Molten salt strategies towards carbon materials for energy storage and conversion

Porous carbon materials are at the core of many energy storage and conversion technologies. Accordingly, demand for them is steadily increasing. To satisfy this demand without compromising the environment to a larger extent, researchers are continuously looking for novel synthesis strategies. In this context, molten salts or salt melts have emerged as a powerful, eco-friendly alternative for the synthesis of porous carbons with tuneable chemical and textural properties. These salt systems play a dual role as solvent/reaction medium (they have negligible vapor pressure withstanding carbonization temperatures) and as templates. Similar to traditional templating strategies, pore generation does not take place at the expense of carbon yield, but unlike those traditional methods, removal of the template can be accomplished by washing with water or diluted acid. This review summarizes the production of porous carbons by molten salt strategies, focusing on the characteristics of the main molten salts used to date, the mechanism of pore generation, and the structure of the carbons produced. The use of molten salts as a medium for performing chemical activation processes is also described. Finally, the use of salt-templated carbons in a variety of energy storage and conversion applications is analysed in detail.