Ultra-thin films of nickel and iron oxides appear to be very effective catalysts for the solar-powered splitting of water into hydrogen and oxygen, new research from the University of Oregon has found. Such devices could be used to produce hydrogen fuel from the simple and abundant resources of sunlight and water, but are as of now not cost competitive with other forms of energy production. Improvements to the technology could change this though.
For the new work, researchers in the Solar Materials and Electrochemistry Laboratory investigated the catalyst material and worked to develop a computer model that can approximate the effectiveness of different catalyst thin films in solar water-splitting devices.
The results of that work show that “nickel-iron mixed oxide with an atomic structure similar to naturally occurring minerals shows the highest catalytic activity for forming oxygen from water, based on a side-by-side comparison of eight oxide-based materials targeted in various research efforts.” And also that, when in combination with semiconductor light absorbers, the nickel-iron oxide catalyst is most effective in a film 0.4 nano-meters in thickness.
“When you want to pull the protons off a water molecule to make hydrogen gas for fuel, you also have to take the leftover oxygen atoms and make oxygen gas out of them,” Shannon Boettcher, professor of chemistry, stated in the UO press release. “It turns out that the slowest, hardest, most-energy-consuming step in the water-splitting process is actually the oxygen-making step. We’ve been studying catalysts for making oxygen. Specifically, we’re seeking catalysts that reduce the amount of energy it takes in this step and that don’t use expensive precious metals.”
“What we found is that when we take nickel oxide films that start out as a crystalline material with the rock-salt structure like table salt, they absorb iron impurities and spontaneously convert into materials with a layered structure during the catalysis process,” Boettcher said. “The semiconductors absorb the light, generating electron-hole pairs which move onto the catalyst material and proceed to drive the water-splitting reaction, creating fuel.”
For now this is just a laboratory discovery, but the researchers think that this merits advancement to a prototype stage. As the Department of Energy supported this research, the researchers think that the possibility is there for the material to be used in a prototype at the U.S. DOE’s Joint Center for Artificial Photosynthesis.
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