Mimicking photosynthesis for cheap hydrogen fuel
UNIVERSITY PARK, Pa. – Production of inexpensive hydrogen for automotive or jet fuel may one day be possible by mimicking
photosynthesis, but a number of hurdles first must be overcome.
Scientists at Pennsylvania State University have developed an
artificial system that can mimic photosynthesis in the hope of creating a practical,
inexpensive way to make jet fuel. Using the energy in blue light, their work has
yielded only 2 to 3 percent hydrogen. The blue light is much less efficient than
other solar energy conversion technologies, but the investigators have hope.
Although some researchers have used solar cells to make electricity
or used concentrated solar heat to split water, both processes are energy-intensive.
The key to direct conversion, scientists say, is electrons. As with the dyes that
occur naturally in plants, inorganic dyes absorb sunlight, and the energy kicks
out an electron. When left on its own, the electron can recombine to create heat,
but if channeled – molecule to molecule – far enough away from where
it originated, it can reach the catalyst and split the hydrogen from the oxygen
Recombination of electrons is not the only problem the scientists
face. They also must address the oxygen-evolving end of the system, which currently
limits the lifetime of the system to a few hours. Even though natural photosynthesis
has the same problem, it can repair itself by periodically replacing the oxygen-evolving
complex and the protein molecules around it. The researchers have not yet been able
to provide a fix to the oxidation process.
Currently, they are using only blue light, but they would like
to expand into the entire visible spectrum from the sun. In addition, their experiments
use only expensive components – titanium oxide and platinum dark electrodes,
and an iridium oxide catalyst. Substitutions are necessary, and researchers at other
institutions have begun working on an alternative solution. An MIT group is investigating
cobalt and nickel catalysts, and manganese is under investigation at Yale and Princeton
The system uses only one photon at a time, but the Penn State
researchers anticipate that a two-photon system, albeit more complicated, would
be more effective in using the full spectrum of sunlight. Research will continue,
and they will focus their efforts to track all the energy pathways in the cell to
understand the kinetics, with the hope of modeling the cells and adjusting the portions
to decrease energy loss and increase efficiency.
- visible spectrum
- That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to 750 nm in wavelength.
MORE FROM PHOTONICS MEDIA