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Ionic-liquid materials for the electrochemical challenges of the future

Abstract

Ionic liquids are room-temperature molten salts, composed mostly of organic ions that may undergo almost unlimited structural variations. This review covers the newest aspects of ionic liquids in applications where their ion conductivity is exploited; as electrochemical solvents for metal/semiconductor electrodeposition, and as batteries and fuel cells where conventional media, organic solvents (in batteries) or water (in polymer-electrolyte-membrane fuel cells), fail. Biology and biomimetic processes in ionic liquids are also discussed. In these decidedly different materials, some enzymes show activity that is not exhibited in more traditional systems, creating huge potential for bioinspired catalysis and biofuel cells. Our goal in this review is to survey the recent key developments and issues within ionic-liquid research in these areas. As well as informing materials scientists, we hope to generate interest in the wider community and encourage others to make use of ionic liquids in tackling scientific challenges.

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Figure 1: Ionic liquids, that is, salts with melting points below 100 °C, are potential candidates to be new 'green' reaction media with a number of important properties.
Figure 2: Processes that are impossible in water baths become viable if an ionic liquid solvent is used.
Figure 3: Deposits of photoluminescent semiconductors, for example GexSi1−x obtained from ionic liquid baths.
Figure 4: In their basic structure, lithium batteries are formed by two lithium-exchanging electrodes separated by a lithium-ion-conducting electrolyte.
Figure 5: Although polymer-electrolyte-membrane fuel cells have been known for a long time, they have not yet reached large-scale development as some issues are still unresolved.
Figure 6: There are several strategies to solubilize proteins into ionic liquids.
Figure 7: Sketch for a biofuel cell, that is, a device capable of generating energy with the aid of enzymes.
Figure 8: An electromechanical actuator produces a mechanical bending or axial motion in response to an electrical stimulus.

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Acknowledgements

We thank M. Mastragostino for discussions and information concerning supercapacitors.

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Correspondence to Bruno Scrosati.

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Armand, M., Endres, F., MacFarlane, D. et al. Ionic-liquid materials for the electrochemical challenges of the future. Nature Mater 8, 621–629 (2009). https://doi.org/10.1038/nmat2448

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