Syngas is currently made from a mixture of hydrogen and carbon monoxide and is used to produce a range of commodities such as fuels, pharmaceuticals, plastics, and fertilizers. Producing it sustainably could be a critical step in closing the global carbon cycle and establishing a sustainable chemical and fuel industry.
Researchers have developed an “artificial leaf” that uses only sunlight, carbon dioxide, and water to directly produce syngas in a sustainable manner. Rather than running on fossil fuel, the artificial leaf is powered by sunlight, although it still works efficiently on cloudy and overcast days. And unlike the current industrial processes for producing syngas, the leaf does not release any additional carbon dioxide into the atmosphere.
The device is inspired by photosynthesis — the natural process by which plants use the energy from sunlight to turn carbon dioxide into food. On the artificial leaf, two light absorbers, similar to the molecules in plants that harvest sunlight, are combined with a catalyst made from the naturally abundant element cobalt. When the device is immersed in water, one light absorber uses the catalyst to produce oxygen. The other carries out the chemical reaction that reduces carbon dioxide and water into carbon monoxide and hydrogen, forming the syngas mixture. The light absorbers work even under the low levels of sunlight on a rainy or overcast day.
Other similar devices have been developed but they usually only produce hydrogen. The new device produces syngas sustainably through a combination of materials and catalysts. These include perovskite light absorbers that provide a high photovoltage and electrical current to power the chemical reaction by which carbon dioxide is reduced to carbon monoxide, in comparison to light absorbers made from silicon or dye-sensitized materials. Cobalt also was used as the molecular catalyst instead of platinum or silver.
Syngas is already used as a building block in the production of liquid fuels. Rather than first making syngas and then converting it into liquid fuel, the team aims to make the liquid fuel in one step from carbon dioxide and water.