The transition from hydrocarbon-based energy sources to renewable and sustainable clean ones has become a top priority worldwide due to the severe effects of pollution endangering public health and the environment. A hydrogen-based energy source is ideal as it produces zero carbon emission (only water), and consumer hydrogen fuel cell powered cars as well as public transportation are becoming available in our societies. Yet, most of the hydrogen produced nowadays still comes from nonrenewable sources, made by steam reforming of natural gas which produces carbon mono/dioxide. The most natural and cleanest way to sustainably produce hydrogen at large scale is by splitting water. 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^[1,2].

Our strategy is to fabricate heteronanostructures consisting of oriented arrays of quantum rods and dots of high purity synthesized by aqueous chemical growth at low temperature without surfactant and with controlled dimensionalities and surface chemistry^[3,4] 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 bias without sacrificial agent^[5]. Such unique characteristics, combined with the in-depth investigation of their size-dependent^[6], interfacial^[7] electronic structure^[8], and conductivity^[9] effects do provide better fundamental understanding and structure-efficiency relationships for a cost-effective and sustainable generation of hydrogen from the two most abundant and geographically-balanced free resources, the sun and seawater.

Latest advances in controlled fabrication of highly ordered hybrids consisting of a visible light active semiconductor and a molecular co-catalyst^[10], the atomic-scale origin of performance and stability of nitride nanorod-arrays^[11] for overall water splitting in neutral and simulated seawater^[12] and the latest development in highly efficient single junctions for solar hydrogen generation without transparent substrates will be presented.

References

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• [2] C. X. Kronawitter et al, Energy Environ. Sci. 7, 3100 (2014); ibid 4, 3889 (2011)
• [3] L. Vayssieres, J. Phys. Chem. C 113, 4733 (2009); Int. J. Nanotechnol. 2, 411 (2005)
• [4] L. Vayssieres, Appl. Phys. A 89, 1 (2007); Angew. Chem. Int. Ed. 43, 3666 (2004); Adv. Mater. 15, 464 (2003); J. Phys. Chem. B 107, 2623 (2003); Chem. Mater. 13, 4395 (2001); Chem. Mater. 13, 233 (2001); J. Phys. Chem. B 105, 3350 (2001); Pure Appl. Chem. 72, 47 (2000)
• [5] On Solar Hydrogen & Nanotechnology, L. Vayssieres ed. (Wiley, 2010), Ch. 17, pp. 523-558
• [6] L. Vayssieres et al, Appl. Phys. Lett. 99, 183101 (2011); Adv. Mater. 17, 2320 (2005)
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• [8] C. X. Kronawitter et al, PhysChemChemPhys 15, 13483 (2013); C. L. Dong et al, Phys. Rev. B 70, 195325 (2004); J.-H. Guo et al, J. Phys.: Condens. Matter 14, 6969 (2002)
• [9] J. Engel et al, Adv. Funct. Mater. 24, 4952 (2014)
• [10] Y.K. Wei et al, Nano Res. 9, 1561 (2016)
• [11] M.G. Kibria et al. Adv. Mater. 28, 8388 (2016)
• [12] X.J. Guan et al. J. Phys. Chem. C (2018) Special issue dedicated to Prof. Prashant Kamat