polymerization was utilized to achieve continuous accumulation of the Mic-H-ZIF-8 fillers across the membrane. The Mic-H-ZIF-8 presents cavity size of 4 μm and shell thickness of 100 nm, and three or four Mic-H-ZIF-8 microspheres are aligned sequentially across the membrane, in which the effective gas transport distance is decreased from 13 μm to the range of 0.8–3 μm. Consequently, the CO 2 permeability of 5 wt% Mic-H-ZIF-8/PEO MMM is 224.6 % and 63.5 % higher than those of pure PEO membrane and nanosized hollow ZIF-8/PEO MMM at 0.1 MPa. Meanwhile, the CO 2 /N 2 selectivity is still as high as 70.0. This CO 2 separation performance is far exceeding the Robeson upper bound in 2008, and beyond the McKeown upper bound in 2019 as the feed pressure increasing, confirming the significance of continuous transport highway constructed by micron-sized hollow MOFs on improving CO 2 separation of MMMs. [ABSTRACT FROM AUTHOR]

Table of contents for mechanism model of Cu-N 3 and Cu-N 4 moieties. • Highly exposed isolated Cu-N x sites were embedded in microporous carbon frameworks. • CO 2 -to-CO conversion was boosted with tailored Cu–N coordination environment. • Cu-N 4 exhibited a maximum FE CO of 98% and over 90% from −0.6 to −1.1 V vs. RHE. • Edge-hosted Cu-N 4 was identified as the accurate configuration of active site by DFT calculations. Although considerable progress has been achieved by Cu nanoparticles for catalyzing CO 2 reduction reaction (CO2RR), Cu single atom catalysts (Cu SACs) are generally suffered from inferior performance to that of widely investigated Fe, Co, Ni SACs. This phenomenon mainly ascribes to the lack of effective geometry and electronic engineering of copper active center from an atomic level. Herein, highly exposed atomically dispersed Cu-N x (x denotes Cu–N coordination number) sites anchored on 3D porous carbon matrix are successfully synthesized through facile one step thermal activation, and Cu-N 4 sites exhibit boosted activity and selectivity compared to its nearly inert Cu-N 3 counterparts. Aided by density functional theory (DFT) calculations, the edge-hosted Cu-N 4 moieties are revealed as key active sites for efficient CO generation via optimized local coordination environment and electronic properties, which strongly interact with *COOH intermediate and facilitate the desorption of *CO. As a result, Cu-N 4 catalyst achieves high CO Faradaic efficiency (FE CO) of over 90% from −0.6 to −1.1 V vs. RHE with a maximum value of 98%, surpassing the previously reported Cu SACs for CO 2 -to-CO conversion. This work provides new insight into proper Cu SACs design and fundamental mechanism understanding to boost CO2RR. [ABSTRACT FROM AUTHOR]

[Display omitted] • PSA modified hollow ZIF-8 were designed by a hard template-incomplete etching strategy. • The hollow core of PHZ builds a low-resistance CO 2 transport freeway. • The outside PSA layer intensifies the interface affinity between ZIF-8 and Pebax. The trade-off between gas permeability and selectivity represents a huge challenge for membrane separation. In this work, we design unique polystyrene-acrylate (PSA) modified hollow ZIF-8 (PHZ) nanospheres via a facile hard template-incomplete etching strategy as fillers for mixed matrix membranes (MMMs). In the vesicles shaped PHZ, the hollow core builds a low-resistance CO 2 transport freeway, leading to improved CO 2 permeability. Meanwhile, the outside PSA layer intensifies the interface affinity between ZIF-8 and Pebax through molecular chains entanglements and hydrogen bonding, enhancing membrane selectivity. Through controlling the PSA etching process, both the hollow core with tunable size and the outside PSA layer with adjustable thickness are achieved. The 10 wt% PHZ-2/Pebax MMMs present the best performance with a CO 2 permeability of 172.4 Barrer and CO 2 /N 2 selectivity of 87.9. The higher CO 2 /N 2 selectivity proves that the PSA layer on the PHZ has better compatibility with Pebax. The higher CO 2 permeability is attributed to the low-resistance hollow core. The gas separation performance of PHZ-based MMMs not only well exceeded the 2008 Robeson upper-bond line but also was superior to those of other published MOF-based MMMs. The concept of vesicle-shaped PHZ paves a way to concurrently enhance both the gas permeability and selectivity of MMMs. [ABSTRACT FROM AUTHOR]