Artificial photosynthesis is one step close to producing fuel utilizing the same basic chemical process seen in plants.

California Institute of Technology (Caltech) researchers have developed a new electrically-conductive film that could aid in developing devices that can separate water molecules into hydrogen and oxygen. Following this process, hydrogen can be stored in fuel cells capable of powering vehicles and production plants.

The nickel oxide layer assists in the production of hydrogen or methane in artificial leaves and prevents the buildup of rust on the devices.

"We have developed a new type of protective coating that enables a key process in the solar-driven production of fuels to be performed with record efficiency, stability, and effectiveness, and in a system that is intrinsically safe and does not produce explosive mixtures of hydrogen and oxygen," Nate Lewis, chemistry professor at Caltech, said.

Artificial leaves, sometimes known as solar fuel generators, can manufacture environmentally-friendly fuels by mimicking the natural processes plants use to generate sugars from sunlight, oxygen and water.

The new device created by the researchers consists of three parts — a photocathode, photoanode and membrane. Water is converted into oxygen, protons and electrons by the photoanode and the photocathode combines the subatomic particles back into hydrogen, which could be stored in fuel cells. The membrane serves to keep the two gases separated to prevent an explosion.

Silicon and gallium arsenide have both been used as semiconductors in the production of solar panels, but each of these materials can oxidize or rust in the presence of water. Several different materials have been used in experiments to develop a coating that would prevent oxidation while allowing the chemical process to continue. Such a material would need to be impervious to water, transparent to allow light to pass through, capable of acting as a catalyst, and compatible with the material in the devices.

"Creating a protective layer that displayed any one of these attributes would be a significant leap forward, but what we've now discovered is a material that can do all of these things at once," Lewis said.

The nickel oxide film is produced by colliding argon atoms into a sample of nickel within an oxygen-rich environment. Tiny nickel fragments flying off the pellet combine with oxygen in the air and are layered on the semiconductor.

The film is compatible with a wide range of materials currently used in the development of artificial leaves, meaning they could be used with a wide range of potential technologies.

Testing of artificial leaves using the new film produced record performance for 500 hours.

Development of the new film was profiled in the Proceedings of the National Academy of Sciences.

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