Gradient doping of phosphorus in Fe2O3 nanoarray photoanodes for enhanced charge separation

Sunbathing nanorods split water

15 May 2017

A catalytic electrode developed by researchers at the Collaborative Innovation Center of Chemical Science and Engineering in Tianjin can harvest sunlight to split water into oxygen and hydrogen, a ‘green’ fuel.

The electrode bristles with iron oxide (hematite) rods roughly 200 nanometres long. Sunlight frees electrons in the hematite to leave positively-charged holes, generating a current. However, hematite itself is a poor conductor, and its electrons and holes tend to recombine too quickly to be useful. So the researchers seasoned the nanorods with phosphorus atoms, positioned so that their concentration gradually decreased from a few per cent at the surface to almost zero in the core. This gradient helps to separate electrons and holes, while the electron-rich phosphorus atoms improve the nanorods’ conductivity.

Coating these nanorods with cobalt phosphate helped further catalyse water splitting, raising the electrode’s overall efficiency to 0.32 per cent, more than six times higher than plain hematite.

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References

1. Chemical Science 8, 91–100 (2017). doi: 10.1039/c6sc03707k