At standard temperature and pressure, CO2 exists as a gas. On cooling to -78.5 °C, it becomes a solid called dry ice, which is a common refrigerant. At a critical temperature of 31.1 °C and pressure 72.9 atmospheres, however, CO2 becomes a supercritical fluid with properties intermediate to a gas and liquid. In this form, CO2 fills a containment vessel and exhibits a low viscosity reminiscent of a gas but retains the high density of a liquid. It turns out that supercritical CO2 also has rather appealing properties as both solvent and reagent in the electrochemical reduction of CO2 to a variety of products.
See full article at Advanced Science News.