SUSTAINABILITYARTIFICIAL
PHOTOSYNTHESIS:A STEP TOWARD A CARBON-FREE FUTURE

Dr. FUJISHIMA Akira, the discoverer of photocatalysis, is working to produce fuel by combining thehydrogen produced from solar energy with greenhouse gases.
It is not widely known that theglass pyramid in the courtyardof the Louvre Museum in Paris
has a transparent coating thatexhibits an antifouling effectupon exposure to natural light.
Dr. FUJISHIMA Akira, aJapanese researcher, pioneered thediscovery of that photocatalysis
reaction, which involves theprinciple of breaking down dirt
without using any energy or
Dr. FUJISHIMA Akira is
the director of thePhotocatalysis
International ResearchCenter at the Tokyo
University of Science. He
discovered photocatalysis
reaction using titaniumoxide while enrolled at theUniversity of Tokyo
Graduate School. Thatdiscovery was later called
the Honda-Fujishimaeffect, with research on
artificial photosynthesis
then being initiatedaround the world.

incurring any cost. Althoughphotocatalysis has been widely
developed and put into practicaluse in the areas of antifouling andantifogging, research on artificial
photosynthesis—the process of
extracting hydrogen throughphotocatalysis—has also beengarnering significant attention inrecent years as a technology withthe potential to contribute to a
decarbonized society.

It was in 1967, while he wasat a graduate school under
the supervision of the lateDr. HONDA Kenichi, thatDr. Fujishima, alongside hissupervisor,
discovered
thephotocatalysis reaction. Thisphenomenon produces hydrogenand oxygen when titanium oxide
is exposed to light under water,in effect reproducing the redox(or oxidation-reduction) reaction
similar to that of photosynthesis
in plants. So excited was Dr.
Fujishima with his discovery—
the knowledge that oxygen could
be extracted simply throughexposure to light—that he wasunable to sleep for some time.
Dr. Fujishima’s paper, written
jointly with Dr. Honda, waspublished in the journal Naturein 1972, following which thephotocatalysis reaction became
known as the Honda-Fujishimaeffect. Ever since the oil crisisof the 1970s, the process of
being able to extract hydrogenthrough photocatalysis has been
greatly anticipated as a source ofalternative energy to replace oil,and researchers around the world
have been working on an efficientmeans to extract hydrogen via
artificial photosynthesis usingthat principle.
With the United Nations
Sustainable Development Goals(SDGs) aiming to reducegreenhouse gases, research on
artificial photosynthesis has
been increasingly gaining pace,though many challenges still
remain. Dr. Fujishima says, “Toachieve the practical applicationsof hydrogen production using
artificial photosynthesis, the highefficiency of hydrogen extractionis, of course, the basic key factor.
However, the other key factors areConverting CO2
into a resource
toward adecarbonizedsociety

Fujishima (left) conducting an experiment with Dr. Honda in 1967. Initially, nobody believed the pair’s
findings, namely, that water could be broken down with light energy alone.

whether we can find a catalyst thatsatisfies the remaining various
conditions; this includes whether
the materials used as catalysts canbe easily obtained, whether a large
surface area photocatalyst can bemanufactured, and whether any
harmful substances are containedin the material. We are waiting fora breakthrough for those things inthe future.”
Along with the shift to replacefossil fuels with renewableenergies such as hydrogen, anotherimportant measure to achieving adecarbonized society is carbon
recycling, effectively using CO2
as a resource. In consideration ofthat viewpoint, Dr. Fujishima has
proposed the following method;
first, extract hydrogen throughwater electrolysis using theelectricity produced from highly
efficient solar cells. Next, combine

the extracted hydrogen with
the CO2 emitted from power
plants and factories to produce
methanol, which can be used as
an energy source. If this process isrealized, gases containing carbon,
such as CO2, will no longercontribute to the greenhouseeffect. Rather, those gases willbecome “resources” to replace oiland natural gas.
Dr. Fujishima currently heads
the Photocatalysis International
Research Center at the Tokyo
University of Science, where heis leading research on further
progress of photocatalysis in thefields of the environment andenergy. “I think it’s importantfor science to contribute to theworld,” he says. Based on his
discovery, a decarbonized society,where even CO2 is used as aresource, will soon be realized. WaterGas

CO2Renewablesolar power

Generating new energy
from sunlight, water,and CO2

H2
Electricity

Photocatalysis acts as an antifouling and antifogging
effect simply by the irradiation of light. It has also beenused in the glass covering the pyramid-shaped entrance of
the Louvre Museum. The glass maintains its transparent
beauty by decomposing dirt.

Solar cells

Waterelectrolysis

Methanol
synthesis