Creating Water Power From An “Artificial Leaf”

The idea of separating water into hydrogen and oxygen has been around for some time. Often dismissed as impractical, such a fuel source could provide clean, sustainable energy for our world if it could be made to work reliably and efficiently. One Harvard scientist has made great strides toward making that dream a reality. Daniel Nocera, the Patterson Rockwood Professor of Energy at Harvard University, has refined an “artificial leaf” that has the potential to revolutionize the way we produce energy.
The artificial leaf has been sought after by scientists for decades; an efficient device that, like plants, can use sunlight to create energy. But where plant leaves produce sugars, artificial leaves would split water into clean-burning fuel. Some prototypes had been developed in recent years, but these devices had a weakness: the water had to be pure. In the absence of distilled, pure water, bacteria would grow and form a film over the device, halting hydrogen and oxygen production. This weakness was a major barrier in making the technology practical, given that much of the world does not have access to clean drinking water, let alone ultra-pure water.

Dr. Nocera has developed the world’s first practical artificial leaf and his findings indicate that his design is able to self-heal and to work even in dirty water. In presenting his work at the recent American Chemical Society meeting in New Orleans, Dr. Nocera says that he’s developed a cobalt-based coating that breaks off during the gas-producing reaction and then slowly reassembles back onto the silicon wafer. Because it’s constantly re-forming itself, the bacteria don’t have an unbroken surface to stick to – which makes the new and improved artificial leaf a more rough-and-ready device that can be deployed even in dirty water.

Nocera’s artificial leaf is elegantly simple: It’s a coated silicon wafer roughly the size of a credit card that can be dropped into a cup of water. When the wafer is placed in sunlight, pure oxygen will bubble up from one side and pure hydrogen from the other. Such a device, placed in a bucket (and with the two sides properly separated, of course) could create enough clean fuel to power a home in a developing country.

Such a device could radically revolutionize clean energy, reducing dependence on fossil fuels and providing an even better solution than plain old solar cells, which are perfect for sunny days but don’t store energy for nighttime use. In addition, it would allow for onsite power generation in virtually every region where people live. Such power could be used not only to light homes, but it would also be critical in pumping fresh drinking water and assisting in local sanitation needs. The lack of reliable electrical power is a key barrier to water and sanitation worldwide.

Dr. Nocera admits that there are limitations. While his energy-to-fuel system is currently around 70% to 80% efficient, Nocera said, it’s only as good as the silicon-based solar underlying it – and given that current solar cells have an efficiency rate of 7%, that means an overall rate of about 5% for his artificial leaf. But Nocera expects solar cells in general to vastly improve over the next few years.

While it will likely be a few years before artificial leaves are field tested, the technology is exciting and offers the promise of reliable, clean energy in even the most remote locations. This invention certainly adds to the clean energy “toolbox” and increases the likelihood that one day, people worldwide will have access to electricity and sanitation.

Nocera notes that his research was aided in funding from the National Science Foundation, the Department of Energy and the Air Force Office of Scientific Research.