The evolution from hydrocarbon-based energy sources to renewable and sustainable clean ones is a top priority worldwide due to the severe effects of pollution endangering public health and the environment and the exponential demand from emerging countries. A hydrogen-based energy source [1,2] is ideal as it produces zero carbon emission (only water), and consumer hydrogen fuel cell-powered cars and trucks as well as buses are already available in our societies. Unfortunately, most of the hydrogen industrially produced nowadays still comes from nonrenewable sources, made by steam reforming of methane which produces significant amount of carbon mono/dioxide.

The most natural and cleanest way to sustainably produce hydrogen at large scale is by splitting seawater photocatalytically. Consequently, a great increase in research during the past decade, with dedicated studies on material design, surface and electronic structure engineering have been conducted to identify ideal materials and systems [1,3,4].

Our approach consists of fabricating heteronanostructures featuring oriented arrays of quantum rods and dots of high purity synthesized by low cost aqueous chemical growth at low temperature without surfactant and with controlled dimensionalities and surface chemistry [5,6] with intermediate bands for high visible-light conversion, bandgap and band edges optimized for stability against photocorrosion and operation conditions at neutral pH and low or no bias without sacrificial agent [7].

Such unique characteristics, combined with the in-depth investigation of their size-dependent [8], surface [9], doped [10] and bulk electronic structure [11], and electrical conductivity [12] effects do provide better fundamental understanding and structure-efficiency relationships for a cost-effective and sustainable generation of clean hydrogen from the two most abundant and geographically-balanced free resources on earth’s surface, the sun and seawater.

An overview of the past decades progress along with the latest advances in controlled fabrication of highly ordered hybrids consisting of visible-light active semiconductors and molecular co-catalysts [13], the atomic-scale origin of performance and stability of gallium nitrides [14] for overall unassisted water splitting in pure water and seawater [15] as well as the latest development in highly efficient single junctions for solar hydrogen generation without transparent substrates will be presented.

References

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