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
Laser sensor LAH-G1 - optical distance sensors with measurement value display
15.08.2017 | WayCon Positionsmesstechnik GmbH
Engineers find better way to detect nanoparticles
14.08.2017 | Washington University in St. Louis
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences