Atomically Precise, Ligand-Stabilized Au25(SR)25 Nanocatalysts for Highly Efficient Electrochemical CO2 Reduction

Atomically precise Au₂₅(SR)₁₈ nanoclusters are exciting catalyst candidates for reactions like CO₂ reduction because they have an inherently anionic charge (q = -1), their surface structure is precisely known from single-crystal x-ray diffraction studies, and they bridge the size-gap between molecules and nanoparticles. One problem facing traditional electrocatalysts is the large overpotential typically required to convert CO₂ into useful products like CO, CH₄, CH₃OH, etc. Remarkably, we found the Au₂₅ nanocatalyst can promote the reduction of CO₂ into CO within 90 mV of the formal electrochemical potential (thermodynamic limit). This represents a ~300 mV improvement over larger Au nanoparticles and bulk Au. Peak CO₂ conversion occurred at -1V vs. the reversible hydrogen electrode with ~100% efficiency and rates ~7-700 times higher than larger Au catalysts and ~10-100 times higher than current state-of-the-art processes. Optical spectroscopy, non-aqueous electrochemistry and density functional theory (DFT) were used to study the Au₂₅-CO₂ interaction. Specifically, we found CO₂ adsorption was based on an electrostatic interaction with the Au₂₅ surface. Our studies indicate the low-voltage conversion of CO₂ was promoted by unique reaction centers at the Au₂₅ nanocatalyst surface.