Center for Functional Nanomaterials Seminar

Photocatalytic water splitting, i.e., artificial photosynthesis, has been actively studied as a promising way for solar energy harvesting and storage. Despite much effort in the past decades, reported energy conversion efficiencies remain low, and the most significant challenge is to develop stable photocatalyst materials that can effectively utilize solar spectrum. In this presentation I will discuss a photocatalyst model system based on cross-linked n-type TiO2 nanowire thin films, in which several strategies are explored to significantly improve the energy conversion efficiency. Under simulated AM 1.5 G illumination, a solar energy conversion efficiency of 1.05% is achieved, setting a new record for undoped TiO2 photocatalysts. The high surface area architecture afforded by the cross-linked TiO2 nanowires enables both long optical path lengths and high photon-to-electron conversion efficiency. At 350-nm excitation, incident photon-to-current efficiency (IPCE) reaches 90%. The device also exhibits photocurrent under visible light due to sub-band gap absorption. I will present a way to exploit this sub-band gap absorption, using the local field enhancement of plasmonic (gold or silver) nanoparticles to enhance optical absorption in the semiconductor photocatalyst. Finally, I will discuss other potentially important strategies including band structure engineering and light trapping in thin film photocatalysts using photonic and plasmonics nanostructures.