Driven by the potential applications of ionic liquids (ILs) in many emerging electrochemical technologies, recent research efforts have been directed at understanding the complex ion ordering in these systems, to uncover novel energy storage mechanisms at IL/electrode interfaces. Here, we discover that surface-active ionic liquids (SAILs), which contain amphiphilic structures inducing self-assembly, exhibit enhanced charge storage performance at electrified surfaces. Unlike conventional nonamphiphilic ILs (NAILs), for which ion distribution is dominated by Coulombic interactions, SAILs exhibit significant and competing van der Waals interactions owing to the nonpolar surfactant tails, leading to unusual interfacial ion distributions. We reveal that at an intermediate degree of electrode polarization SAILs display optimal performance, because the low-charge-density alkyl tails are effectively excluded from the electrode surfaces, whereas the formation of nonpolar domains along the 2 surface suppresses undesired overscreening effects. This work represents a crucial step towards understanding the unique interfacial behavior and electrochemical properties of amphiphilic liquid systems showing long-range ordering, and offers insights into the design principles for high-energydensity electrolytes based on spontaneous self-assembly behavior. Research interest in ionic liquids (ILs) as electrolytes for energy devices stems from several unique properties such as low volatility and flammability, as well as high electrochemical stability 1-5. An understanding of the molecular-level interactions between ILs and electrified interfaces is crucial for optimization of device performance 6. For instance, interfacial IL layers at charged surfaces govern the electric double layer (EDL) structure, a key factor determining the device energy density 2,4,6,7. The EDL structure with ILs is drastically different from that in aqueous and organic electrolytes 8-10 ; the complex ion ordering in ILs exhibits many subtleties, and remains an active area of debate 11-14. Here we present the first detailed investigation into electrocapacitive characteristics and fundamental EDL structures of an emerging IL class based on surface-active agents, or surface-active ILs (SAILs) 13,15-19. Our study reveals a novel material design principle for enhancing charge storage owing to the self-assembled nanostructures in amphiphilic liquids, and introduces a class of liquids with long-range ordering, having broad implications for diverse fields, ranging from interfacial science 20,21 to energy technologies 22,23. SAILs are inherently amphiphilic, and can self-assemble into nanostructures composed of distinct polar and nonpolar domains 13,15-19. Most previous studies on the IL EDL structure and IL-based energy devices focus on non-amphiphilic ILs (NAILs) where neither ion is based on a classical surfactant structure 6,24. Whereas nanostructuring was observed under confinement for some NAILs where one of the ions, usually the cation, bears moderate to long chai...

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Surface-plasmon (SP) enhanced catalysis on plasmonic nanostructures brings opportunities to increase catalytic efficiency and alter catalytic selectivity. Understanding the underlying mechanism requires quantitative measurements of catalytic enhancement on these nanostructures, whose intrinsic structural heterogeneity presents experimental challenges. Using correlated super-resolution fluorescence microscopy and electron microscopy, here we report a quantitative visualization of SP-enhanced catalytic activity at the nanoscale within single plasmonic nanostructures. We focus on two Au- and Ag-based linked nanostructures that present plasmonic hotspots at nanoscale gaps. Spatially localized higher reaction rates at these gaps vs nongap regions report the SP-induced catalytic enhancements, which show direct correlations with the nanostructure geometries and local electric field enhancements. Furthermore, the catalytic enhancement scales quadratically with the local actual light intensity, attributable to hot electron involvement in the catalytic enhancement mechanism. These discoveries highlight the effectiveness of correlated super-resolution and electron microscopy in interrogating nanoscale catalytic properties.

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Abstract:The applications of electrospun carbon fiber webs to the development of energy storages devices, including both supercapacitors and lithium ion batteries (LIB), are reviewed.Following a brief discussion of the fabrication process and characterization methods for ultrafine electrospun carbon fibers, recent advances in their performance as supercapacitors and LIBs anode materials are summarized. Optimization of the overall electrochemical properties of these materials through choice of thermal treatment conditions, incorporation of additional active components (such as carbon nanotubes, metal oxides, and catalysts), and generation of novel fibrous structures (such as core-shell, multi-channel or porous fibers) is highlighted. Further challenges related to improving the conductivity, surface area, and mechanical properties of the carbon nanofiber webs, as well as the scale-up ability of the fabrication technique, are discussed.

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As part of the efforts to address the global energy issues, the identification of electrocatalysts for efficient and selective conversion of carbon dioxide to value-added products is a research topic of scientific and technological significance. Metal-free catalysts are considered next-generation, renewable materials that promise to be cost-effective, relative to their metal-containing counterparts, particularly relative to noble-metal-based catalysts. In this article, recent progress toward identification of metal-free catalysts for electrochemical reduction of carbon dioxide is reviewed. These catalysts are classified into four categories, including conducting polymers, pyridinium derivatives, aromatic anion radicals, and heteroatom-doped carbon materials. We provide a detailed investigation of the overall catalytic performance of each material, in terms of the product distribution, overpotential required, Faradaic yield, stability of the catalyst, and reaction mechanism. Several important factors that affect the catalytic performance, including the pH value, solvent type, carbon dioxide pressure/concentration, nature of the auxiliary electrode, and morphology of the catalyst, are discussed. The main issues and challenges associated with large-scale electrochemical reduction of carbon dioxide using metal-free catalysts are identified and analyzed, and future research directions for addressing these problems are suggested.

We report noncovalent dispersion of carbon nanotubes (CNTs) in organic liquids with extremely high loading (∼2 mg mL(-1)) using polyvinylferrocene (PVF). In contrast to common dispersants, PVF does not contain any conjugated structures or ionic moieties. PVF is also shown to be effective in controlling nanotube dispersion and reprecipitation because it exhibits redox-switchable affinity for solvents, while maintaining stable physical attachment to CNTs during redox transformation. This switchability provides a novel approach to creating CNT-functionalized surfaces. The material systems described here offer new opportunities for applications of CNTs in nonaqueous media, such as nanotube-polymer composites and organic liquid-based optical limiters, and expand the means of tailoring nanotube dispersion behavior via external stimuli, with potential applications in switching devices. The PVF/CNT hybrid system with enhanced redox response of ferrocene may also find applications in high-performance biosensors and pseudocapacitors.