Artificial Leaf Moves Two Steps Closer to Reality
In the first, researchers led by Daniel Nocera, a chemist at the Massachusetts Institute of Technology in Cambridge, report that they’ve created an “artificial leaf” from cheap, abundant materials that splits water into molecular hydrogen (H2) and oxygen (O2), somewhat similar to the way plants carry out the first step in photosynthesis. The leaf consists of a thin, flat, three-layered silicon solar cell with catalysts bonded to both faces of the silicon. When placed in a beaker of water and exposed to sunlight, silicon absorbs photons of sunlight, generating electrons with enough energy to conduct through the silicon.
In the second study, a team led by chemists Richard Masel of Dioxide Materials in Champaign, Illinois, and Paul Kenis of the University of Illinois Urbana-Champaign, report that they’ve come up with a more energy-efficient approach to converting carbon dioxide (CO2) into carbon monoxide (CO), the first step to making a hydrocarbon fuel. Other researchers have worked for decades to devise catalysts and the right reaction conditions to carry out this conversion. But converting CO2 to CO has always required applying large electrical voltages to CO2 to make the change. That excess voltage is an energy loss, meaning it takes far more energy to make the CO than it can store in its chemical bonds.
“These papers are nice advances,” says Daniel DuBois, a chemist at Pacific Northwest National Laboratory in Richland, Washington, who works on catalysts for both splitting water and re-energizing CO2. But he cautions that neither solves all of their respective issues. The oxygen-forming catalyst in the artificial leaf, for example, remains slow, DuBois says. And the efficiency of the overall leaf is only 4.7% at most, and just 2.3% in its most simplest design. The catalyst in the CO2 system is even slower. But DuBois says that because other researchers in the field now have a good examples of systems that work, they can now focus on designing improved catalysts to speed them up.