by Liza Farr
In 2011, Daniel Nocera engineered an artificial leaf that uses only sun and water to produce energy (Chandler, Sep 30, 2011). The leaf was made of silicon solar plates with different catalytic materials bonded on each side (Chandler, Sep 30, 2011). When the plate is placed in water and exposed to sunlight, one side produces hydrogen bubbles, and one side oxygen bubbles, which can be stored and used for energy (Chandler, Sep 30, 2011). Although this was an important innovation in renewable energy, major shortcomings of the invention was that it produced hydrogen, which does not easily fit into our existing energy infrastructure, rather than liquid fuel. Recently, Nocera has collaborated with biologists at Harvard University to engineer bacteria that convert hydrogen into an alcohol-based fuel (Nunez, Feb 9, 2015).
In natural photosynthesis, biomass is produced when sunlight meets water and carbon dioxide, but an extra step is needed to turn the biomass into fuel, such as the ferrmenting of corn to make ethanol, which can be energy intensive and inefficient (Nunez, Feb 9, 2015). The new bacteria bypass this step to produce liquid fuel immediately, by absorbing the hydrogen and combining it with carbon dioxide to produce isopropanol, an alcohol-based fuel similar to ethanol (Nunez, Feb 9, 2015). In order to make this bacteria economically viable, researchers needed to produce a ten percent solar-to-fuel conversion efficiency rate, which they achieved and published in a scientific article in August, 2014 (Coxa et al. 2014). Both the leaf and the bacteria catalyst are made using non-precious, earth-abundant materials, bringing the project another step closer to economic viability (Coxa et al. 2014). Nunez (Feb 9, 2015) predicts that the next step needed to make this innovation commercially viable is to figure out how the carbon dioxide required to complete the reaction can be obtained directly from the atmosphere. This process is quite energy intensive, and it is a major barrier to the viability of the innovation. This will undoubtedly be the next problem Nocera and others will address to make the artificial leaf a viable innovation (Nunez, Feb 9, 2015).
Casandra R. Coxa, Jungwoo Z. Leeb, Daniel G. Noceraa, and Tonio Buonassisi. 2014. Ten-percent solar-to-fuel conversion with nonprecious materials. Proceedings of the National Academy fo Sciences. August 1, 2014:14057–14061.
Chandler, David L. ‘Artificial leaf’ makes fuel from sunlight. September 30, 2011. [http://newsoffice.mit.edu/2011/artificial-leaf-0930]
Nunez, Christina. “Tweaking Bacteria, Scientist Turn Sunlight into Liquid Fuel.” February 9, 2015. [http://news.nationalgeographic.com/news/energy/2015/02/150209-solar-energy-to-liquid-fuel/]