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New catalyst sheds light on solar energy

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Plants have us beat. Every day, trillions of them convert sunlight into stored energy, because they, like us, still need energy when the sun doesn’t shine. Finding a way to mimic plants and convert sunlight into stored energy has been one of solar power’s biggest challenges, but new research suggests that sunlight may not slip through our fingers for much longer.

Hydrogen gas is the most promising potential form of energy storage, given that it can be burned to produce energy like gasoline. So far it has been hard to make. Researchers have struggled to get water to break into hydrogen gas cheaply and easily, though this remains an energy-consuming process. Recently, however, Drs. Daniel Nocera and Matthew Kanan of MIT have developed a process similar to that in plants, an important advancement in the generation of hydrogen gas.

Nocera and Kanan have found a cobalt catalyst that facilitates the production of oxygen gas from water and electricity. Although creating oxygen isn’t the same as creating hydrogen, the two processes are connected. Now that oxygen refinement is cheap and easy, hydrogen refinement should soon follow. If solar energy can provide enough power to efficiently produce hydrogen gas, the result would be independent, uninterrupted energy with little to no carbon footprint – an alluring alternative to problem-riddled fossil fuels.

Dr. Cortlandt Pierpont, a professor in the Department of Chemistry and Biochemistry at University of Colorado at Boulder, suggests that though using cobalt to oxidize oxygen is nothing new, this is a step forward for the alternative energy industry.

“It has been known for a long time that cobalt can be used in oxygen oxidation,” Pierpont said. “The innovative part of this research is that the oxygen oxidation occurs under a very low overpotential.” In other words, oxygen generation takes very little energy, a requirement for making hydrogen production commercially viable, Eisenberg explained.

“This opens a whole new line of research,” he said.

Other catalysts have been used to extract oxygen from water, but they all have their limitations: some are made of costly precious metals, require lots of energy, or work only under harsh conditions, like strong acidity. Nocera and Kanan’s cobalt catalyst, on the other hand, is cheap, abundant, and works under everyday conditions. Additionally, the catalyst recreates itself during the process, allowing it to withstand the intense conditions required for the reaction.

Does this mean that we are ready to go solar? According to Dr. Richard Eisenberg in the Department of Chemistry at the University of Rochester, we still have a long road ahead of us.

“The idea of making oxygen from water is really one of the major catalytic challenges in solar energy conversion, and in that sense it’s a first rate development on a really important problem,” explained Eisenberg.

But does it solve the solar energy problem? “The answer is no,” he said.

Dr. Harry Gray from the Division of Chemistry and Chemical Engineering, California Institute of Technology, also acknowledged that this is an achievement for water electrolysis. However, it still needs to fit into a larger picture to be truly significant. “The real step is to incorporate this into a larger photosynthetic system,” Gray said.

We still need to overcome to make this happen? The limitation of developing an inexpensive and efficient catalyst for hydrogen production, the gas everybody really wants to get their hands on. For now, the oxygen catalyst can only accept low levels of current and has yet to be hooked up to solar cells that will provide the electricity for the reaction.

These hurdles aside, once the hydrogen is produced, there is still the problem of hydrogen storage and distribution. According to Eisenberg, it is difficult to store hydrogen because it cannot be efficiently converted to a liquid form.

“We have a tremendous infrastructure for moving petroleum around. If we were distributing hydrogen it would be a very different kettle of fish,” he said. “The whole infrastructure would need to be built over a period of time.”