Stanford Engineers Use Rust to Build a Solar-powered Battery

Estimated reading time: 4 minutes

The recent crash in oil prices notwithstanding, an economy based on fossil fuels seems unsustainable. Supplies of oil, coal and similar fuels are finite, and even if new sources are found, global warming must be considered. Limitless solar power remains the Holy Grail, but among other obstacles to widespread adoption, society needs ways to store solar energy and deliver power when the sun isn't shining.

As energy experts would say, engineers must make solar power "dispatchable," using an industry term to describe how utilities boost power output or throttle back depending on demand, something they now do by burning more or less fossil fuel.

Now a team led by William Chueh, an assistant professor of materials science and engineering, and Nicholas Melosh, an associate professor in the same department, has made a discovery that could make large-scale solar power storage a reality.

The breakthrough is based on the fact that ordinary metal oxides, such as rust, can be fashioned into solar cells capable of splitting water into hydrogen and oxygen.

Using solar cells to split H2O by day is a way to store energy for use at night. The photons captured by the cell are converted into the electrons that provide the energy to split water. Recombining hydrogen and oxygen after dark would be a way to reclaim that energy and "dispatch" power back into the electrical grid – without burning fossil fuels and releasing more carbon into the atmosphere.

The solar power potential of metal oxides was previously known. But metal oxide solar cells were also known to be less efficient at converting photons to electrons than silicon solar cells.

A discovery reported in the journal Energy & Environmental Science makes metal oxide solar cells a better candidate for energy storage. The Stanford team showed that as metal oxide solar cells grow hotter, they convert photons into electrons more efficiently. The exact opposite is true with silicon solar cells, which lose efficiency as they heat up.

"We've shown that inexpensive, abundant and readily processed metal oxides could become better producers of electricity than was previously supposed," Chueh said.

This unexpected discovery could lead to a revolutionary change in how we produce, store and consume energy.

"By combining heat and light, solar water-splitting cells based on metal oxides become significantly more efficient at storing the inexhaustible power of the sun for use on demand," he said.

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