Ligand‐Protected Au 55 with a Novel Structure and Remarkable CO 2 Electroreduction Performance

A Au 55 nanocluster with the composition of [Au 55 (p‐MBT) 24 (Ph 3 P) 6 ](SbF 6 ) 3 (p‐MBT=4‐methylbenzenethiolate) is synthesized via direct reduction of gold‐phosphine and gold‐thiolate precursors. Single‐crystal X‐ray diffraction reveals that this Au 55 nanocluster features a face‐centered cubic (fcc) Au 55 kernel, different from the well‐known two‐shell cuboctahedral arrangement in Au 55 (Ph 3 P) 12 Cl 6 . The Au 55 cluster shows a wide optical absorption band with optical energy gap ( E g =1.28 eV). It is found that the exclusion of chloride is crucial for the formation of the title cluster, otherwise rod‐like [Au 25 (SR) 5 (PPh 3 ) 10 Cl 2 ] 2+ is obtained. The strategy to run synthetic reaction in the absence of halide leads to new members of phosphine/thiolate co‐protected metal nanoclusters. The Au 55 nanocluster exhibits high catalytic activity and selectivity for electrochemical reduction of CO 2 to CO; the Faradaic efficiency (FE) reaches 94.1 % at −0.6 V vs. reversible hydrogen electrode (RHE).