When most people think of rust, a naturally occurring byproduct of iron or steel interacting with water, they don’t see it as good thing. West Virginia University’s Nick Wu isn’t most people.
“While most people see rust as an everyday nuisance, scientists have shown that by re-engineering its structure, it can become a very powerful material for splitting water to generate hydrogen gas,” said Wu, an associate professor of mechanical and aerospace engineering in the Statler College of Engineering and Mineral Resources. “Solar-to-hydrogen conversion is very similar to a solar panel creating electricity, only now the final product is hydrogen gas, which can be easily stored and transported for long-term use.”
According to Wu, while it’s easy to coerce water to split and release its oxygen to iron to form rust, it’s very difficult to trick the rust into further breaking down water molecules into hydrogen molecules.
“When rust absorbs sunlight it can create the energy necessary for the reaction, but unfortunately this energy is lost within one billionth of a second or less,” said Wu, whose research group, which includes post-doctoral fellow Jiangtian Li and graduate student Scott Cushing, recently had its work published in Nature Communications.
To overcome this, Wu and his team did two things. First, they made hematite, which is a crystalized form of rust, on the nanometer scale. This small size, Li explains, allows the energy to be absorbed immediately at the surface without having to transport through the bulk of the material. This allows the resulting solar energy to immediately start the water-splitting reaction and makes up the difference in time, raising efficiency.
The group’s second innovation was to use a gold nano-hole array, which looks much like a tiny fishnet, as a template for hematite fiber growth. “The gold nano-hole array has a special property that allows the material’s electrons to oscillate together, resulting in an enhanced and focused transmission of sunlight through the small metal holes within the larger pattern,” Cushing explained. “The hematite becomes like an optical fiber, just like those used in telecommunications, only now the sunlight is being trapped and transported. The optical fiber effect means the sunlight bounces around inside the rust fiber until it is absorbed, increasing the amount of light absorbed without increasing the overall size of the structure.”
The combination of the two effects, Wu said, greatly increases solar energy conversion efficiency and could someday lead to solar-to-hydrogen energy stations replacing gas stations on the world’s street corners.
CONTACT: Mary C. Dillon, Statler College of Engineering and Mineral Resources
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