The quest for molecular hydrogen – the answer to all our clean-energy prayers – has taken a hopeful turn at the Lawrence Berkeley National Laboratory. Scientists there say that by jumbling the surface layer of titanium dioxide nanocrystals, they have created an efficient photocatalyst for using sun energy to extract hydrogen from water.
As the Berkeley Lab explains it, titanium dioxide is commonly dosed with impurities and modified in order to increase its efficiency. Building on that, Samuel Mao and his research group used hydrogenation to engineer disorder “into the ordinarily perfect atom-by-atom lattice structure of the surface layer of titanium dioxide nanocrystals.”
Immersing the disorder-engineered nanocrystals in water and exposing them to simulated sunlight revealed that nearly a quarter of the sunlight absorbed by the photocatalyst could be converted into hydrogen when using a sacrificial reagent. That’s about 100 times better than the yields of most semiconductor photocatalysts under the same conditions. (Going forward, one of the team’s challenges will be to reach such high levels of efficiency without use of the sacrificial reagent.)
The researchers said the key here is the photocatalyst’s ability to absorb so much of the light spectrum. Typically, titanium dioxide photocatalysts only absorb ultraviolet light, and those containing defects might also absorb visible light. But in the disordered state, it absorbs light from those two parts of the spectrum as well infrared light, making it the first titanium dioxide photocatalyst to do so. In this sense, it performs something like the full-spectrum solar cell we told you about recently, also developed at the Berkeley Lab .