Ligand-Protected Au55 with a Novel Structure and Remarkable CO2 Electroreduction Performance.

In this work, a novel Au 55 nanocluster with the composition of [Au 55 (p-MBT) 24 (Ph 3 P) 6 ](SbF 6 ) 3 (p-MBT = 4-methylbenzenethiolate) has been 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 proposed by Schmid et al. 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 presence of no halide opens the door 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, and the Faradaic efficiency (FE) reaches 94.1% at -0.6 V vs reversible hydrogen electrode (RHE).