Splitting Water Molecules the Next "Green" Power Source?

Brian Handwerk
for National Geographic News
March 5, 2007

A limitless renewable energy source that can wean humans off fossil fuels has existed for billions of years, according to the latest report from a "green" scientist.

The trick to using it is figuring out how to make our power sources more like plants—and a recent discovery may bring scientists closer to the goal.

Plants use photosynthesis to capture energy directly from the sun, a feat that humans have been striving to achieve for years via solar cells.

"How will mankind be able to supply itself with the levels of energy it needs?" asked James Barber, a biochemist at Imperial College London.

"Really, there is only one solution … to use the enormous amount of sunlight available to us."

An hour of sunlight falling on Earth equals all the energy that humans use on average in a year.

But to date solar cells have been inefficient energy converters—the most efficient plastic solar cells on today's market convert only 6 percent of sunlight into usable energy.

Another option is to mimic the chemical reactions in photosynthesis, Barber said, specifically a step known as water splitting.

Using Sunlight to Split Water

Water splitting is a complex chemical reaction that takes place in leaves, algae, phytoplankton, and other green organisms.

The plants use the sun's energy to break down water into its components: oxygen and hydrogen.

The oxygen produced is released into the atmosphere. The hydrogen is used to convert carbon dioxide taken from the air into the carbon-based organic molecules that form plants' tissues.

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