Materials Discovery, Theory, and Characterization of Intermetallics for Electrochemical CO2 Reduction
Jeremy T. Feaster, Daniel A. Torelli, Zachary W. Ulissi, Maryam Farmand, Sean W. Fackler, Jeffrey W. Beeman, Apurva Mehta, Ryan Davis, Alan T. Landers, John C. Lin, Drew C. Higgins, Sonja A. Francis, J. Chance Crompton, Alnald Javier, Jonathan R. Thompson, Michael T. Tang, Jianping Xiao, Xinyan Liu, Mohammadreza Karamad, Robert Sandberg, Karen Chan, Christopher Hahn, Bruce S. Brunschwig, Manuel P. Soriaga, Walter S. Drisdell, Junko Yano, Thomas F. Jaramillo, Nathan S. Lewis, Jens K. Nørskov
Despite the explosive growth of renewable sources of electricity, making hydrocarbon building blocks and high energy density fuel sources in a renewable fashion is a major challenge. The challenge lies in designing catalysts to perform this hydrogenation selectively in solution. This joint experimental-theoretical work presents the first material with better performance for this reaction than copper, and has required contributions from materials discovery, first-principles theory, and operando characterization at the Joint Center for Artificial Photosynthesis.
Our team started with a nickel-gallium intermetallic catalyst known to be active for thermal CO hydrogenation. Nickel-gallium thin films of various stoichiometries were found to reduce CO2 to methane, ethane, and ethylene, at overpotentials lower than the best polycrystalline catalyst, copper. Ex-situ characterization was carried out before and after catalysis to demonstrate the stability of the catalysts. It was found that even after long-term polarizations both Ni and Ga are present on the surface and contribute to the observed activity. These experiments raised two questions: what was the active site of these new catalysts, and why did existing theoretical screens not capture their activity for electrochemical CO2 reduction? Answering these questions required modeling the many diverse active sites on these polycrystalline bimetallic samples. Adsorption sites for every stable facet were cataloged. Using machine learning methods, we inferred that most of these facets had similar activity to Ni surfaces but that a few exposed Ni sites surrounded by Ga atoms had a favorable on-top CO configuration with improved kinetics. This motif emerged from the predictive modeling and suggested that these surfaces represent a new class of intermetallic CO2 reduction catalysts. Finally, we used operando grazing incidence x-ray absorption and diffraction characterization at the Stanford Synchrotron Radiation Lightsource to compare theoretical and measured reaction rates. These techniques show that kinetically trapped surface oxide species exist at reducing potentials and confirm that the surface structure changes at different reaction conditions. These results provide the foundation for our team at JCAP to screen, characterize, and deploy new catalysts for the most challenging electrochemical reactions.
JCAP student and postodoc team won 2017 Team Science Contest at 2017 EFRC-Hub-CMS Principal Investigators’ Meeting in Washington, D.C. on July 24-25, 2017.
Each Director was invited to nominate a team of two or more graduate student and/or postdoctoral researchers to present a joint talk about their center research that included both theory and experiment. The DOE EFRC, Hub, and CMS management teams selected 16 finalists from more than 25 nominations. At the meeting, teams of DOE program managers selected the top six teams based on how well the research exemplified the opportunities provided by the center funding modality, scientific excellence, integration of theory and experiment, topical diversity, and quality of the presentation. The winners received an award certificate from Harriet Kung, Associate Director of the DOE Office of Basic Energy Sciences, during a ceremony at the end of the meeting.