materials derive from their formation of protective surface oxide layers in the presence of carbon dioxide, however in most cases further evaluation of the reaction mechanics and corrosion/erosion kinetics and mechanisms is required, as none of the materials meet the necessary goals. Other Work is underway to develop a s closed-cycle gas turbine to operate at temperatures near 550 °C. This would have implications for bulk thermal and nuclear generation of electricity, because the supercritical properties of carbon dioxide at above 500 °C and 20 MPa enable thermal efficiencies approaching 45 percent. This could increase the electrical power produced per unit of fuel required by 40 percent or more. Given the volume of carbon fuels used in producing electricity, the environmental impact of cycle efficiency increases would be significant. Supercritical is an emerging natural refrigerant, used in new, low carbon solutions for domestic heat pumps. Supercritical heat pumps are commercially marketed in Asia. EcoCute systems from Japan, developed by Mayekawa, develop high temperature domestic water with small inputs of electric power by moving heat into the system from the surroundings. Supercritical has been used since the 1980s to enhance recovery in mature oil fields. "Clean coal" technologies are emerging that could combine such enhanced recovery methods with carbon sequestration. Using gasifiers instead of conventional furnaces, coal and water is reduced to hydrogen gas, carbon dioxide and ash. This hydrogen gas can be used to produce electrical power In combined cycle gas turbines, is captured, compressed to the supercritical state and injected into geological storage, possibly into existing oil fields to improve yields. The unique properties of s ensure that it remains out of the atmosphere. Supercritical can be used as a working fluid for geothermal electricity generation in both enhanced geothermal systems and sedimentary geothermal systems (so-called Plume Geothermal). EGS systems utilize an artificially fractured reservoir in basement rock while CPG systems utilize shallower naturally-permeable sedimentary reservoirs. Possible advantages of using in a geologic reservoir, compared to water, include higher energy yield resulting from its lower viscosity, better chemical interaction, and permanent storage as the reservoir must be filled with large masses of . As of 2011, the concept had not been tested in the field. Aerogel production Supercritical carbon dioxide is used in the production of silica, carbon and metal based aerogels. For example, silicon dioxide gel is formed and then exposed to s. When the goes supercritical, all