June 2024 ESRFnews
14
during CO
2
electrolysis. In a very basic cell design, CO
2
is dissolved in water in contact with a catalyst-covered
cathode, separated with a permeable membrane from
the anode. When a voltage is applied across the cell,
the hydrogen from the water reacts on the cathode with
the CO
2
to form carbon monoxide (CO), hydroxide
ions or hydrocarbons.
One of the problems with this basic set-up is that CO
2
is able to react with the hydroxide ions in the electrolyte
to form carbonate and bicarbonate products, which then
cross the membrane to reform CO
2
at the anode, reducing
the reaction efficiency. To avoid this, Sargent’s group has
designed a cascade cell that converts CO
2
to CO, before
converting CO to the desired hydrocarbons. The XAS
at ID26 allowed the researchers to monitor what was
going on in the catalyst, made of Ag–CuO. “The high
flux of the beamline allows us to analyse elements with
concentrations as low as 1 a level typically encountered
in doped catalysts where the effect of the dopant is being
studied says Dorakhan Meanwhile the beamlines
wide energy range broadens the number of elements
accessible especially those with higher atomic numbers
In experiments last year the cell operated for 18
hours and produced acetate with an energy efficiency
of 25 twice as much as anyone had achieved before
Nat Synth 2 448 That bodes well for the sustainable
production of acetic acid an important feedstock for
polymers textiles solvents and food additives with a
market size of 13bn Still there are a wealth of other
hydrocarbons needed by industry, and one of the
major challenges of research into CO
2
reduction is
to improve the selectivity and stability of catalysts so
that they produce exactly the right products for a long
time. Formic acid is another important feedstock, for
example, used in leather tanning, de-icing aircraft and
extracting metals from ores. Among several potential
catalysts for this chemical, such as lead and indium,
bismuth has gained recent attention because it has
relatively low toxicity and high abundance, but its active
sites and structure during operation have been debated.
Experience required
Ward van der Stam, a chemist at Utrecht University in
the Netherlands, wanted to study the formation of bis-
muth active sites using synchrotron XAS, as it can probe
structural features over multiple length scales. “We
applied to use ID26 mainly because of the X-ray flux
and the energy range, but also because of their staff’s
previous experience with electrocatalysis,” he says. “We
wanted to look into the dynamics of the activation with
high time resolution, so the high flux was useful. Also,
the information from the in situ XAS measurements
complemented and confirmed our in situ labbased
diffraction results
Last year in their in situ experiment at ID26 van
der Stam and colleagues were able to show that halides
present in a bismuth oxyhalide precatalyst are able
to guide the catalysts activation with bromide in
particular promoting the exposure of planar bismuth
surfaces for more activity Indeed the bromide
activated bismuth achieved a formic acid selectivity
of 90 at high current density of 150 mAcm
2
Nat
Catal 6 796 In future experiments Van der Stam
believes the combination of XAS with other Xray
techniques such as Xray diffraction will be powerful
CO
2
REDUCTION
“The high quality data provided by ESRF
beamlines is crucial in this endeavour”
ESRF group head
Pieter Glatzel
assists with CO
2
reduction studies
at the ESRF’s ID26
beamline.
E S R F/ S T E F C A N D É