New discovery could change the hydrogen economy

July 5, 2013 | By Barbara Vergetis Lundin

The University of Wisconsin-Madison may have found the catalyst to facilitate the use of electricity to produce hydrogen gas from water -- a significant advance to storing and transferring energy.

Producing hydrogen from water, and then storing and using the gas, has proven difficult in the past -- although it's great in theory, as it produces water but no carbon dioxide when burned for energy. The material being studied, molybdenum disulfide, is far less expensive than the catalysts that normally drive this reaction.

"Most people have tried to reduce the cost of the catalyst by making small particles that use less platinum, but here we got rid of the platinum altogether and still got reasonably high performance," said Mark Lukowski, a Ph.D. student working with associate professor Song Jin in the UW-Madison chemistry department. "…in principle you could scale this up. Molybdenum disulfide is a commercially available product. To control purity and structure, we go through the trouble of synthesizing it from the bottom up, but you could buy it today."

Just as carbon can form diamond for jewelry and graphite for writing, molybdenum disulfide can be a semiconductor or a metallic phase, depending on structure. When the compound is grown on the graphite, it is a semiconductor, but it becomes metallic after the lithium treatment. The metallic phase has far greater catalytic properties.

"Like graphite, which is made up of a stack of sheets that easily separate, molybdenum disulfide is made up of individual sheets that can come apart, and previous studies have shown that the catalytically active sites are located along the edges of the sheets," said Lukowski. "The lithium treatment both causes the semiconducting-to-metallic phase change and separates the sheets, creating more edges. We have taken away the limitation from molybdenum disulfide and made the active sites both more pervasive and more reactive."

In January of this year, Lux Research contended from their research that a hydrogen economy was no closer than it was decades ago. This discovery could very well prove that prediction wrong. The next steps include finding ways to further improve the performance by optimizing all aspects of the process and exploring related compounds.

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