The development of porous metals has led to the need for an accurate prediction of the physical and mechanical properties of the many possible fabricated structures. For applications where yield stress needs to be reduced, while maintaining a high conductivity, the optimization of the pore dimensions, volume fraction, and pore spacing is required. A finite element model has been developed to simulate the effects of these factors on the electromechanical behavior of porous copper. This model was validated against samples of copper with mechanically induced pores as well as a copper GASAR sample. Good agreement (within an error of ±3%) was shown between the model and experimental data for the resistivity and effective modulus for both the mechanically induced pore and the GASAR samples, although the low ductility of the samples was not predicted and restricts the application of the simulation.

Incorporation of porosity into a monolithic material decreases the effective thermal conductivity. Porous ceramics were prepared by different methods to achieve pore volume fractions from 4 to 95%. A toolbox of analytical relations is proposed to describe the effective thermal conductivity as a function of solid phase thermal conductivity, pore thermal conductivity, and pore volume fraction (νp). For νp < 0.65, the Maxwell–Eucken relation for closed porosity and Landauer relation for open porosity give good agreement to experimental data on tin oxide, alumina, and zirconia ceramics. For νp > 0.65, the thermal conductivity of kaolin-based foams and calcium aluminate foams was well described by the Hashin Shtrikman upper bound and Russell’s relation. Finally, numerical simulation on artificially generated microstructures yields accurate predictions of thermal conductivity when fine detail of the spatial distribution of the phases needs to be accounted for, as demonstrated with a bio-aggregate material.

This article reports the search for nonflammable, stable electrolytes based on ionic liquid (IL) compounds, able to effectively improve the needed safety and reliability of lithium batteries. The most significant results are reviewed with the aim of elucidating critical aspects governing the properties of IL electrolytes, including (1) transport properties affecting ionic conductivity and the cycling rate of battery systems, (2) electrochemical/chemical stability toward most conventional electrode materials, and (3) thermal properties determining the range of applicability. Both liquid and polymer electrolytes, adopting ILs as the main component or as an additive to standard electrolyte solutions, are considered. Very promising results, in terms of battery prototype performances in scaled-up configurations, demonstrate the validity of the use of ILs for practical applications. Even though further improvements are necessary, particularly at high current density operations in both lithium-metal and lithium-ion systems, the realization of safer, high-performance batteries based on IL electrolytes is certainly possible. It can be concluded that ILs represent a viable solution to disappointing compromises between energy density and acceptable safety features in lithium batteries.

Ionic liquids are well suited to the electrochemical synthesis of freestanding metallic nanowires as well as macroporous metals and semiconductors. Such materials are potentially interesting for future generation Li-ion batteries. As the energy density of current Li-ion batteries barely exceeds 0.15 kWh/kg (in contrast to the 12 kWh/kg of hydrocarbons), there is a need for new anode and cathode materials if electrically driven cars are to have more than a 150 km cruising range at an affordable price. Freestanding aluminum nanowires and macroporous aluminum are easily feasible from AlCl3-based ionic liquids and show promising charge/discharge behavior even with ionic liquids as electrolytes. The challenges and the potential to make nanowires or macroporous structures of semiconductors (Si, Ge) are also briefly discussed.

We have investigated protic ionic liquids (PILs) as proton conductors for non-humidified intermediate-temperature fuel cells. PILs exhibit proton conductivity and activity in fuel cell electrode reactions, as seen in acidic aqueous solutions and acidic polymer membranes. The wide molecular designability of PILs enabled the finding of a promising candidate, diethylmethylammonium trifluoromethanesulfonate ([dema][ TfO]), which exhibits favorable bulk properties and electrochemical activity. Solid thin films containing [dema][ TfO] were fabricated using sulfonated polyimide as a matrix polymer. By using the composite membrane, non-humidifying fuel cell operation at 120°C succeeded. The fuel cell performance can be further improved by the optimization of the catalyst layer and with further research on PILs.

There is an urgent need for new energy storage and conversion systems in order to tackle the environmental problems we face today and to make the transition to a fossil fuel-free society. New batteries, supercapacitors, and fuel cells have the potential to be key devices for large-scale energy storage systems for load leveling and electric vehicles. In many cases, the concepts are known, but the right materials solutions are lacking. Ionic liquids (ILs) have been highlighted as suitable materials to be included in new devices, most commonly as electrolytes. Attractive features of ILs such as high ionic conductivity, low vapor pressure, high thermal and electrochemical stability, large temperature range for the liquid phase, and flexibility in molecular design have drawn the attention of researchers from many different fields. In addition, there is the possibility of designing new materials and morphologies using electrochemical synthesis with ILs. In this article, we provide an introduction to ILs and their properties, serving as a base for the topical articles in this issue.