Nov 05 2019
Another Artificial Leaf
Scientists report a new process for using sunlight to convert atmospheric carbon dioxide into oxygen and fuel. Anything that does a version of this basic process has been called an “artificial leaf” because that is what photosynsthesis does, convert CO2 and water into oxygen and glucose. The balanced equation is this: 6CO2 + 6H2O ——> C6H12O6 + 6O2, and the process is driven by energy from sunlight.
Plants evolved to do this efficiently. So, if we want an efficient system to remove CO2 from the air and make useful molecules, we can use life that already does this: plants, algae, or photoplankton. This is the basic concept of biofuels. Of course, when you burn biofuels you release the CO2 back into the atmosphere, so this isn’t a way to remove CO2 permanently, but it is a potentially carbon neutral process, with the energy ultimately coming from the sun.
I say potentially carbon neutral, because it depends how you are growing the biomass. If you are using fossil fuel based fertilizer and the farming itself is energy intensive, then you may release more CO2 than you take out. This is a limiting factor for using biofuels as a strategy for decarbonizing the energy infrastructure. Also, farming is very land intensive, and we need that land to grow food. For these reasons I don’t see biofuels as a major solution to the carbon problem. At best it can be used to recycle biomass that would otherwise be wasted to replace fuels for applications (like jet fuel) that are not easily replaced with electric motors.
The “artificial leaf” approach is very similar to the biofuel approach, except we use technology instead of biology. The key is in developing catalysts that will efficiently produce the reactions we need, getting their primary energy from sunlight. The advantage over biofuels is that if we could develop a scalable, efficient, and cost effective process it may not depend at all on farmland or large amounts of water. In the end this is an energy storage solution for solar energy, and in that manner is similar to using photovoltaics and batteries. In the case of the artificial leaf, the leaf is the photovoltaic, and the end product is the “battery” or energy storage medium.