Yesterday’s part I of this article explained how a team of Caltech scientists called the Joint Center for Artificial Photosynthesis (or JCAP) has created a cost effective system that uses only CO2, water, and sunlight to split water into oxygen and hydrogen, for the first time allowing solar energy to be directly stored. It also explained that one major breakthrough the JCAP team made was figuring out that by coating the electrodes of their electrolysis device with titanium dioxide they could keep them from corroding in the water they were immersed in to split it apart. Another key advance made by the JCAP team is the use of active, inexpensive catalysts for fuel production.
The photoanode (the solar powered anode) requires a catalyst to drive the essential water-splitting reaction. The most commonly used catalysts for electrolosys are expensive metals like platinum, but the JCAP team found that by adding a layer of nickel that was a mere 2-nanometers thick to the surface of the titanium dioxide, they could create a catalyst that was not just much less expensive than more commonly used catalysts, but one that was among the most active currently known for splitting water molecules into oxygen, protons, and electrons. This active nature caused the team’s new catalyst to be highly efficient. and is a key element in the device’s high efficiency overall.
The team realized that they could use the same technique for creating a photocathode, which, like the photoanode, also contains a highly active, and inexpensive catalyst of nickel-molybdenum. This fully integrated single material serves as a complete solar-driven water-splitting system.
The other critical component in the JCAP team’s system is the special plastic membrane. It simultaneously keeps the oxygen and hydrogen separate, preventing the possibility of an explosion, while at the same time allowing the ions to flow through it to seamlessly complete the electrical circuit in the system.
All three components work together to produce a high-performance, fully integrated system. The proof of concept version of the system is about one square centimeter in size. It converts 10 percent of the energy in sunlight it’s exposed to into stored energy in the form of hydrogen fuel. It can operate continuously for more than 40 hours.
Nate Lewis, a Caltech professor of chemistry, and the JCAP scientific director says, ”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. … Our work shows that it is indeed possible to produce fuels from sunlight safely and efficiently in an integrated system with inexpensive components. … Of course,” adds Lewis, “we still have work to do to extend the lifetime of the system and to develop methods for cost-effectively manufacturing full systems, both of which are in progress.”
Andrew J. Dunlop lives and writes in a little town near Boston. He's interested in space, the Earth, and the way that humans and other species live on it.
