Stability and Activity of Bimetallic Tips as Reduction Co-Catalysts

The search for alternative clean and renewable energy source is a major pressing issue. One promising direction is the use of semiconductor nanoparticles as photocatalysts which absorb the solar radiation and produce hydrogen from water. Upon radiation, excited electrons and holes are created. They then migrate to the surface and react with the aqueous solution. Efficient photocatalysts should maintain charge separation of hole and electron and contain different sites for oxidation and reduction. Usually a small metallic particle is deposited on the semiconductor as a co-catalyst which acts as an electron sink and a reduction site for protons. Hybrid core-shell structures such as CdS@CdSe increase the charge separation and reduce the particle dissolution by confining the holes to the core and leaving the electrons delocalized over the entire structure. A bi-metallic co-catalyst composed of metals such as gold and palladium should improve the photocatalytic activity of the system. Such bimetallic particles possess the ability to attract electrons from the semiconductor and discharge them into the aqueous solution more efficiently then each of the metals on their own. Here we use the CdSe@CdS-Au\Pd system as a case study to explore the effect of the inner structure of the bimetallic tip on the photocatalytic performance. In addition we study the dynamic processes which occur during photocatalysis using both high resolution EDS imaging and online photocatalytic measurements.