Cobalt-based derivative catalyses oxidation of water

The new catalyst (right) has a lattice structure similar to Prussian blue (left)

Prussian blue has been used for over 300 years as a pigment in dyes and an antidote to heavy metal poisoning. Now, researchers say it could help improve water splitting ‘artificial leaf’ technology, thanks to the catalytic activity of a cobalt-containing derivative.

The pigment’s famously complicated structure features a cubic arrangement of iron and hexacyanoferrate ions. The iron is readily substituted for other metal cations, which allows it to mop up toxic caesium and thallium ions in the body. A team led by José Ramón Galán-Mascarós at the Institute of Chemical Research of Catalonia, Spain, have found that substituting the iron for cobalt transforms Prussian blue into a promising catalyst.

Electrodes coated with cobalt hexacyanoferrate catalyse the oxidation of water, the energy-demanding first step in the water splitting reaction. Any artificial photosynthetic device must master this process, so finding a fast, efficient catalyst is crucial. The team say their Prussian blue-based catalyst works just as well as state-of-the art metal oxide catalysts, as well as being transparent, low density and stable at neutral pH and room temperature.