Sandia researchers, at the Sandia-University of New Mexico Advanced Materials Laboratory, have engineered a hydrogen-generating catalyst from commonplace molybdenum disulfide (MoS2, $0.37/g)—to supplant the current most-effective hydrogen catalyst: platinum (Pt, $1,500/g). The improved catalyst, discussed in a Nature Communications paper (Understanding catalysis in a multiphasic two-dimensional transition metal dichalcogenide), has released four times the amount of hydrogen ever produced by molybdenum from water.
To Sandia lead author Stan Chou, this is just the beginning: “We should get far more output as we learn to better integrate molybdenum with, for example, fuel-cell systems,” he said. An additional benefit is that molybdenum’s action can be triggered by sunlight, a feature which eventually may provide users an off-the-grid means of securing hydrogen fuel.
“The idea was to understand MoS2 molecular structural changes, so that it can be a better catalyst for hydrogen production: closer to platinum in efficiency, but earth-abundant and cheap,” said Chou. “We did this by investigating MoS2 structural transformations at the atomic scale, so that all of the materials parts that were ‘dead’ can now work to make H2.”
In what sense were the parts “dead?” — Visualize an orange slice where only the orange rind is useful; the rest—the edible bulk of the orange—must be thrown away. Molybdenum exists as a stack of flat nanostructures, like a pile of very thin orange slices. But here’s the rub: while the edges of these nanostructure “slices” match platinum in their ability to catalyze hydrogen, the relatively immense surface area of each slice’s interior was useless because the molecular arrangements within the nanostructure are different from the molecular arrangement at the edges. Because of this “excess baggage,” a commercial-grade catalyst would require a huge amount of molybdenum. The slender edges would work hard, but the interior mass would just “hang out,” doing nothing.
“Why Stan’s work is impactful is that there was so much confusion as to how this process works and what structures are actually formed,” said co-author Bryan Kaehr. “He unambiguously showed that this desirable catalytic form is the end result of the completed reaction.”
Said Sandia Fellow and University of New Mexico professor Jeff Brinker, another paper author, “People want a nonplatinum catalyst. Molybdenum is dirt cheap and abundant. By making these relatively enormous surface areas catalytically active, Stan established understanding of the structural relation of these two-dimensional materials that will determine how they will be used in the long run. You have to basically understand the material before you can move forward in changing industrial use.”
Kaehr cautions that what’s been established is a fundamental proof of principle, not an industrial process. “Water splitting is a challenging reaction. It can be poisoned, stopping the molybdenum reaction after some time period. Then you can restart it with acid. There are many intricacies to be worked out. “But getting inexpensive molybdenum to work this much more efficiently could drive hydrogen production costs way down.”
Read the Sandia news release.