When it comes to making efficient fuel cells, it’s all about the catalyst. A good catalyst will result in faster, more efficient chemical reactions and, thus, increased energy output. Today’s fuel cells typically rely on platinum-based catalysts. But scientists at American University believe that spinach—considered a “superfood” because it is so packed with nutrients—would make an excellent renewable carbon-rich catalyst, based on their proof-of-principle experiments described in a recent paper published in the journal ACS Omega. Popeye would definitely approve.
The notion of exploiting the photosynthetic properties of spinach has been around for about 40 years now. Spinach is plentiful, cheap, easy to grow, and rich in iron and nitrogen. Many (many!) years ago, as a budding young science writer, I attended a conference talk by physicist Elias Greenbaum (then with Oak Ridge National Labs) about his spinach-related research. Specifically, he was interested in the protein-based “reaction centers” in spinach leaves that are the basic mechanism for 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), splits water to produce oxygen. Most of the scientific interest is in PS1, which acts like a tiny photosensitive battery, absorbing energy from sunlight and emitting electrons with nearly 100-percent efficiency. In essence, energy from 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.
Granted, it’s not a huge amount of power, but it is sufficient to one day run small molecular machines. Greenbaum’s work held promise for building artificial retinas, for instance, replacing damaged retinal cells with light-sensitive PS1s to restore vision in those suffering from a degenerative eye condition. Since PS1s can be tweaked to behave like diodes, passing current in one direction but not the other, they could be used to construct logic gates for a rudimentary computer processor if one could connect them via molecule-sized wires made of carbon nanotubes.
Greenbaum is just one of many researchers who are interested in the electrochemical properties of spinach. For instance, in 2012, scientists at Vanderbilt University combined PS1s with silicon to get current levels nearly 1,000 times higher than achieved when depositing the protein centers onto 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 collect activated carbon from spinach for capacitor electrodes, while just last December, another group of Chinese scientists examined the potential of making nanocomposites based on spinach to serve as photocatalysts.