Chlorine is an essential feedstock for polymers and pharmaceuticals, with annual production exceeding 100 Mt. Nearly all Cl2 is obtained by chlor–alkali electrolysis, which consumes about 2.58 MWh of electricity per tonne. Renewable energies such as wind and solar would lower CO2 emissions, but electrolysers would then have to adopt to fluctuating, renewable energies while downstream processes still require a constant chlorine supply. Large inventories of pressurised, liquefied Cl2 are impractical owing to toxicity and stringent safety setbacks. Triethylmethylammonium trichloride, [NEt3Me][Cl(Cl2)], could become a key technology enabling safe chlorine storage. This room-temperature ionic liquid, made from inexpensive [NEt3Me]Cl and chlorine, can store 0.79 tCl2 t−1 while maintaining a low chlorine vapour pressure. Chlorine can be released by mild heating, vacuum, or water addition; alternatively, the loaded liquid can serve directly as a chlorinating agent. With an energy density near 1.1 MWh t−1, the trichloride could couple electrolysis with real-time power availability and allow chlorine to be produced in sun-rich regions and shipped safely elsewhere.
