Credit: © 2008 AAAS

As the world's energy demands continue to grow, the search for clean and renewable sources is becoming increasingly important. Harnessing the power of the Sun is particularly appealing, but the widespread adoption of this technology requires simple and effective methods for storing solar energy. Now, inspired by how nature uses photosynthesis to convert sunlight into chemical fuel, researchers in the USA have developed1 a catalyst that can split water to produce oxygen and hydrogen.

Daniel Nocera and Matthew Kanan from MIT used electrolysis to generate an oxygen-evolving catalyst from aqueous solutions containing cobalt(II) ions and a phosphate buffer. The catalyst forms in situ as a dark film on an indium tin oxide anode, and although its exact chemical make-up has not yet been determined, analytical techniques suggest that it is cobalt oxide or hydroxide containing large amounts of phosphate. The mechanism of action of the catalyst has yet to be established, but almost certainly involves cycling between Co(II), Co(III) and Co(IV) oxidation states. The catalyst oxidizes water to produce O2 and hydrogen ions that are carried off to the cathode in the form of hydrogen phosphate anions (HPO42−).

The catalyst works at neutral pH under ambient conditions and the materials used by Nocera and Kanan are abundant and relatively inexpensive. Moreover, the electric current needed to drive the electrolysis could potentially be provided by a photovoltaic cell, enabling water-splitting reactions to be powered by sunlight.