A Heteroleptic Gold Hydride Nanocluster for Efficient and Selective Electrocatalytic Reduction of CO 2 to CO.

It has been a long-standing challenge to create and identify the active sites of heterogeneous catalysts, because it is difficult to precisely control the interfacial chemistry at the molecular level. Here we report the synthesis and catalysis of a heteroleptic gold trihydride nanocluster, [Au 22 H 3 (dppe) 3 (PPh 3 ) 8 ] 3+ [dppe = 1,2-bis(diphenylphosphino)ethane, PPh 3 = triphenylphosphine]. The Au 22 H 3 core consists of two Au 11 units bonded via six uncoordinated Au sites. The three H atoms bridge the six uncoordinated Au atoms and are found to play a key role in catalyzing electrochemical reduction of CO 2 to CO with a 92.7% Faradaic efficiency (FE) at -0.6 V (vs RHE) and high reaction activity (134 A/g Au mass activity). The CO current density and FE CO remained nearly constant for the CO 2 reduction reaction for more than 10 h, indicating remarkable stability of the Au 22 H 3 catalyst. The Au 22 H 3 catalytic performance is among the best Au-based catalysts reported thus far for electrochemical reduction of CO 2 . Density functional theory (DFT) calculations suggest that the hydride coordinated Au sites are the active centers, which facilitate the formation of the key *COOH intermediate.