Researchers Discover Inexpensive Catalyst That Generates Hydrogen from Buffered Water or Sea Water

[(PY5Me2)Mo(CF3SO3)]1+ reacts with water to form [(PY5Me2)MoO]2+ and H2. Credit: Nature, Karunadasa et al. Click to enlarge.

A team of researchers with the US Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley has discovered an inexpensive metal catalyst that can effectively generate hydrogen gas from water at neutral pH or from sea water.

The new proton reduction catalyst is based on a molybdenum-oxo metal complex that is about 70 times cheaper than platinum—currently the most widely used metal catalyst for splitting the water molecule—according to Hemamala Karunadasa, one of the co-discoverers of this complex and lead author of a paper describing the work published 29 April in the journal Nature.

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.

—Hemamala Karunadasa

The electrolytic production of water requires a water-splitting catalyst. Plants uses hydrogenases during photosynthesis; however, these enzymes are unstable and easily deactivated when removed from their native environment. Human activities seem to demand a stable metal catalyst that can operate under non-biological settings.

Metal catalysts are commercially available, but they are low valence precious metals the high costs of which 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. 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.

—Christopher Chang, co-author

The molybdenum-oxo complex that Karunadasa, Chang and Jeffrey Long discovered is a high valence metal named (PY5Me₂)Mo-oxo. In their studies, the research team found that this complex catalyzes the generation of hydrogen from neutral buffered water or even sea water with a turnover frequency of 2.4 moles of hydrogen per mole of catalyst per second.

The work shows that high-valency metal-oxo species can be used to create reduction catalysts that are robust and functional in water, the authors said, a concept that has broad implications for the design of ‘green’ and sustainable chemistry cycles.

This metal-oxo complex represents a distinct molecular motif for reduction catalysis that has high activity and stability in water. We are now focused on modifying the PY5Me ligand portion of the complex and investigating other metal complexes based on similar ligand platforms to further facilitate electrical charge-driven as well as light-driven catalytic processes. Our particular emphasis is on chemistry relevant to sustainable energy cycles

—Jeffrey Long

This research was supported in part by the DOE Office of Science through Berkeley Lab’s Helios Solar Energy Research Center, and in part by a grant from the National Science Foundation.

Resources

• Hemamala I. Karunadasa, Christopher J. Chang & Jeffrey R. Long (2010) A molecular molybdenum-oxo catalyst for generating hydrogen from water. Nature 464, 1329-1333 doi: 10.1038/nature08969