Diamonds through Hydrogen Production and Storage

Photo: A diamond

"The idea we explored was based on ball milling graphite processes found in the hydrogen storage literature," said Angela D. Lueking, assistant professor of energy and geoenvironmental engineering. "We substituted anthracite coal for graphite because it is abundant and inexpensive. Now, with 20/20 hindsight, we are struck by the fact that coal gasification is currently the most economical way to produce hydrogen."

Lueking's group was exploring a way to store hydrogen in carbon-based materials, and inadvertently stumbled upon a method that combines production and storage and produces nanocrystalline diamonds as a by-product.

Lueking ball milled powdered anthracite coal with cyclohexene. Ball milling involves mixing a slurry of anthracite powder and cyclohexene with small steel balls and mixing so that the steel balls pound the coal particles and the cyclohexene causing physical and chemical changes.

Lueking is puzzled because, unlike the graphite experiments, her anthracite experiment has hydrogen gas evolving from the mixture at room temperature. The hydrogen is either trapped in the material in a tight pore structure or a new carbon structure is being formed. The hydrogen outgassing continued for about a year and increased with addition of moderate heat.

Wanting to know the structure of the ball milled product, and looking for carbon nanotubes, the researchers used transmission electron microscopy to investigate the small particles. What the researchers had were Bucky diamonds, a nanocrystalline diamond surrounded by onion–like layers of graphite.

"Bucky diamonds are relatively unexplored in terms of applications," said Lueking. "Nanocrystalline diamonds, however, have major industrial uses as abrasives and in electronics. These nanodiamonds are usually created by exploding TNT in a carbon source."

COMPAMED.de; Source: Penn State