The current interest in ionic liquids (ILs) is motivated by some unique properties, such as negligible vapour pressure, thermal stability and non-flammability, combined with high ionic conductivity and wide electrochemical stability window. However, for material applications, there is a challenging need for immobilizing ILs in solid devices, while keeping their specific properties. In this critical review, ionogels are presented as a new class of hybrid materials, in which the properties of the IL are hybridized with those of another component, which may be organic (low molecular weight gelator, (bio)polymer), inorganic (e.g. carbon nanotubes, silica etc.) or hybrid organic-inorganic (e.g. polymer and inorganic fillers). Actually, ILs act as structuring media during the formation of inorganic ionogels, their intrinsic organization and physicochemical properties influencing the building of the solid host network. Conversely, some effects of confinement can modify some properties of the guest IL, even though liquid-like dynamics and ion mobility are preserved. Ionogels, which keep the main properties of ILs except outflow, while allowing easy shaping, considerably enlarge the array of applications of ILs. Thus, they form a promising family of solid electrolyte membranes, which gives access to all-solid devices, a topical industrial challenge in domains such as lithium batteries, fuel cells and dye-sensitized solar cells. Replacing conventional media, organic solvents in lithium batteries or water in proton-exchange-membrane fuel cells (PEMFC), by low-vapour-pressure and non flammable ILs presents major advantages such as improved safety and a higher operating temperature range. Implementation of ILs in separation techniques, where they benefit from huge advantages as well, relies again on the development of supported IL membranes such as ionogels. Moreover, functionalization of ionogels can be achieved both by incorporation of organic functions in the solid matrix, and by encapsulation of molecular species (from metal complexes to enzymes) in the immobilized IL phase, which opens new routes for designing advanced materials, especially (bio)catalytic membranes, sensors and drug release systems (194 references).

Titanium oxide particles were treated using six organophosphorus compounds chosen as model coupling molecules: phenylphosphonic and diphenylphosphinic acids, their ethyl esters, and their trimethylsilyl esters. The ability of all of these coupling molecules to modify the surface of the TiO2 particles was demonstrated by elemental analysis, thermogravimetric analysis, and nitrogen adsorption. The bonding modes on the surface were investigated by means of diffuse reflectance IR Fourier transform (DRIFT) and 31P solid-state MAS NMR spectroscopy. Upon irradiation in water, a marked trend to the photooxidative degradation of the anchored organophosphorus groups was evidenced, especially in the case of phosphinate groups.

A simple nonaqueous sol-gel processing led to ionogels, resulting in the confinement of an ionic liquid within a silica-like network. In the case of a non-water-soluble ionic liquid, ionogels were made stable toward water immersion by the presence of hydrophobic methyl groups in the solid network. A set of ionogels with different ionic liquid content was studied by DSC and 1 H NMR spectroscopy. The nanometric level of the confinement of the ionic liquid turned out to significantly modify the phase transitions, while still allowing some molecular mobility. Moreover, ionogels were found to keep the high conducting performances of the ionic liquid.

This review surveys the chemistry of various nonhydrolytic sol−gel processes including hydroxylation in nonaqueous systems and aprotic condensation reactions. Some examples of applications in the field of single and multicomponent oxides demonstrate the interest of these approaches as alternatives to the usual hydrolytic routes. More particularly nonhydrolytic methods lead to improved control over the molecular level homogeneity and stoichiometry of multicomponent oxides.

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Luminescent ionogels were prepared by doping an europium(III) tetrakis-diketonate complex into an imidazolium ionic liquid, followed by immobilization of the ionic liquid by confinement in a silica network. The ionogels were obtained by a non-hydrolytic method as perfect monoliths featuring both the transparency of silica and the ionic conductivity performances of ionic liquids. The ionogels contain 80 vol % of ionic liquid. The organic-inorganic hybrid materials showed a very intense red photoluminescence under ultraviolet irradiation. The red emission has a very high coloric purity.

Kinetics of electrochemical reactions are several orders of magnitude slower in solids than in liquids as a result of the much lower ion diffusivity. Yet, the solid state maximizes the density of redox species, which is at least two orders of magnitude lower in liquids because of solubility limitations. With regard to electrochemical energy storage devices, this leads to high-energy batteries with limited power and high-power supercapacitors with a well-known energy deficiency. For such devices the ideal system should endow the liquid state with a density of redox species close to the solid state. Here we report an approach based on biredox ionic liquids to achieve bulk-like redox density at liquid-like fast kinetics. The cation and anion of these biredox ionic liquids bear moieties that undergo very fast reversible redox reactions. As a first demonstration of their potential for high-capacity/high-rate charge storage, we used them in redox supercapacitors. These ionic liquids are able to decouple charge storage from an ion-accessible electrode surface, by storing significant charge in the pores of the electrodes, to minimize self-discharge and leakage current as a result of retaining the redox species in the pores, and to raise working voltage due to their wide electrochemical window.

Over the past decade, there has been an increasing number of reports on low-temperature preparations of oxides and organic−inorganic hybrids (including sol−gel, solvothermal synthesis, and atomic layer deposition) that take place in nonaqueous media and involve no water as a reactant. This growing interest lies on the ability of these nonhydrolytic routes (in organic solvents, unusual media, condensed phase or under vapor deposition conditions) to reach a higher control over composition, morphology, and structure. An overview of the main results is proposed here, which emphasizes the molecular approach (molecular precursors used, nonhydrolytic reactions involved), the ability to design oxide-based materials with a high degree of homogeneity (mixed oxides, organically modified silicates and ceramics, polysiloxane resins, polymer nanocomposites, etc.) and specific nanostructures (nanoparticles, mesocrystals, nanoporous materials, nanocomposites, nanolayers).