As a poisonous gas, carbon monoxide is often converted into carbon dioxide, such as in cars and trucks equipped with catalytic converters. This process is the reverse, which at first may sound a bit odd, but provides an important role in synthesizing valuable chemicals to use as electricity in lieu of the Earth's quickly depleting fossil fuels.
However, a better understanding of the atomic structure of this concoction is needed before nickel-embedded graphene can be used on a regular basis. To help with this challenge, researchers from the University of Texas at Austin recently simulated the catalytic mechanism and atomic structure of nickel-doped graphene using Comet at the San Diego Supercomputer Center (SDSC) and Stampede2 at the Texas Advanced Computing Center (TACC). The simulations showed a clear picture of the catalysts atomic structure so that researchers were able to better understand critical effects of surface change and hydrogen bonding, which were overlooked in previous models.
"Our work unveils the structure and mechanism underlying the performance of the catalyst - we found that the catalysis arises from the structure where the nickel atom is bonded with one nitrogen and three carbon atoms", stated Yuanyue Liu, an assistant professor of computational materials science at UT-Austin. "This structure can carry more charges than other hypothesized structures, and having more charges makes the electrochemical reaction faster, which means that the carbon dioxide can be converted to carbon monoxide with a higher rate."
Yuanyue Liu further explained that this reaction can be facilitated by hydrogen bonding between water and the polar intermediate species generated during reaction, making it more favourable over other competing reactions that do not produce polar intermediate.
"This study not only explained a long-standing puzzle for an important catalyst but also highlighted the critical roles of change capacity and hydrogen bonding, which can help elucidate the mechanisms of other heterogeneous electrocatalysts in water to enable better design", stated Yuanyue Liu.
Published last month in the Journal of The American Chemical Society , Yuanyue Liu and co-author Xunhua Zhao discussed their future plans to advance their studies on electrochemical reactions for energy conversion. Xunhua Zhao, a postdoctoral student at UT-Austin, explained the importance of utilizing supercomputers for this work.
"Our simulations required hundreds of CPUs running parallelly for tens of hours per calculation", stated Xunhua Zhao. "We relied heavily on Comet and Stampede2 to accurately model the complex processes of charge transfer and dynamically evolving hydrogen-bond networks."
Specifically, Yuanyue Liu and Xunhua Zhao used a molecular dynamics simulation technique based on quantum mechanics - an examination of molecular structure. They are now focused on collaborations with experimentalists to test their computational results.
This research was funded by National Science Foundation (1900039), the Welch Foundation (F-1959-20180324), and the Extreme Science and Engineering Discovery Environment (TG-CHE1900065).
Computer simulations reveal how water reacts with carbon dioxide, catalyzed by charged single nickel atom in graphene. Video Credit: Xunhua Zhao and Yuanyue Liu, UT- Austin.