Hydrogen fuel cells may someday power automobiles and trucks, offering a source of energy that's free of carbon emissions and pollutants. But their potential has been limited thus far by the high cost and instability of the platinum-nickel catalyst needed to spark the chemical reaction that produces clean electricity.
Using experiments and computer simulations, materials scientists from Johns Hopkins University and the University of California, Los Angeles have taken a major leap toward making that future possible. Their study, published in Matter, sheds new light on a method of stabilizing catalysts by adding copper and provides details on why the method works.
"The problem is that platinum-nickel catalysts, which are very promising for use in fuel cells, degrade over time as the nickel dissolves," explains Mueller, whose research focuses on developing and applying computational methods to allow researchers to understand the real-world behavior of materials and to develop new materials for advanced technologies. "Professor Huang's group discovered that adding copper to the catalysts helped reduce the amount of nickel dissolution, and our group helped them figure out why, which is important for people who want to build on this research."
In experiments, the UCLA researchers found that introducing copper atoms into specially shaped nanoparticles of platinum-nickel resulted in durability that proved to be 40% better, in terms of catalyst efficiency, than those without copper. These new catalysts were very stable—that is, more transition metals were retained in the platinum-nickel-copper particles, despite the corrosive condition that could leach them out. They were also more efficient in catalyzing the chemical reaction, compared to alloys of platinum-nickel and commercially used platinum-carbon.
To figure out why this was happening, Mueller's team at Hopkins devised a model based on experimental data and performed computer simulations that revealed how individual atoms moved around the nanoparticles in the type of environment that the catalysts would encounter in a fuel cell.
"We ran simulations of the particles, both with and without copper, to see how the addition of copper affected the degradation of the particles," said Liang Cao, a Johns Hopkins postdoctoral scholar of materials science and engineering, and a co-lead author of the study. "We were able to track the particles' evolution on an atomic scale, and our simulations indicated that the particles that contained copper were more stable because they initially had more platinum on the surface, which protected the nickel and copper atoms from dissolving."
According to Huang, the new study is a milestone in understanding the "atomistic structure-function relations in nanoscale materials and opens the door to new design strategies for high-performing nanoscale catalysts."