ZnO nanoparticles have been synthesized by precipitation method from Zinc nitrate. The powder was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction, UV-vis optical absorption, and photoluminescence spectroscopy analyses. XRD patterns showed that ZnO nanoparticles have hexagonal unit cell structure. SEM and TEM pictures reveal the morphology and particle size of prepared ZnO nanoparticles. The UV-vis absorption spectrum shows an absorption band at 355 nm due to ZnO nanoparticles. The photoluminescence spectrum exhibits two emission peaks one at 392 nm corresponding to band gap excitonic emission and another located at 520 nm due to the presence of singly ionized oxygen vacancies. The synthesis method has potential for application in manufacturing units due to ease processing and more economical reagents.
Enhancing the ionic conductivity across the electrolyte separator in nonaqueous redox flow batteries (NRFBs) is essential for improving their performance and enabling their widespread utilization. Separating redox-active species by size exclusion without greatly impeding the transport of supporting electrolyte is a potentially powerful alternative to the use of poorly performing ion-exchange membranes. However, this strategy has not been explored possibly due to the lack of suitable redox-active species that are easily varied in size, remain highly soluble, and exhibit good electrochemical properties. Here we report the synthesis, electrochemical characterization, and transport properties of redox-active poly(vinylbenzyl ethylviologen) (RAPs) with molecular weights between 21 and 318 kDa. The RAPs reported here show very good solubility (up to at least 2.0 M) in acetonitrile and propylene carbonate. Ultramicroelectrode voltammetry reveals facile electron transfer with E1/2 ∼ -0.7 V vs Ag/Ag(+)(0.1 M) for the viologen 2+/+ reduction at concentrations as high as 1.0 M in acetonitrile. Controlled potential bulk electrolysis indicates that 94-99% of the nominal charge on different RAPs is accessible and that the electrolysis products are stable upon cycling. The dependence of the diffusion coefficient on molecular weight suggests the adequacy of the Stokes-Einstein formalism to describe RAPs. The size-selective transport properties of LiBF4 and RAPs across commercial off-the-shelf (COTS) separators such as Celgard 2400 and Celgard 2325 were tested. COTS porous separators show ca. 70 times higher selectivity for charge balancing ions (Li(+)BF4(-)) compared to high molecular weight RAPs. RAPs rejection across these separators showed a strong dependence on polymer molecular weight as well as the pore size; the rejection increased with both increasing polymer molecular weight and reduction in pore size. Significant rejection was observed even for rpoly/rpore (polymer solvodynamic size relative to pore size) values as low as 0.3. The high concentration attainable (>2.0 M) for RAPs in common nonaqueous battery solvents, their electrochemical and chemical reversibility, and their hindered transport across porous separators make them attractive materials for nonaqueous redox flow batteries based on the enabling concept of size-selectivity.
Versatile and readily available battery materials compatible with a range of electrode configurations and cell designs are desirable for renewable energy storage. Here we report a promising class of materials based on redox active colloids (RACs) that are inherently modular in their design and overcome challenges faced by small-molecule organic materials for battery applications, such as crossover and chemical/morphological stability. RACs are cross-linked polymer spheres, synthesized with uniform diameters between 80 and 800 nm, and exhibit reversible redox activity as single particles, as monolayer films, and in the form of flowable dispersions. Viologen-based RACs display reversible cycling, accessing up to 99% of their capacity and 99 ± 1% Coulombic efficiency over 50 cycles by bulk electrolysis owing to efficient, long-distance intraparticle charge transfer. Ferrocene-based RACs paired with viologen-based RACs cycled efficiently in a nonaqueous redox flow battery employing a simple size-selective separator, thus demonstrating a possible application that benefits from their colloidal dimensions. The unprecedented versatility in RAC synthetic and electrochemical design opens new avenues for energy storage.
Intermittent energy sources, including solar and wind, require scalable, low‐cost, multi‐hour energy storage solutions in order to be effectively incorporated into the grid. All‐Organic non‐aqueous redox‐flow batteries offer a solution, but suffer from rapid capacity fade and low Coulombic efficiency due to the high permeability of redox‐active species across the battery's membrane. Here we show that active‐species crossover is arrested by scaling the membrane's pore size to molecular dimensions and in turn increasing the size of the active material above the membrane's pore‐size exclusion limit. When oligomeric redox‐active organics (RAOs) were paired with microporous polymer membranes, the rate of active‐material crossover was reduced more than 9000‐fold compared to traditional separators at minimal cost to ionic conductivity. This corresponds to an absolute rate of RAO crossover of less than 3 μmol cm−2 day−1 (for a 1.0 m concentration gradient), which exceeds performance targets recently set forth by the battery industry. This strategy was generalizable to both high and low‐potential RAOs in a variety of non‐aqueous electrolytes, highlighting the versatility of macromolecular design in implementing next‐generation redox‐flow batteries.
What are the stumbling blocks for achieving high-efficiency organic photovoltaic devices? This question is examined from a molecular architecture and molecular packing perspective. The intermolecular interaction between the electron donor and electron acceptor influences the charge separation. The packing of electron donors and acceptors influences the charge transport. Therefore, there is a need to strike a balance between the chargetransfer interactions and packing interactions and obtain nanoscale segregated morphologies for efficient charge separation and charge transport. Molecular architecture is key toward striking this balance and, therefore, its impact on charge-transfer interactions and packing interactions; thus, the active-layer morphology and photovoltaic metrics are examined. A variety of molecular architectures for the packing of π-conjugated organic molecules to structures relevant for photovoltaic devices is also discussed.
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