Water molecules can be split using solar energy to create hydrogen fuel. This is an important means for chemically storing the fluctuating incoming solar energy and replacing fossil fuels. Now an international team has succeeded in considerably increasing the efficiency for direct solar water splitting.
They are using a tandem solar cell whose surfaces have been selectively modified. The new record value is 14 % and thus considerably above the previous record of 12.4 % held by the National Renewable Energy Laboratory (NREL) in the USA, broken now for the first time in 17 years.
Researchers from TU Ilmenau, the Institute for Solar Fuels at the Helmholtz-Zentrum Berlin, the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, and the California Institute of Technology (Caltech) participated in the collaboration. The results have been published in Nature Communications (doi:10.1038/ncomms9286).
Solar energy is certainly abundantly available globally, but unfortunately not constantly and not everywhere. One especially interesting solution for storing this energy is artificial photosynthesis. This is what every leaf can do, namely converting sunlight to “chemical energy”.
That can take place with artificial systems based on semiconductors as well. These use the electrical power that sunlight creates in individual semiconductor components to split water into oxygen and hydrogen. Hydrogen possesses very high energy density, can be employed in many ways and could replace fossil fuels. In addition, no carbon dioxide harmful to the climate is released from hydrogen during combustion, instead only water.
Until now, manufacturing of solar hydrogen at the industrial level has failed due to the costs, however. This is because the efficiency of artificial photosynthesis, i.e. the energy content of the hydrogen compared to that of sunlight, has simply been too low to produce hydrogen from the sun economically. Scientific facilities worldwide have therefore been researching for many years how to break the existing record for artificial photosynthesis of 12.4 %, which has been held for 17 years by the NREL.
Now a team from TU Ilmenau, HZB, the California Institute of Technology as well as the Fraunhofer ISE has considerably exceeded this record value. Lead author Matthias May, active at TU Ilmenau and the HZB Institute for Solar Fuels, processed and surveyed about one hundred samples in his excellent doctoral dissertation to achieve this. The fundamental components are tandem solar cells of what are known as III-V semiconductors. Using a now patented photo-electrochemical process, May could modify certain surfaces of these semiconductor systems in such a way that they functioned better in water splitting.
“We have electronically and chemically passivated in situ the aluminium-indium-phosphide layers in particular and thereby efficiently coupled to the catalyst layer for hydrogen generation. In this way, we were able to control the composition of the surface at sub-nanometre scales”, explains May. There was enormous improvement in long-term stability as well. At the beginning, the samples only survived a few seconds before their power output collapsed. Following about a year of optimising, they remain stable for over 40 hours. Further steps toward a long-term stability goal of 1000 hours are already underway.
“Forecasts indicate that the generation of hydrogen from sunlight using high-efficiency semiconductors could be economically competitive to fossil energy sources at efficiency levels of 15 % or more. This corresponds to a hydrogen price of about four US dollars per kilogramme", says Prof. Thomas Hannappel, from the photovoltaics group at TU Ilmenau, who was academic advisor for the work.
Prof. Hans-Joachim Lewerenz from the Joint Center for Artificial Photosynthesis at the California Institute of Technology, who worked closely with May, said “We are nearly there. If we are successful now in reducing the charge carrier losses at the interfaces somewhat more, we might be able to chemically store more than even 17 % of the incident solar energy in the form of hydrogen using this semiconductor system.”
The scientific article is being published in the renowned science periodical Nature Communications [May, M. M. et al. Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure. Nat. Commun. 6:8286. Doi: 10. 1038/ncomms9286 (2015)].
Univ.-Prof. Dr. Thomas Hannappel
Technische Universität Ilmenau
Institute of Physics, Dep. Photovoltaics
Phone: +49 3677 69 2566
Bettina Wegner | Technische Universität Ilmenau
First-ever visualizations of electrical gating effects on electronic structure
18.07.2019 | University of Warwick
New safer, inexpensive way to propel small satellites
16.07.2019 | Purdue University
Scientists have visualised the electronic structure in a microelectronic device for the first time, opening up opportunities for finely-tuned high performance electronic devices.
Physicists from the University of Warwick and the University of Washington have developed a technique to measure the energy and momentum of electrons in...
Scientists at the University Würzburg and University Hospital of Würzburg found that megakaryocytes act as “bouncers” and thus modulate bone marrow niche properties and cell migration dynamics. The study was published in July in the Journal “Haematologica”.
Hematopoiesis is the process of forming blood cells, which occurs predominantly in the bone marrow. The bone marrow produces all types of blood cells: red...
For some phenomena in quantum many-body physics several competing theories exist. But which of them describes a quantum phenomenon best? A team of researchers from the Technical University of Munich (TUM) and Harvard University in the United States has now successfully deployed artificial neural networks for image analysis of quantum systems.
Is that a dog or a cat? Such a classification is a prime example of machine learning: artificial neural networks can be trained to analyze images by looking...
An international research group led by scientists from the University of Bayreuth has produced a previously unknown material: Rhenium nitride pernitride. Thanks to combining properties that were previously considered incompatible, it looks set to become highly attractive for technological applications. Indeed, it is a super-hard metallic conductor that can withstand extremely high pressures like a diamond. A process now developed in Bayreuth opens up the possibility of producing rhenium nitride pernitride and other technologically interesting materials in sufficiently large quantity for their properties characterisation. The new findings are presented in "Nature Communications".
The possibility of finding a compound that was metallically conductive, super-hard, and ultra-incompressible was long considered unlikely in science. It was...
An interdisciplinary research team at the Technical University of Munich (TUM) has built platinum nanoparticles for catalysis in fuel cells: The new size-optimized catalysts are twice as good as the best process commercially available today.
Fuel cells may well replace batteries as the power source for electric cars. They consume hydrogen, a gas which could be produced for example using surplus...
24.06.2019 | Event News
29.04.2019 | Event News
17.04.2019 | Event News
18.07.2019 | Health and Medicine
18.07.2019 | Life Sciences
18.07.2019 | Health and Medicine