Electrocatalytic CO2 Reduction with Atomically Precise Au13 Nanoclusters: Effect of Ligand Shell on Catalytic Performance

Supported gold nanoclusters of the formula Au13(L)5Cl23+ where L = N-heterocyclic carbene (NHC) or phosphine ligands are examined in the electrocatalytic CO2 reduction reaction (eCO2RR) in a membrane electrode assembly cell configuration. Gold nanoclusters bearing bisNHC ligands are shown to exhibit improved catalytic performance compared with diphosphine-stabilized nanoclusters after activation at the optimum treatment temperatures. The thermal properties of the nanoclusters are shown to have a significant impact on their catalytic activity. Thermogravimetric analysis, UV–vis absorption spectroscopy, and X-ray photoelectron spectroscopy revealed that thermal treatment of Au13(diphosphine)5Cl23+ nanoclusters results in complete loss of diphosphine ligands while Au13(bisNHC)5Cl23+ nanoclusters show stepwise and partial removal of bisNHC ligands. We propose that the partial removal of bisNHC ligands enables efficient activation of Au13(bisNHC)5Cl23+ clusters while conserving the core structure. This leads to the implication that intact clusters retaining at least some ligands in their coordination environment are more active than ligand-free clusters.