Core/shell-structured bimetallic nanocluster catalysts for visible-light-induced electron transfer*

It has been found that the bimetallic nanoclusters often have so-called core/shell structure if they are prepared by alcohol-reduction of two kinds of noble metal ions in the presence of a water-soluble polymer like poly(N-vinyl-2-pyrolidone)(PVP), and that the core/ shell structured bimetallic nanoclusters have much higher catalytic activity than the corresponding monometallic nanoclusters. Here, several kinds of monometallic and bimetallic nanoclusters are synthesized by the similar method, and the catalyses are measured. Thus, the colloidal dispersions of Au, Pt, Pd, Rh, and Ru monometallic, and Au/Pt, Au/Pd, Au/Rh, and Pt/Ru bimetallic nanoclusters were synthesized and applied as the catalysts for visiblelight-induced hydrogen generation. The core/shell structures are analyzed mainly by UV–vis spectra. The rate of electron transfer from the methyl viologen cation radical to the metal nanoclusters is proportional to the hydrogen generation rate at the steady state. All the electrons accepted by the metal nanoclusters are used for the hydrogen generation. Both electron transfer and hydrogen generation rates increase when the bimetallic nanoclusters are used in place of the corresponding monometallic nanoclusters. The most active catalysts were Au/Rh and Pt/Ru bimetallic nanoclusters.