Hydrogen would command a key role in future renewable-energy technologies if a relatively cheap, efficient and carbon-neutral means of producing it could be developed.
It seems that an important step towards this elusive goal has been taken by a team of American researchers, who have discovered an apparently inexpensive metal catalyst that can effectively generate hydrogen gas from water.
“Our new proton-reduction catalyst is based on a molybdenum-oxo metal complex that is about 70 times cheaper than platinum, today’s most widely used metal catalyst for splitting the water molecule,” said Hemamala Karunadasa, one of the co-discoverers of the new catalyst.
“In addition, our catalyst does not require organic additives and can operate in neutral water, even if it is dirty, and can operate in seawater, the most abundant source of hydrogen on Earth and a natural electrolyte.
“These qualities make our catalyst ideal for renewable energy and sustainable chemistry.”
Hydrogen gas, whether combusted or used in fuel cells to generate electricity, emits only water vapour as an exhaust product.
However, hydrogen gas does not occur as a free element. Most hydrogen gas used today is derived from natural gas, a fossil fuel.
While inexpensive, this technique adds huge volumes of carbon emissions to the atmosphere.
As many a science student at school knows, hydrogen can also be produced through the electrolysis of water – using electricity to split molecules of water into molecules of hydrogen and oxygen. It is a classic experiment.
It is also an environmentally clean and potentially sustainable method of production, especially if the electricity is generated via a renewable technology such as solar or wind – but it requires a water-splitting catalyst.
Nature has developed extremely efficient water-splitting enzymes – called hydrogenases – for use by plants during photosynthesis, but these enzymes are highly unstable and easily deactivated when removed from their native environment.
Human activities demand a stable metal catalyst that can operate under non-biological settings.
Metal catalysts are commercially available, but they are expensive. Platinum, the best of them, costs some $1,500 an ounce.
The basic scientific challenge has been to create Earth-abundant molecular systems that produce hydrogen from water with high catalytic activity and stability.
This is what the American team reckon they have come up with.
They believe their discovery of a molecular molybdenum-oxo catalyst for generating hydrogen from water without the use of additional acids or organic co-solvents sets a new benchmark.
Not only that, it can work with freshwater and seawater.