Michigan State University researchers develop process for solar-powered syngas

In Michigan, solar-powered synthesis gas could recycle carbon dioxide into fuels and useful chemicals, an international team of researchers has shown. Composed mainly of hydrogen and carbon monoxide with a little methane, syngas is commonly derived from fossil fuels with the help of electricity. In addition, toxic chemicals are often added to make the process more efficient.

To create a process that uses only solar energy, researchers from Michigan State University overcame the difficulty of splitting carbon dioxide molecules, which are among the most stable in the universe. For this, they peppered a forest of semiconductor nanowires with nanoparticles. Those nanoparticles, made of gold coated with chromium oxide, attracted the carbon dioxide molecules and bent them, weakening the bonds between the carbon and oxygen.

The gallium nitride nanowires used the light energy to free electrons and the positively charged spaces they leave behind, known as holes. The holes split water molecules, separating the protons (hydrogen) from the oxygen. Then, at the metal catalysts, the electrons split the carbon dioxide, producing carbon monoxide and sometimes drawing in the free hydrogen to make methane. Processes are under development to separate the oxygen from the other gases.

By changing the ratio of gold to chromium oxide in the nanoparticles, the team was able to control the relative amounts of hydrogen and carbon monoxide produced in the reaction. This is important because the ratio of hydrogen to carbon monoxide affects how easy it is to produce a type of fuel or chemical.