Unique Octupolar 2D-Polymer Frameworks as Mixed Conductors and Metal-Free Catalysts for Dual-Promoted Li and S Electrochemistry: Multi-regulation Role of Ethoxylation Chemistry.

Here, we for the first time introduce ethoxylation chemistry to develop a new octupolar cyano-vinylene-linked 2D polymer framework (Cyano-OCF-EO) capable of acting as efficient mixed electron/ion conductors and metal-free sulfur evolution catalysts for dual-promoted Li and S electrochemistry. Our strategy creates a unique interconnected network of strongly-coupled donor 3-(acceptor-core) octupoles in Cyano-OCF-EO, affording enhanced intramolecular charge transfer, substantial active sites and crowded open channels. This enables Cyano-OCF-EO as a new versatile separator modifier, which endows the modified separator with superior catalytic activity for sulfur conversion and rapid Li ion conduction with the high Li+ transference number up to 0.94. Thus, the incorporation of Cyano-OCF-EO can concurrently regulate sulfur redox reactions and Li-ion flux in Li-S cells, attaining boosted bidirectional redox kinetics, inhibited polysulfide shuttle and dendrite-free Li anodes. The Cyano-OCF-EO-involved Li-S cell is endowed with excellent overall electrochemical performance especially large areal capacity of 7.5 mAh cm-2 at high sulfur loading of 8.7 mg cm-2 . Mechanistic studies unveil the dominant multi-promoting effect of the triethoxylation on electron and ion conduction, polysulfide adsorption and catalytic conversion as well as previously-unexplored -CN/C-O dual-site synergistic effect for enhanced polysulfide adsorption and reduced energy barrier toward Li2 S conversion.

Octupolar Acrylonitrile-Bridged 2D-Conjugated Polymers Enable Bright Far-Red Emission with Intense Two-Photon Absorption via Alkoxylation Chemistry.

Herein, alkoxylation chemistry is introduced as a "one-stone-three-birds" solution for exploring a new family of highly-fluorescent octupolar 2D-conjugated organic polymers/frameworks (OCOPs/OCOFs) combining far-red emission, high fluorescence quantum yield (QY), and strong two-photon absorption (TPA). Both alkoxy-substituted OCOP and OCOF comprising acrylonitrile-bridged strongly-coupled donor3-(acceptor core) chromophores densely packed in either disordered or ordered forms, exhibit significantly redshifted emission. They produce high QY of 22.2% and 27.8% in tetrahydrofuran, large TPA cross section of 600 and 1124 GM, and 2-3 folds and 15-30 folds that of non-alkoxylate amorphous counterpart respectively. Combined theoretical and experimental studies reveal unique "one-stone-three-birds" role of the alkoxylation in realizing red-shifted-emission, improved QY and TPA enabled by inducing steric hindrance effect for weakened π-π stacking, and triggering p-π conjugation effect for electronically engineering octupolar chromophores, while the crystalline engineering enables enforced coplanarity conformation and improved π-electron delocalization for further improved QY and TPA. The robust and biocompatible pentoxy-substituted polymer can be used not only as metal-free red-emissive phosphor for efficient warm white light-emitting diodes, but also as efficient two-photon fluorescence probes for bio-imaging.

Capturing Visible Light in Low-Band-Gap C4 N-Derived Responsive Bifunctional Air Electrodes for Solar Energy Conversion and Storage.

We report facile synthesis of low-band-gap mesoporous C4 N particles and their use as responsive bifunctional oxygen catalysts for visible-light-sensitive (VLS) rechargeable Zn-air battery (RZAB) and polymer-air battery (RPAB). Compared to widely studied g-C3 N4 , C4 N shows a smaller band gap of 1.99 eV, with a larger photocurrent response, and it can function as visible-light-harvesting antenna and bifunctional oxygen reduction/evolution (ORR/OER) catalysts, enabling effective photocoupling to tune oxygen catalysis. The C4 N-enabled VLS-RZAB displays a low charge voltage of 1.35 V under visible light, which is below the theoretical RZAB voltage of 1.65 V, corresponding to a high energy efficiency of 97.78 %. Pairing a C4 N cathode with a polymer anode also endows an VLS-RPAB with light-boosted charge performance. It is revealed that the ORR and OER active sites in C4 N are separate carbon sites near pyrazine-nitrogen atoms and photogenerated energetic holes can activate OER for improved reaction kinetics.

Redox Donor-Acceptor Conjugated Microporous Polymers as Ultralong-Lived Organic Anodes for Rechargeable Air Batteries.

Herein, we explore a new redox donor-acceptor conjugated microporous polymer (AQ-CMP) by utilizing anthraquinone and benzene as linkers via C-C linkages and demonstrate the first use of CMP as ultralong-lived anodes for rechargeable air batteries. AQ-CMP features an interconnected octupole network, which affords not only favorable electronic structure for enhanced electron transport and n-doping activity compared to linear counterpart, but also high density of active sites for maximizing the formula-weight-based redox capability. This coupled with highly cross-linked and porous structure endows AQ-CMP with a specific capacity of 202 mAh g-1 (96 % of theoretical capacity) at 2 Ag-1 and ≈100 % capacity retention over 60000 charge/discharge cycles. The assembled CMP-air full cell shows a stable and high capacity with full capacity recovery after only refreshing cathodes, while the decoupled electrolyte and cathode design boosts the discharge voltage and voltage efficiency to ≈1 V and 87.5 %.

Alkene-Linked Covalent Organic Frameworks Boosting Photocatalytic Hydrogen Evolution by Efficient Charge Separation and Transfer in the Presence of Sacrificial Electron Donors.

Covalent organic frameworks (COFs) are potential photocatalysts for artificial photosynthesis but they are much less explored for photocatalytic hydrogen evolution (PHE). COFs, while intriguing due to crystallinity, tunability, and porosity, tend to have low apparent quantum efficiency (AQE) and little is explored on atomistic structure-performance correlation. Here, adopting triphenylbenzene knots and phenyl linkers as a proof of concept, three structurally related COFs with different linkages are constructed to achieve a tunable COF platform and probe the effect of the linkage chemistry on PHE. Cyano-substituted alkene-linked COF (COF-alkene) yields a stable 2330 µmol h-1 g-1 PHE rate, much superior to imine- and imide-linked counterparts (<40 µmol h-1 g-1) under visible light irradiation. Impressively, COF-alkene achieves an AQE of 6.7% at 420 nm. Combined femtosecond transient absorption spectroscopy and theoretical calculation disclose the critical role of cyano-substituted alkene linkages toward high efficiency of charge separation and transfer in the presence of sacrificial electron donors-the decisive key to the superior PHE performance. Such alkene linkages can also be extended to design a series of high-performance polymeric photocatalysts, highlighting a general design idea for efficient PHE.

Erratum: In Situ Activating Strategy to Significantly Boost Oxygen Electrocatalysis of Commercial Carbon Cloth for Flexible and Rechargeable Zn-Air Batteries.

[This corrects the article DOI: 10.1002/advs.201800760.].

In Situ Activating Strategy to Significantly Boost Oxygen Electrocatalysis of Commercial Carbon Cloth for Flexible and Rechargeable Zn-Air Batteries.

An in situ strategy to simultaneously boost oxygen reduction and oxygen evolution (ORR/OER) activities of commercial carbon textiles is reported and the direct use of such ubiquitous raw material as low-cost, efficient, robust, self-supporting, and bifunctional air electrodes in rechargeable Zn-air batteries is demonstrated. This strategy not only furnishes carbon textiles with a large surface area and hierarchical meso-microporosity, but also enables efficient dual-doping of N and S into carbon skeletons while retaining high conductivity and stable monolithic structures. Thus, although original carbon textile has rather poor catalytic activity, the activated textiles without loading other active materials yield effective ORR/OER bifunctionality and stability with a much lower reversible overpotential (0.87 V) than those of Pt/C (1.10 V) and RuO2 (1.02 V) and many reported metal-free bifunctional catalysts. Importantly, they can concurrently function as current collectors and as ORR/OER catalysts for rechargeable aqueous and flexible solid-state Zn-air batteries, showing excellent cell performance, long lifetime, and high flexibility.