Ag-Au nanoparticles encapsulated inside porous hollow carbon nanospheres: a molecular dynamics study

Increasing interest has been seen for the new kinds of complex structure, yolk-shell and nanorattles, in which the properties of hollow and core-shell structures have been combined. It has also been reported that small bimetallic nanoclusters in hollow carbon spheres show outstanding catalytic performances. Therefore, we have simulated bare Ag/Au nanoclusters and Ag/Au nanoclusters encapsulated into hollow carbon spheres (AgAu@C) with various structures (core-shell, hollow core-shell, rattle core-shell, and alloy nanoclusters) from 300 to 700 K. To investigate the stability of the different nanoclusters, we have calculated the structural stability parameters and the strain distributions among the cores and shells of the different structures. We have also investigated the radial chemical distribution functions (RCDFs) and the radial distribution functions (RDFs) of the different nanoclusters to further study the structures of the cluster atoms. The results indicated that the relative stability of the bare Ag/Au nanoclusters at 300 K is in the order: alloy rattle core-shell > core-shell > hollow core-shell. By increasing the temperature up to 500 K, the stability trend of the nanoclusters changes and the hollow core-shell nanocluster shows a higher stability than the other clusters because of the occupation of its hollow core. The relative stability of the supported nanoclusters, AgAu@C, is almost the reverse throughout the temperature range: hollow core-shell@C > core-shell@C alloy@C > rattle core-shell@C. These results mean that the carbon capsulation of the nanoclusters is an effective way of stabilizing the unstable clusters, especially the hollow core-shell clusters.