One of the biggest obstacles to widespread use of solar energy is the lack of a low-cost, effective way to store it when the sun is not shining. To get around this, two MIT chemists have devised a method of hoarding solar energy that functionally mimics what plants do during photosynthesis. “We spent a lot of time understanding how a leaf works,” Daniel Nocera says, “and then built something that looks totally different but operates in the same way.”
During photosynthesis, plants convert solar energy into chemical form. A key aspect of this process involves splitting water into oxygen and hydrogen. The oxygen is given off, and the hydrogen is ultimately incorporated into sugars that the plant stores as fuel. Nocera and his postdoctoral student, Matthew Kanan, discovered that cobalt (a widely available metal) can be used to create a catalyst that similarly splits water molecules—in this case, in the presence of an electric current. This process could form the basis of a practical solar-energy storage system, Nocera says, in which electric current from a solar cell passes through water to the catalyst, breaking the water into oxygen and hydrogen through electrolysis. Those gases could be stored and later turned back into electricity in a fuel cell. Cobalt is both easier to engineer and less expensive than metals currently used in electrolyzers.
