Does photosynthesis hold the key to large-scale solar power?

by Antonio Pasolini on July 31, 2008

The Massachusetts Institute of Technology (MIT) today announced that two of its researchers have overcome a major barrier to large-scale solar power: storing energy for use when the sun doesn’t shine. They have done so by mimicking the essence of plants’ energy storage system.

One of the challenges faced by solar power is that it is limited to being a daytime-only energy source, because storing extra solar energy for later use is expensive and inefficient. But, once again, nature may provide the answer to the problem. Inspired by the photosynthesis performed by plants, MIT’s Daniel Nocera and Matthew Kanan, a postdoctoral fellow in Nocera’s lab, have developed an unprecedented process that will allow the sun’s energy to be used to split water into hydrogen and oxygen gases. Later, the oxygen and hydrogen may be recombined inside a fuel cell, creating carbon-free electricity that can power homes or electric cars day or night.

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. 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.

The new catalyst works at room temperature, in neutral pH water, and it’s easy to set up, Nocera said. “That’s why I know this is going to work. It’s so easy to implement,” he said.

Sunlight has the greatest potential of any power source to solve the world’s energy problems, said Nocera. In one hour, enough sunlight strikes the Earth to provide the entire planet’s energy needs for one year.

Currently available electrolyzers, which split water with electricity and are often used industrially, are not suited for artificial photosynthesis because they are very expensive and require a highly basic (non-benign) environment that has little to do with the conditions under which photosynthesis operates. More engineering work needs to be done to integrate the new scientific discovery into existing photovoltaic systems, but Nocera said he is confident that such systems will become a reality.

Nocera hopes that within 10 years, homeowners will be able to power their homes in daylight through photovoltaic cells, while using excess solar energy to produce hydrogen and oxygen to power their own household fuel cell. Electricity-by-wire from a central source may well become a thing of the past. We hope so too.

The project is part of the MIT Energy Initiative, a program designed to help transform the global energy system to meet the needs of the future and to help build a bridge to that future by improving today’s energy systems.

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