Vinayak S. Kale

Abstract Covalent organic frameworks (COFs) are potentially promising electrode materials for electrochemical charge storage applications thanks to their pre‐designable reticular chemistry with atomic precision, allowing precise control of pore size, redox‐active functional moieties, and stable covalent frameworks. However, studies on the mechanistic and practical aspects of their zinc‐ion storage behavior are still limited. In this study, a strategy to enhance the electrochemical performance of COF cathodes in zinc‐ion batteries (ZIBs) by introducing the quinone group into 1,4,5,8,9,12‐hexaazatriphenylene‐based COFs is reported. Electrochemical characterization demonstrates that the introduction of the quinone groups in the COF significantly pushes up the Zn 2+ storage capability against H + and elevates the average (dis‐)charge potential in aqueous ZIBs. Computational and experimental analysis further reveals the favorable redox‐active sites that host Zn 2+ /H + in COF electrodes and the root cause for the enhanced electrochemical performance. This work demonstrates that molecular engineering of the COF structure is an effective approach to achieve practical charge storage performance.

Aqueous zinc-ion batteries and capacitors are potentially competitive grid-scale energy storage devices because of their great features such as safety, environmental friendliness, and low cost. Herein, a completely new phenanthroline covalent organic framework (PA-COF) was synthesized and introduced in zinc-ion supercapatteries (ZISs) for the first time. Our as-synthesized PA-COF shows a high capacity of 247 mAh g-1 at a current density of 0.1 A g-1, with only 0.38% capacity decay per cycle during 10※000 cycles at a current density of 1.0 A g-1. Although covalent organic frameworks (COFs) are attracting great attention in many fields, our PA-COF has been synthesized using a new strategy involving the condensation reaction of hexaketocyclohexanone and 2,3,7,8-phenazinetetramine. Detailed mechanistic investigations, through experimental and theoretical methods, reveal that the phenanthroline functional groups in PA-COF are the active zinc ion storage sites. Furthermore, we provide evidence for the cointercalation of Zn2+ (60%) and H+ (40%) into PA-COF using inductively coupled plasma atomic emission spectroscopy and deuterium solid-state nuclear magnetic resonance (NMR). We believe that this study opens a new avenue for COF material design for zinc-ion storage in aqueous ZISs.

ion storage in host materials based on hydrogen bond chemistry. This mechanism can be leveraged to design and develop COFs for electrochemical energy storage.

Abstract Displaying information on transparent screens offers new opportunities in next‐generation electronics, such as augmented reality devices, smart surgical glasses, and smart windows. Outstanding luminance and transparency are essential for such “see‐through” displays to show vivid images over clear background view. Here transparent quantum dot light‐emitting diodes (Tr‐QLEDs) are reported with high brightness (bottom: ≈43 000 cd m −2 , top: ≈30 000 cd m −2 , total: ≈73 000 cd m −2 at 9 V), excellent transmittance (90% at 550 nm, 84% over visible range), and an ultrathin form factor (≈2.7 µm thickness). These superb characteristics are accomplished by novel electron transport layers (ETLs) and engineered quantum dots (QDs). The ETLs, ZnO nanoparticle assemblies with ultrathin alumina overlayers, dramatically enhance durability of active layers, and balance electron/hole injection into QDs, which prevents nonradiative recombination processes. In addition, the QD structure is further optimized to fully exploit the device architecture. The ultrathin nature of Tr‐QLEDs allows their conformal integration on various shaped objects. Finally, the high resolution patterning of red, green, and blue Tr‐QLEDs (513 pixels in. −1 ) shows the potential of the full‐color transparent display.