Improving Hematite's Solar Water Splitting Efficiency by Incorporating Rare-Earth Upconversion Nanomaterials.

Confounded by global energy needs, much research has been devoted to convert solar energy to various usable forms, such as chemical energy in the form of hydrogen via water splitting. Most photoelectrodes, such as hematite, utilize UV and visible radiation, whereas ∼40% infrared (IR) energy remains unconverted. This work represents our initial attempt to utilize IR radiation, that is, adding rare-earth materials to existing photoelectrodes. A simple substrate composed of hematite film and rare-earth nanocrystals (RENs) was prepared and characterized. Spectroscopy evidence indicates that the RENs in the composite absorb IR radiation (980 nm) and emit at 550 and 670 nm. The emitted photons are absorbed by surrounding hematite films, leading to improvement of water splitting efficiency as measured by photocurrent enhancement. This initial work demonstrates the feasibility and concept of using RENs for utilizing more solar radiation, thus improving the efficiency of existing solar materials and devices.