The Catalyst Review September 2024 - 15

Experimental Abstracts
Porous Thermoelectric Materials for Energy Conversion by Thermoelectrocatalysis
Thermoelectric (TE) materials can convert a temperature difference into a voltage and are considered promising for energy harvesting from waste heat.
Conversely, they can also convert electricity into a temperature gradient for precision temperature control. TE materials possessing an open-circuit
configuration have recently been reported to function as a catalyst, catalyst support, and promoter; TE Seebeck voltage V (= -S·ΔT) was found to increase
the catalytic activities by tens to hundreds of times. Herein, the authors discuss the application of sol-gel-prepared porous TE materials for thermoelectrocatalysis.
In
order to facilitate the
selection of
the most
appropriate TE materials for
thermocatalytic applications,
these workers proposed a new
figure of merit, β= S/κ , where
S=Seebeck coefficient and
κ=thermal conductivity. They
then surveyed a large number
of TE materials, calculated
their β values, and summarized
them
in Table
1. BiCuSeObased
oxyselenides were found
to show high β values, with
undoped compounds reaching
up to 1328 μV m W -
¹. Since they
are easy to prepare, inexpensive,
and can work at moderately
elevated temperatures (up to
723K), they were selected for
evaluation as a thermoelectric
catalyst.
These workers employed a
sol-gel process to prepare
oxyselenides BiCuSeO with a
minimum amount of second
phases. The gels obtained under
these conditions were used
for the preparation of different
porous samples, making use
of solid-state reaction (called
BCSO dense), sol-gel method,
a mixture of 50% wt. of solidstate
reaction and 50 wt.%. of
the sol-gel powders (called 50%
sol-gel) and then dip coating of
the gel on a dense BCSO pellet.
Techniques such as dense bulk
porous surface and increased
thickness of the TE materials
were then used to optimize the
thermoelectrocatalysis of
the
oxyselenide BiCuSeO for the
carbon dioxide hydrogenation
reactions.
Table 1. Summary of
thermoelectric properties
including their thermal conductivity κ, Seebeck coefficient S, electrical
conductivity σ, the energy conversion dimensionless figure of merit ZT,
the power factor, and the newly defined figure of merit (FOM) β= S/κ for
thermoelectrocatalysis applications for a number of thermoelectric materials.
These TE materials were found to have inferior TE properties
as compared to their dense counterparts prepared by solidstate
reactions and SPS sintering. However, its surface area has
increased by at least one order of magnitude. This enhanced
surface area was more than enough to compensate for the
smaller effect from a smaller Seebeck voltage for catalysis
promotion, achieving CO2
conversion higher than the thermal
equilibrium conversion of the RWGS across a large temperature
range (Figure 1). A Seebeck voltage also enhanced CO
selectivity. These findings suggest that porous TE materials,
despite their lower thermoelectric performance, can be highly
effective in thermoelectrocatalysis applications due to their
increased surface area and ability to enhance catalytic activity.
Wu J, Chen K, Reece MJ, et al. (2024). Energy Technol., 2400973
Figure 1. a) Seebeck voltage V, b) CO2
function of Th
between Ln (Y) and -eV/kb
conversion Y, and c) CO selectivity as a
for stacked dense and porous BCSO samples, and d) the relationship
Th can be approximated by a linear line. The calculated
thermal equilibrium conversions (ref. [53]) of the RWGS in Equation 1 and the
combined conversions for RWGS + methanization (Equation (1) and (2)) are plotted
in the figure for comparison.
The Catalyst Review
September 2024
15

The Catalyst Review September 2024

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