By Bill Dockery
It’s a tiny bit of alchemy.
A microscopic knot of proteins buried in the green matter of a plant is exposed to sunlight in the presence of carbon dioxide and water. In an intricate interaction, the protein complex strips the hydrogen atom from the water molecule and begins to form a new compound: glucose, a sugar made up of atoms of carbon, oxygen, and hydrogen. The plant uses the glucose it produces to create the starch and cellulose it needs to live and grow.
From pond scum to giant redwoods, from cyanobacteria to cornfields, most organisms in the plant kingdom depend on this process known scientifically as photosynthesis. In the animal kingdom, the food chain for all creatures eventually comes back to using the carbon compounds created by plants as a source of vital energy. Even the waste product—oxygen—is crucial to most life on Earth.
Barry Bruce, a UT professor of biochemistry and cellular and molecular biology, is a master of that alchemy. He has built a distinguished career exploring the complexity of photosynthesis, teasing out the workings of chloroplasts that are at the heart of the photosynthetic process, and understanding the miracle that can turn sunlight into biochemical energy.
In recent years, Bruce’s research has turned toward what he calls “applied photosynthesis.” By extracting the essential photosystem I (PS-I) protein complexes that occur in spinach or blue-green algae and combining them with human-made devices, either a direct electric current or molecular hydrogen can be generated and stored.
“Photosynthesis is a preferred method of sustainable energy because it is clean and potentially very efficient,” Bruce says. “As opposed to conventional photovoltaic solar power systems, we are using renewable biological materials rather than toxic chemicals to generate energy.”
Almost a decade ago, Bruce collaborated on early efforts to harness the power of the photosynthetic process, working with Shuguang Zhang of the Center for Biomedical Engineering at the Massachusetts Institute of Technology. The team layered the PS-I complexes on a glass surface that produced an electric current when exposed to light.
In 2007, that research won Bruce the attention of Forbes magazine, which featured him as one of ten “revolutionaries” with potentially world-changing ideas. Although the project proved PS-I could be used to generate electricity, the actual mechanism developed by that team was expensive and not very efficient or robust.
In an effort to further enhance the technology, Bruce partnered with Paul Frymier, a UT professor of chemical and biomolecular engineering, to demonstrate a self-organizing nanoparticle capable of using PS-I and a platinum catalyst to produce molecular hydrogen. This remarkably stable discovery could eventually be used to produce a cost-effective method of converting the power of the sun into a fuel source for hydrogen-based fuel cells for transportation. This work was published in Nature Nanotechnology in 2010.
Bruce’s MIT collaboration continued with Andreas Mershin, who created a new foundation for the thin layer of PS-I. Inspired by the way needles are arranged on a pine tree, Mershin created an array of zinc oxide nano-wires on a sponge-like surface made of titanium dioxide. He conjectured that Bruce’s coating of PS-I would be exposed to more light on this type of framework, creating a stronger electric current. The metallic mesh had the added advantage of conducting the electric charge away from the biogenerator and into a circuit.
It was left to scientists at a third research institution—L’Ecole Polytechnique Federale in Lausanne, Switzerland—to determine whether the new development actually improved the mechanism. After complex testing directed by Michael Graetzel, a pioneer in energy and electron transfer reactions and their application in solar energy conversion, the new configuration proved successful.
In February 2012, the researchers described their breakthrough in an article for Nature: Scientific Reports: “Using inexpensive raw materials and simple processes, we have achieved record biophotovoltaic performances.…We hope these results encourage optimization efforts to deliver biosolar power that is truly ‘green.’”
However, don’t expect to see an algae-based electric generator on store shelves any time soon. The latest breakthrough only adds further proof to the viability of the process. The chief value of the work is that it simplifies the process and lowers the price threshold. Now, other laboratories can begin working out the best methods and refining processes that will ultimately make mass production possible.
“Commandeering this intricately organized photo-synthetic nanocircuitry and rewiring it to produce electricity carries the promise of inexpensive and environmentally friendly solar power,” Bruce and his colleagues wrote in the paper announcing the finding. They note that, despite the dramatic increase in efficiency, the mechanism still must become ten times more efficient to provide useful amounts of electricity.
As a research thrust leader for the TN-SCORE project, Bruce is collaborating on solar energy solutions with other scientists and engineers across the state of Tennessee. The $20 million NSF EPSCoR award (formally known as Tennessee Solar Conversion and Storage Using Outreach, Research, and Education) is targeted at improving alternative energy research at Tennessee’s educational institutions, particularly in the areas of advanced solar conversion, energy devices, and nanomaterials.
Bruce’s success with PS-I has also piqued the interest of the US Army Research Laboratory (ARL). Since transporting fuel to remote locations is expensive and increases the vulnerability of military operations and troops, the Army is looking at the PS-I technology to develop reactors that could create and store fuel on site. This project was one of only twelve selected nationwide to receive support from the ARL Director’s Strategic Initiative.
“Because the system is so cheap and simple, my hope is that it will develop with additional improvements to lead to a green, sustainable energy source,” Bruce says.
Now that the biosolar foundation is in place, it’s only a matter of time until the full promise of that basic photosynthetic alchemy is achieved and modern civilization can move on from extracting the fossil energy of ancient sunlight—with all the environmental damages that can bring—to harvesting the power of tomorrow morning’s dawn.
Check out the “Power Plants” audio podcast from NSF’s Discovery Files.