Published on February 11th, 2014 | by Tina Casey2
Friendly Mutant Algae Could Churn Out Sustainable Hydrogen On Your Desktop
The Jetsons could only dream about a gizmo like this: a desktop bioreactor swimming with microalgae that churn out hydrogen for your home fuel cell. For those of you who keep fish at home, the leap to a small scale bioreactor doesn’t seem like that big of a deal, right?
As the hydrogen fuel cell market begins to rev up, you’re going to be hearing more about off-grid solutions for distributed, sustainable hydrogen generation. We’ve been following several photosynthesis based pathways using non-living materials (here and here, for example), and bacteria-based processes are also in the works (like here), but this algae thing is new on our radar.
A Microalgae Fuel Cell
The algae in question is a single celled green algae called Chlamydomonas reinhardtii. It is widely used as a research model due to its high degree of adaptability and fast reproductive cycle (that’s why we call it friendly, though apparently its official nickname is pronounced “Clammy”). Its main energy source is photosynthesis but it can also thrive on carbon in a dark environment.
According to the Carnegie Institute of Science, a sequencing of its 15,000 genes has revealed that it is “more plant than animal” (some critters that we call algae are actually bacteria), but it shares many genes that are either directly associated with human functions or are associated with key metabolic processes. According to one researcher on the project:
Although Chlamydomonas is certainly more plant than animal, there are clear similarities between this photosynthetic organism and animals that would surprise the average person on the street.
So, now that you have a bit of background on this intriguing critter, the hydrogen angle won’t surprise you.
Researchers at the National Renewable Energy Laboratory have been tinkering around with C. reinhardtii to see if they can get it to produce more hydrogen, and their latest results have just been published online at the Journal of Biological Chemistry under the title, “Identification of global ferredoxin interaction networks in Chlamydomonas reinhardtii.”
In a nutshell, here are the findings:
Scientists at the Energy Department’s National Renewable Energy Laboratory have demonstrated that just two of six iron-sulfur-containing ferredoxins in a representative species of algae promote electron transfers to and from hydrogenases.
That might not sound like such a big deal, but in terms of foundational research it is a giant step forward.
Ferredoxins are redox mediators containing iron and sulfur (redox mediator refers to electron transfer). They also happen to be one of the characteristics of C. reinhardtii with functions that have not yet been clearly determined.
By narrowing the field down from six to two ferredoxins, the NREL team has pushed forward the understanding of electron competition in C. reinhardtii. The idea moving forward would be to modify C. reinhardtii to force more electrons through the most productive pathways and block it from others.
That line of work is already promising, as NREL refers to previous studies showing that C. reinhardtii could be genetically modified to outright eliminate certain pathways. That would steer more electrons to the cell’s hydrogenase, which is the enzyme that catalyzes the hydrogen reaction.
If you’re wondering why the hydrogen fuel cell market hasn’t exploded yet, one key reason is the enormous amount of conventional energy that it takes to manufacture hydrogen.
That could change in the near future. Although the new NREL research is a foundational project that won’t bear commercial fruit for a long time, sustainable hydrogen generation by microorganisms is coming into play.
Another federal lab, Lawrence Livermore National Laboratory, has been revving up a new wastewater-to-hydrogen demo project that extracts a hydrogen compound from decomposing solids using an energy efficient thermochemical process. If the process proves cost-effective, it could be deployed on a large scale at hundreds of municipal wastewater treatment plants around the country.
Similarly, a company called HyperSolar is already envisioning a network of hydrogen “farms”using nanoscale solar devices floating in waste feedstock including both municipal and industrial wastewater.
At the other end of the scale there’s a solar-powered toilet hitched up to a reactor that separates hydrogen gas from water and solids, which is currently being developed to help underserved communities improve their sanitary facilities.
Let’s also not forget the snail modded out to form a living fuel cell that could power small electronic devices, but for now we’re putting that in the category of sometime way in the future.
Another pathway is the aforementioned non-living materials, which basically means the development of photochemical cells that directly strip hydrogen from water using solar energy, without going through the mediator of electricity produced by a photovoltaic cell.
One promising example of this kind of sustainable hydrogen technology comes from Ecole Polytechnique Fédérale de Lausanne and Technion–Israel Institute of Technology, which have teamed up to create a photochemical cell based on an electrode made of nanostructured iron oxide (aka rust) particles.
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