Water-soluble pH-responsive dendritic core-shell nanocarriers for polar dyes based on poly(ethylene imine)

A simple general synthetic concept to build dendritic core-shell architectures with pH-labile linkers based on hyperbranched PEI cores and biocompatible PEG shells is presented. Using these dendritic core-shell architectures as nanocarriers, the encapsulation and transport of polar dyes of different sizes is studied. The results show that the acid-labile nanocarriers exhibit much higher transport capacities for dyes than unfunctionalized hyperbranched PEI. The cleavage of imine bonds and controlled release of the polar dyes revealed that weak acidic condition (pH approximately 5.0) could cleave the imine bonds linker and release the dyes up to five times faster than neutral conditions (pH = 7.4).     

Catalysis of slow charge transfer reactions at polypyrrole-coated glassy carbon electrodes

Oxidation of ascorbic acid, dihydroxyphenylacetic acid and dopamine are compared at polypyrrole-coated glassy carbon and naked glassy carbon electrodes. These currents are mass-transport limited and not limited by permeation into or through the polypyrrole film. Ascorbic acid oxidation occurs at potentials 300 mV more negative at polypyrrole-coated electrodes and the rising slope of rotated disk voltammograms changes by over 100 mV. A similar enhancement in electrochemical reversibility is observed for dihydroxyphenylacetic acid, whereas dopamine is oxidized at slightly more positive potentials at polypyrrole-coated electrodes. Comparing the electrochemistry of dopamine and dihydroxyphenyl-acetic acid, it appears that the electrochemical reversibility differences for these substances are to some degree result of electrostatic interactions between the anionic solutes, or anionic reaction intermediates, and anionic functional groups on carbon or cationic fixed sites in oxidized polypyrrole.     

锂离子电池LiBF4基液体电解质研究进展

LiBF4基电解质的热稳定性较好,对环境水分不太敏感,有希望发展成为被民用、军事、三航领域微型、储能及动力锂离子电池广泛采用的优秀电解质体系。本文综述了近期在改善LiBF4的电导率、拓宽应用温度范围、促进SEI膜的形成、提高其电解液电导率及与电极材料的相容性等方面所取得的进展,并对其未来发展方向作了展望。     

Recent studies on small molecular and polymeric hole-transporting materials for high-performance perovskite solar cells

A decade of significant research has led to the emergence of photovoltaic solar cells based on perovskites that have achieved an exceptionally high-power conversion efficiency of 26.08%. A key breakthrough in perovskite solar cells (PSCs) occurred when solid hole-transporting materials (HTMs) replaced liquid electrolytes in dye-sensitized solar cells (DSSCs), because HTMs play a crucial role in improving photovoltaic performance as well as cell stability. This review is mainly focused on the HTMs that are responsible for hole transport and extraction in PSCs, which is one of the crucial components for efficient devices. Here, we have reviewed small molecular as well as polymeric HTMs that have been reported in the last two years and discussed their performance based on the analysis of their molecular architectures. Finally, we include a perspective on the molecular engineering of new functional HTMs for highly efficient stable PSCs.     

聚合物固体电解质研究进展

本文概述近十几年来聚合物固体电解质材料开发研究的状况,包括线型高分子、为改进性能而发展起来的枝型、梳型及交联型高分子,并对高分子与金属盐络合的离子聚合物结构和性能作了描述。阐述了高分子固体电解质的导电行为、导电模型及导电机理。对聚合物固体电解质的各种应用作了介绍并简要讨论了高分子固体电解质的发展趋向及前景。     

A simplified model of oscillating electrolytes

Unstable electrophoretic transport leading to oscillations in concentration profiles occur in certain electrolyte systems known as oscillating electrolytes whose eigenmobilities are complex valued. The study of the nonlinear behavior of such systems is of great interest but is constrained due to a high degree of complexity in the governing equations. Here we present a simplified model of unstable electrophoretic transport in a binary system that reduces the governing equations to two partial differential equations only and does away with other equations that characterize acid–base dissociation reactions and electroneutrality. We present analytical expressions for electromigration fluxes and validate the model with full nonlinear simulations. The model exhibits similar nonlinear behavior as the actual unstable electrophoretic system under various initial disturbances. For comparison, we also show that similar modeling for a stable system predicts concentration profiles that quantitatively agree with its nonoscillating dynamics. Moreover, the unique feature of electromigration flux in oscillating electrolytes that unfolds from the modeling led us to find an elegant explanation of the instability mechanism. Our theory gives a qualitative understanding of the existence and growth of large oscillation patterns in oscillating electrolytes.     

New approaches to developing lithium polymer batteries

The electrochemical and physical-chemical properties of two families of lithium ion conducting membranes, i.e., the blends between high molecular weight poly(ethylene oxide) with a lithium salt commonly named "polymer electrolytes" and the gels of liquid solutions in a polymer matrix commonly named "gel electrolytes," are repoted and discussed. Particular attention is devoted to the newly developed approach of dispersing ceramic powders at the nanoscale particle dimension into the two types of membranes. This leads "nanocomposite" membranes having unique features, such as improved transport and interfacial properties in the case of the polymer electrolytes and enhanced liquid retention capability in the case of the gel electrolytes. Finally, the use of the gel electrolytes for the development of new-design, plastic-like, lithium-ion batteries is illustrated.     

Series approach to modeling ion size effects for asymmetric electrolytes in the diffuse double layer

The theory of the diffuse layer for asymmetric electrolytes is reconsidered with emphasis on the effects of ion size on the diffuse layer potential drop and differential capacity. For asymmetric 2:1 and 1:2 electrolytes, this potential drop is expressed in terms of a polynomial with a linear, quadratic, and cubic term in the corresponding estimate in the Gouy-Chapman theory. Optimal polynomial coefficients and model validation for 2:1 electrolytes are provided by least-squares regression of Monte Carlo data obtained for a restricted electrolyte in a primitive solvent. These coefficients are then expressed as simple functions of the parameters commonly associated with the mean spherical approximation. The series approach accurately describes potential drops and differential capacities of the diffuse layer for 2:1 and 1:2 electrolytes for the chosen assumptions.     

The preparation of highly ordered TiO2 nanotube arrays by an anodization method and their applications

The tubular-shaped nanostructure of TiO(2) is very interesting, and highly ordered arrays of TiO(2) nanotubes (TNTs) can be easily fabricated by anodization of the Ti substrate in specific electrolytes. Here in this feature article, we review synthesis methods for various TNTs including normal, alloy, and architectural forms such as bamboos, lace, and flowers. Specific nanosize architectures such as bamboo and lace types can be regulated by alternating voltage and further anodizing. In order to extend light response of TNTs to visible solar spectra, various dopings of specific elements have been discussed. The normal and modified TNTs are suggested for applications such as dye sensitized solar cells, water splitting, photocatalytic degradation of pollutants, CO(2) reduction, sensors, energy storage devices including Li ion batteries and supercapacitors, and other applications such as flexible substrate and biomaterials.     

A numerical study on the coalescence of emulsion droplets in a constricted capillary tube

Using a new computational model, we have studied the dynamics and coalescence of a pair of two-dimensional droplets in pressure-driven flow through a constricted capillary tube, which is a prototype problem for the analysis of the interaction of emulsion droplets in porous media. We present simulations that quantify the effects of various system parameters on the droplet stability. These include the capillary number, the interfacial tension, the suspended-to-suspending-phase viscosity ratio, the valence and concentration of added electrolytes, the droplet-to-pore-size ratio, the pore-body-to-throat-size ratio, and the type of pore geometry. Our simulations show that the capillary number Ca plays an important role in determining whether the drops coalesce. At low Ca, drops deform only slightly and coalescence occurs at the entrance of the pore throat, whereas significant deformation enables the drops move through the pore without coalescence at high Ca. Coalescence is favored at intermediate values of the viscosity ratio. The destabilizing effect of added electrolytes is found to be insignificant for 10-mum drops, but significant for micron-size drops. Among the geometric-related parameters, the drop-to-pore-size ratio is the most significant.     

Electrochemical hydrogen storage in porous carbons with acidic electrolytes: Uncovering the potential

Electrochemical hydrogen storage in porous carbon materials is emerging as a cost-effective hydrogen storage and transport technology with competitive power and energy densities. The merits of electrochemical hydrogen storage using porous conductive carbon-based electrodes are reviewed. The employment of acidic electrolytes in such storage systems is compared with alkaline electrolytes. The recent innovations of a proton battery for smaller-scale electricity storage, and a proton flow reactor system for larger (grid)-scale storage and bulk export of hydrogen produced from renewable energy, are briefly described. It is argued that such systems, along with variants proposed by others, all of which rely on electrochemical hydrogen storage in porous carbons, can contribute to the search for energy storage technologies essential for the transition to a zero-emission global economy.     

From stability to permeability of adhesive emulsion bilayers

Water drops dispersed in chloroform and stabilized with phospholipids become adhesive if a bad solvent for lipids, such as silicone oil, is added to the continuous phase. In this way, two sticking drops are separated by a bilayer of phospholipids. By using microfluidic technologies, we probe the stability and properties of such membranes likewise encountered in foams or vesicles. We first establish the stability diagram of adhering drop pairs as a function of the continuous phase composition. We found two regimes of destabilization of the bilayer. The first one concerns a competition between the dynamics of adhesion and the transport of surfactants toward the interfaces that leads to a dilute surfactant coverage. The second one corresponds to a dense surface coverage where the lifetime distribution of the bilayer exponentially decreases as a signature of a nucleation process. In the stable regime, we observe the propagation of adhesion among a concentrated collection of drops. This is another remarkable illustration of the suction consequence when two close deformable objects are pulled apart. Moreover, the present experimental strategy offers a novel way to study the phase diagrams of bilayers from a single phospholipid to a mixture of phospholipids. Indeed, we detect phase transitions at a liquid-liquid interface that are ruled by the amount of bad solvent. Finally, we probe the transport of water molecules through the bilayer and show that its permeability is linked to the adhesion energy that reflects its fluidity.     

Crystal Channel Engineering for Rapid Ion Transport: From Nature to Batteries

Ion transport behaviours through cell membranes are commonly identified in biological systems, which are crucial for sustaining life for organisms. Similarly, ion transport is significant for electrochemical ion storage in rechargeable batteries, which has attracted much attention in recent years. Rapid ion transport can be well achieved by crystal channels engineering, such as creating pores or tailoring interlayer spacing down to the nanometre or even sub-nanometre scale. Furthermore, some functional channels, such as ion selective channels and stimulus-responsive channels, are developed for smart ion storage applications. In this review, the typical ion transport phenomena in the biological systems, including ion channels and pumps, are first introduced, and then ion transport mechanisms in solid and liquid crystals are comprehensively reviewed, particularly for the widely studied porous inorganic/organic hybrid crystals and ultrathin inorganic materials. Subsequently, recent progress on the ion transport properties in electrodes and electrolytes is reviewed for rechargeable batteries. Finally, current challenges in the ion transport behaviours in rechargeable batteries are analysed and some potential research approaches, such as bioinspired ultrafast ion transport structures and membranes, are proposed for future studies. It is expected that this review can give a comprehensive understanding on the ion transport mechanisms within crystals and provide some novel design concepts on promoting electrochemical ion storage capability in rechargeable batteries.     

Free-standing aluminium nanowire architectures made in an ionic liquid

We report on the electrochemical synthesis of free‐standing aluminium nanowire architectures through a template‐assisted electrodeposition technique. For this purpose, nuclear track‐etched polycarbonate membranes were employed as templates. One side of the template was sputtered with a thin gold film to serve as a working electrode. Subsequently the nanowires were made in the ionic liquid 1‐ethyl‐3‐methylimidazolium chloride ([EMIm]Cl)/AlCl₃ (40/60 mol %) under potentiostatic conditions. Two different electrodeposition procedures were employed to fabricate strongly adherent Al nanowire structures on an electrodeposited Al layer. In the first procedure, electrodeposition simultaneously occurs along the pores of the template and on the Au‐sputtered side of the template. In the second procedure, electrodeposition takes place in two different steps: first a thick supporting film of Al is deposited on the sputtered side of the membrane and second Al nanowires are grown within the pores. After chemical dissolution of the membrane in dichloromethane, an aluminium foil of a controlled thickness with a three‐dimensional nanowire structure on one side was obtained. Different nanowire architectures, such as free‐standing nanowires, vertically aligned tree‐shaped arrays, and bunched nanowire films, were obtained. Such nanowire architectures are of particular interest for applications in Li‐ion micro‐batteries.     

Series approach to modeling ion size effects for symmetric electrolytes in the diffuse double layer

An analytical model is developed for the potential drop and differential capacity across the diffuse layer which considers the effects of ion size on these properties. For symmetric electrolytes, this potential drop is expressed in terms of a cubic polynomial in the corresponding estimate in the Gouy-Chapman theory. Optimal polynomial coefficients and model validation for 1:1 and 2:2 electrolytes are provided by fits of Monte Carlo data obtained for a restricted electrolyte in a primitive solvent. Simple relationships between these coefficients and parameters commonly associated with the mean spherical approximation are obtained. It is shown that the series approach accurately describes potential drops and differential capacities of the diffuse layer for 1:1 and 2:2 electrolytes for the chosen assumptions.     

当前和下一代锂离子电池电解液的原子尺度微观认识和研究进展

电解液及构筑电极电解液界面对于开发和应用高比容量储能系统至关重要。具体来说，电解液的机械（抗压性、粘度）、热（热导率和热容）、化学（溶解性、活度、反应性）、输运和电化学（界面及界面层）等性质，与其所组成的储能器件的性能直接相关。目前，大量的实验研究通过调控电解液的物理和/或化学组成来改善电解液性能，以满足新型电极材料的工作运行。与此同时，理论模拟方法近年来得到了迅速发展，使人们可以从原子尺度来理解电解液在控制离子输运和构筑功能化界面的作用。站在理论模拟研究的前沿上，人们可以利用其所揭示的机理性认识对新型电解液开展理性设计。本文首先总结了传统电解液的组成、溶剂化结构和输运性质以及电极电解液界面层的形成机理，进一步讨论了利用新型电解液设计稳定电极电解液界面层的方法，包括使用电解液添加剂、高浓电解液和固态电解质，并着重讨论了对这些新型电解液体系进行原子尺度模拟的最新进展，为了解和认识电解液提供更为基本的理解，并为未来电解液的设计提供系统的指导。最后，作者对新型电解液的理论筛选进行了展望。     

Numerical calculation of the Onsager transport coefficients for isothermal binary electrolytes

The Ebeling-Falkenhagen diffusion equations are applied to calculate the Onsager transport coefficients as well as the electrical conductances, transference numbers, and mutual diffusion coefficients for isothermal binary electrolytes. For this purpose the hierarchy of diffusion equations is closed on the level of the binary distribution functions by the superposition approximation. The resulting system of common differential equations is solved by numerical methods. Hydrodynamic interactions are taken into account up to first order. Some results are given for symmetrically charged binary electrolytes with hard-core ions (restricted primitive interaction model). The model parameters (Bjerrum parameter and Debye screening length) are chosen to represent strong electrolytes up to the molar region.     

Advances in Ordered Architecture Design of Composite Solid Electrolytes for Solid-State Lithium Batteries

Solid electrolyte lithium batteries are the next generation of advanced energy devices. The incorporation of solid electrolytes can significantly improve the safety issue of lithium-ion batteries. Organic-inorganic composite solid electrolytes (CSE) are promising candidates for solid-state batteries, but their application is mainly limited by low ionic conductivity. Many studies have shown that the architecture of ordered inorganic fillers in CSE can act as fast lithium-ion transfer channels by auxiliary means, thus significantly improving the ionic conductivities. This review summarises the recent advances in CSE with different dimensional inorganic fillers. Various effective strategies for the construction of ordered structures in CSE are then presented. The review concludes with an outlook on the future development of CSE. This review aims to provide researchers with an in-depth understanding of how to achieve ordered architectures in CSE for advanced solid state lithium batteries.     

Electrodeposited conductive polymers for controlled drug release: polypyrrole

Over the last 40 years, electrically conductive polymers have become well established as important electrode materials. Polyanilines, polythiophenes and polypyrroles have received particular attention due to their ease of synthesis, chemical stability, mechanical robustness and the ability to tailor their properties. Electrochemical synthesis of these materials as films have proved to be a robust and simple way to realise surface layers with controlled thickness, electrical conductivity and ion transport. In the last decade, the biomedical compatibility of electrodeposited polymers has become recognised; in particular, polypyrroles have been studied extensively and can provide an effective route to pharmaceutical drug release. The factors controlling the electrodeposition of this polymer from practical electrolytes are considered in this review including electrolyte composition and operating conditions such as the temperature and electrode potential. Voltammetry and current-time behaviour are seen to be effective techniques for film characterisation during and after their formation. The degree of take-up and the rate of drug release depend greatly on the structure, composition and oxidation state of the polymer film. Specialised aspects are considered, including galvanic cells with a Mg anode, use of catalytic nanomotors or implantable biofuel cells for a self-powered drug delivery system and nanoporous surfaces and nanostructures. Following a survey of polymer and drug types, progress in this field is summarised and aspects requiring further research are highlighted.     

Effects of crosslinking density and Lewis acidic sites on conductivity and viscoelasticity of dynamic network electrolytes

Polymers are promising materials for replacing organic liquids as electrolytes, and network architectures allow for the modulus to be tuned pseudo-independently of conductivity. When the crosslinks are dynamic bonds, they offer the additional benefits of recyclability and self-healing in response to damage. Dynamic network electrolytes (DNEs) comprised of precise linker lengths of 2, 3, or 4 repeat units of ethylene oxide and boronic ester junctions were prepared to investigate the roles of dense networks and bond exchange on conductivity and rheological properties. A range of salt concentrations were probed, and longer linker lengths led to consistently higher conductivities even after accounting for difference in the glass transition. In contrast, non-monotonic trends are observed in the salt dependence of viscosity as a function of linker length. The interaction of anions from the salt with boron leads to a drop in the viscosity, and at a critical salt content the networks no longer form a percolated network. From the bulk viscosity, a Walden Plot shows a transition from superionic to subionic behavior with added salt. These structure–property relationships offer key valuable insights for designing sustainable electrolytes.