Researchers develop computational tool to aid understanding of ORR on platinum catalysts in fuel cells
Researchers at the University of Colorado Boulder are developing new computational tools and models to better understand and manage the oxygen reduction reaction (ORR) in fuel cells. Hendrik Heinz, an 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 an open-access paper in the journal Science Advances.
Heinz said a key goal to making fuel cell vehicles viable is to find an effective catalyst in the fuel cell that can operate at near room temperature, with high efficiency and a long lifetime in acidic solution. Platinum metal is commonly used, but predicting the reactions and best materials to use for scaling up or different conditions has been a challenge to date.
For decades, researchers have struggled to predict the complex processes needed for this work, though enormous progress has been made using nanoplates, nanowires and many other nanostructures. To address this, we have developed models for metal nanostructures and oxygen, water and metal interactions that exceed the accuracy of current quantum methods by more than 10 times. The models also enable the inclusion of the solvent and dynamics and reveal quantitative correlations between oxygen accessibility to the surface and catalytic activity in the oxygen reduction reaction.—Hendrik Heinz
Heinz said the quantitative simulations his team developed show the interaction between oxygen molecules as they encounter different barriers by molecular layers of water on the platinum surface. These interactions make the difference between a slow or fast follow-on reaction and need to be controlled for the process to work efficiently. These reactions happen quite fast—the conversion into water takes about a millisecond per square nanometer to complete—and happen on a tiny catalyst surface. All of those variables come together in an intricate, complex dance that his team has found a way to model in predictive ways.
Engineering the atomic-scale surface features of the platinum electrode in contact with the electrolyte helps in attracting molecular oxygen and faster conversion to water. A strongly bound oxygen molecule is highlighted in blue before the reaction on a platinum nanoplate surface. Credit: Heinz et al., 2021
The computational and data-intensive methods described in the paper can be used to create designer-nanostructures that would max out the catalytic efficiency, as well as possible surface modifications to further optimize the cost-benefit ratio of fuel cells, Heinz added. His collaborators are exploring the commercial implication of that aspect, and he is applying the tools to help to study a wider range of potential alloys and gain further insights into the mechanics at play.
The tools described in the paper, especially the interface force field for order-of-magnitude more reliable molecular dynamics simulations, can also be applied to other catalyst and electrocatalyst interfaces for similar groundbreaking and practically useful advances.—Hendrik Heinz
This work was funded by the National Science Foundation. Other partners include the Argonne Leadership Computing Facility and Research Computing at the University of Colorado Boulder.
Shiyi Wang, Enbo Zhu, YU Huang, Hendrik Heinz (2021) “Direct correlation of oxygen adsorption on platinum-electrolyte interfaces with the activity in the oxygen reduction reaction” Science Advances doi: 10.1126/sciadv.abb1435