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Organic materials have attracted considerable attention as potential positive electrodes in lithium-ion batteries owing to their high densities of active surface sites, which can promote fast redox reactions. Rational design strategies for developing redox-active organic materials, however, have not been established systematically. In this work, recent approaches to rational development of organic positive electrodes are comprehensively reviewed to establish design strategies for organic positive electrodes. Three primary conclusions are highlighted: (i) The ability of pristine organic materials to exhibit excellent cell performance is limited. (ii) Incorporation of appropriate functionalities into organic materials can significantly improve their redox activities. (iii) Uniform dispersion of redox-active inorganic materials in a matrix of conductive carbon materials provides nanostructured organic-inorganic composites with optimized cell performance. The strategies outlined in this review will play a critical role in the design of promising organic positive electrodes with appropriate redox activities for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are performed to investigate the cooperatively catalyzed aldol condensation between acetone and 4-nitrobenzaldehyde on alkylamine (or alkylenamine)-grafted silica surfaces, focusing on the mechanism of the catalytic activation of the acetone and 4-nitrobenzaldehyde by the acidic surface silanols followed by the nucleophilic attack of the basic amine functional group toward the activated reactant. From the analysis of the correlations between the catalytically active acid-base sites and reactants, it is concluded that the catalytic cooperativity of the acid-base pair can be affected by two factors: (1) the competition between the silanol and the amine (or enamine) to form a hydrogen bond with a reactant and (2) the flexibility of the alkylamine (or alkylenamine) backbone. Increasing the flexibility of the alkylamine facilitates the nucleophilic attack of the amine on the reactants. From the molecular dynamics simulations, it is found that C3 propylamine and C4 butylamine linkers exhibit the highest probability of reaction, which is consistent with the experimental observation that the activity of the aldol reaction on mesoporous silica depends on the length of alkylamine grafted on the silica surface. This simulation work serves as a pioneering study demonstrating how the molecular simulation approach can be successfully employed to investigate the cooperative catalytic activity of such bifunctional acid-base catalysts. [ABSTRACT FROM AUTHOR]

The Li-binding thermodynamics and redox potentials of seven different quinone derivatives are investigated to determine their suitability as positive electrode materials for lithium-ion batteries. First, using density functional theory (DFT) calculations on the interactions between the quinone derivatives and Li atoms, we find that the Li atoms primarily bind with the carbonyl groups in the test molecules. Next, we observed that the redox properties of the quinone derivatives can be tuned in the desired direction by systematically modifying their chemical structures using electron-withdrawing functional groups. Further, DFT-based investigations of the redox potentials of the Li-bound quinone derivatives provide insights regarding the changes induced in their redox properties during the discharging process. The redox potential decreases as the number of bound Li atoms is increased. However, we found that the functionalization of the quinone derivatives with carboxylic acids can improve their redox potential as well as their charge capacity. Through this study, we also determined that the cathodic activity of quinone derivatives during the discharging process relies strongly on the solvation effect as well as on the number of carbonyl groups available for further Li binding. [ABSTRACT FROM AUTHOR]

Reducedgraphene oxides are active as positive electrodes for lithium-ionenergy storage based on the surface redox reactions between oxygenfunctional groups and Li ions. For effective Li-ion energy storagewithin a confined mass and volume, free-standing, high-packing density,and redox-active graphene films were fabricated by a simple two-stepcompression and vacuum-drying process from a hydrothermally reducedgraphene hydrogel. The assembled graphene films showed a folded microstructurewith high packing densities up to ∼0.64 g/cm3. Redox-activeoxygen functional groups on the graphene oxide were activated andcontrolled by the hydrothermal reduction temperature. Density functionaltheory (DFT) calculations revealed that the carbonyl and epoxide groupsamong various oxygen functional groups on graphene were the main contributorsfor the high potential redox reactions with Li ions. The folded graphenefilm electrodes delivered both a high gravimetric energy of ∼419Wh/kg and a high volumetric energy of ∼239 Wh/L. In addition,the folded graphene film electrodes exhibited an exceptional cyclingstability, retaining a gravimetric capacity of ∼160 mAh/g after50 000 cycles. These results provide significant insights onthe effective utilization of surface redox reactions to design graphene-basedelectrodes for high-performance Li-ion energy storage devices. [ABSTRACT FROM AUTHOR]

The excellent photophysical properties of C60 fullerenes have spurred much research on their application to aqueous systems for biological and environmental applications. Spontaneous aggregation of C60 in water and the consequent diminution of photoactivity present a significant challenge to aqueous applications. The mechanisms driving the reduction of photoactivity in fullerene aggregates and the effects of functionalization on these processes, however, are not well understood. Here, we take a closer look at the molecular phenomena of functionalized fullerene interactions in water utilizing simulation and experimental tools. Molecular dynamic simulations were performed to investigate time-evolved molecular interactions in systems containing fullerenes with water, oxygen, and/or neighboring fullerene molecules, complimented by physical and chemical characterizations of the fullerenes pre- and postaggregation. Aggregates with widely different photoactivities exhibit similar fullerene-water interactions as well as surface and aggregation characteristics. Photoactive fullerene aggregates had weaker fullerene-fullerene and fullerene-O2 interactions, suggesting the importance of molecular interactions in the sensitization route. [ABSTRACT FROM AUTHOR]

Contamination of metal films by sulfur-containing compounds presents a major challenge to using metal membranes for H2purification in processes involving large-scale gasification of coal or biomass. Formation of bulk sulfide phases in these applications is typically associated with irreversible loss of performance and ultimately membrane failure. The concept of using metal alloys to reduce sensitivity to sulfide formation has been explored in a variety of experiments, but development of alloys for this purpose has been hampered by a lack of thermodynamic data on formation of the relevant sulfide phases. We show that first principles calculations using density functional theory can be used to predict the formation of bulk sulfide phases from metal alloys under conditions that are relevant for operation of metal membranes. Our methods are illustrated by assessing the formation of sulfides for PdAg, PdAu, and PdCu alloys of all possible binary compositions. [ABSTRACT FROM AUTHOR]