How can solar energy be stored so that it can be available any time, day or night, when the sun shining or not? EPFL scientists are developing a technology that can transform light energy into a clean fuel that has a neutral carbon footprint: hydrogen.
The basic ingredients of the recipe are water and metal oxides, such as iron oxide, better known as rust. Kevin Sivula and his colleagues purposefully limited themselves to inexpensive materials and easily scalable production processes in order to enable an economically viable method for solar hydrogen production. The device, still in the experimental stages, is described in an article published in the journal Nature Photonics.
The idea of converting solar energy into hydrogen is not a new one; researchers have been working on it for more than four decades. During the 1990s, EPFL joined the fray, with the research of Michaël Grätzel. With a colleague form University of Geneva, he invented the photoelectrochemical (PEC) tandem solar cell, a technique for producing hydrogen directly from water. Their prototypes shared the same basic principle: a dye-sensitized solar cell – also invented by Michael Grätzel – combined with an oxide-based semiconductor.
The device is completely self-contained. The electrons produced are used to break up water molecules and reform the pieces into oxygen and hydrogen. In the same liquid, two distinct layers in the device have the job of generating electrons when stimulated by light; an oxide semiconductor, which performs the oxygen evolution reaction, and a dye-sensitized cell, which liberates the hydrogen.
The most expensive part? The glass plate
The team's latest prototype focused on resolving the main outstanding problem with PEC technology: its cost. "A U.S. team managed to attain an impressive efficiency of 12.4%," says Sivula. "The system is very interesting from a theoretical perspective, but with their method it would cost 10,000 dollars to produce a 10 square centimeter surface."
So the scientists set themselves a limitation from the start – to use only affordable materials and techniques. It wasn't an easy task, but they managed. "The most expensive material in our device is the glass plate," explains Sivula. The efficiency is still low – between 1.4% and 3.6%, 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% in a few years, for less than $80 per square meter. At that price, we'll be competitive with traditional methods of hydrogen production."
The semiconductor, which performs the oxygen evolution reaction, is just iron oxide. "It's a stable and abundant material. There's no way it will rust any further! But it's one of the worst semiconductors available," Sivula admits.
That's why the iron oxide used by the team is a bit more developed than what you'd find on an old nail. Nanostructured, enhanced with silicon oxide, covered with a nanometer-thin layer of aluminum oxide and cobalt oxide – these treatments optimize the electrochemical properties of the material, but are nonetheless simple to apply. "We needed to develop easy preparation methods, like ones in which you could just dip or paint the material."
The second part of the device is composed of a dye and titanium dioxide – the basic ingredients of a dye-sensitized solar cell. This second layer lets the electrons transferred by the iron oxide gain enough energy to extract hydrogen from water.
An outstanding potential – up to 16%
The results presented in the Nature Photonics paper represent a breakthrough in performance that has been enabled by recent advances in the study of both the iron oxide and dye-sensitized titanium dioxide, and both of these technologies are rapidly advancing. Sivula predicts that the tandem cell technology will eventually be able to attain an efficiency of 16% with iron oxide, while still remaining low cost, which is, after all, the attractiveness of the approach. By making it possible to store solar energy inexpensively, the system developed at EPFL could considerably increase the potential of solar energy to serve as a viable renewable energy source for the future.
Lionel Pousaz | EurekAlert!
Factory networks energy, buildings and production
12.07.2018 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH
Manipulating single atoms with an electron beam
10.07.2018 | University of Vienna
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
16.07.2018 | Physics and Astronomy
16.07.2018 | Life Sciences
16.07.2018 | Earth Sciences