Professor Matthew Kanan of the Department of Chemistry at Stanford University is supported by the Chemical Catalysis program of the Division of Chemistry to investigate a new design principle for catalysts that use electrical energy to convert carbon dioxide (CO2) into useful chemicals. These catalysts are of interest for applications in renewable energy storage and for making chemicals from CO2 instead of petroleum. The research focuses on materials known as metal nanoparticles (NPs), which are tiny pieces of metal with dimensions ranging from about 1 to 100 nanometers (ca. 5-50 atoms). The aim is to investigate how a particular type of defect in these particles, known as grain boundaries, affect catalysis. Grain boundaries provide unusual surface structures and catalytic properties that are often different from defect-free surfaces. The research aims to probe these unusual structures and to elucidate how they impact CO2 catalysis. In addition, metal NPs are widely used as catalysts for many industrially important, high-volume chemical reactions and this research may lead to improvements in those applications. On the educational front, CO2 recycling is being incorporated into educational material to enhance student awareness of the global carbon cycle, the formation of fossil fuels, and the flux of CO2 into the atmosphere from fossil fuel combustion.
The research encompasses two synergistic objectives: i) characterize grain boundary surface terminations on metal NPs with atomic-level resolution to assess the possible surface sites for catalysis ii) elucidate grain boundary-activity relationships in metal catalysts with different grain boundary densities and geometries. The structures of grain boundaries and their surface terminations are probed using a combination of high-resolution transmission electron microscopy, electron diffraction, and molecular dynamics simulations. Catalysts spanning a range of grain boundary densities and character distributions are prepared using established synthetic methods as well as new methods developed in this research. These properties are correlated to the CO2 electroreduction activity to establish quantitative grain boundary-activity relationships.
