For Solar Fuels, More Surface Area on Photoelectrodes Makes a Difference

The Science

Scientists are working to use light to transform carbon dioxide into liquid fuels. In a laboratory, carbon dioxide can be converted to carbon monoxide or methanol in a light-driven process that relies on silicon photoelectrodes. These are systems that absorb light, including simulated sunlight in a lab, to begin a chemical reaction. This process relies on the integration of catalysts on the surface of the silicon. Recently, researchers showed that three-dimensional silicon materials can improve the efficiency of these reactions.

The Impact

Scientists have identified a new way to improve the process for using sunlight to make a liquid fuel from carbon dioxide. Researchers showed that three-dimensional silicon scaffolds on photoelectrodes improve the yield of the desired products of chemical reactions. Notably, the process can convert carbon dioxide to methanol, which can potentially be used as a fuel. In addition, the process allows researchers to study the catalysts on the photoelectrodes at the molecular level. The photoelectrodes represent a state-of-the-art approach to liquid solar fuel generation.

Summary

While scientists have known of high-surface area silicon for many decades, they have not used these materials as light absorbing semiconductors for liquid fuel formation. Research carried out by the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE) demonstrates that high-surface area silicon materials have important benefits for use in hybrid photoelectrodes. In the first example, a cobalt catalyst deposited on silicon micropillars reduces carbon dioxide to methanol with improved current density providing the state-of-the-art photoelectrode for potential liquid fuel generation. The second hybrid photoelectrode example consisted of a rhenium catalyst integrated with nanoporous silicon. This example reduced carbon dioxide to carbon monoxide with high selectivity and durability.

Together, these studies demonstrate that there are inherent advantages to building higher surface area silicon semiconductors for application in hybrid photoelectrodes. This research is an important step toward generating liquid fuels using sunlight as the energy source and only the carbon dioxide and water in the air as the inputs.

Funding

This work was primarily supported as part of CHASE, an Energy Innovation Hub funded by the Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences. Funding for equipment used in this research was provided by DOE, the U.S. National Institutes of Health, the Air Force Office of Scientific Research, and the National Science Foundation. AFM characterization work was supported by the U.S. National Science Foundation and by the U.S.-Israel Binational Science Foundation.