When it comes to producing efficient fuel cells, it’s all about the catalyst. A good catalyst will result in faster and more efficient chemical reactions and, therefore, in an increase in energy production. Fuel cells today typically rely on platinum-based catalysts. But scientists at the American University believe that spinach, considered a “superfood” because it is so rich in nutrients, would make an excellent, carbon-rich renewable catalyst, based on their proof-of-principle experiments described in a recent article published in the journal ACS Omega. Popeye would definitely approve.
The idea of exploiting the photosynthetic properties of spinach has been around for about 40 years. Spinach is abundant, inexpensive, easy to grow, and high in iron and nitrogen. Many (many!) Years ago, as a budding young science writer, I attended a lecture given by physicist Elias Greenbaum (then with Oak Ridge National Labs) about his research on spinach. In particular, he was interested in the protein-based “reaction centers” in spinach leaves which are the basic mechanism of photosynthesis, the chemical process by which plants convert carbon dioxide into oxygen and carbohydrates.
There are two types of reaction centers. One type, known as photosystem 1 (PS1), converts carbon dioxide into sugar; the other, photosystem 2 (PS2), divides the water to produce oxygen. Most of the scientific interest is in PS1, which acts as a tiny photosensitive battery, absorbing energy from sunlight and emitting electrons with nearly 100% efficiency. In essence, the energy of sunlight converts water into an oxygen molecule, a positively charged hydrogen ion, and a free electron. These three molecules then combine to form a sugar molecule. PS1s are capable of generating a light-induced flow of electricity in fractions of a second.
Sure, that’s not a huge amount of power, but it’s enough to one day run small molecular machines. Greenbaum’s work was promising for constructing artificial retinas, for example, replacing damaged retinal cells with light-sensitive PS1 to restore vision in those suffering from a degenerative eye condition. Because PS1s can be modified to behave like diodes, passing current in one direction but not the other, they could be used to build logic gates for a rudimentary computer processor if they could be connected via molecule-sized wires made of carbon nanotubes.
Greenbaum is just one of many researchers interested in the electrochemical properties of spinach. For example, in 2012, scientists at Vanderbilt University combined PS1 with silicon to achieve current levels nearly 1,000 times higher than those achieved when protein centers are deposited on metals, along with a modest increase in voltage. The goal was to eventually build “biohybrid” solar cells that could compete with standard silicon solar cells in terms of voltage and current levels. A 2014 paper by Chinese researchers reported on experiments to harvest activated carbon from spinach for capacitor electrodes, while just last December another group of Chinese scientists examined the potential of making spinach-based nanocomposites to act as photocatalysts.