The_Catalyst_Review_November_2023 - 19

Process News
Researchers Develop a Promising Molecular Catalyst for Aqueous Polysulfide-based
Redox Flow Batteries
Researchers at The Chinese University of Hong Kong recently introduced a new molecular catalyst that could help to boost the
performance of flow batteries based on polysulfides. This catalyst is both durable and active, thus enabling fast redox reactions inside
a battery cell. Isoalloxazine and quinone are two substances often used in energy applications, as they are known to be efficiently
electron shuttles. In living cells, these molecules can proficiently transfer electrons in the so-called respiratory chain, which is what
ultimately produces energy. The new molecular catalyst introduced by Lu and his colleagues is based on a compound derived from
isoalloxazine, namely riboflavin sodium phosphate (FMN-Na). The design strategy proposed by this team of researchers can improve
the electrochemical reduction capabilities of polysulfides, which can in turn facilitate redox reactions inside polysulfide-based battery
cells. This is achieved thanks to the rapid redox kinetics of the FMN-Na molecular catalyst they identified. In experiments, flow battery
cells containing the team's catalyst were found to perform well, decaying at a rate of 0.00004% per cycle after running for 2,000 cycles
at 40mA cm-2
. To demonstrate the catalyst's scalability, Lu and his colleagues used it to create a 100 cm2 cell stack. This approach for
improving the performance of polysulfide-based flow batteries could also be scaled up to create larger flow battery systems. Future
studies could help to further assess and validate the potential of this approach, by testing the performance of various battery cells
containing the FMN-Na catalyst. Source: Tech Xplore, 10/13/2023.
Tuning Properties of Membrane and Catalyst
Layers Optimizes Reactors for Fuel Cells
and More
University of Michigan researchers have designed a
multifunctional membrane-catalyst reactor that minimizes
reactions between oxygen and ethylene while maintaining high
methane oxidation rates. The team's reactor uses a hollow
fiber membrane-catalyst system made with multiple layers of
gadolinium-doped barium cerate catalyst. The barium cerate
fibers have a high surface-to-volume ratio that supports high
volumetric ethylene production. These multifunctional systems
are fabricated in one step by employing additive manufacturing
approaches that take advantage of co-extrusion of the catalyst
and membrane. This approach allows the team to make thin
membranes interspersed between thicker, more porous catalyst
layers that facilitate the reaction between oxygen and methane,
and more broadly to tune the transport and reaction rates so that
these match each other. The thinner membranes increase the
rate at which surface oxygen reacts with methane, which ramps
up ethylene production but could also allow for more undesired
oxygen to accumulate and react with ethylene. To get around this
problem, the team changed the number of OCM-active sites in
their reactor such that methane-oxygen reaction rates precisely
matched the oxygen diffusion rate. Source: Phys.org, 10/27/2023.
Researchers Advance Green Hydrogen
with MXene Catalysts
A sustainable route to green hydrogen production
is becoming possible through the use of efficient
electrocatalysts, according to research from Texas A&M
University. Their research uses MXenes - a new class of
2D-layered material - as a catalyst supporting Ru-atom
for hydrogen evolution reaction (HER) catalysis for green
hydrogen production. The researchers demonstrated that
the reaction rate of the electrochemical conversion processes
could be increased by modifying the electrochemical
responses of these 2D nanostructured materials (MXenes)
fabricated in the laboratory at Texas A&M University.
By inserting metal, the researchers were able to tune
inexpensive materials and enhance their performance to
match closely that of noble metals. Specifically, into the
structure of the material, the process can appreciably
enhance the electro-catalytic performance of the material.
Results showed the Ru atoms attach preferably to the
surfaces of the MXene. From these findings, a new approach
of tuning the electrocatalytic activity of MXenes was found
to accelerate the development of cost-effective, efficient and
sustainable hydrogen technology. Source: Chemical
Processing, 10/16/2023.
New Method Demonstrates Continuous Hydrogen Production Using Formic Acid
Researchers in Japan have used an iridium-immobilized catalyst based on polyethyleneimine (PEI) for hydrogen production via formic
acid (CH2
O2
) dehydrogenation (FADH). The iridium complex and its ligand cross-linked with PEI for the catalyst; the iridium content
could be easily varied in the range of 1-10%. The structure of the iridium-immobilized catalyst was confirmed using solid-state NMR,
DNP NMR, and FT-IR spectroscopies. Formic acid is a strong organic acid that has replaced inorganic acids in manufacturing and has
shown potential use in new energy technology. Most formic acid is made from carbon monoxide, either by heating it with sodium
hydroxide to produce sodium formate, which is then acidified, or via the base-catalyzed reaction of CO and methanol to make methyl
formate, which is hydrolyzed to the acid. Formic acid is also a major byproduct of acetic acid manufacture. There is increasing interest
in the potential role for formic acid in a closed carbon cycle, via its production by the hydrogenation of captured CO2
. According to
the researchers, the iridium-immobilized catalyst with PEI showed excellent catalytic activity for FADH, exhibiting the catalyst's highest
turnover frequency (TOF) value of 73,200 h-1
and a large turnover number (TON) value of over 201,500. The catalyst could be used
for continuous hydrogen production via FADH, exhibiting high durability for over 1150 h without any degradation in catalytic activity.
The obtained hydrogen gas was evaluated for power generation using a standard fuel cell, and 5 h of stable power generation was
achieved. Source: Green Car Congress, 10/16/2023.
The Catalyst Review
November 2023
19

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