Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

Unique tripodal S-donor capping agents with an attached carboxylate are found to bind tightly to the surface of CdSe nanocrystals (NCs), making the latter water soluble. Unlike that in similarly solubilized CdSe NCs with one-sulfur or two-sulfur capping agents, dissociation from the NC surface is greatly reduced. The impact of this behavior is seen in the photochemical generation of H-2 in which the CdSe NCs function as the light absorber with metal complexes in aqueous solution as the H-2-forming catalyst and ascorbic acid as the electron donor source. This precious-metal-free system for H-2 generation from water using [Co(bdt)(2)](-) (bdt, benzene-1,2-dithiolate) as the catalyst exhibits excellent activity with a quantum yield for H-2 formation of 24% at 520 nm light and durability with >300,000 turnovers relative to catalyst in 60 h.