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When iron rusts, it swaps an electron for an oxygen molecule. Usually, that electron goes to waste. Form Energy’s batteries, which are the size of a washer-dryer set, take in oxygen to convert iron to rust, harnessing the resulting electrons and their energy. The devices can discharge power for about four straight days – lasting far longer than lithium-ion batteries, which, unlike Form Energy’s solution, require mining rare-earth minerals. “It’s like having a new tool in the tool chest,” says Mateo Jaramillo, co-founder and CEO of Form Energy. The company has five pilot projects in the works, including 10-megawatt power storage facilities in Minnesota and Colorado.

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