Researchers use cheap production materials to make solar-to-hydrogen …

February 26, 2014 by  
Filed under Solar Energy Tips

Researchers at the University of Wisconsin-Madison report that they have used inexpensive production materials to split water into hydrogen and oxygen gases via solar energy, at an unprecedented solar-to-hydrogen conversion efficiency of 1.7 percent.  The use of cheap, oxide-based materials offers an attractive alternative to the current high price of solar fuel production, which – due to the pricey sun-capturing semiconductors and the catalysts necessary to efficiently generate fuel – cannot compete with the price of gasoline.

“In order to make commercially viable devices for solar fuel production, the material and the processing costs should be reduced significantly while achieving a high solar-to-fuel conversion efficiency,” said Kyoung-Shin Choi, a chemistry professor at the University of Wisconsin–Madison.

Choi and postdoctoral researcher Tae Woo Kim combined cheap, oxide-based materials to split water into hydrogen and oxygen gases via solar energy with a solar-to-hydrogen conversion efficiency of 1.7 percent – the highest reported for any oxide-based photoelectrode system.  Choi created solar cells from bismuth vanadate using electrodeposition — the same process used to make gold-plated jewelry or surface-coat car bodies — to increase the compound’s surface area to an astonishing 32 square meters for each gram.

The researchers published their results last week in the journal Science.

“Without fancy equipment, high temperature or high pressure, we made a nanoporous semiconductor of very tiny particles that have a high surface area,” said Choi, whose work is supported by the National Science Foundation.  ”More surface area means more contact area with water, and, therefore, more efficient water splitting.”

Since bismuth vanadate needs a boost to speed up the reaction that produces fuel, the paired catalysts were a necessary addition.  Choi said that this semiconductor-catalyst junction gets relatively little attention from other researchers.

Choi and Kim used a pair of cheap and a bit flawed catalysts — iron oxide and nickel oxide — by stacking them on the bismuth vanadate to exploit their relative strengths.

“Since no one catalyst can make a good interface with both the semiconductor and the water that is our reactant, we choose to split that work into two parts,” Choi said.  ”The iron oxide makes a good junction with bismuth vanadate, and the nickel oxide makes a good catalytic interface with water.  So we use them together.”

The dual-layer catalyst design enabled instantaneous optimization of the semiconductor-catalyst junction and the catalyst-water junction, which resulted in the record-high efficiency rate for solar fuel production.  Choi expects the basic work done to demonstrate the efficiency improvement by nanoporous bismuth vanadate electrode and dual catalyst layers will provide labs around the world with fodder for leaps forward.

According to Nubiola, bismuth vanadate is manufactured by dissolving bismuth nitrate, sodium vanadate, and sodium molybdate in nitric acid followed by the precipitation of a complex mixture of the metals.  The product was first reported in a medical patent in 1924 and manufactured as a solid substance in 1964.

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