A team led by Thomas Nann and Christopher J. Pickett at the University of East Anglia (Norwich, UK) has introduced an efficient, robust photoelectrode made of common, inexpensive materials for the production of hydrogen by splitting water with sunlight. A paper on their work was published online 5 February in the journal Angewandte Chemie.
The new system consists of a gold electrode that is covered with layers of indium phosphide (InP) nanoparticles. The researchers then introduced an iron–sulfur complex, [Fe2S2(CO)6], into the layered arrangement. When submerged in water and irradiated with light under a relatively small electric current, this photoelectrocatalytic system produces hydrogen with an efficiency of 60%.
The UEA researchers have proposed the following mechanism for the reaction: The incoming light particles are absorbed by the InP nanocrystals and excite electrons within the InP. In this excited state, the electrons can be transferred to the iron–sulfur complexes.
In a catalytic reaction, the iron–sulfur complexes then pass their electrons on to hydrogen ions (H+) in the surrounding water, which are then released in the form of hydrogen (H2). The gold electrode supplies the necessary electrons to replenish the InP nanocrystals.
|“This relatively high efficiency is a breakthrough.”|
In contrast to current processes, the new system works without organic molecules. These must be converted into an excited state to react, which causes them to degrade over time. This problem limits the lifetime of systems with organic components. The new system is purely inorganic and lasts correspondingly longer.
Our newly developed photocatalytic electrode system is robust, efficient, inexpensive, and free of toxic heavy metals. It may be a highly promising alternative for industrial hydrogen production.—Thomas Nann
Thomas Nann et al. (2010) Water Splitting by Visible Light: A Nanophotocathode for Hydrogen Production. Angewandte Chemie International Edition doi: 10.1002/anie.200906262