Why the concern over removing carbon dioxide? The important thing about
such technology is that it produces hydrogen directly, which can in turn
be stored and used to generate electricity or propel vehicles in its own
right, or used as feedstock for methane or ammonia production. In this
way it will displace fossil fuels and lead to less CO2 being emitted.
Oliver.
On 09/07/2013 22:18, Andrew Lockley wrote:
Article link
http://www.ecopedia.com/environment/artificial-photosynthesis-the-future-of-carbon-dioxide-removal-in-solar-forests/
Paper link
http://pubs.acs.org/doi/abs/10.1021/nl401615t
In a May, 2013 paper in NANO Letters, titled “A Fully Integrated
Nanosystem of Semiconductor Nanowires for Direct Solar Water
Splitting.” With co-authors are Chong Liu, Jinyao Tang, Hao Ming Chen
and Bin Liu, Scientists with the U.S. Department of Energy (DOE)’s
Lawrence Berkeley National Laboratory (Berkeley Lab) have reported the
first fully integrated nanosystem for artificial photosynthesis. The
article is about as fun to read as the title, but it makes a very
clear point – artificial photosynthesis is not only possible, it can
potentially be done at even greater efficiency than by the plants it
is based on. The research is based on solar cells that split water
molecules and combine them with airborne carbon dioxide to produce the
simple sugar glucose and oxygen. Peidong Yang, a chemist with Berkeley
Lab’s Materials Sciences Division, explains it like this, “The
photo-generated electrons in the silicon nanowires migrate to the
surface and reduce protons to generate hydrogen while the
photo-generated holes in the titanium oxide nanowires oxidize water to
evolve oxygen molecules. The majority charge carriers from both
semiconductors recombine at the ohmic contact, completing the relay of
the Z-scheme, similar to that of natural photosynthesis.” In English,
the artificial photosynthesis cells are comprised of two sides, one
made of titanium oxide and the other of silicon. There are also a host
of co-catalysts that help the process get started. Each cell works
almost identically to a standard solar voltaic cell, but instead of
using the displaced electron to create a current, it uses the electron
to chemically adjust the structure of molecules in the cell. The
photosynthesis inside the artificial leaf structures is currently not
very efficient; in fact it is a paltry 12% efficient. That’s slightly
lower than the efficiency of plants. Up to this point, all such
projects have been focused on a single solar leaf. This is the first
successful attempt at creating a viable network of integrated leaves
that act in a similar manner as trees. The total output of the system
was similar to that of a 10 ft. Maple tree. This could be a hugely
important advance in solar technology as it has the potential to
remove the need for inverters or batteries in solar applications. The
solar leaf will produce a storable energy and remove carbon dioxide
from the air. This would allow the installation of solar leaves in
areas where traditional battery storage systems are not feasible. At
the current efficiency level, it doesn’t make sense to pursue this
technology, but there are several carbon reducing catalysts that, in
theory, should be able to break the 12% threshold. The only real
sticking point in the entire artificial photosynthesis game is that
artificial catalysts are still not able to efficiently utilize carbon
dioxide in the concentrations that are currently in the atmosphere.
Until researchers are able to overcome this fundamental issue, even
the most efficient carbon dioxide transferring solar trees will not be
feasible on a large scale.
See more at:
http://www.ecopedia.com/environment/artificial-photosynthesis-the-future-of-carbon-dioxide-removal-in-solar-forests/#sthash.PQDVflEm.dpuf
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