February 23rd, 2014 by James Ayre
While hydrogen fuel production — via the splitting of water into hydrogen and oxygen using sunlight — has long been prominent in the public imagination, the reality is that the technology is still quite a ways off from being economical. That gap between the economical and the reality is narrowing though, as new research from the University of Wisconsin-Madison shows.
Researchers there have succeeded in achieving a new record (with regard to oxide-based photoelectrode systems) solar-to-hydrogen conversion efficiency of 1.7% — while using relatively inexpensive new materials.
“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,” states researcher Kyoung-Shin Choi, a chemistry professor at the University of Wisconsin-Madison.
So, to address this, the researchers created solar cells from bismuth vanadate and used electrodeposition (think gold-plated jewelry) to boost “the compound’s surface area to a remarkable 32 square meters for each gram.”
“Without fancy equipment, high temperature or high pressure, we made a nanoporous semiconductor of very tiny particles that have a high surface area,” explains Choi. “More surface area means more contact area with water, and, therefore, more efficient water splitting.”
The University of Wisconsin-Madison provides more:
Bismuth vanadate needs a hand in speeding the reaction that produces fuel, and that’s where the paired catalysts come in. While there are many research groups working on the development of photoelectric semiconductors, and many working on the development of water-splitting catalysts, according to Choi, the semiconductor-catalyst junction gets relatively little attention.
Choi and Kim exploited a pair of cheap and somewhat flawed catalysts — iron oxide and nickel oxide — by stacking them on the bismuth vanadate to take advantage of 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 states. “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 approach allows for the simultaneous optimization of the semiconductor-catalyst junction and also the catalyst-water junction.
“Combining this cheap catalyst duo with our nanoporous high surface area semiconductor electrode resulted in the construction of an inexpensive all oxide-based photoelectrode system with a record high efficiency,” Choi continues.
“Other researchers studying different types of semiconductors or different types of catalysts can start to use this approach to identify which combinations of materials can be even more efficient,” says Choi. “Which some engineering, the efficiency we achieved could be further improved very fast.”
The researchers are currently working to tweak their design further.
The new research was just published in the journal Science.
Image Credit: UW-Madison/Bryce Richter
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