Nano technology experts from the Stanford School of Engineering and from Denmark’s Aarhus University have found how to liberate hydrogen from water on an industrial scale by using an old catalyst, molybdenum sulfide, for electrolysis.

With the new engineering molybdenum sulfide would be an efficient and environmentally friendly catalyst for the production of molecular hydrogen (H2), a compound used extensively in modern industry to manufacture fertilizer and refine crude oil into gasoline.

The team’s work has been published in Nature Chemistry.

Moly Sulfide Nanocluster on a Graphite Surface. Click image for more info.

Moly Sulfide Nanocluster on a Graphite Surface. Click image for more info.

Hydrogen is abundant element that is generally not found on earth as the pure gas H2. It is generally bound to oxygen in water (H2O) or to carbon in methane (CH4), the primary component in natural gas. At present, industrial hydrogen is produced from natural gas using a process that consumes a great deal of energy while also releasing carbon that is in part recovered for making dry ice or simply lost back into the air.

Electrolysis is an electrical current flowing through a metallic electrode immersed in water. This electron flow induces a chemical reaction that breaks the bonds between hydrogen and oxygen atoms. The electrode serves as a catalyst, a material that can spur one reaction after another without ever being used up. Platinum is the best catalyst for electrolysis and might be used to produce hydrogen from water today if cost were no object.

The world economy consumes about 55 billion kilograms of hydrogen per year. It now costs about $1 to $2 per kilogram to produce hydrogen from methane. So any competing process, even if it’s greener, must hit that production cost, which rules out electrolysis based on platinum.

The Stanford Aarhus team’s paper shows how they re-engineered the atomic structure of molybdenum sulfide to make it nearly as efficient at electrolysis as platinum – a finding that has the potential to revolutionize industrial hydrogen production.

Molybdenum sulfide (“moly sulfide“) is an old catalytic friend.  Since World War II petroleum engineers have used molybdenum sulfide to help refine oil.  For six decades moly sulfide was not considered a good catalyst to produce hydrogen from water through electrolysis. However scientists and engineers came to understand why: the most commonly used moly sulfide materials had an unsuitable arrangement of atoms at their surface.

Typically, each sulfur atom on the surface of a moly sulfide crystal is bound to three molybdenum atoms underneath. For complex reasons involving the atomic bonding properties of hydrogen, that configuration isn’t conducive to electrolysis.

In 2004, Stanford chemical engineering professor Jens Norskov, then at the Technical University of Denmark, made an important discovery creating a slow forming “Eureka moment”. Around the edges of the crystal, some sulfur atoms are bound to just two molybdenum atoms. At these edge sites, which are characterized by double rather than triple bonds, moly sulfide was much more effective at forming H2.

Then Jakob Kibsgaard started this project while working with Flemming Besenbacher, a professor at the Interdisciplinary Nanoscience Center (iNANO) at Aarhus in Denmark.  Kibsgaard became a post-doctoral researcher and joined with Thomas Jaramillo, an assistant professor of chemical engineering at Stanford.

Armed with Norskov’s knowledge, Kibsgaard found a 30-year-old recipe for making a form of moly sulfide with lots of these double-bonded sulfurs at the edge.

Using simple chemistry, he synthesized nanoclusters of this special moly sulfide. Then he deposited the nanoclusters onto a sheet of graphite, a material that conducts electricity. Together the graphite and moly sulfide formed a cheap electrode. It was meant to be a substitute for platinum, the ideal but expensive catalyst for electrolysis.

The question then became: could this composite electrode efficiently spur the chemical reaction that rearranges hydrogen and oxygen atoms in water?

As Jaramillo put it: “Chemistry is all about where electrons want to go, and catalysis is about getting those electrons to move to make and break chemical bonds.”

The experimenters put their system to the acid test. They immersed their composite electrode into water that was slightly acidified, meaning it contained positively charged hydrogen ions. These positive ions were attracted to the moly sulfide clusters. Their double-bonded shape gave them just the right atomic characteristic to pass electrons from the graphite conductor up to the positive ions. This electron transfer turned the positive ions into neutral molecular hydrogen, which bubbled up and away as a gas.

Most importantly, the experimenters found that their cheap moly sulfide catalyst had the potential to liberate hydrogen from water on something approaching the efficiency of a system based on prohibitively expensive platinum.

The team is further along than the most recent paper suggests.  Last year, Jaramillo and a dozen co-authors studied four factory-scale production schemes in an article for The Royal Society of Chemistry’s journal of Energy and Environmental Science.

They concluded that it could be feasible to produce hydrogen in factory-scale electrolysis facilities at costs ranging from $1.60 to $10.40 per kilogram, which is competitive at the low end with current practices based on methane, allowing that some of their assumptions were based on new plant designs and materials.

Jaramillo said, “There are many pieces of the puzzle still needed to make this work, and much effort ahead to realize them. However, we can get huge returns by moving from carbon-intensive resources to renewable, sustainable technologies to produce the chemicals we need for food and energy.”

The new tech can scale up and looks to be quite competitive.  Corporate number crunchers might be looking into it and soon.


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