Hämatitkristall von der Insel Hormus, Iran (Wikipedia)
Hydrogen production by solar water splitting in photoelectrochemical cells (PEC) has long been considered the holy grail of sustainable energy research. Iron oxide is a promising electrode material. An international team of researchers led by Empa, the Swiss Federal Laboratories for Materials Science and Technology, have now gained in-depth insights into the electronic structure of an iron oxide electrode - while it was in operation. This opens up new possibilities for an affordable hydrogen production from solar energy. Hematite, the mineral form of iron oxide (or trivially, rust), is a promising anode material for photoelectro-chemical cells (PEC) because of its affordability, availability, high stability and good spectral match to the solar spectrum. Although it has the potential of a 15% solar-to-hydrogen energy conversion efficiency, its actual efficiency is lower than that of other metal oxides. This is due to hematite's electronic structure, which only allows for ultrashort electron-hole excited-state lifetimes.
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