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Cobalt film efficiently draws hydrogen and oxygen from water

16 April 2015

A cobalt-based thin film produced by Rice University researchers serves as a new catalyst that produces both hydrogen and oxygen from water for fuel cells.

A side view of a porous cobalt phosphide/phosphate thin film. The scale bar represents 500nm (image : Tour Group/Rice University)

The inexpensive, highly porous material created by the Rice lab of chemist James Tour, might have advantages as a catalyst for the production of hydrogen via water electrolysis. A single film far thinner than a hair can be used as both the anode and cathode in an electrolysis device.

They determined their cobalt film is much better at producing hydrogen than most state-of-the-art materials and is competitive with (and much cheaper than) commercial platinum catalysts. They reported the catalyst also produced an oxygen evolution reaction comparable to current materials.

"It is amazing that in water-splitting, the same material can make both hydrogen and oxygen," Tour says. "Usually materials make one or the other, but not both."

The researchers suggested applying alternating current from wind or solar energy sources to cobalt-based electrolysis could be an environmentally friendly source of hydrogen and oxygen.

"Here we can just alternate the current from positive to negative and back again, and hydrogen and oxygen are made with the same material," says Tour. "And the material itself is very easy to make." The researchers believe that manufacturing the film will be inexpensive and scalable.

The lab fabricated the 500nm films by anodising a cobalt film electro-deposited on a substrate. The assembly was then baked for two hours in a phosphorus vapour that converted it to a cobalt/phosphide/phosphate thin film without damaging its porous structure.

The material proved to be robust in both durability tests and in acidic and alkaline conditions.

The discovery is reported in the journal, Advanced Materials.

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