If you have installed solar panels on your roof to generate electricity, you will already know that solar power holds a promise of cheaper electric power, without the pollution caused by burning carbon fuels. One difficulty to date has been, that solar cells only work in day time, which means you have to be able to store the power. Now a new solar cell stores its own power.
A team at Ohio State University led by Professor Yiying Wu, and assisted by Mingzhe Yu, Xiaodi Ren, Lu Ma, Yiying Wu, has invented a solar battery:
Researchers at The Ohio State University have invented a solar battery -- a combination solar cell and battery -- which recharges itself using air and light. The design required a solar panel which captured light, but admitted air to the battery. Here, scanning electron microscope images show the solution: nanometer-sized rods of titanium dioxide (larger image) which cover the surface of a piece of titanium gauze (inset). The holes in the gauze are approximately 200 micrometers across, allowing air to enter the battery while the rods gather light.
Credit: Yiying Wu, The Ohio State University An extract from the Science Daily report ( http://www.sciencedaily.com/releases/2014/10/141003064336.htm ) describes the new process:
The mesh solar panel forms the first electrode. Beneath, the researchers placed a thin sheet of porous carbon (the second electrode) and a lithium plate (the third electrode). Between the electrodes, they sandwiched layers of electrolyte to carry electrons back and forth.
Here's how the solar battery works: during charging, light hits the mesh solar panel and creates electrons. Inside the battery, electrons are involved in the chemical decomposition of lithium peroxide into lithium ions and oxygen. The oxygen is released into the air, and the lithium ions are stored in the battery as lithium metal after capturing the electrons.
When the battery discharges, it chemically consumes oxygen from the air to re-form the lithium peroxide.
An iodide additive in the electrolyte acts as a "shuttle" that carries electrons, and transports them between the battery electrode and the mesh solar panel. The use of the additive represents a distinct approach on improving the battery performance and efficiency, the team said.
The mesh belongs to a class of devices called dye-sensitized solar cells, because the researchers used a red dye to tune the wavelength of light it captures.
In tests, they charged and discharged the battery repeatedly, while doctoral student Lu Ma used X-ray photoelectron spectroscopy to analyze how well the electrode materials survived -- an indication of battery life.
First they used a ruthenium compound as the red dye, but since the dye was consumed in the light capture, the battery ran out of dye after eight hours of charging and discharging -- too short a lifetime. So they turned to a dark red semiconductor that wouldn't be consumed: hematite, or iron oxide -- more commonly called rust.
Coating the mesh with rust enabled the battery to charge from sunlight while retaining its red color. Based on early tests, Wu and his team think that the solar battery's lifetime will be comparable to rechargeable batteries already on the market.
The U.S. Department of Energy funds this project, which will continue as the researchers explore ways to enhance the solar battery's performance with new materials.
A Academic account (for those interested) can be found at:
- Mingzhe Yu, Xiaodi Ren, Lu Ma, Yiying Wu. Integrating a redox-coupled dye-sensitized photoelectrode into a lithium–oxygen battery for photoassisted charging. Nature Communications, 2014; 5: 5111 DOI: 10.1038/ncomms6111