with Nafi on/SiO 2 hybrid membrane at the current density, 10 mA cm −2 . [ 10 ] Apart from the modifi cation of Nafi on membrane, the enhanced performances of VRB were recently also achieved with several kinds of sulfonated aromatic polymers in terms of the minimized hydrophilic domains. [11][12][13] Therefore, it is understood that the control of hydrophobic nature seems to be a common way to reduce the vanadium cross-over.More recently, Zhang et al. reported a VRB with a nanofi ltration type porous membrane that achieved competitive performances, a CE up to 95% and an EE of 76%. [ 14 ] The working principle has been based on the size sieving separation owing to the quite different size of proton and vanadium ions. [ 15 ] This strategy offers not only tremendously decreased cost owing to the already commercialized product, but also an ultimate insight toward maximizing H + /V selectivity. If the pore size of the membrane only enables protons (or water) transfer, the maximized performances could be achieved through the maximized H + /V selectivity. Thus, the subnano-sieving membrane for proton permselective transport is challenging. Here we report a fundamentally new concept to realize such proton/ vanadium selectivity. The concept is unprecedented as the material is hydrophobic, does not swell in water, contains micro porosity hosting water molecules along which protons can migrate and does not allow any other (vanadium) whatsoever. The proposed working principle of such hydrophobic polymers with intrinsic microporosity is disclosed in Scheme 1 .PIM-1 is the fi rst generation polymer having an intrinsic microporosity. We hypothesize that these materials can transport protons preferentially in VRBs because of its hydrophobic molecular structure, limited swelling in aqueous solution, inherent microporous structure with a pore diameter less than 2 nm, high free volume fraction above 20%, good solution processability, and relatively slow physical ageing compared to other high free volume polymers. [16][17][18] Even though hydrophobic, its microporosity is suspected to transport water molecules at high rates: Kentish and co-workers demonstrated water vapor permeation through PIM-1 at no fewer than 30 000 Barrer (1 Barrer = 10 −10 cm 3 (STP) cm (cm 2 s cm Hg) −1 ) above a water activity of 0.7. [ 19 ] Yet, little is known about the state of water inside such microporous polymers: one may anticipate the water being preferentially partitioned in the free-volume forming the microporosity rather than being absorbed into the polymer matrix. This could imply that a certain degree of proton transfer could occur by water molecules inside PIM-1. Meanwhile, the partitioning of hydro-solvated vanadium ions is expected to be limited by both the small radius of its pores and the difference of dielectric property, as illustrated in Scheme 1 .Recent increasing interest in the integration of renewable energy sources has accelerated efforts to develop electric energy storage (EES). [ 1,2 ] Among many approaches for EES, the allvanad...

A new concept of nanocomposites, MOFs on porous two-dimensional nanosheets (MP2), was demonstrated and showed great potential in real gas separation.

The unique pore structure of PIM-1 as a solid interphase can suppress transport of solvent and consequently unwanted chemical reactions at the interface of anodes.

Highly H+/V selective membranes are desired in high-performance vanadium redox flow batteries (VFRBs) to overcome the crossover phenomena of vanadium species. Herein, we demonstrate the molecular-sieving nanochannels (∼0.84 nm) inside a graphene oxide (GO) laminate efficiently blocked the transport of vanadium ions, while allowing the transport of H+. Furthermore, an ultrathin (sub-5 nm) and highly selective GO nanofilm was successfully coated on a porous substrate to improve the H+ flux using a facile spin-coating method. The GO-coated thin-film composite (TFC) membrane showed much higher H+ flux with an exceptionally high H+/V selectivity (H+ permeation rate/VO2+ permeation rate, up to 850) due to the molecular-sieving nanochannels inside the GO nanofilm, leading to a much more enhanced VRFB performance in terms of energy efficiency (EE, 84.7%) compared to the benchmark Nafion membrane (EE, 69.2%), at 20 mA cm–2.

Bipolar membranes (BPMs) have recently received much attention for their potential to improve the water dissociation reaction (WDR) at their junction by utilizing catalysts. Herein, composite catalysts (Fe2O3@GO) comprising hematite nanoparticles (α‐Fe2O3) grown on 2D graphene oxide (GO) nanosheets are reported, which show unprecedentedly high water dissociation performance in the BPM. Furthermore, new catalytic roles in facilitating WDR at the catalyst–water interface are mechanistically elucidated. It is demonstrated that the partially dissociated bound water, formed by the strongly Lewis‐acidic Fe atoms of the Fe2O3@GO catalyst, helps the “ice‐like water” to become tighter, consequently resulting in weaker intramolecular OH bonds, which reduces activation barriers and thus significantly improves the WDR rate. Notably, Fe2O3@GO‐incorporated BPM shows an extremely low water dissociation potential (0.89 V), compared to commercially available BPM (BP‐1E, 1.13 V) at 100 mA cm−2, and it is quite close to the theoretical potential required for WDR (0.83 V). This performance reduces the required electrical energy consumption for water splitting by ≈40%, as compared to monopolar (Nafion 212 and Selemion AMV) membranes. These results can provide a new approach for the development of water dissociation catalysts and BPMs for realizing highly efficient water splitting systems.

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We report the formation of a reversible complex between CO2 and a bound water coordinating alkaline metal cation (Lewis-acidic water) by nuclear magnetic resonance (NMR) analysis for the first time.

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