The discovery, formally presented by its leader, MIT chemist Daniel Nocera, at the National Meeting of the American Chemical Society, doesn't look like a leaf, but rather like a very thin credit card. But placed in a gallon of water, the biomimicked leaf can produce enough electricity for a day in a house in a developing country...And here is some background from 2008 in MIT News:
There have been other successful attempts at creating electricity from water, but they were too expensive to produce on a large scale. The MIT leaf is made of inexpensive materials that are readily available - silicone, electronics, and special catalysts... It was Nocera's recent discovery of several catalysts made from nickel and cobalt, that created his breakthrough. These catalysts are what split the water into hydrogen and oxygen under very simple conditions - even dirty water can be used. His artificial leaf is now 10 times more powerful than a natural leaf at photosynthesis...
The key component in Nocera and Kanan's new process is a new catalyst that produces oxygen gas from water; another catalyst produces valuable hydrogen gas. The new catalyst consists of cobalt metal, phosphate and an electrode, placed in water. When electricity — whether from a photovoltaic cell, a wind turbine or any other source — runs through the electrode, the cobalt and phosphate form a thin film on the electrode, and oxygen gas is produced.The hydrogen and oxygen are then used in a fuel cell. A brief video at the second link explains.
Combined with another catalyst, such as platinum, that can produce hydrogen gas from water, the system can duplicate the water splitting reaction that occurs during photosynthesis.