May
26
Cracking the Fuel Cell Platinum Problem
May 26, 2010 | 14 Comments
Platinum – the joy of a jewelry designer – the bane of a catalyst user, and in the current economy its the most expensive element on earth. Platinum is the cost problem for fuel cells. Developing alternatives are treasure hunts of the highest caliber.
Chemists at Brown University have demonstrated that a nanoparticle with a palladium core and an iron-platinum shell outperforms commercially available pure-platinum catalysts and lasts longer. A writer could be tempted to repeat, bold or add emphasis. If the Brown team’s work can be replicated and can show a commercial path they have the first treasure. The race to the ‘Platinum Replacement Prize’ is on.
The team’s leaders Shouheng Sun, professor of chemistry at Brown and co-author of the paper and Brown graduate student and co-author Vismadeb Mazumder’s findings are now reported in the Journal of the American Chemical Society.
The precious metal platinum has two major downsides: It is very expensive, and it breaks down over time in fuel-cell reactions.
The Brown University chemists report a promising advance with the new study. The team built a unique palladium core and an iron-platinum shell nanoparticle that uses far less platinum yet performs more efficiently and lasts longer than commercially available pure-platinum catalysts at the cathode end of fuel-cell reactions.
Palladium Core Iron-Platinum Shell Fuel Cell Catalyst. Click image for more info.
The research team created a five-nanometer palladium (Pd) core and enclosed it within a shell consisting of iron and platinum (FePt). The trick, Mazumder said, was in molding a shell that would retain its shape and require the smallest amount of platinum to pull off an efficient reaction. The team created the iron-platinum shell by decomposing iron pentacarbonyl [Fe(CO)5] and reducing platinum acetylacetonate [Pt(acac)2], a technique Professor Sun first reported in a 2000 Science paper. The result is a shell that uses only 30 percent as much platinum, although the researchers say they expect they will be able to make thinner shells and use even less platinum.
Mazumder said in accrediting Sun’s earlier work, “If we don’t use iron pentacarbonyl, then the platinum doesn’t form on the (palladium) core.”
The test results, Ready? The team demonstrated for the first time that they could consistently produce the unique core-shell structures. In the laboratory performance tests the palladium/iron-platinum nanoparticles generated 12 times more current than commercially available pure-platinum catalysts at the same catalyst weight. The output also remained consistent over 10,000 cycles, at least ten times longer than commercially available platinum models that begin to deteriorate after 1,000 cycles. That’s a “Wow!” moment.
The team created iron-platinum shells that varied in width from one to three nanometers. In lab tests, the group found the one-nanometer shells performed best.
Mazumber says, “This is a very good demonstration that catalysts with a core and a shell can be made readily in half-gram quantities in the lab, they’re active, and they last. The next step is to scale them up for commercial use, and we are confident we’ll be able to do that.”
Mazumder and Sun are studying why the palladium core increases the catalytic abilities of the iron platinum shell, although they think it has something to do with the transfer of electrons between the core and shell metals. To that end, they are trying to use a chemically more active metal than palladium as the core to confirm the transfer of electrons in the core-shell arrangement and its importance to the catalyst’s function.
The team leaders are hinting that this, a stunning of a result as it is, has room for more research and innovation.
The rest of the team and coauthors includes Miaofang Chi and Karren More at the Oak Ridge National Laboratory. The U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy funded the research as part of its Fuel Cell Technologies Program.
The issue in a fuel cell is the chemistry known as oxygen reduction reaction takes place at the fuel cell’s cathode, creating water as its only waste. Sun explains the cathode is also where up to 40 percent of a fuel cell’s efficiency is lost, so “this is a crucial step in making fuel cells a more competitive technology with internal combustion engines and batteries.”
For those of us with a deep-seated intuition that fuel cells are a critical segment of fuel to energy conversion power units for the future, the Brown University research team’s paper is the most important news in months. At lower cost with useful cycles measured up to 10,000 times with 12 times the current flow – this writer is . . . just thrilled.
Congratulations to Professor Sun, Mazumber, Chi and More. To use an overworked word, but applies here, it’s a breakthrough.
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