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...

We describe a water treatment strategy, electrochemically tunable affinity separation (ETAS), which, unlike other previously developed electrochemical processes, targets uncharged organic pollutants in water. Key to achieving ETAS resides in the development of multicomponent polymeric nanostructures that simultaneously exhibit the following characteristics: an oxidation-state dependent affinity towards neutral organics, high porosity for sufficient adsorption capacity, and high conductivity to permit electrical manipulation. A prototype ETAS adsorbent composed of nanostructured binary polymeric surfaces that can undergo an electrically-induced hydrophilic-hydrophobic transition can provide programmable control of capture and release of neutral organics in a cyclic fashion. A quantitative energetic analysis of ETAS offers insights into the tradeoff between energy cost and separation extent through manipulation of electrical swing conditions. We also introduce a generalizable materials design approach to improve the separation degree and energetic efficiency simultaneously, and identify the critical factors responsible for such enhancement via redox electrode simulations and theoretical calculations of electron transfer kinetics. The effect of operation mode and multistage configuration on ETAS performance is examined, highlighting the practicality of ETAS and providing useful guidelines for its operation at large scale. The ETAS approach is energetically efficient, environmentally friendly, broadly applicable to a wide range of organic contaminants of various molecular structures, hydrophobicity and functionality, and opens up new avenues for addressing the urgent, global challenge of water purification and wastewater management. Broader contextSeparation processes are of paramount importance in the chemical and environmental industries, accounting for 10-25% of the world's energy consumption, and about a third of total capital and operation costs in industrial plants. The development of separation technologies for water treatment with high energy efficiency and low environmental impact has become a primary engineering challenge for the 21st century due to the worldwide occurrence of water contamination and its associated negative impacts on the environment and human health. Electrochemically controlled processes, such as capacitive deionization, have emerged as promising candidates for wastewater management and water desalination. However, since these previously developed electrochemical methods rely primarily on the electrostatic interaction between the electrode and the target pollutant, they only work for charged species (e.g., anions, cations), and are not applicable to uncharged organic pollutants, which constitute the majority of industrial and municipal water contaminants, including many dyes, pesticides, pharmaceuticals and carcinogenic aromatics. This study investigates a conceptually novel separation strategy that enables sensitive, programmable electrochemical control over the release and capture of u...

Polymeric adsorbents show great potential for the replacement of activated carbon for removing a wide range of toxic organic pollutants from wastewater streams since they do not suffer from costly regeneration needs and high attrition rates. Herein, an electrochemically regenerable polymeric adsorbent based on an intrinsically conducting polymer (CP), polypyrrole (PPy), doped with anionic surfactant dioctylsulfosuccinate (AOT), denoted PPy(AOT), for mitigating organic pollutants in wastewater is reported. A facile electropolymerization protocol to synthesize highly porous PPy(AOT) is developed, with an adsorption capacity of greater than 570 mg pollutant/g polymer in its superhydrophobic oxidized state. It is demonstrated that the hydrophobicity of PPy(AOT) and hence its affinity for organics can be modulated electrochemically through the re-orientation of AOT dopants, which can be exploited to regenerate the adsorbent and use it repeatedly for multiple adsorption/desorption cycles. It also explores the interactions between the adsorbed organic molecules and the surfactant-doped CP adsorbent using a combined density functional theory and molecular dynamics approach to elucidate the mechanism of electrochemical modulations of hydrophobicity and affinity of the material. The physicochemical insights are significant for developing broader applications of such material in drug delivery, sensing, self-cleaning surfaces, microfluidics, and artificial muscles.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201801466. negative effects on aquatic ecosystems and human health. [3][4][5] Adsorption is a common technology for removing organic pollutants from wastewater, and activated carbon (AC) is one of the most widespread adsorbents due to its high specific surface area and strong interactions with target compounds. [6][7][8] Methods for AC regeneration have drawbacks, however, thermal desorption is energy-intensive, while solvent regeneration may lead to substantial loss of AC and result in secondary pollution. [7][8][9][10] To overcome recyclability problems such as observed with AC, our group has previously developed a redox-responsive polymer gel with tunable hydrophobicity that reversibly adsorbs and releases organics in the presence of water. [11] However, in this case, the redox switching relied on the addition of chemicals, which introduced additional chemical agents to the remediation process, and the efficacy of the chemical stimuli was hampered by mass transfer limitations. [11,12] Therefore, it is desirable to design new adsorbent materials whose redox-responsive hydrophobicity can be tuned using mild electrical stimuli, thereby eliminating the use of chemicals in the regeneration process, and ultimately reducing the material waste and operating cost of adsorption technology for wastewater remediation. We have addressed this problem by developing two different methods for electrochemical control of the hydrophobic environment within the adsorb...

Conducting polymers modified with redox-active moieties or amphiphilic surfactants are promising adsorbent materials for the separation of neutral organic species from water. We develop an asymmetric system combining a polyvinylferrocene–polypyrrole hybrid (PVF–PPy) and an amphiphilic surfactant dioctyl sulfosuccinate (AOT)-doped polypyrrole (PPy(AOT)) that have complementary hydrophobicity tunability in response to electrochemical modulations. Both materials are hydrophobic in their respective neutral states, exhibiting high affinities toward organics. Upon application of a mild potential to oxidize PVF–PPy and reduce PPy(AOT), these polymers can be simultaneously rendered hydrophilic, thereby driving desorption of organics and regeneration of the materials. The asymmetric system can be used in a cyclic fashion, through repeated electrical shorting of the two electrodes to program the capture of organics from a large volume of feed solution, and application of a potential (above 0.9 V) to stimulate the release of the adsorbed organics into a small volume of desorption solution. The asymmetric configuration has multiple benefits, including suppression of water parasitic reactions, high energetic efficiency, and selectivity for target organic species. Therefore, the electrode system has the potential to reduce the energy consumption in the mitigation of organic contaminants over conventional methods, with the additional ability to recover valuable organic products, opening up new possibilities for addressing the water–energy nexus.