Development of Nanomaterial-based Photoelectrodes: Producing Hydrocarbon Fuel Directly from Carbon Dioxide and Water under Sunlight

“Plants absorb sunlight and use the energy to produce nutrients from carbon dioxide and water. Optimized as a result of a long evolution process, natural photosynthesis has a low energy conversion efficiency, below one percent, because the efficiency, or lack thereof, is sufficient for the plants to sustain their species. However, it is necessary to improve this efficiency if the goal is not to sustain plant species, but to reduce CO2 emissions resulting from the use of fossil fuels. In artificial photosynthesis, we aspire to design a photoelectrode that absorbs sunlight and ultimately converts CO2 into chemical fuel with higher efficiency than that of natural photosynthesis. This research is an outcome of collaborative efforts by five different research teams. It is hoped that the development of a photoelectrode to produce chemical fuel will be a complimentary means to addressing the pressing issue of CO2 reduction.”

Photoelectrode-based Artificial Photosynthesis Now Recognized as Core Technology for CO2 Reduction

In an attempt to solve the environmental problems faced by humankind, a number of researchers around the world have studied artificial photosynthesis to reduce carbon dioxide, since developing highly efficient photosynthesis can be a key to dealing with environmental challenges. Unlike the natural photosynthesis of plants involving carbon, oxygen, and nitrogen, its artificial counterpart uses inorganic substances such as elements found in stone and rocks. A team led by Prof. Doh Chang Lee at the Saudi Aramco-KAIST CO2 Management Center took artificial photosynthesis a step further and developed the technology to convert CO2 by making a nanomaterial-based photoelectrode that absorbs sunlight. This process of CO2 conversion during artificial photosynthesis involving a photoelectrode enables the production of chemical fuel and reduction of CO2 as well.

Although the photoelectrode has been studied by many researchers for several decades, the joint research team led by Prof. Lee focused on designing and making photoelectrodes with silicon-based, nano-scale heterostructure composites. This material allows for control the semiconductor absorption range to absorb light, serving as the core technology to maximize energy efficiency.

When the electrode creates electrons or holes by means of light, the electrically-connected electrode generates the CO2 conversion reaction. Various products come from this process, such as methanol, methane, formic acid, and carbon monoxide, and selectivity of products becomes another important issue. The research team created a hybrid electrode with nanomaterial and developed a nanometer electrode that can positively assist the catalyst reaction. Testing different materials, the team continued the research for two years.

About one year was spent on fine tuning the equipment in order to reliably analyze chemical fuel product as a result of CO2 conversion. Prof. Jihun Oh was responsible for designing the nanomaterial that constitutes the photoelectrode, and Prof. Il-Doo Kim optimized the surface treatment technology. In addition, Prof. Yoon Sung Nam designed molecular catalysts surrounding ruthenium and derived reactions, and Prof. Dong Ki Yoon studied molecular films and polymer layers that protect the catalyst so that molecular catalyst can be stably adsorbed into the surface. Finally, Prof. Lee led research to observe the effect of optical absorption material upon the surface of the catalyst in action. The collaborative efforts of these five research teams resulted in the creation of an efficient photoelectrode made with nanomaterial.

The technology to develop a photoelectrode aimed at creating chemical fuel was created using the findings of studies on various nanomaterials applied to other types of technologies, and research centered upon semiconductors and metals can be used for a range of electronic devices based on composite material. Furthermore, electrochemical research will help secure a core technology to study batteries and other energy storage devices. Ultimately, the photoelectrode-based artificial photosynthesis system is expected to help address the environmental challenges facing humankind based on its efficiency, which surpasses the one-percent level of natural photosynthesis.

Prof. Lee, Doh Chang
2015 Annual Report