Bio-Platinum Hybrid Catalyst for Solar Hydrogen Production Can Deliver Up to 25x Greater Energy Yield Than Current Biomass-to-Fuel Strategies
|Schematic of the electron flow in the photosystem I catalytic nanoparticle. Source: Iwuchukwu et al., Nature Nanotechnology. Click to enlarge.|
Researchers at the University of Tennessee at Knoxville have shown that a combination of photosystem I from a thermophilic bacterium and cytochrome-c6 can, in combination with a platinum catalyst, generate a stable supply of hydrogen in vitro upon illumination. A paper on their work was published online 8 November in the journal Nature Nanotechnology.
The system produces hydrogen at temperatures up to 55 °C (131 °F) and is temporally stable for >85 days with no decrease in hydrogen yield when tested intermittently. The maximum yield is ~5.5 mmol H2 h-1 mg-1 chlorophyll and is estimated to be ~25-fold greater than current biomass-to-fuel strategies. If scaled linearly, a solar collector 1 acre in size with a solution depth of 10 cm operating at 55 °C would be capable of producing hydrogen with an energy yield equivalent to that of 300 litres of gasoline per hectare per day (gross yield, ignoring production separation and distribution energy costs).
Current biomass-to-fuels schemes yield relatively low fuel value per unit land area, the authors note. One way to improve production yield is to use solar energy directly, as plants do in photosynthesis.
In oxygenic photosynthesis, two reaction centers, photosystem II and photosystem I (PSI), function together to transfer electrons derived from water, producing both oxygen and ATP. Several studies have shown that coupling either platinum nanoclusters or covalently linked hydrogenase to the acceptor end of PSI complexes can harvest the photochemically produced electrons to reduce protons to hydrogen in vitro.
The University of Tennessee team showed that a stable supply of hydrogen can be generated using a platinum catalyst and a system made of PSI isolated from the thermophilic cyanobacterium T. elongatus and a recombinant form of cytochrome-c6 (cyt c6) protein.
This potential yield [300 litres of gasoline per hectare per day] is more than an order of magnitude higher than the gross yield in terms of gasoline equivalents of agricultural biomass systems such as corn-based ethanol (5.43 litres per day per hectare), soy based biodiesel (1.42 litres per day per hectare) or projected yields of switchgrass-produced ethanol (12.1 litres per day per hectare). Comparing this fuel production rate to the average available solar radiation at latitudes in the middle of the US, this system is capable of converting ~6% of solar radiation into usable fuel.
This system provides a more direct route to fuel production with no need for the harvesting, converting, fermenting and distilling processes involved in conversion of biomass to ethanol. Moreover, other processing and transportation costs would be much lower because the bio–platinum hybrid catalyst is reused through many cycles, unlike in single-use methods such as biomass accumulation.
Finally, the fact that our PSI operates with high thermal tolerance suggests that this approach may be viable in non-arable regions with high solar irradiances. This is in contrast to the cultivation of biofuels that may compete directly with agricultural production.
—Iwuchukwu et al.
(A hat-tip to Matt!)
Ifeyinwa J. Iwuchukwu, Michael Vaughn, Natalie Myers, Hugh O’Neill, Paul Frymier & Barry D. Bruce (2009) Self-organized photosynthetic nanoparticle for cell-free hydrogen production. Nature Nanotechnology doi: 10.1038/nnano.2009.315