Quantum rods and dots-based structures & devices: Low cost aqueous synthesis and bandgap engineering for solar hydro
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Quantum rods and dots-based structures & devices: Low cost aqueous synthesis and bandgap engineering for solar hydrogen and solar cells applications Lionel Vayssieres International Center for Materials NanoArchitectonics, National Institute for Materials Science, Namiki 1-1, Tsukuba, 305-0044 Japan ABSTRACT If one considers the largest and geographically balanced free natural resource available on Earth, that is seawater, and that more sunlight energy is striking our blue planet in one hour than all of our annual energy consumption, the direct solar-to-hydrogen conversion by photooxidation of seawater is a very straightforward and attractive solution for the production of hydrogen, as it is clean, sustainable and renewable. It offers an alternative solution to fossil-fuelbased energy sources and explains the tremendous interest in renewable, sustainable energy sources and materials for energy conversion. However, the materials requirements for water splitting and thus the direct solar-to-hydrogen generation are drastic. The materials must be stable in water, which rules out many classes of materials. They must also be stable under illumination against photocorrosion and their bandgap must be small enough to absorb visible light, but large enough not to “dissolve” once illuminated. Finally, their band edges must be positioned below and above the redox potential of hydrogen and oxygen, respectively. Bandgap energy and band-edge positions, as well as the overall band structure of semiconductors are of crucial importance in photoelectrochemical and photocatalytic applications. The energy position of the band edges can be controlled by the electronegativity of the dopants and solution pH, as well as by new concepts such as quantum confinement effects and the fabrication of novel hetero-nanostructures. Fulfilling those requirements while keeping the cost of the materials low is a tremendously difficult challenge, which explains why solar hydrogen generation is still in its infancy. Novel approach and latest development combining low cost aqueous synthesis techniques, vertically oriented metal oxide nanorods and quantum confinement effects probed by x-ray spectroscopies from synchrotron radiation is presented leading to stable and cost-effective visible-light-active semiconductors for seawater splitting, the holy grail of photocatalysis. INTRODUCTION Meeting the future demand of energy (which should double by 2050) and managing the environmental consequences of energy production is of major importance nowadays with the rise of emerging highly populated countries such as India and China. Considering that more energy of sunlight is striking earth in an hour than all of the energy consumed by humans in a year offers an alternative solution to fossil fuels-based energy source and explains the tremendous interest in renewable sustainable energy source and materials for energy conversion. Thus, finding new ways to power the future by making safer energy without creating extra CO2 in the atmosphere to reduce urban air pollution a
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