Fuel cells are a favorite topic of mine, and I try to follow publications that release news about fuel cell design or components. A fuel cell is a device which takes in a supply of some fuel component, for example hydrogen gas (for a hydrogen fuel cell), and then converts it to another product while generating useful electricity in the process. The reaction product is pumped out of the cell and the electricity is used to power devices. It’s similar in function to a simple diesel generator, but simpler in design and usually cheaper to operate. A key component in any fuel cell is the catalyst, which is the heart and soul of a fuel cell and is the primary component responsible for the fuel cells operation and function.
The search is constant for better catalysts that have longer lifetimes and which are less expensive to maintain. For many chemists, the most popular choice is a catalyst made from platinum metal. However, not only is platinum extremely expensive (it’s called a “precious metal” for a reason), but it also tends to become “poisoned” during the process of the fuel-cell operation, and gradually loses reactivity until it finally has to be discarded. Constantly replacing an expensive catalyst is not an economically viable solution, and so much of the research into fuel cells is concerned with methods of protecting the platinum from the constant degradation.
New results published in the flagship science magazine, Journal of the American Chemical Society, describe how chemists at Brown University have created a new type of catalyst which uses less platinum than conventional approaches but yet outperforms most normal platinum catalysts. They took an extremely tiny, microscopic specks of palladium (a precious metal related to platinum, but less expensive) and coated them with a shell of an iron-platinum alloy, like the outer shell of an onion around the dense core. The coating step was accomplished by decomposing two organometallic compounds (iron carbonyl and a platinum complex) in the presence of the palladium nanoparticles. The resulting shell is only about 30% platinum, with the remainder made up of the iron; this shaves quite a lot off the total cost for the catalyst, even when the palladium cost is taken into account.
The chemist team tested a wide variety of nanoparticles, ranging from one nanometer in size up to five nanometers. This allowed them to home in on the best possible size which produced the catalyst with the best performance. They determined that an iron-platinum nanoshell around a center of palladium metal, about 1 nanometer in diameter, performed the best. The catalyst particles were still going strong after 10,000 cycles of the fuel cell, compared to 100% palladium catalysts which give up after about 1,000 cycles. A ten-fold increase in performance combined with a lower material cost is definitely worth celebrating, and I have no doubt that this new type of catalyst will rapidly find its way into commercial fuel cells very soon.
Source: http://pubs.acs.org/doi/abs/10.1021/ja1024436
