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