Could moly sulfide be the key to cheaper hydrogen production?
By Grant Banks
February 9, 2014
Chemical engineers have found a 30-year-old recipe that stands to make future hydrogen production cheaper and greener. The recipe has led researchers to a way to liberate hydrogen from water via electrolysis using molybdenum sulfide – moly sulfide for short – as the catalyst in place of the expensive metal platinum.
While hydrogen is relatively abundant here on Earth, it is generally bound to either carbon or oxygen to form methane and water respectively. Producing hydrogen currently involves liberating it from methane at a cost of between US$1 and $2 per kilogram. And the world’s hunger for hydrogen continues to grow, currently we consume 55 billion kilograms of the element per year, making freeing it from methane or water big business. And with numerous automakers dipping their tires in the hydrogen fuel waters, it's set to get much bigger.
The other side of the equation is the by-product of production. When hydrogen is freed from methane the waste product is carbon, which is released into the atmosphere furthering climate change. Producing hydrogen from water on the other hand produces oxygen as waste.
The limiting factor to getting hydrogen from water in the past has been the expense of electrolysis, the process were hydrogen atoms are liberated from their bond with oxygen in water by passing an electrical current through an electrode immersed in the water. The main expense in this process was the use of platinum as the electrode. The efficiency of platinum to catalyze the breaking of hydrogen-oxygen bonds in water to free the hydrogen until now has been unmatched.
Enter moly sulfide. Since World War II, moly sulfide has been used by petroleum engineers in the refinement of oil. It was thought to be inefficient for the electrolysis of hydrogen from water due to the molecular structure at its surface.
That was until Stanford Engineering's Jens Nørskov, then at the Technical University of Denmark, noticed this structure differed at the edges of the crystal lattice. Around the edges, hydrogen production was possible as the structure has only two chemical bonds rather than the three seen elsewhere in its structure. This meant moly sulfide was capable of electrolyzing hydrogen, if only at the edges.
Next came the Eureka moment, when the researchers uncovered a 30-year-old recipe for double bonded moly sulfide. Using this recipe, nanoclusters of double-bonded moly sulfide were synthesized and deposited on an electrically conductive sheet of graphite to form a cheap electrode alternative to platinum.
Initial tests show the new technology to work at an efficiency approaching that of platinum. Early cost predictions for factory-scale production range from $1.60 to $10.40, which at the lower end would be competitive with current methane-based methods.
"There are many pieces of the puzzle still needed to make this work and much effort ahead to realize them," said Stanford Engineering Assistant Professor Thomas Jaramillo. "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.”
Findings of the research, which is a collaboration between Stanford University and Aarhus University in Denmark, were published in Nature Chemistry .
Source: Stanford University