Bimetallic Au-Cu Nanocatalysts with Enhanced Electrochemical CO2 Conversion Activity

Wednesday, 31 May 2017: 09:00
Grand Salon A - Section 6 (Hilton New Orleans Riverside)
D. R. Kauffman, D. R. Alfonso (National Energy Technology Laboratory), and D. Tafen (National Energy Technology Laboratory, AECOM)
Converting waste CO2 emissions into value added chemicals and fuels is one approach to mitigating greenhouse gases and reducing the carbon footprint of fossil-fuel processes. The electrochemical CO2 reduction reaction (CO2RR) is a promising carbon mitigation strategy because it can operate at high reaction rates and excellent efficiency at ambient conditions using environmentally friendly aqueous electrolytes. Moreover, the ability to couple carbon-free electricity sources (wind, solar, etc.) enables "carbon neutral" or "carbon negative" technologies that convert CO2into value added products without producing additional emissions.

We’ve combined experimental and computational techniques to characterize the catalytic activity of 2-3 nm, bimetallic gold-copper nanoparticles (NPs) for CO2RR. The catalysts showed composition-dependent CO2RR activity that exceeded both the parent gold and copper metals. Interestingly, the bimetallic NPs produced only CO and H2, whereas bulk, polycrystalline copper also produced methane and ethylene. Electrocatalytic activity studies identified 21% Cu NPs as the most active composition with reaction turnover (TOF) frequencies exceeding 60 s-1 and Faradaic Efficiencies approaching 100% FE at -1.0V vs. RHE. The enhanced activity indicates a synergistic effect upon diluting gold atoms in copper. Laboratory and synchrotron-based X-ray spectroscopies were coupled with density functional theory (DFT) to confirm Au-Cu charge transfer within the NPs and identify mixing between near Fermi-level electronic states. We found a strong correlation between the experimentally-determined TOFs and the computationally-predicted binding energy of key reaction products. The superior performance of 21% Cu NPs stemmed from facile desorption of reaction products and extremely weak H binding. This study shows that atomic composition can be used to tune the electronic structure and chemical reactivity of small bimetallic NPs.