Hydrogen fuel cells generate electricity when fed with hydrogen, which combines with oxygen and results water. Still, hydrogen fuel cells are expensive due to the catalyst used in the cathode for the reaction known as oxygen reduction. That catalyst is 100% pure platinum, which is a rare and expensive material.
A research team from Brown University of Rhode Island has developed a new type of catalyst that only uses 30% platinum. They created a nanoparticle which contains a unique core and shell and that lasts much longer than current pure-platinum catalysts found in fuel cells (which also degrade over time).
The cathode is the place where almost 40% of the fuel cell’s efficiency is lost, so improving the way the catalyst works is directly increasing the efficiency, and making the fuel cell compete with internal combustion engines and batteries.
What the researchers did was create a five-nanometer palladium core and encircle it with a shell of iron and platinum. The secret to making the nanoparticle 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 Shouheng Sun, professor of chemistry at Brown first reported in a 2000 Science paper. The result was a shell that uses only 30 percent platinum, although the researchers say they expect they will be able to make thinner shells and use even less platinum.
“If we don’t use iron pentacarbonyl, then the platinum doesn’t form on the (palladium) core,” Mazumder said.
The iron-platinum shells that the researchers created had one to three nanometers in width, but lab tests revealed that one-nanometer shells were the best. “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,” Mazumder said. “The next step is to scale them up for commercial use, and we are confident we’ll be able to do that.”
There are still some unexplained phenomena that Mazumder and Sun try to hack into. They believe that the palladium core increases the catalytic abilities of iron platinum because of the transfer of electrons between the core and shell metals. To be sure about that, they are trying to use a chemically more active metal than palladium as core to the nanoparticle to tinker with the core-shell electron transfer and how important this is to the overall catalyst function.
May solutions that replace platinum had been found before, but the market hasn’t seen any of them in action so far. Let’s hope that one of them (at least) will penetrate the barrier to become commercial and will improve the final price of electric/fuel cell powered cars.