PORTLAND, Ore.—The Massachusetts Institute of Technology (MIT) laid out a roadmap to sustainability based on artificial photosynthesis technologies this week at the prestigious National Academy of Sciences (NAS).
The detailed scientific analysis establishes baselines for efficiency and outlines the technological research and development milestones needed to establish a sustainable hydrogen economy based on artificial photosynthesis. Engineers can use the document to identify where the technology stands today as well as how to make it practical, inexpensive and commercially viable, according to MIT.
"What is most significant is that the technology we describe as a starting point is already known," said MIT professor Tonio Buonassisi. "We also point out all the challenges, so that scientists and engineers can begin experimentally addressing each challenge separately." The roadmap was a cooperative effort of Buonassisi, former MIT professor Daniel Nocera (now at Harvard), former MIT postdoctoral researcher Mark Winkler (now at IBM) and former MIT doctoral candiate Casandra Cox (now at Harvard). The researchers together have already produced a proof-of-concept prototype of artificial photosynthesis, but the NAS presentation for the first time lays out a realizable roadmap.
In nature, photosynthetic plants convert natural resources—water and nutrients from earth—into a fuel called adenosine triphosphate (ATP)—which can be stored and used on-demand to power metabolic processes in the plant. For first-generation artificial photosynthesis, as proposed by MIT, photovoltaic cells coated with chemical catalysts that optimize the conversion of water into hydrogen-fuel using electrolysis. A fuel-cell is then used to convert the stored energy into electricity on-demand.
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Block diagram (A) for electrochemical cell using direct photovoltaic coupling, to a single PV cell (B, left) and three inter-digitated PV cells (B, right).
The current baseline is just below 5 percent efficiency, but by following the roadmap the researchers predict efficiencies of better than 16 percent using standard crystalline-silicon PV cells and up to 18 percent using gallium arsenide (GaAs). The roadmap matches different types of next-generation photocells to specific chemical catalysts as well as offering alternative ways of stacking cells to achieve the higher voltages needed to optimize electrolysis. The roadmap also catalogs how to eke out incremental improvements that lower the resistance of electrolytes using both chemistry and physical architecture, such as interleaved plates.
Funding for the project was provided by the National Science Foundation, the Air Force Office of Scientific Research, the Singapore National Research Foundation through the Singapore-MIT Alliance for Research and Technology, and the Chesonis Family Foundation.