Liquid sunshine

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Science  13 Jul 2018:
Vol. 361, Issue 6398, pp. 120-123
DOI: 10.1126/science.361.6398.120

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Renewable energy sources, such as wind and solar electricity, are the fastest growing energy sources in the world. But the sunniest and windiest spots on Earth are often far from cities where the power is needed, and there are few effective ways to ship electricity over long distances. That leaves much of the world's renewable energy potential untapped. Now, researchers are looking to use renewable electricity to make ammonia, which is already produced on an industrial scale as the main ingredient in fertilizer, and shipped worldwide. Today, ammonia is made primarily by stripping hydrogen molecules from natural gas and combining them with nitrogen purified from air, a process that generates about 1% of all humanmade carbon dioxide. In the future, ammonia could be produced by combining that nitrogen with hydrogen generated by splitting water. Devices called reverse fuel cells could also make it directly by using electricity and catalysts to split water and combine the hydrogen with nitrogen. These advances could enable ammonia to be produced economically on a small scale, allowing farmers to make their own fertilizer and renewable energy producers to store any excess power they may have and ship it where it's needed.