A nitrogen-doped graphene/sulfur composite was further modified with atomic layers of TiO2and used as the cathode of lithium–sulfur batteries, exhibiting superior cycling stability, good rate capability and high coulombic efficiency.

We synthesize and systematically study a series of conjugated polymers with oligo(ethylene glycol) (OEG) or alkyl chain as the side chain and poly [2,7-fluorene-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] as the polymer backbone. Replacing alkyl chain with OEG chain can decrease the π−π stacking distance of polymer backbone in thin film from 0.44 to 0.41 nm because OEG chain is more flexible than alkyl chain. As the result, the conjugated polymer with OEG side chain exhibits higher hole mobility, red-shifted absorption spectrum in thin film and smaller bandgap than those of the conjugated polymer with alkyl side chain. With the increase of the length of OEG side chain, the resulting conjugated polymers exhibit unchanged π−π stacking distance and decreased hole mobility. Moreover, owing to the large polarity of OEG chain, OEG side chain makes the conjugated polymer suitable for polymer solar cell (PSC) devices processed with polar nonhalogenated solvent, methoxybenzene. A power conversion efficiency of 4.04% is demonstrated with the resulting PSC devices. This work provides the new insight into the effect of OEG side chain on conjugated polymer, which can be used in the molecular design of novel conjugated polymer materials with excellent optoelectronic device performance. ■ INTRODUCTIONConjugated polymers have been widely used in optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and polymer solar cells (PSCs), with the great advantages of low cost, flexibility, and solution processing. 1 For solubility of conjugated polymers, a rigid conjugated polymer backbone is always equipped with an alkyl side chain. 2 Oligo(ethylene glycol) (OEG) chain is well-known for its hydrophilicity and is always used to endow molecules/ polymers solubility in water or polar organic solvents. 3 Thus, OEG chain has been used as side chain of conjugated polymers for efficient OLED, OFET, and PSC devices processed with polar nonhalogenated solvents. 4 As optoelectronic properties of conjugated polymers are affected by the side chain, 5 the effect of OEG side chain on properties of conjugated polymers is less investigated and poorly understood. Researchers may doubt whether hydrophilic OEG side chain would disturb the π−π stacking of hydrophobic polymer backbone in conjugated polymers. This manuscript aims to provide an insight into the effect of OEG side chain on conjugated polymers.We note that OEG chain is more flexible than alkyl chain. As shown in Scheme 1, the two hydrogen atom in CH 2 unit act as steric hindrance for the rotation of CH 2 −CH 2 unit in alkyl chain, while the two lone electron pair in oxygen atom result in no steric hindrance for the rotation of O−CH 2 in OEG chain. 6 Therefore, the energy barrier of the rotation of O−CH 2 in OEG chain (E = 0.08 eV) is smaller than that of CH 2 −CH 2 in alkyl chain (E = 0.11 eV), 6 making OEG chain more flexible than alkyl chain. For conjugated polymers, alkyl side chain impedes the close π−π Scheme 1. Schematic Il...

The atomic-level tunability that results from alloying multiple transition metals with d electrons in concentrated solid solution alloys (CSAs), including high-entropy alloys (HEAs), has produced remarkable properties for advanced energy applications, in particular, damage resistance in high-radiation environments. The key to understanding CSAs' radiation performance is quantitatively characterizing their complex local physical and chemical environments. In this study, the local structure of a FeCoNiCrPd HEA is quantitatively analyzed with X-ray total scattering and extended X-ray absorption fine

IntroductionAs the most popular energy storage devices, lithium-ion batteries (LIBs) enjoy the merits of relatively high energy densities, good reliability, and stability. However, LIBs are still expensive and nearing their ceiling performance. Currently, lithiumsulfur (Li-S) battery has spurred a great deal of attention and hold potential to serve as next-generation energy storage system due to its unique characteristics. Based on the complete reduction of elemental S to Li 2 S, the Li-S battery has a high theoretical energy density of 2600 W h kg −1 , 3-5 times higher than those conventional Li-ion battery cathode materials, such as layered LiCoO 2 and olivine LiFePO 4 . [1,2] Furthermore, sulfur as abundant, economical, and environment-friendly, are all in line with current public transportation and health priorities. The past years have also witnessed unprecedented improvements made by the research groups worldwide. [2][3][4][5][6][7] However, its practical application is still hinged on several tough challenges, such as the inherent poor electronic conductivity of sulfur and its insoluble discharging products (i.e., Li 2 S/Li 2 S 2 ), large volume variation (over 80%) due to the density difference between sulfur and Li 2 S/Li 2 S 2 . More importantly, the shuttle phenomenon caused by the dissolution and migration of long-chain polysulfides (Li 2 S n , 4 ≤ n ≤ 8) lead to the fast capacity decay, self-discharge, and low coulombic efficiency, which further exacerbate the serious problem.In order to address these problems, various hierarchical structured carbonaceous materials, such as porous carbons, [8,9] carbon nanotubes (CNTs), [10,11] and graphene, [12,13] have been thoroughly explored to host sulfur and confine lithium polysulfides (LiPSs). Moreover, they could offer intrinsic high conductivity for charge transport and cushion volume expansion. However, the interactions between the nonpolar hydrophobic carbonaceous materials and polar hydrophilic LiPSs are weak, [14] leading to the out-diffusion, thus deteriorating the battery performance. Electrode modification, such as the addition Freestanding cathode materials with sandwich-structured characteristic are synthesized for high-performance lithium-sulfur battery. Sulfur is impregnated in nitrogen-doped graphene and constructed as primary active material, which is further welded in the carbon nanotube/nanofibrillated cellulose (CNT/NFC) framework. Interconnected CNT/NFC layers on both sides of active layer are uniquely synthesized to entrap polysulfide species and supply efficient electron transport. The 3D composite network creates a hierarchical architecture with outstanding electrical and mechanical properties. Synergistic effects generated from physical and chemical interaction could effectively alleviate the dissolution and shuttling of the polysulfide ions. Theoretical calculations reveal the hydroxyl functionization exhibits a strong chemical binding with the discharge product (i.e., Li 2 S). Electrochemical measurements suggest that the rationally d...

A series of ZnO/Cr 2 O 3 catalysts with different Zn:Cr ratios was prepared by coprecipitation at a constant pH of 7 and applied in methanol synthesis at 260−300 °C and 60 bar. The X-ray diffraction (XRD) results showed that the calcined catalysts with ratios from 65:35 to 55:45 consist of ZnCr 2 O 4 spinel with a low degree of crystallinity. For catalysts with Zn:Cr ratios smaller than 1, the formation of chromates was observed in agreement with temperature-programmed reduction results. Raman and XRD results did not provide evidence for the presence of segregated ZnO, indicating the existence of Zn-rich nonstoichiometric Zn−Cr spinel in the calcined catalyst. The catalyst with Zn:Cr = 65:35 exhibits the best performance in methanol synthesis. The Zn:Cr ratio of this catalyst corresponds to that of the Zn 4 Cr 2 (OH) 12 CO 3 precursor with hydrotalcitelike structure obtained by coprecipitation, which is converted during calcination into a nonstoichiometric Zn−Cr spinel with an optimum amount of oxygen vacancies resulting in high activity in methanol synthesis. Density functional theory calculations are used to examine the formation of oxygen vacancies and to measure the reducibility of the methanol synthesis catalysts. Doping Cr into bulk and the (10−10) surface of ZnO does not enhance the reducibility of ZnO, confirming that Cr:ZnO cannot be the active phase. The (100) surface of the ZnCr 2 O 4 spinel has a favorable oxygen vacancy formation energy of 1.58 eV. Doping this surface with excess Zn charge-balanced by oxygen vacancies to give a 60% Zn content yields a catalyst composed of an amorphous ZnO layer supported on the spinel with high reducibility, confirming this as the active phase for the methanol synthesis catalyst.

A reduced graphene oxide (rGO)-sulfur composite aerogel with a compact self-assembled rGO skin was further modified by an atomic layer deposition (ALD) of ZnO or MgO layer, and used as a free-standing electrode material of a lithium-sulfur (Li-S) battery. The rGO skin and ALD-oxide coating worked as natural and artificial barriers to constrain the polysulfides within the cathode region. As a result, the Li-S battery based on this electrode material exhibited superior cycling stability, good rate capability and high coulombic efficiency. Furthermore, ALD-ZnO coating was tested for performance improvement and found to be more effective than ALD-MgO coating. The ZnO modified G-S electrode with 55 wt% sulfur loading delivered a maximum discharge capacity of 998 mA h g(-1) at a current density of 0.2 C. A high capacity of 846 mA h g(-1) was achieved after charging/discharging for 100 cycles with a coulombic efficiency of over 92%. In the case of using LiNO3 as a shuttle inhibitor, this electrode showed an initial discharge capacity of 796 mA h g(-1) and a capacity retention of 81% after 250 cycles at a current density of 1 C with an average coulombic efficiency higher than 99.7%.

The self-assembled three-dimensional graphene nanohybrids with in situ-formed Fe3O4 and Pd nanoparticles on it (3DRGO_Fe3O4-Pd) are first synthesized by the one-pot solvothermal method, which have intrinsic peroxidase-like and oxidase-like activity. The catalytic mechanism is analyzed by the electron spin resonance (ESR), fluorescence, and electrochemical methods. The mimic enzyme catalytic activity of 3DRGO_Fe3O4-Pd is much higher than those of monometallic loaded nanohybrids and their physical mixture, probably caused by synergistic effect between Pd and Fe3O4 nanoparticles. The 3DRGO_Fe3O4-Pd nanohybrids was reproducible, stable, and reusable. After 10 cycles, the catalytic activity was still higher than 90%, and the morphology and structure were basically unchanged. Based on its high peroxidase-like activity, especially the enhanced affinity toward H2O2, a new colorimetric detection method for reduced glutathione (GSH) and glucose has been designed using H2O2 as an intermediary, which provides a simple, sensitive, and selective way to detect urine glucose of diabetes with a wide linear range and low detection limit.

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