Researchers at the National Renewable Energy Laboratory are working on a novel way to use green algae to produce hydrogen directly from water and sunlight. 

Green alga produces oxygen during photosynthesis but oxygen inhibits the function of algal hydrogenase, the enzyme that allows the release of hydrogen gas. Under normal conditions such as sunlight, the alga cannot sustain hydrogen production for more than a few minutes. 

NREL researchers are addressing this issue by screening for naturally occurring organisms that are more oxygen tolerant and by creating new genetic organisms that can sustain hydrogen production in the presence of oxygen. Further research will determine if the modified enzymes will lead to the most-cost-effective, efficient route to hydrogen. 

Background:

NREL's biological scientists are working to help the nation develop environmentally benign fuels and chemicals. Our research on microorganisms, which includes studies of photosynthetic bacteria and algae, is revealing new ways to produce hydrogen fuel and valuable reduced-carbon compounds. We are studying how, through photosynthesis, algae can split water to produce hydrogen. Algae can also be used in the production of hydrocarbons, oils, lipids, and other products.

Algal Hydrogen Production

Green algae can produce hydrogen by splitting water through a process called "biophotolysis" or "photobiological hydrogen production." This photosynthetic pathway produces renewable fuels without producing greenhouse gases. The scientific challenge associated with the approach is that the enzyme (a reversible hydrogenase) that actually releases the hydrogen is sensitive to oxygen. The process of photosynthesis, of course, produces oxygen and this normally stops hydrogen production very quickly in green algae. So, to overcome this problem, NREL scientists are generating O2-tolerant, H2-producing mutants from the green alga Chlamydomonas reinhardtii by various genetic approaches (see photo). The ultimate goal of this work is to develop a water- splitting process that will result in a commercial H2-producing system that is cost effective, scalable to large production, non-polluting, and self-sustaining.

Basic Studies of Photosynthesis

The process of plant photosynthesis produces the oxygen we breathe, the food we eat, and important materials for our houses, clothes, and industries. In the future, it will also provide plant biomass for our fuel and more of our chemical needs through a process called "photoconversion." Through photoconversion, these products will be renewable and non-polluting, and they won't contribute to global warming. NREL researchers are trying to understand the detailed workings of the part of the photosynthetic process that provides the energy and electrons that plants require to grow. This particular process splits water molecules and supplies us with oxygen (which to the plant is waste product). Our research has visualized the protein structure (see photo) that performs these basic processes and has measured the extremely fast photochemical reactions (in trillionths of a second!) that drive these processes. This understanding may someday help us improve the efficiency of natural photosynthesis and design artificial photosynthetic processes as next-generation systems to produce renewable energy.

Hydrogen is the simplest and most abundant element in the world. Hydrogen (H2) can be produced from a wide variety of domestic resources using a number of different technologies. NREL has developed an exciting new technology that produces hydrogen from a renewable resource. Mutant algal hydrogenases is a new technology that produces hydrogen from renewable resources, the sun, and green algae. NREL researchers are making great advancements in developing this new technology that has great market potential and significant advantages over other photobiological systems. The advantages are high theoretical efficiencies, as well as an inexpensive hydrogen source, water.

Overall mutant algal hydrogenases have achieved excellent results and demonstrate high market value through the use oinexpensive and abundant materials to produce hydrogen. However, currently there are performance limitations that research is focusing on improving such as algal Hf 2 photoproduction is sensitive to O2, a co-product of photosynthesis. NREL is investigating ways to surmount this by focusing on genetically engineering the reversible [Fe]-hydrogenase (the enzyme that releases H2 gas). Previous studies indicate that site directed mutagenesis could be used to decrease the O2 sensitivity of the hydrogenase and thus eventually lead to a system that produces H2 under aerobic conditions, in the presence of oxygen.

Overall this new innovative technology provides an opportunity for a strategic partner to further develop and decrease the time to market for this technology. This new innovative technology provides a strategic partner the opportunity to be the first-in-line to secure an inexpensive, easy to produce renewable energy resource that has the potential to play a major role in the Hydrogen Economy.

Hydrogenase-catalyzed photosynthetic algal hydrogen production from water is a potentially efficient source of clean, renewable energy. However, practical implementation of this system has been hampered in the past due to the extreme sensitivity of the hydrogenase enzyme to oxygen, one of the byproducts of photosynthesis. In this project, researchers will complete an initial assessment of the potential of a novel algal H2-production system that overcomes these barriers to commercial production. The objective of this research is to design, fabricate, and operate an innovative photobioreactor to study the technical and economic feasibility of using a novel H2- producing system as a commercial process for production of renewable energy.