Eco News

A manganese-oxo complex catalyzes the electro-oxidation of water when suspended within the aqueous channels of a Nafion membrane. Click to enlarge.

An Australian-US research team led by Monash University has developed a bio-inspired water photo-oxidizing catalyst for the splitting of water into oxygen and hydrogen using solar energy. A paper on their work is published online in the journal Angewandte Chemie International Edition.

Professor Leone Spiccia, Robin Brimblecombe and Dr Annette Koo from Monash University teamed with Dr Gerhard Swiegers at the CSIRO Division of Molecular Science, Melbourne and Professor Charles Dismukes at Princeton University to develop a system that uses an anode coated with Nafion impregnated with a manganese-oxo complex with a cubic {Mn₄O₄}⁷⁺ core.

We have copied nature, taking the elements and mechanisms found in plant life that have evolved over 3 billion years and recreated one of those processes in the laboratory. A manganese cluster is central to a plant’s ability to use water, carbon dioxide and sunlight to make carbohydrates and oxygen. Man-made mimics of this cluster were developed by Professor Charles Dismukes some time ago, and we’ve taken it a step further, harnessing the ability of these molecules to convert water into its component elements, oxygen and hydrogen.

—Professor Spiccia

The researchers coated Nafion—a proton conductor also which is also the most widely used polyelectrolyte membrane in fuel cells—onto an anode to form a polymer membrane a few micrometers thick to act as the host for the manganese clusters.

Normally insoluble in water, when we bound the catalyst within the pores of the Nafion membrane, it was stabilized against decomposition and, importantly, water could reach the catalyst where it was oxidized on exposure to light. Whilst man has been able to split water into hydrogen and oxygen for years, we have been able to do the same thing for the first time using just sunlight, an electrical potential of 1.2 volts and the very chemical that nature has selected for this purpose.

—Professor Spiccia

Basic concept of the Monash system. Click to enlarge.

Testing revealed the catalyst assembly was still active after three days of continuous use, producing oxygen and hydrogen gas in the presence of water, an electrical potential and visible light.

Professor Spiccia said the efficiency of the system needed to be improved, but that it had potential for the clean generation of hydrogen on a large scale.

In July, researchers at MIT reported on their discovery of a new water-splitting catalyst that is prepared from earth-abundant materials (cobalt and phosphorous) and operates in benign conditions: pH neutral water at room temperature and 1 atm pressure. The cobalt-phosphorous catalyst targets the generation of oxygen gas from water; another catalyst generates the hydrogen. (Earlier post.)

Resources

• Robin Brimblecombe, Gerhard F. Swiegers, G. Charles Dismukes, Leone Spiccia (2008) Sustained Water Oxidation Photocatalysis by a Bioinspired Manganese Cluster.
  Angewandte Chemie International Edition doi: 10.1002/anie.200801132

• Water Oxidation Catalysts for Bio-Inspired Photoelectrochemical Cells (Spiccia research projects)

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