Fuel cells are attractive as eco-friendly energy sources, for example for hydrogen-powered vehicles. But due to the large amounts of expensive platinum required, they are expensive. In the magazine Science, a team of researchers from DTU and the University of Copenhagen have described a group of cheaper and efficient platinum alloys which can pave the way for more widespread use of the fuel cell technology.
The so-called polymer electrolyte membrane fuel cells (PEMFC) that convert hydrogen and oxygen to electricity—for example in hydrogen-powered vehicles—require a platinum catalyst. This is a problem, as quite substantial amounts of platinum are required at the cathode, where oxygen is reduced to water. The scarcity and high cost of platinum constitute the main barriers to the widespread use of hydrogen-powered vehicles.
Now a team of researchers from DTU and the University of Copenhagen have discovered a group of platinum alloys that are not only cheaper, but also efficient. The fuel cells typically used today feature platinum alloyed with nickel or cobalt, which is unfortunately broken down in the fuel cell.
The researchers have studied alloys of platinum and seven of the rare earth elements (lanthanides) as well as calcium, and in an article in Science they have demonstrated that the alloys change the crystal structure and slightly reduce the distance between the platinum atoms in the surface compared to the conventional cathodes. In fact, it is the distance between the platinum atoms that controls the catalytic activity and stability.
Mixing platinum with lanthanide atoms of different sizes allows them to control this distance. This has resulted in platinum-based catalysts for the reduction of oxygen, which are among the most efficient catalysts known. It also reduces platinum consumption, as six times more cathodes can be made with the new alloys using same amount of platinum. Finally, the new alloys appear to be more resistant to degradation. This bodes well for the use of fuel cells, explains Associate Professor Ifan Stephens from DTU Physics:
“Together with the Danish companies IRD Fuel Cells and Danish Power Systems, we continue our work to develop methods for large-scale production and industrial testing of the alloys. This way, we hope to give a huge boost to fuel cell use,” he says.