Producing Fuel from Sunshine

A press release from Cal Tech reports on a promising new development in moving toward a renewable energy supply.  A team of researchers, led by Sossina Haile, professor of materials science and chemical engineering, has developed a new reactor that uses solar energy to break down carbon dioxide [CO2] and water [H2O] into fuels.

The device works by concentrating sunlight into a cylinder made of cerium(IV) oxide (also called cerium dioxide, or ceria), CeO2.  (Cerium is one of the rare earths, atomic number 58, but it is actually about as common as copper.)

Ceria—a metal oxide that is commonly embedded in the walls of self-cleaning ovens, where it catalyzes reactions that decompose food and other stuck-on gunk—propels the solar-driven reactions. The reactor takes advantage of ceria’s ability to “exhale” oxygen from its crystalline framework at very high temperatures and then “inhale” oxygen back in at lower temperatures.

The net effect is to split off oxygen atoms from the water or carbon dioxide, giving carbon monoxide [CO] and hydrogen [H2]. The hydrogen can be used in fuel cells to generate electricity, or it can be combined with the carbon monoxide to produce synthetic gas, which can be used as a feedstock for producing liquid fuels.

The present experimental reactor is not terribly efficient, capturing only about 1% of the solar energy it absorbs; it also has a very high operating temperature of about 3000°F.  But the research team is working on refinements to the design that will address these problems; their thermodynamic estimates suggest that efficiencies ~15% are possible.

The research has been published [abstract] in the journal Science.

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