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The cost of platinum catalysts that drive cells is a factor that is slowing the widespread use of environmentally friendly hydrogen fuel cells in cars, trucks and other vehicles. One approach to using less valuable platinum is to combine it with other less expensive metals, but these alloy catalysts tend to degrade rapidly under fuel cell conditions.
Researchers at Brown University have developed a new alloy catalyst that reduces both the use of platinum and resists fuel cell testing. The catalyst, made from platinum and cobalt alloy in nanoparticles, has been shown to be superior to the US Department of Energy's goals for the year 2020 in terms responsiveness and durability, according to the tests described in the journal Joule.
"The durability of alloy catalysts is a major problem in the field," said Junrui Li, a graduate student in chemistry at Brown and senior author of the study. "It has been shown that alloys initially have better performance than pure platinum, but under current conditions, in a fuel cell, the non-precious metal part of the catalyst oxidizes and leaches very quickly. "
To solve this leaching problem, Li and his colleagues developed alloy nanoparticles with a specialized structure. The particles have a pure platinum outer shell surrounding a core consisting of alternating layers of platinum and cobalt atoms. This central layered structure is key to the catalyst's responsiveness and durability, says Shouheng Sun, a chemistry professor at Brown and lead author of the research.
"The layered arrangement of the atoms in the core helps to smooth and tighten the platinum network in the outer shell," Sun said. "This increases the platinum's reactivity and at the same time protects the cobalt atoms from being eaten away during a reaction. This is why these particles are so much more efficient than alloy particles with random arrangements of metal atoms. "
The details of how the ordered structure enhances catalyst activity are briefly described in Joule document but more specifically in a separate computer modeling document published in the Journal of Physical Chemistry. The modeling work was led by Andrew Peterson, associate professor at Brown's School of Engineering, also co-author of Joule paper.
For the experimental work, the researchers tested the ability of the catalyst to perform the oxygen reduction reaction, essential for the performance and durability of the fuel cell. On one side of a proton exchange membrane (PEM) fuel cell, electrons removed from the hydrogen create a current that drives an electric motor. On the other side of the cell, oxygen atoms absorb these electrons to complete the circuit. This is done by the oxygen reduction reaction.
Initial tests showed that the catalyst worked well in the laboratory, outperforming the more conventional platinum alloy catalysts. The new catalyst maintained its activity after 30,000 voltage cycles, while the performance of the traditional catalyst dropped significantly.
But laboratory tests are important for evaluating the properties of a catalyst, but researchers do not necessarily say whether the catalyst will work properly in a real fuel cell. The environment of the fuel cell is much warmer and its acidity differs from that of laboratory test environments, which can accelerate the degradation of the catalyst. To find out how far the catalyst would withstand this environment, the researchers sent it to the Los Alamos National Laboratory for testing it in a real fuel cell.
The tests showed that the catalyst exceeded the targets set by the Department of Energy (DOE) for initial activity and long-term sustainability. The DOE challenged researchers to develop a catalyst with an initial activity of 0.44 ampere per milligram of platinum by 2020 and an activity of at least 0.26 amps per milligram after 30,000 cycles. voltage (about the equivalent of five years of use in a fuel cell vehicle). The new catalyst test showed that it had an initial activity of 0.56 ampere per milligram and an activity after 30,000 cycles of 0.45 ampere.
"Even after 30,000 cycles, our catalyst has consistently exceeded the DOE's initial business target," said Sun. "This kind of performance in a real-world fuel cell environment is really promising."
The researchers have applied for a provisional patent on the catalyst and hope to continue to develop and perfect it.
More information:
Joule (2018). DOI: 10.1016 / j.joule.2018.09.016
The cost of platinum catalysts that drive cells is a factor that is slowing the widespread use of environmentally friendly hydrogen fuel cells in cars, trucks and other vehicles. One approach to using less valuable platinum is to combine it with other less expensive metals, but these alloy catalysts tend to degrade rapidly under fuel cell conditions.
Researchers at Brown University have developed a new alloy catalyst that reduces both the use of platinum and resists fuel cell testing. The catalyst, made from platinum and cobalt alloy in nanoparticles, has been shown to be superior to the US Department of Energy's goals for the year 2020 in terms responsiveness and durability, according to the tests described in the journal Joule.
"The durability of alloy catalysts is a major problem in the field," said Junrui Li, a graduate student in chemistry at Brown and senior author of the study. "It has been shown that alloys initially have better performance than pure platinum, but under current conditions, in a fuel cell, the non-precious metal part of the catalyst oxidizes and leaches very quickly. "
To solve this leaching problem, Li and his colleagues developed alloy nanoparticles with a specialized structure. The particles have a pure platinum outer shell surrounding a core consisting of alternating layers of platinum and cobalt atoms. This central layered structure is key to the catalyst's responsiveness and durability, says Shouheng Sun, a chemistry professor at Brown and lead author of the research.
"The layered arrangement of the atoms in the core helps to smooth and tighten the platinum network in the outer shell," Sun said. "This increases the platinum's reactivity and at the same time protects the cobalt atoms from being eaten away during a reaction. This is why these particles are so much more efficient than alloy particles with random arrangements of metal atoms. "
The details of how the ordered structure enhances catalyst activity are briefly described in Joule document but more specifically in a separate computer modeling document published in the Journal of Physical Chemistry. The modeling work was led by Andrew Peterson, associate professor at Brown's School of Engineering, also co-author of Joule paper.
For the experimental work, the researchers tested the ability of the catalyst to perform the oxygen reduction reaction, essential for the performance and durability of the fuel cell. On one side of a proton exchange membrane (PEM) fuel cell, electrons removed from the hydrogen create a current that drives an electric motor. On the other side of the cell, oxygen atoms absorb these electrons to complete the circuit. This is done by the oxygen reduction reaction.
Initial tests showed that the catalyst worked well in the laboratory, outperforming the more conventional platinum alloy catalysts. The new catalyst maintained its activity after 30,000 voltage cycles, while the performance of the traditional catalyst dropped significantly.
But laboratory tests are important for evaluating the properties of a catalyst, but researchers do not necessarily say whether the catalyst will work properly in a real fuel cell. The environment of the fuel cell is much warmer and its acidity differs from that of laboratory test environments, which can accelerate the degradation of the catalyst. To find out how far the catalyst would withstand this environment, the researchers sent it to the Los Alamos National Laboratory for testing it in a real fuel cell.
The tests showed that the catalyst exceeded the targets set by the Department of Energy (DOE) for initial activity and long-term sustainability. The DOE challenged researchers to develop a catalyst with an initial activity of 0.44 ampere per milligram of platinum by 2020 and an activity of at least 0.26 amps per milligram after 30,000 cycles. voltage (about the equivalent of five years of use in a fuel cell vehicle). The new catalyst test showed that it had an initial activity of 0.56 ampere per milligram and an activity after 30,000 cycles of 0.45 ampere.
"Even after 30,000 cycles, our catalyst has consistently exceeded the DOE's initial business target," said Sun. "This kind of performance in a real-world fuel cell environment is really promising."
The researchers have applied for a provisional patent on the catalyst and hope to continue to develop and perfect it.
More information:
Joule (2018). DOI: 10.1016 / j.joule.2018.09.016
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