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New process could make hydrogen fuel without using costly platinum

July 3, 2013
Courtesy of University of Wisconsin-Madison 
and World Science staff

A new find­ing could ad­vance the quest to cre­ate a “hy­dro­gen econ­o­my” that would use that abun­dant el­e­ment to store and trans­fer en­er­gy, sci­en­tists say.

The­o­ret­ic­ally, hy­dro­gen is the ul­ti­mate non-polluting fu­el for stor­ing in­ter­mit­tent en­er­gy from the wind or sun. When burned for en­er­gy, hy­dro­gen pro­duces wa­ter but no car­bon di­ox­ide, con­sid­ered the chief cul­prit in glob­al warm­ing. 

But pro­duc­ing hy­dro­gen from wa­ter, and then stor­ing and us­ing the gas, have prov­en dif­fi­cult. The new stu­dy, pub­lished on­line at the Jour­nal of the Amer­i­can Chem­i­cal So­ci­e­ty, in­tro­duces a new sys­tem to fa­cil­i­tate the use of elec­tri­city to pro­duce the gas.

It in­volves a new cat­a­lyst—a sub­stance that speeds up a chem­i­cal re­ac­tion—to re­place the rare, ex­pen­sive met­al plat­i­num nor­mally re­quired for the re­ac­tion.

The cat­a­lyst, mo­lyb­de­num di­sul­fide, con­tains two com­mon el­e­ments, said Mark Lukowski, a Ph.D. stu­dent work­ing with chem­ist Song Jin at the Uni­vers­ity of Wisconsin-Madison. “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,” he said.

The re­search­ers pro­duced mil­li­gram quantities of the cat­a­lyst, “but in prin­ci­ple you could scale this up,” said Lukowski. “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.”

To make the new ma­te­ri­al, Lukowski and Jin de­posited nano­struc­tures, or molecular-scale struc­tures, of mo­lyb­de­num di­sul­fide on a disk of graph­ite. They then ap­plied a treat­ment us­ing the el­e­ment lith­i­um to cre­ate a dif­fer­ent struc­ture with met­allic prop­er­ties, and great­er cat­a­lyt­ic ca­pa­ci­ties.

“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.

As tech­no­log­i­cal ad­vances put fur­ther strain on the supply of plat­i­num and oth­er rare el­e­ments, us­ing com­mon el­e­ments is a ma­jor ad­van­tage, Jin said. “The el­e­ments we use are cheap and abun­dant in earth’s crust, and the raw ma­te­ri­al is al­ready com­mer­cially avail­a­ble at low cost. Build­ing on this dis­cov­ery and new un­der­stand­ing, we would like to fur­ther im­prove these ma­te­ri­als to achieve the ef­fi­cient prod­uction of hy­dro­gen with­out us­ing pre­cious met­als.”


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A new finding could advance the quest to create a “hydrogen economy” that would use that abundant element to store and transfer energy, scientists say. Theoretically, hydrogen is the ultimate non-polluting fuel for storing intermittent energy from the wind or sun. When burned for energy, hydrogen produces water but no carbon dioxide, reducing concerns about global warming. But producing hydrogen from water, and then storing and using the gas, have proven difficult. The new study, published online at the Journal of the American Chemical Society, introduces a new system to facilitate the use of electricity to produce the gas. It involves a new catalyst—a substance that speeds up a chemical reaction—to replace the rare, expensive metal platinum normally required for the reaction. The catalyst, molybdenum disulfide, contains two common elements, said Mark Lukowski, a Ph.D. student working with chemist Song Jin at the University of Wisconsin-Madison. “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,” he said. The researchers produced milligram quantities of the catalyst, “but in principle you could scale this up,” said Lukowski. “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.” To make the new material, Lukowski and Jin deposited nanostructures, or molecular-scale structures, of molybdenum disulfide on a disk of graphite. They then applied a treatment using the element lithium to create a different structure with metallic properties, and greater catalytic capacities. “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. As technological advances put further strain on the supply of platinum and other rare elements, using common elements is a major advantage, Jin said. “The elements we use are cheap and abundant in earth’s crust, and the raw material is already commercially available at low cost. Building on this discovery and new understanding, we would like to further improve these materials to achieve the efficient production of hydrogen without using precious metals.”