We’ve coupled experimental and computational techniques to characterize the electronic structure and catalytic activity of 2-3 nm gold-copper nanoparticles for the electrochemical CO2 reduction reaction (CO2RR). This reaction is a promising carbon mitigation strategy because it can operate at high reaction rates and excellent efficiency at ambient conditions and in environmentally friendly aqueous electrolytes. Moreover, the ability to couple carbon-free electricity sources (wind, solar, etc.) enables carbon negative technologies that convert CO2 into value added products without producing additional emissions. Our bimetallic Au-Cu NPs contained between 0-44% Cu and showed composition-dependent electronic structure and CO2RR activity that surpassed the parent metals. Laboratory and synchrotron-based X-ray spectroscopies were coupled with density functional theory (DFT) to confirm that Au-Cu charge transfer stabilized Cu+ species within the NPs and identify strong mixing between near Fermi-level electronic states. The Au-Cu NPs demonstrated NIR photoluminescence (PL) that shifted to longer wavelengths with increasing Cu content. Sulfur L-edge X-ray absorption spectroscopy indicated Cu heteroatoms introduced new states NP electronic structure that directly impacted Au-Cu PL energy. Electrocatalytic activity studies identified 20% Cu NPs as the most active composition with maximum reaction turnover (TOF) frequencies and Faradaic Efficiencies (FE) approaching 75 s-1 and 100% FE, respectively. We found a strong correlation between the experimentally-determined TOFs and the computationally-predicted binding energy of key reaction products. A volcano plot comparing TOF and product binding energy suggest superior performance of 21% Cu NPs stemmed from facile desorption of the CO reaction product 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.

Bimetallic Au-Cu nanocatalysts for enhanced electrochemical CO2 conversion

253rd National Meeting (2017)

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