Atomically Precise Au25 Nanoclusters for Efficient Electrochemical CO2 Conversion

Two problems facing traditional electrocatalysts are large overpotentials and poor product selectivity. Atomically precise, ligand-stabilized Au₂₅ nanoclusters are exciting catalyst candidates for reactions like CO₂ reduction because they have an inherent negative charge, their crystallographic surface structure is precisely known, and they bridge the size-gap between molecules and nanoparticles. Remarkably, the Au₂₅ nanocatalysts promoted the reduction of CO₂ into CO within 100 mV of the electrochemical formal potential (thermodynamic limit). This represents an approximate 200-300 mV improvement over larger Au nanoparticles and bulk Au. Peak CO₂ conversion occurred at -1 V vs. the reversible hydrogen electrode with ~100% efficiency and rates 7-700 times higher than larger Au catalysts and 5-100 times higher than current state-of-the-art processes. Optical spectroscopy, non-aqueous electrochemistry and density functional theory studied the Au₂₅-CO₂ interaction. Our data suggests CO₂ adsorption facilitated through and electrostatic interaction with Au₂₅, while the highly efficient conversion of CO₂ into CO was promoted by the clusters negative charge. Ongoing efforts include electrode optimization, and long term stability testing of the Au₂₅^- nanocatalysts.  The Au₂₅^- clusters show reaction turnover frequencies of approximately 70-100 molecules/Au₂₅/s and stable operation in excess of 24 hours at -1 V. This work was published in the Journal of the American Chemical Society 2012, 134, 10237-10243; electronic DOI: 10.1021/ja303259q.