Metal nanoclusters with a core size smaller than 2 nm have attracted much attention because of their unique physical and chemical properties.Among the studied metal nanoclusters,gold and silver have been studied extensively by size-controlled synthesis, structural characterization and properties investigations.Recently,considerable research effort has been devoted to the investiga- tion of copper nanoclusters.In this review,we highlight recent progress in the study of copper nanoclusters in terms of synthesis methods,characterization techniques and their novel optical and catalytic properties.
By using 2-mercapto-5-n-propylpyrimidine(MPP)as capping ligands,copper nanoclusters with different core sizes were prepared using a chemical reduction method.The as-prepared copper nanoclusters were loaded onto a glassy carbon electrode and their size effect on the electrocatalytic activity towards the oxygen reduction reaction(ORR)was investigated with electrochemical techniques in alkaline electrolyte.Cyclic voltammetric(CV)studies showed that the onset potential of ORR on smaller copper nanoclusters is more positive than that on larger copper nanoclusters.Compared to the larger clusters,higher current density of ORR was obtained using the smaller copper nanoclusters.These CV results indicate that the smaller Cu nanoclusters exhibit higher catalytic performance for ORR.In rotating-disk voltammetric studies,ORR on the synthesized MPP monolayer-protected copper nanoclusters is mainly dominated by a two-electron transfer pathway to produce H_(2)O_(2).
