Lab leaf recycles carbon dioxide

Syngas, an intermediate product in the manufacturing of synthetic liquid fuels and methanol, is a mixture of mostly carbon monoxide and molecular hydrogen. Generating the two ingredients typically involves exposing fossil fuels to high temperatures and pressures, so researchers have been studying alternative solar-driven processes to make syngas more cleanly and with a lower thermodynamic burden. Rather than use the photovoltaic cells and noble metals that other researchers have tried, Virgil Andrei, Bertrand Reuillard, and Erwin Reisner at the University of Cambridge turned to photoelectrochemical devices inspired by plant photosynthesis. The molecular catalyst they chose, a cobalt atom surrounded by an organic frame, allows them to produce syngas from a standalone device.

The image, courtesy of Andrei, shows the researchers’ artificial leaf immersed in water. It’s composed of a yellow bismuth vanadate photoanode coupled to a perovskite-based photocathode. When illuminated by sunlight, the photocathode reduces aqueous CO₂ and water in a neutral pH solution to CO and H₂ gas. The leaf can maintain constant syngas production and water oxidation for several days. Andrei and his colleagues experimented further with the light source and found that the perovskite photocathodes yield CO with as little as a tenth of the Sun’s intensity. Although commercialization is far off, the device’s potential to operate throughout the day could improve its economic feasibility. (V. Andrei, B. Reuillard, E. Reisner, Nat. Mater., 2019, doi:10.1038/s41563-019-0501-6 .)