As scientists endeavor to increase the efficiency of solar panels, the challenge of storing the resultant energy cheaply and in an environmentally responsible way must also be met. To this end, researchers at Switzerland’s École polytechnique fédérale de Lausann (EPFL) have developed an inexpensive device that transforms light energy into hydrogen, for storage and later use. The new prototype makes use of sunlight, water, and metal oxides, including iron oxide – or rust.
Converting solar energy into hydrogen has been the goal of EPFL scientists for some time, with researcher Michaël Grätzel previously inventing the photoelectrochemical (PEC) tandem solar cell, which also used an iron oxide-based semiconductor, along with a dye-sensitized solar cell, to produce hydrogen directly from water. However, while Grätzel’s approach has merit, it is also prohibitively expensive. Therefore, this new research led by Kevin Sivula was focused on constructing a prototype from only affordable materials and techniques.
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“The most expensive material in our device is the glass plate,” explains Sivula. “The efficiency is still low – between 1.4 percent and 3.6 percent, depending on the prototype used. But the technology has great potential. With our less expensive concept based on iron oxide, we hope to be able to attain efficiencies of 10 percent in a few years, for less than US$80 per square meter [10.8 sq ft]. At that price, we’ll be competitive with traditional methods of hydrogen production.”
The current EPFL prototype is completely self-contained and uses electrons stimulated by light to break up water molecules, reforming the resulting pieces into oxygen and hydrogen. This is achieved with a dual system working in tandem: an oxide-based semiconductor performs the oxygen evolution reaction, while a dye-sensitized cell liberates the all-important hydrogen.
As already noted, the semiconductor implemented within the new EPFL research makes use of iron oxide. However, this iron oxide is a little more complex than the rust which is the scourge of car wheel arches, as it has been treated with a nanometer layer of aluminum oxide and cobalt oxide – both of which are easy to apply, but increase the electrochemical properties of the rust markedly.
At this early stage of development, the performance of the rust-based device is still relatively inefficient, making it impractical for widespread use. That said, Sivula predicts the technology will eventually be able to reach an efficiency of 16 percent, while remaining affordable.
The current prototype and the research itself is described in an article published in the journal Nature Photonics.
The short video below offers more details on the research.