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Scientists advance method for chemically storing solar energy

23 February 2016

A photo-electrochemical cell has been developed at TU Wien that can chemically store the energy of ultraviolet light even at high temperatures.

Light creates free charge carriers; oxygen (blue) is pumped through a membrane (illustration: TU Wien)

Scientists at the Vienna University of Technology (TU) Wien have combined high temperature photovoltaics with an electrochemical cell in an arrangement that allows ultraviolet light to be directly used to pump oxygen ions through a solid oxide electrolyte. The energy of the UV light is thus stored chemically. The researchers believe this method could also be used to split water into hydrogen and oxygen.

Instead of the usual silicon based photovoltaics, special metal oxides (perovskites) were used. By combining several different metal oxides, researcher, Georg Brunauer assembled a layered, combined cell with the photovoltaics placed on top of an electrochemical cell.

In the upper layer, ultraviolet light creates free charge carriers, as in a standard solar cell. The electrons in this layer are removed and travel to the bottom layer of the electrochemical cell. Once there, they are used to ionize oxygen to negative oxygen ions, which can then travel through a membrane in the electrochemical part of the cell.

"This is the crucial photo-electrochemical step, which we hope will lead to the possibility of splitting water and producing hydrogen", says Brunauer.

The heated reactor (photo: TU Wien)

In its current form, the cell works as a UV-light driven oxygen pump. It yields an open-current voltage of up to 920mV at a temperature of 400°C.

"We want to understand the origin of these effects by carrying out a few more experiments, and we hope that we will be able to improve our materials even further", says Brunauer. If the electrical power can be increased slightly, the cell will be able to split water into oxygen and hydrogen. "This goal is within reach, now that we have shown that the cell is working," Brunauer adds.

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