A 3D photothermal cone was developed to optimize light harvesting via multiple reflections within rational morphology for high-efficiency solar-driven evaporation.
Polymeric dielectrics have attracted intensive attention worldwide because of their huge potential for advanced energy storage capacitors. Thus far, various effective strategies have been developed to improve the inherent low energy densities of polymer dielectrics. However, enhanced energy density is always accompanied by suppressed discharge efficiency, which is detrimental to practical applications and deserves considerable concern. Targeting at achieving simultaneous high energy density and high discharge efficiency, the unique design of asymmetric all-polymer trilayer composite consisting of a transition layer sandwiched by a linear dielectric layer and a nonlinear dielectric layer is herein reported. It is demonstrated that the nonlinear dielectric layer offers high energy density, while the linear dielectric layer provides high discharge efficiency. Especially, the transition layer can effectively homogenize the electric field distribution, resulting in greatly elevated breakdown strength and improved energy density. In particular, a high efficiency of 89.9% along with a high energy density of 12.15 J cm −3 are concurrently obtained. The asymmetric trilayer all-polymer design strategy represents a new way to achieve high-performance dielectric energy storage materials.
It is a major challenge to achieve fast charging and high reversible capacity in potassium ion storing carbons. Here, we synthesized sulfur-rich graphene nanoboxes (SGNs) by one-step chemical vapor deposition to deliver exceptional rate and cyclability performance as potassium ion battery and potassium ion capacitor (PIC) anodes. The SGN electrode exhibits a record reversible capacity of 516 mAh g −1 at 0.05 A g −1 , record fast charge capacity of 223 mA h g −1 at 1 A g −1 , and exceptional stability with 89% capacity retention after 1000 cycles. Additionally, the SGN-based PIC displays highly favorable Ragone chart characteristics: 112 Wh kg −1 at 505 W kg −1 and 28 Wh kg −1 at 14618 W kg −1 with 92% capacity retention after 6000 cycles. X-ray photoelectron spectroscopy analysis illustrates a charge storage sequence based primarily on reversible ion binding at the structural−chemical defects in the carbon and the reversible formation of K−S−C and K 2 S compounds. Transmission electron microscopy analysis demonstrates reversible dilation of graphene due to ion intercalation, which is a secondary source of capacity at low voltage. This intercalation mechanism is shown to be stable even at cycle 1000. Galvanostatic intermittent titration technique analysis yields diffusion coefficients from 10 −10 to 10 −12 cm 2 s −1 , an order of magnitude higher than S-free carbons. The direct electroanalytic/analytic comparison indicates that chemically bound sulfur increases the number of reversible ion bonding sites, promotes reaction-controlled over diffusion-controlled kinetics, and stabilizes the solid electrolyte interphase. It is also demonstrated that the initial Coulombic efficiency can be significantly improved by switching from a standard carbonate-based electrolyte to an ether-based one.
An amorphous cobalt–cobalt oxide/cobalt selenide composite film has been fabricated directly on a 3D macro-porous Ni foam substrate by a facile electrodeposition method, which can be an efficient and cheap bifunctional electrocatalyst for both the OER and HER and offer potential applications in the field of full water splitting.
The principle of polymer-controlled crystallization of inorganic materials has been successfully transferred to functional aromatic organic dyes, in this instance 3,4,9,10-perylenetetracarboxylic acid potassium salt (PTCAPS), after its single-crystal structure was determined. The cationic double hydrophilic block copolymer poly(ethylene glycol)-block-branched-poly(ethyleneimine) (PEG-b-PEI) was used as the polymer additive to modify the crystallization of PTCAPS. Ultralong hierarchically structured PTCAPS microbelts with constant width and thickness of each individual belt have been fabricated. The belts are a mesocrystalline assembly of primary nanoparticles with high-energy anionic {001} faces stabilized by polymer complexation. Polarization microscopy, X-ray diffraction, optical absorption spectra, and fluorescence spectra indicate the favorable orientation of the 1D microbelts in the close-stacking direction and reveal a specific 1D superstructure fluorescence. Electrical conductivity measurements performed on a single nanobelt disclose in the doped state a remarkably high electronic conductivity and further demonstrate extended, wirelike pi-pi interactions along the [020] long axis of the belts. Together with the very large length of the belts and their organic-organic hybrid nanostructure, this makes these organic wires potentially interesting for the field of nano-/micro-optoelectronics.
The current imbalance in the biogeochemical cycle of nitrogen is as serious as that of carbon. One way to mitigate this problem is through the electrochemical reduction of nitrates under mild conditions, which is an appealing though not fully understood process. Therefore, deeper insight into the electrocatalytic reaction mechanism is needed to optimize this process. Here we thoroughly analyse the adsorption energy of nitrate with DFT calculations on various surface facets of pure Au, Ag, and their near-surface and surface alloys, as the adsorption and subsequent reduction of nitrate are thought to be rate limiting in the electrocatalytic reaction. The observed systematic trends allow prediction of the surface with highest electrocatalytic activity for the reduction of nitrate. This prediction was verified experimentally by depositing sub-monolayer amounts of Ag on polycrystalline Au electrodes. We observe a well-defined volcano curve which correlates the amount of Ag deposited on the surface with the current density at a fixed potential, with the peak activity around 2/3 ML Ag surface coverage. The electrocatalytic activity and stability of the bimetallic Ag-Au systems, found through the interplay of theoretical modelling and empirical observations, serve as a clear example for the rational design of novel catalytic materials and confirm the key role that the adsorption of nitrate plays in the overall nitrate reduction rate.
Developing cost‐effective and high‐performance catalysts for oxygen evolution reaction (OER) is essential to improve the efficiency of electrochemical conversion devices. Unfortunately, current studies greatly depend on empirical exploration and ignore the inherent relationship between electronic structure and catalytic activity, which impedes the rational design of high‐efficiency OER catalysts. Herein, a series of bimetallic Ni‐based metal‐organic frameworks (Ni‐M‐MOFs, M = Fe, Co, Cu, Mn, and Zn) with well‐defined morphology and active sites are selected as the ideal platform to explore the electronic‐structure/catalytic‐activity relationship. By integrating density‐functional theory calculations and experimental measurements, a volcano‐shaped relationship between electronic properties (d‐band center and eg filling) and OER activity is demonstrated, in which the NiFe‐MOF with the optimized energy level and electronic structure situated closer to the volcano summit. It delivers ultra‐low overpotentials of 215 and 297 mV for 10 and 500 mA cm−2, respectively. The identified electronic‐structure/catalytic activity relationship is found to be universal for other Ni‐based MOF catalysts (e.g., Ni‐M‐BDC‐NH2, Ni‐M‐BTC, Ni‐M‐NDC, Ni‐M‐DOBDC, and Ni‐M‐PYDC). This work widens the applicability of d band center and eg filling descriptors to activity prediction of MOF‐based electrocatalysts, providing an insightful perspective to design highly efficient OER catalysts.
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