Nanowire-Nanoparticle Conjugate Photolytic Fuel Generators

Background

Conversion of sunlight to chemical fuels by artificial photosynthesis has been a long-sought goal. In particular, significant research activity was stimulated towards photolytic cells producing hydrogen in 1972, when Fujishima and Honda demonstrated water could split to hydrogen and oxygen under sunlight (photolysis) using an n-type TiO2 electrode. Although nanostructured TiO2 photolytic cells exploiting high surface to volume have recently been demonstrated, unfortunately TiO2 can absorb only the ultraviolet portion of the sunlight due to its large band gap. Numerous efforts to increase light absorption with non-oxide semiconductor having lower band gaps or using sensitizers resulted in photodecomposition. An equally important challenge has been to establish efficient charge transfer, so photogenerated electrons and holes can drive reduction and oxidation reactions, respectively, and store their energy as chemical energy rather than thermalize through recombination.

Summary

A novel physical mechanisms, structural architecture and fabrication technique for the realization of a novel fuel-generating photolytic device. This device consists of a low band gap oxide semiconductor nanowire decorated with metal nanoparticles.

Potential Applications

Fabrication of novel fuel-generating (e.g. hydrogen) photolytic devices consisting of low band gap oxide semiconductor nanowires decorated with metal nanoparticles.

Main Advantages

• Low-cost, high photolytic conversion energy and stability by making use of multifunctional nanostructures with unique electronic, photonic, and plasmonic attributes at the nanoscale.
• Plasmonic metal nanoparticles decorating the nanowire serve as near-filed concentrators enhancing absorption of light in the semiconductor nanowire.
• The plasmonic nanoparticles also couple the incident radiation to the waveguide modes of the nanowires in the direction of the wire axis, maximizing optical absorption.
• A further role of the nanoparticles is in separation of electron/hole pair. They collect the photogenerated electrons efficiently by virtue of their being a high work function metal before channeling them to the reduction reaction. This aspect differs from having a counter metal electrode (cathode) in a bulk photolytic cell, where a semiconductor/cathode interface is absent.
• Low-cost and scalable technology, simply by fabricating and utilizing the nanowire-nanoparticle conjugate devices in the form of a suspension (e.g., in water) using solution chemistry.

Stage of development

Prototype is available.