Scientists combined a pigment with semiconducting nanoparticles to create a system that uses light to spark a catalytic process that creates hydrogen fuel.  Argonne nanoscientist Elena Rozhkova and her colleagues combined a pigment called bacteriorhodopsin, a protein found in the membranes of ancient microorganisms that live in desert salt flats, with sunlight to generate environmentally friendly hydrogen fuel in a system called nanophotocatalysis.

The background Rozhkova explains is scientists have been aware of the potential of titanium dioxide nanoparticles for light-based reactions since the early 1970s, when Japanese researchers discovered that a titanium dioxide electrode exposed to bright ultraviolet light could split water molecules in a phenomenon that came to be known as the Honda-Fujishima effect. Since then, scientists have made continuous efforts to extend the light reactivity of titanium dioxide photocatalysts into the visible part of the spectrum. The promise of these photocatalysts prompted scientists to experiment with different modifications to their basic chemistry in hope of making the reaction more efficient.

Nanophotocatalysis Using Bio Material and TiO2. Click image for the largest view.

Nanophotocatalysis Using Bio Material and TiO2. Click image for the largest view.

“Titanium dioxide alone reacts with ultraviolet light, but not with visible light, so we used biological photoreactive molecules as a building block to create a hybrid system that could use visible light efficiently,” Rozhkova said.

Rozhkova and her colleagues turned to bacteriorhodopsin – which is responsible for the unusual purple color of a number of salt flats in California and Nevada – because it uses sunlight as an energy source that allows it to act as a “proton pump.” Proton pumps are proteins that typically straddle a cellular membrane and transfer protons from inside the cell to the extracellular space.

In the Argonne system, the protons provided by the bacteriorhodopsin are combined with free electrons at small platinum sites interspersed in the titanium dioxide matrix. “The platinum nanoparticles are essential for creating a distinct spot for the production of the hydrogen molecule,” said Peng Wang, an Argonne postdoctoral researcher in Rozhkova’s group at Argonne’s Center for Nanoscale Materials.

Rozhkova said, “It is interesting that in biology, bacteriorhodopsin does not naturally participate in these kind of reactions. Its natural function really doesn’t have much to do at all with creating hydrogen. But as part of this hybrid, it helps make hydrogen under white light and at environmentally friendly conditions.”

The study paper has been published at the ACS  journal Nano Letters.

The bio-assisted hybrid photocatalyst outperforms many other similar systems in hydrogen generation and could be a good candidate for fabrication of green energy devices that consume virtually infinite sources – salt water and sunlight.

Nanophotocatalysis is one of the potentially efficient ways of capturing and storing solar energy.  The Argonne team’s production announced in the hybrid system study is up to 5275 μmole of H2 (μmole protein)−1 h–1 at pH 7 in the presence of methanol as a sacrificial electron donor under white light.

The team’s early work is very encouraging.  When something of this kind is commercially practical most everyone could have a system to produce free fuel.

The downside along with the unknowns that will come up during development is the platinum needed. Like most basic researchers the Argonne team used the obvious, and conspicuously expensive, most likely to work material – platinum.  But more progress could ignite a hunt for less costly materials that will surely cost less, and may well add to the efficiency.

This is basic and early research with astonishing results.  The brainstorm of innovation to look into this path has paid off.  Lets hope the momentum stays behind this and sets up a low cost hydrogen generator market for home and business roofs.


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