October 7, 2015

Way cheaper catalyst may lower fuel costs for hydrogen-powered cars

Sandia National Laboratories post-doctoral fellow Stan Chou
demonstrates the reaction of more efficiently catalyzing hydrogen.
In this simulation, the color is from dye excited by light and generating electrons
for the catalyst molybdenum disulfide to evolve hydrogen. (Photo by Randy Montoya)

‘Green’ process runs on sunlight

(October 7, 2015)  Sandia National Laboratories researchers seeking to make hydrogen a less expensive fuel for cars have upgraded a catalyst nearly as cheap as dirt — molybdenum disulfide, “molly” for short — to stand in for platinum, a rare element with the moonlike price of $1,500 a gram.

Sandia-induced changes elevate the plentiful, 37-cents-a-gram molly from being a welterweight outsider in the energy-catalyst field — put crudely, a lazy bum that never amounted to much — to a possible contender with the heavyweight champ.

The improved catalyst, expected to be the subject of an Oct. 7 Nature Communications paper, has already released four times the amount of hydrogen ever produced by molly from water. To Sandia postdoctoral fellow and lead author Stan Chou, this is just the beginning: “We should get far more output as we learn to better integrate molly with, for example, fuel-cell systems,” he said.

An additional benefit is that molly’s action can be triggered by sunlight, a feature which eventually may provide users an off-the-grid means of securing hydrogen fuel.

Hydrogen fuel is desirable because, unlike gasoline, it doesn’t release carbon into the atmosphere when burned. The combustion of hydrogen with oxygen produces an exhaust of only water.

In Chou’s measured words, “The idea was to understand the changes in the molecular structure of molybdenum disulfide (MOS), so that it can be a better catalyst for hydrogen production: closer to platinum in efficiency, but earth-abundant and cheap. We did this by investigating the structural transformations of MOS at the atomic scale, so that all of the materials parts that were ‘dead’ can now work to make H [hydrogen].”

Sandia National Laboratories researchers, from right, Stan Chou, Bryan Kaehr,
Jeff Brinker, Ping Lu and Eric Coker, gather in a lab where work on the catalyst
molybdenum disulfide was achieved. (Photo by Randy Montoya)

The rind of an orange

in what sense were the parts “dead,” one might ask?

Visualize an orange slice where only the rind of the orange is useful; the rest — the edible bulk of the orange — must be thrown away. Molly exists as a stack of flat nanostructures, like a pile of orange slices. These layers are not molecularly bolted together like a metal but instead are loose enough to slide over one another — a kind of grease, similar to the structure of graphene, and with huge internal surface areas.

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