New Artificial Leaf safely creates Fuel from Sunlight and Water with record Efficiency and Stability

 

The new Artificial Leaf JCAP system has 3 main components: 2 electrodes–one photoanode and one photocathode, and a membrane. The photoanode uses sunlight to oxidize water molecules, generating protons and electrons as well as oxygen gas. The photocathode recombines the protons and electrons to form H2. A key part of the JCAP design is the plastic membrane, which keeps the O2 and H2 gases separate. If the 2 gases are allowed to mix and are accidentally ignited, an explosion can occur; the membrane lets the H fuel be separately collected under pressure and safely pushed into a pipeline.

Semiconductors such as silicon or gallium arsenide absorb light efficiently and are therefore used in solar panels but they oxidize (or rust) when exposed to water, so cannot be used to directly generate fuel. A major advance that allowed the integrated system to be developed was work in Lewis’s laboratory, which showed adding a 62.5nm-thick layer of titanium dioxide (TiO2) onto the electrodes could prevent them from corroding while still allowing light and electrons to pass through. The new complete solar fuel generation system improves stability of a gallium arsenide-based photoelectrode.

Another key advance is the use of active, inexpensive catalysts for fuel production. The photoanode requires a catalyst to drive the essential water-splitting reaction. Rare, expensive platinum can serve as effective catalysts, but they could create a much cheaper, active catalyst by adding a 2-nm-thick layer of nickel to the surface of the TiO2. This catalyst is among the most active known catalysts for splitting water molecules into oxygen, protons, and electrons and is a key to the high efficiency displayed by the device.

The photoanode was grown onto a photocathode, which also contains a highly active, inexpensive, nickel-molybdenum catalyst, to create a fully integrated single material that serves as a complete solar-driven water-splitting system.

A special plastic membrane separates the gases and prevents the possibility of an explosion, while still allowing the ions to flow seamlessly to complete the electrical circuit in the cell. The demonstration system is 1cm sq, converts 10% of the energy in sunlight into stored energy in the chemical fuel, and can operate for more than 40 hrs continuously.

“This new system shatters all of the combined safety, performance, and stability records for artificial leaf technology by factors of 5 to 10 or more ,” Lewis says. http://www.caltech.edu/news/artificial-leaf-harnesses-sunlight-efficient-fuel-production-47635