Towards Artificial Photosynthesis
[Music]
well here you can see the most
successful
energy conversion system of our planet
yes
i’m talking about plants they have
mastered the ability to harvest the
energy of sunlight
and use it to convert carbon dioxide
into vital chemicals that now sustain
life on earth
this process known as photosynthesis has
been crafted
over billions of years of evolution but
what if we could also learn this
i’m working in the field of artificial
photosynthesis
where this is exactly what we are trying
to achieve
our ultimate aim is to design human-made
materials
able to harvest the energy of light and
use it to produce a useful chemical
on demand let me give you my perspective
our society is strongly dependent on
fossil fuels
we use them as a source to generate
electricity
and as a resource to feed our chemical
industry
but in light of the challenges posed by
climate change
we have to reduce this reliance and
explore renewable resources
well the energy the sun provides to our
planet is the most vast and equally
distributed
source of renewable energy a good
example here
are solar cells just look how quickly
they’ve changed the landscape of the
energy sector
in the last 15 20 years but
solar cells only allow for a very
specific energy conversion
from light to electricity
and while it’s of course great to have
access to zero emission charging and
power
we also need to think of the other
economic sectors that still
heavily rely on fossil fuels
our transportation means for example
cars and planes
are still dependent on petroleum
chemical industry products
petrochemicals plastics are still
derived from oil
and natural gas well all these
industries continue to generate
greenhouse co2 and thus continue to
contribute to
global warming so the point is
although solar cells are great at
utilizing sunlight
they are simply not enough in order to
facilitate the transition to the
sustainable economy of the future
we need a green process that also allows
a direct production of chemicals
fuels and plastics using sunlight
imagine for example that cars can be run
on a fuel
that is derived solely from water and
sunlight
a fuel that has no
toxic byproducts and has a zero carbon
footprint
that would be the aim in our research
group a team of chemists physicists and
material scientists
approach this problem from a very
fundamental perspective
our research takes inspiration from
natural photosynthesis
the process in which plants convert
stable and abundant molecules
water and carbon dioxide into variable
sugars and other chemicals using the
energy of light photons
well we aim to design human made
materials
that mimic what nature has been doing
for billions of years
this is a big task so where do you start
how can we learn from nature
the first essential step to this point
is to make sure that we understand how
plants photosynthesize
and here oh into the enormous scientific
progress
of the last 80 years we have learned a
great deal on the structure and
functions of natural system
just to give you a taste of it let me
show you its core
this is a leaf a basic unit of
photosynthesis
but is it if we magnify its structure
by a thousand times we will enter the
world of living cells
inside the cells of the leaf you see
these
green colored circles these are
chloroplasts
the main photosynthetic unit of the
plant
on the microscopic level but this is not
enough
only if we magnify the structure of the
chloroplast by another thousand times
will you see the world of molecular
machines
responsible for the most important
functions of photosynthesis
so here on the scale of 10 to 20
nanometers
you will find the so-called photosystem
2
and it is here on this molecular scale
where photosynthesis truly begins what
you can
see on the schematic reconstruction is a
bunch of molecules
proteins enzymes lipids co-factors
they are all intertwined to create this
fascinating
but highly complex biological system
so now if you want to create an
artificial system like that
you could of course think of replicating
this entire structure one-to-one
using the tools of chemistry but this
would be
too complex instead
why don’t we try to get inspired by this
structure
and only create its minimalistic version
that only contains the necessary
functions
so far we have learned that
functions of natural photosynthetic
systems can be downgraded to
three main processes one of them
is called light absorption the process
that converts the energy of incoming
light photons into a different form of
energy useful for the plant
these small molecules chlorophylls are
responsible for this
step the second
very important function we call it
catalytic
is in charge of the chemical conversion
and generation of
high value sugars that sustain plant
growth
to accomplish this step nature employs a
variety of bio-organic and bio-inorganic
molecules
such as this water oxidation cluster
here
well the third function is to basically
link
these two main parts so that they can
communicate effectively between each
other
well now after we understand the natural
system and its main parts
we can think of designing its artificial
version
to mimic the main functions of natural
photosynthesis
we need a component able to absorb light
a component able to drive the chemical
reaction
and the link between them well it turns
out that you can simplify
this scheme even further so you end up
with such an integrated system
in which these two major components are
linked by design
well this final material is called a
photo catalyst
this is our artificial copy of the
natural photosynthetic system
as it can do both absorb energy of light
photons
and drive the chemical conversion all
right
seems like a practical concept but
does this photocatalyst actually work
let me demonstrate to you the
feasibility of this approach
by looking at the dream reaction of
every chemist
water splitting water is a very simple
substance made of hydrogen and oxygen
atoms
still splitting water into its
constituents
represents one of the most challenging
processes
that’s interesting this is exactly the
reaction that plants can do so well
and that is the reason why our
atmosphere is full of breathable oxygen
but in addition to oxygen if you split
water you also
create hydrogen a very simple gas
that is not only an excellent energy
storage
molecule of the future but is also a
very important component of our
chemical industry so if hydrogen can be
produced
using renewable resources such as water
and sunlight we could contribute to the
climate change issue significantly
but let me come back to the
demonstration
well if you use compatible components
your catalyst and absorber and design
your photocatalyst just right
you can end up with a material that
basically looks like a powder
but is actually made of ultra small
particles
well in this experiment i deposited this
powder onto a piece of window glass
so i took this glass and put it in a
container with water
as expected nothing happens in the dark
but once my photocatalyst sees the light
the reaction begins
light gets absorbed the generated energy
gets transferred to the catalytic
component
which facilitates splitting of water
molecules
as a result we see bubbles of hydrogen
gas emerging from the surface
to be collected and used this process is
extremely simple
it does not require any sophisticated
device
or any additional energy input and
results in a generation of a fuel
from even wastewater and light
well achieving water splitting is a very
important milestone
using photocatalysts but we need to
dream bigger
the next level we want to achieve is to
use these artificial systems
to actually mimic the entire process of
photosynthesis
let me remind you in photosynthesis
plants convert
carbon dioxide into chemicals
so the ultimate aim here would be to
take advantage of the
excessive waste amount of co2 in our
atmosphere
and to rather treat this co2 as a
valuable resource
that can be converted into
interesting chemical products using a
photocatalyst
well this is a goal and if we succeed we
can for example turn co2
into a compound called ethylene which is
the main precursor to plastics
so how can we get there
to allow for such a complex reaction and
such
a selective product formation we have to
take a step back
and reconsider the photocatalyst design
so you already know it is the catalytic
component of the entire system
that is responsible for the chemical
conversion
so if we want to tune the product of our
reaction be it hydrogen
ethanol or ethylene we
need to make sure we can design the
catalytic component in a predictable way
but as of now most of the contemporary
photocatalysts are built
using the catalytic components that are
structurally
extremely complex so achieving this
control
turns into a huge challenge well in my
research
i want to approach this problem by
constructing a photocatalyst system that
is based on
structurally well-defined and thus
tunable
molecular catalysts why would it be of
advantage
well in chemistry it is only at the
molecular
scale at the molecular level where you
can
truly understand the catalytic process
so
the use of this molecular catalyst will
allow me to
unravel this missing link between their
structure
and performance these photocatalysts
will be able to conduct even
complex chemical conversions on demand
this is a very ambitious aim that we
have
but i’m very confident we can actually
achieve it
i have already started recruiting some
excellent future phd students
to contribute to the latest stages of
this project
all right let me wrap it up
natural photosynthesis uses sunlight
to turn co2 and water into a specific
set of chemicals
useful for the plant artificial
photosynthesis
mimics nature but also allows to design
a system for
a specific desired chemical conversion
well if we can achieve that and when we
achieve that we will not only have
access to
green hydrogen we will also be able to
produce
carbon neutral plastics fuels and
chemicals
so next time you see a plant
look closer think of the beauty
and complexity of the biological
photosynthetic machine that is inside
it and think of all the possibilities we
will have
once we learn how to tune it to our
advantage
thank you
[Music]
you