Solar-powered process could decrease carbon dioxide to pre-industrial levels in 10 years
July 22, 2010 By Lisa Zyga


In the Solar Thermal Electrochemical Photo (STEP) carbon capture process, the sunÕs visible light and heat are used to capture large amounts of carbon dioxide from the atmosphere and convert it to solid carbon for storage or carbon monoxide for fuel generation. Image copyright: Stuart Licht, et al. ©2010 American Chemical Society.

(PhysOrg.com) -- By using the sun's visible light and heat to power an electrolysis cell that captures and converts carbon dioxide from the air, a new technique could impressively clean the atmosphere and produce fuel feedstock at the same time. The key advantage of the new solar carbon capture process is that it simultaneously uses the solar visible and solar thermal components, whereas the latter is usually regarded as detrimental due to the degradation that heat causes to photovoltaic materials. However, the new method uses the sunÕs heat to convert more solar energy into carbon than either photovoltaic or solar thermal processes alone.


The new process, called Solar Thermal Electrochemical Photo (STEP) carbon capture, was recently suggested theoretically by a team of scientists from George Washington University and Howard University, both in Washington, DC. Now, in a paper just published in The Journal of Physical Chemistry Letters, the scientists have experimentally demonstrated the STEP process for the first time.

ÒThe significance of the study is twofold,Ó Stuart Licht, a chemistry professor at George Washington University, told PhysOrg.com. ÒCarbon dioxide, a non-reactive and normally difficult-to-remove compound, can be easily captured with solar energy using our new low-energy, lithium carbonate electrolysis STEP process, and with scale-up, sufficient resources exist for STEP to decrease carbon dioxide levels in the atmosphere to pre-industrial levels within 10 years.Ó

As the scientists explain, the process uses visible sunlight to power an electrolysis cell for splitting carbon dioxide, and also uses solar thermal energy to heat the cell in order to decrease the energy required for this conversion process. The electrolysis cell splits carbon dioxide into either solid carbon (when the reaction occurs at temperatures between 750¡C and 850¡C) or carbon monoxide (when the reaction occurs at temperatures above 950¡C). These kinds of temperatures are much higher than those typically used for carbon-splitting electrolysis reactions (e.g., 25¡C), but the advantage of reactions at higher temperatures is that they require less energy to power the reaction than at lower temperatures.
The STEP process is the first and only method that incorporates both visible and thermal energy from the sun for carbon capture. Radiation from the full solar spectrum - including heat - is not usually considered an advantage in solar technologies due to heatÕs damage to photovoltaics. Even in the best solar cells, a large part of sunlight is discarded as intrinsically insufficient to drive solar cells as it is sub-bandgap, and so it is lost as waste heat."