A new recipe based on the chemistry and biology of natural leaves that could lead to working prototypes of an artificial leaf that capture solar energy and use it efficiently to change water into hydrogen fuel was reported the 239th National Meeting of the American Chemical Society last week.
Tongxiang Fan, Ph.D. and colleagues Di Zhang, Ph.D. and Han Zhou, Ph.D. with the State Key Lab of Matrix Composites at Shanghai Jiaotong University, Shanghai, China presented a design strategy to produce the long-sought artificial leaf, which could harness Mother Nature’s ability to produce energy from sunlight and water in the process called photosynthesis. Cleverly the goal isn’t building an organic chemical; rather it’s the short step of gathering out the H2 from water.
The team decided to take a closer look at the leaf, nature’s own photosynthetic system, with plans to use its structure as a blueprint for their next generation of artificial leaf systems. The structure of green leaves provides an extremely high light-harvesting efficiency. In leaf architecture are structures responsible focusing and guiding of solar energy into the light-harvesting sections of the leaf, and other functions.
Dr. Fan said, “This concept may provide a new vista for the design of artificial photosynthetic systems based on biological paradigms and build a working prototype to exploit sustainable energy resources.” Fan pointed out that using sunlight to split water into its components, hydrogen and oxygen, is one of the most promising and sustainable tactics to escape current dependence on coal, oil, and other traditional fuels.
When burned, those fuels release carbon dioxide, the main greenhouse gas. Fan also alluded to combustion of hydrogen, by contrast that forms just water vapor. That appeal is central to the much-discussed “Hydrogen Economy.” Some auto companies, such as Toyota, have developed hydrogen-fueled cars. What’s missing is a cost-effective and sustainable way to produce hydrogen.
The scientists decided to mimic the natural architectural design in the development of a blueprint for artificial leaf-like structures. That led them to report their recipe for the “Artificial Inorganic Leaf” (AIL), based on the natural leaf and titanium dioxide (TiO2) – a chemical already recognized as a photocatalyst for hydrogen production.
The team first infiltrated the leaves of Anemone vitifolia, a native Chinese plant – with titanium dioxide using two-step process. Using advanced spectroscopic techniques; the scientists were then able to confirm that the structural features in the leaf favorable for light harvesting were replicated in the new TiO2 structure.
The artificial leaves are eight times more active for hydrogen production than TiO2 that has not been “biotemplated” as the team did with the A. vitifloia. The artificial leaves are more than three times as active as commercial photo-catalysts as well.
Next, the scientists embedded nanoparticles of platinum into the leaf surface. Platinum, along with the nitrogen found naturally in the leaf, helps increase the activity of the artificial leaves by an additional factor of ten.
During the report at the American Chemical Society meeting Fan reported on various aspects of Artificial Inorganic Leaf production, their spectroscopic work to better understand the macro- and microstructure of the photocatalysts, and their comparison to previously reported systems. The activity of these new “leaves” is significantly higher than those prepared using classic routes. Fan attributes these results to the hierarchical structures derived from natural leaves.
Fan said, “Our results may represent an important first step towards the design of novel artificial solar energy transduction systems based on natural paradigms, particularly based on exploring and mimicking the structural design. Nature still has much to teach us, and human ingenuity can modify the principles of natural systems for enhanced utility.”
As lab experiments go, this is quite encouraging. One hopes that the results can translate up to prototypes and on to demonstration and scale up. But that’s a far way to go. The insight though, is extraordinary. The innovation is clever. The notion that hydrogen could be produced daily in part or in full of individual needs and used with very short storage periods puts more practicality into a “hydrogen economy” concept.
Yet one has to doubt, even should this level of technology become widespread that a “hydrogen economy” is practical. Without low cost fuel cells as an example, to get to electrical output for use, hydrogen is a very limited fuel. Like photovoltaic, solar hydrogen production will require solar exposed land area per person, which in urban settings is in very low proportion indeed.
Post written by: New Energy and Fuel