A membrane with both high ion conductivity and selectivity is critical to high power density and low-cost flow batteries, which are of great importance for the wide application of renewable energies. The trade-off between ion selectivity and conductivity is a bottleneck of ion conductive membranes. In this paper, a thin-film composite membrane with ultrathin polyamide selective layer is found to break the trade-off between ion selectivity and conductivity, and dramatically improve the power density of a flow battery. As a result, a vanadium flow battery with a thin-film composite membrane achieves energy efficiency higher than 80% at a current density of 260 mA cm −2 , which is the highest ever reported to the best of our knowledge. Combining experiments and theoretical calculation, we propose that the high performance is attributed to the proton transfer via Grotthuss mechanism and Vehicle mechanism in sub-1 nm pores of the ultrathin polyamide selective layer.
The metal-catalyzed selective hydrogenation of biomass-derived molecules is in great demand but is challenging due to the complex reaction pathways. Herein, we report a persuasive example for achieving selective hydrogenation of furfural over Pd catalysts by controllable sorption of molecules in zeolite micropores. The key to this success is fixation of Pd nanoparticles inside of silicalite-1 zeolite with controllable wettability (Pd@S-1-OH) by functionalizing silanol groups into the zeolite framework. In the hydrogenation of furfural as a model reaction, the Pd@S-1-OH catalyst with appropriate hydrophilicity exhibits extraordinary selectivity for the formation of furan, giving furan selectivity as high as >99.9% with a complete conversion of furfural, outperforming the conventional Pd nanoparticles supported on zeolite crystals (Pd/S-1) and S-1 zeolite fixed Pd catalysts without an artificially functionalized silanol group (Pd@S-1). The extraordinary performance of Pd@S-1-OH is reasonably attributed to the controllable diffusion of molecules within the hydrophilic zeolite micropores, which favors the adsorption of furfural and a series of byproducts but promotes the desorption of furan. Very importantly, Pd@S-1-OH is stable and gives the furan productivity of ∼583.3 g gPd –1 day–1 in a continuous test.
Membranes with fast and selective ions transport are highly demanded for energy storage devices. Layered double hydroxides (LDHs), bearing uniform interlayer galleries and abundant hydroxyl groups covalently bonded within two-dimensional (2D) host layers, make them superb candidates for high-performance membranes. However, related research on LDHs for ions separation is quite rare, especially the deep-going study on ions transport behavior in LDHs. Here, we report a LDHs-based composite membrane with fast and selective ions transport for flow battery application. The hydroxide ions transport through LDHs via vehicular (standard diffusion) & Grotthuss (proton hopping) mechanisms is uncovered. The LDHs-based membrane enables an alkaline zinc-based flow battery to operate at 200 mA cm−2, along with an energy efficiency of 82.36% for 400 cycles. This study offers an in-depth understanding of ions transport in LDHs and further inspires their applications in other energy-related devices.
The crystallographic pore sizes of zeolites are substantially smaller than those inferred from catalytic transformation and molecular sieving capabilities, which reflects flexible variation in zeolite opening pores. Using in situ electron microscopy, we imaged the straight channels of ZSM-5 zeolite with benzene as a probe molecule and observed subcell flexibility of the framework. The opening pores stretched along the longest direction of confined benzene molecules with a maximum aspect change of 15%, and the Pnma space group symmetry of the MFI framework caused adjacent channels to deform. This compensation maintained the stability and rigidity of the overall unit cell within 0.5% deformation. The subcell flexibility originates mainly from the topologically soft silicon-oxygen-silicon hinges between rigid tetrahedral SiO 4 units, with inner angles varying from 135° to 153°, as confirmed by ab initio molecular dynamics simulations.
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