Hydrogen would command a key role in future renewable energy technologies,
experts agree, if a relatively cheap, efficient and carbon-neutral means of
producing it can be developed. An important step towards this elusive goal has
been taken by a team of researchers with the U.S. Department of Energy’s (DOE)
Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of
California, Berkeley. The team has discovered an 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 this complex. “In addition, our catalyst does not require
organic additives, and can operate in neutral water, even if it is dirty, and
can operate in sea water, the most abundant source of hydrogen on earth and a
natural electrolyte. These qualities make our catalyst ideal for renewable
energy and sustainable chemistry.”
Karunadasa holds joint appointments with Berkeley Lab’s Chemical Sciences
Division and UC Berkeley’s Chemistry Department. She is the lead author of a
paper describing this work that appears in the April 29, 2010 issue of the
journal Nature, titled “A molecular molybdenum-oxo catalyst for
generating hydrogen from water.” Co-authors of this paper were Christopher Chang
and Jeffrey Long, who also hold joint appointments with Berkeley Lab and UC
Berkeley. Chang, in addition, is also an investigator with the Howard Hughes
Medical Institute (HHMI).
Hydrogen gas, whether combusted or used in fuel cells to generate
electricity, emits only water vapor as an exhaust product, which is why this
nation would already be rolling towards a hydrogen economy if only there were
hydrogen wells to tap. However, hydrogen gas does not occur naturally and has to
be produced. Most of the hydrogen gas in the United States today comes from
natural gas, a fossil fuel. While inexpensive, this technique adds huge volumes
of carbon emissions to the atmosphere. Hydrogen can also be produced through the
electrolysis of water – using electricity to split molecules of water into
molecules of hydrogen and oxygen. This is an environmentally clean and
sustainable method of production – especially if the electricity is generated
via a renewable technology such as solar or wind – but requires a
water-splitting catalyst.
Nature has developed extremely efficient water-splitting enzymes – called
hydrogenases – for use by plants during photosynthesis, however, 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 low valence precious
metals whose high costs make their widespread use prohibitive. For example,
platinum, the best of them, costs some $2,000 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,” Chang says. “We believe our discovery of a molecular molybdenum-oxo
catalyst for generating hydrogen from water without the use of additional acids
or organic co-solvents establishes a new chemical paradigm for creating
reduction catalysts that are highly active and robust in aqueous media.”
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