Hydrogen cell catalyst modeled on photosynthetic organisms
Aug. 28, 2008
Hydrogen shapes up to become one of the most important fuels for the future, but scientists need to overcome substantial hurdles to enable an efficient production of hydrogen. We increasingly hear about ideas that suggest that future engines in fact may be able to run on water, breaking down water into oxygen and hydrogen right where it is needed. This process requires significant input energy, which, according to scientist could be provided by sunlight.
The production of hydrogen and implications of the amount of energy that is required to create it has been met with lots of skepticism, especially if the burning of fossil fuels is involved. Scientists from Monash Univ., in Australia, the Commonwealth Scientific and Industrial Research Organization in Australia and Princeton Univ. in the U.S., however, believe they can completely circumvent fossil fuels by applying photolysis, a method to split water using the energy contained in light.
According to an article published in the German journal Angewandte Chemie, the research group claims that has developed a catalyst that “effectively catalyzes” one of the necessary half reactions required by this process, the photooxidation of water representing an anodic half-cell. The catalyst is a manganese-containing complex modeled after those found in photosynthetic organisms, the scientists say.
The basic idea behind creating hydrogen is electrolysis, which is described as the reverse of the process that can be seen in a battery—electrical energy is converted in chemical energy and the goal, of course, is to do this in the most efficient way possible. Electrolysis consists of two half reactions: At the cathode, protons (positively charged hydrogen ions) are reduced to hydrogen, whereas the oxidation of water produces oxygen at the anode. Sunlight and photocatalysts are believed to hold one key to jumpstart this process.
The scientists said they used a manganese oxo complex with a cubic core made of four manganese and four oxygen atoms capped by ancillary phosphinate molecules as a catalyst. The catalytically active species is formed when energy from light causes the release of one the capping molecules from the cube. However, the manganese complex is not soluble in water. The researchers claim to have overcome this problem by coating one electrode with a thin Nafion membrane. Housed within the aqueous channels of this membrane, the catalytic species is stabilized and apparently has good access to the water molecules, completing the anodic half cell.
The scientists said that their development “could be easily paired with a catalytic hydrogen-producing cathode cell” in order to create an entire photoelectrochemical cell that “produces pure hydrogen and oxygen from water and sunlight”.
There was no information whether such a cell has been built or is currently in development.
