June 2024 ESRFnews
15
CO
2
REDUCTION
in elucidating catalyst restructuring and stability in
electrochemical environments. “The high-quality
data provided by ESRF beamlines is crucial in this
endeavour, due to the high brilliance and the possibility
of combining experiments to draw as complete a picture
as possible,” he says.
Several other ESRF beamlines are deeply involved
in CO
2
reduction research, and have been given a big
boost by the EBS upgrade. At ID01, Marie-Ingrid
Richard, a physicist based at CEA Grenoble, has been
developing stress and strain mapping of individual
catalytic nanoparticles via Bragg coherent diffraction
at picometre resolution (see ESRFnews June 2023, p17).
Coupled with theoretical simulations, these maps will
help Richard and her colleagues to understand how
CO
2
molecules adsorb onto the surface of a catalyst in
an alternative gas-phase approach, and to identify active
sites. “Strain engineering has emerged as an effective
tool to tune CO
2
reduction selectivity,” she says.
Performance matters
Meanwhile, there are the state-of-the-art X-ray
absorption beamlines BM23 and ID24-DCM, which
are able to probe the local atomic and electronic
structure of metal centres that convert or store
CO
2
. “This is done under operando conditions,
at process-relevant timescales and using a wide
range of complementary techniques,” says Kirill
Lomachenko, the scientist in charge of ID24-DCM.
“Also, both beamlines are equipped with the brand-
new monochromators designed in-house at the ESRF,
which offer excellent performance in terms of stability
and data quality.”
As Jakub Drnec, a beamline scientist on ID31,
explains, there are many aspects to improving CO
2
reduction, beyond catalytic activity and selectivity.
The catalytic durability, for example. “The catalyst can
chemically degrade in the sense of chemical dissolution,
or it can morph to a different form which is not as
active or selective,” says Drnec. “On top of that, the
catalyst can detach from its support and simply become
electrochemically inactive, or wash out from the system.
These processes are much less researched than activity
or selectivity, but are essential to understand in order to
make a reliable device.”
Recently, Drnec has helped ESRF users perform
research on yet another aspect of CO
2
reduction cell
stability This is a particular problem for socalled zero
gap electrolysers in which the space between electrodes
is totally filled with a membrane electrode assembly
MEA The setup should be easier to scale and be
superior at preserving electric current but suffers from
flooding and salt precipitation at the cathode where the
new products are supposed to be synthesised A group led
by Brian Seger at the Technical University of Denmark
in Kongens Lyngby use a combination of wideangle
Xray scattering and Xray fluorescence operando to
better understand why the problem occurs The ability
to observe the movement of cations and water within
an MEA during operation is truly extraordinary,” says
Bjørt Joensen, one of the group members. “It’s a unique
opportunity to gain insights into our devices.”
In results published this year, the researchers found
that the flooding is linked to movement of cesium ions
contained in the electrolyte near the anode, dragging
water molecules from the anode and into the cathode, a
phenomenon known as electro-osmosis. The knowledge
should enable scientists to improve cell performance,
by regulating the movement of cesium (Joule 8 1).
“We’re sure that continuous cooperation with the ID31
beamline will further enhance our understanding,
and help us optimise the CO
2
electrolysis system,” says
Qiucheng Xu, another group member.
There is still a way to go until CO
2
reduction becomes
mainstream. MEA electrolysers currently operate at
energy efficiencies of up to 34%, and for lifetimes of
up to a few hundred hours, whereas industry requires
minimum 50% efficiencies and thousand-hour
operating times. Yet research is making fast progress.
According to the Web of Science an online platform
that indexes most scientific literature 10 years ago there
were just a handful of papers published annually on the
CO
2
reduction reaction today there are more than
1200 Moreover together with the car manufacturer
Toyota and several other industrial partners the ESRF
is a beneficiary of the Marie SkłodowskaCurie doctoral
network ECOMATES for the improvement of
electrochemical CO
2
conversion The ESRFEBS
is wellsuited to be used for research into all the main
issues says Drnec
ESRF visiting
scientist Marie-
Ingrid Richard has
been using ID01
to map the stress
and strain of
individual catalytic
nanoparticles for
CO
2
reduction.
Jon Cartwright
E S R F/ S T E F C A N D É