Developing sustainable methods of hydrogen production can have significant environmental and energy efficiency benefits. A potentially viable way forward is to produce hydrogen from water by combining solar energy and heterogeneous catalysts. Our results indicate that sub-nm gold particles can provide an enormous enhancement in photocatalytic hydrogen production under visible light. We have observed a 35 times increase in activity for Au modified CdS as compared to that of unmodified catalyst. This activity was much higher than that of any other co-catalysts tested, which included 2-4 nm Pt, Ru, Pd and Rh nanoparticles modified CdS. The activity of sub-nm Au was also much better than that of CdS modified with larger Au particles. Our first-principles calculations of unsupported Au clusters indicated that there is a substantial difference in both shape and electronic properties between charged and neutral bare Au clusters as well as between bare and ligand-protected ones. This is the first ever demonstration of the remarkable potential of sub-nm Au particles for H-2 production. (C) 2012 Elsevier B.V. All rights reserved.