The widespread adoption of hydrogen-powered vehicles over traditional electric vehicles requires fuel cells that can safely convert hydrogen and oxygen to water – a serious implementation problem.
Researchers at the University of Colorado Boulder are addressing one aspect of this hurdle by developing new computing tools and models necessary to better understand and manage the conversion process. Hendrik Heinz, Associate Professor in the Department of Chemical and Biological Engineering, is leading the effort in partnership with the University of California Los Angeles. His team recently published new findings on the subject in Scientific advances.
Fuel cell electric vehicles combine hydrogen in a tank with oxygen from the air to generate the electricity needed to operate. They don’t need to be plugged in to charge and have the added benefit of producing water vapor as a by-product. These and other factors have made them a fascinating option in the fields of green and renewable energy transportation.
Heinz said a key goal for vehicle profitability is to find an effective catalyst in the fuel cell that can “burn” the hydrogen with oxygen under controlled conditions necessary for safe driving. At the same time, the researchers are looking for a catalyst that enables this at almost room temperature with high efficiency and a long service life in an acidic solution. Platinum metal is widely used, but predicting the reactions and the best materials for scale-up or other conditions has been challenging.
“For decades, researchers have struggled to predict the complex processes required for this work, although enormous advances have been made with nanoplates, nanowires and many other nanostructures,” said Heinz. “To address this, we have developed models for metal nanostructures and oxygen, water, and metal interactions that are more than ten times more accurate than current quantum methods. The models also enable the inclusion of the solvent and the dynamics and show quantitative correlations between the oxygen accessibility of the surface and the catalytic activity in the oxygen reduction reaction. “
Heinz said the quantitative simulations his team developed show the interaction between oxygen molecules when they encounter different barriers through molecular water layers on the platinum surface. These interactions make the difference between a slow and fast follow-up reaction and must be controlled in order for the process to work efficiently. These reactions happen pretty quickly – it takes about a millisecond per square nanometer to convert to water – and they happen on a tiny surface of the catalyst. All of these variables come together in an intricate, complex “dance” that his team can model in a predictive manner.
The computational and data-intensive methods described in the paper can be used to create designer nanostructures that maximize catalytic efficiency, as well as possible surface modifications to further optimize the cost-benefit ratio of fuel cells, Heinz added. His staff are investigating the commercial implications of this aspect and he is applying the tools to investigate a wider range of potential alloys and gain further insights into mechanics.
“The tools described in the paper, particularly the interfacial force field for more reliable molecular dynamics simulations on the order of magnitude, can also be applied to other catalyst and electrocatalyst interfaces for similar groundbreaking and practically useful advances,” he said.
This work was funded by the National Science Foundation. Other partners are the Argonne Leadership Computing Facility and Research Computing at the University of Colorado Boulder.