Panasonic develops highly efficient artificial photosynthesis system with gallium nitride semiconductor for conversion of CO2 to formic acid
|Schematic view of artificial photosynthesis system. Click to enlarge.|
Panasonic has developed an artificial photosynthesis system using a gallium nitride photoelectrode and a metal catalyst which uses sunlight to convert CO2 mainly to formic acid (an important intermediate in chemical synthesis) at an efficiency (solar energy to chemical energy) of 0.2%—a comparable level to that of plants.
The reaction rate is completely proportional to the light power due to the low energy loss with the simple structure; in other words, the system can respond to focused light. This will make it possible to realize a simple and compact system for capturing and converting wasted carbon dioxide from incinerators and electric generation plants, according to Panasonic. Panasonic partially presented the technology on 30 July at the 19th International Conference on the Conversion and Storage of Solar Energy (IPS-19) in Pasadena.
Previous approaches to developing artificial photosynthetic systems for the direct conversion of CO2 have used complex structures such as organic complexes or plural photo-electrodes, which made it difficult to improve their efficiency in response to the light, according to the company. Panasonic’s artificial photosynthesis system has a simple structure with highly efficient CO2 conversion, which can utilize direct sunlight or focused light.
Gallium nitride semiconductors have attracted attention for their potential applications in highly efficient optical and power devices for energy saving. Panasonic determined that they can also be used as photo-electrodes for CO2 reduction; a nitride semiconductor has the capability to excite the electrons with enough high energy for the CO2 reduction reaction.
The CO2 reduction takes place on a metal catalyst at the opposite side of nitride semiconductor photo-electrode. The metal catalyst plays an important role in selecting and accelerating the reaction. Panasonic notes that the system comprises only inorganic materials, which can reduce the CO2 with low energy loss. Because of this, the amount of reaction products is exactly proportional to the light power.
This is one of the merits in such an all-inorganic system while some conventional systems cannot follow the light power in general because of their internal or external rate-limiting processes in the complex structures, Panasonic says.
Panasonic holds 18 domestic patents and 11 overseas patents, including pending applications, on the technology.
Also at the IPS-19 conference, a team from Toyota Central research reported on a method for the selective conversion of CO2 to formate (a salt of formic acid) using semiconductor/complex hybrid photocatalysts. The conversion efficiency of solar energy to chemical energy was 0.03-0.04%.
Hiroshi Hashiba et al. (2012) Highly Efficient CO2 Reduction in AlGaN/GaN - In Artificial Photosynthesis System (IPS-19, Nº 5711, oral plus poster)
Yotsuhashi, Satoshi; Deguchi, Masahiro; Hashiba, Hiroshi; Zenitani, Yuji; Hinogami, Reiko; Yamada, Yuka; Ohkawa, Kazuhiro (2012) Enhanced CO2 reduction capability in an AlGaN/GaN photoelectrode. Applied Physics Letters, Volume 100, Issue 24, id. 243904 doi: 10.1063/1.4729298
Shunsuke Sato, Takeo Arai, Takeshi Morikawa, Keiko Uemura, Tomiko M. Suzuki, Hiromitsu Tanaka, and Tsutomu Kajino (2011) Selective CO2 Conversion to Formate Conjugated with H2O Oxidation Utilizing Semiconductor/Complex Hybrid Photocatalysts. Journal of the American Chemical Society 133 (39), 15240-15243 doi: 10.1021/ja204881d