Photosynthesis is one of the most efficient ways known to harvest solar energy to convert into chemical energy. As such, it’s a demonstration of how nature has succeeded through the process of natural selection where we have failed through rational construction and experimentation in trying to create artificial photosynthesis. That is, until now.
The Proceedings of the National Academy of Science recently published a paper explaining how a team of scientists from the U.S. and China have created a simple catalyst capable of using sunlight to oxidize water into oxygen and hydrogen gases. This catalyst is simply two iridium atoms connected by a single oxygen atom (Ir2O), all of which are on an α-Fe2O3 substrate (α-Fe2O3 is found in nature as hematite, also known as the main form of iron ore). The result is a form of photosynthesis that is similar to natural photosynthesis, but at lower cost and higher efficiencies.
The Ir2O catalyst is simple, durable, and highly active, and it not only harvests solar energy, but it also stores that energy in chemical bonds. If these catalysts can be scaled up to truly commercial levels of hydrogen gas production, they could radically transform energy production across the globe. After all, the product of these stable iridium dinuclear catalysts—hydrogen gas—is an important alternative fuel precisely because it produces substantial energy when burned with oxygen to create water. A hydrogen-fueled economy would be one that can provide everyone with the fuel and energy we need, without creating any pollution byproducts. These new catalysts thus offer significant hope and promise.
Unfortunately, iridium is one of the rarest metals on earth, with annual global production at only around 3 tons. While sparse in the earth’s crust, iridium is much more common in meteorites—although mining meteorites won’t happen in the immediate future. This rare metal has found a recent increase in use in a variety of electronics, spark plugs, and devices that need to withstand very high temperatures. Because this iridium dinuclear catalyst is so efficient, however, the scarcity of iridium will hopefully not pose a problem to the further development of these photosynthetic cells.