Storing fluctuating and delivering stable electric power supply are central issues when using energy from solar plants or wind power stations. Here, efficient and flexible energy storage systems need to accommodate for fluctuations in energy gain. Scientists from the Leibniz Institute for Interactive Materials (DWI), RWTH Aachen University and Hanyang University in Seoul now significantly improved a key component for the development of new energy storage systems.
Redox flow batteries are considered a viable next generation technology for highly efficient energy storage. These batteries use electrolytes, chemical components in solution, to store energy. A vanadium redox flow battery, for example, uses vanadium ions dissolved in sulfuric acid.
Lab set-up of a redox flow battery with the hydrophobic membrane (grey device at the bottom of the image) and two electrolyte reservoirs (bottles with yellow liquid).
Philipp Scheffler / DWI
Being separated by a membrane, two energy-storing electrolytes circulate in the system. The storage capacity depends on the amount of electrolytes and can easily be increased or decreased depending on the application. To charge or discharge the battery, the vanadium ions are chemically oxidized or reduced while protons pass the separating membrane.
The membrane plays a central role in this system: On the one hand, it has to separate the electrolytes to prevent energy loss by short-circuiting. On the other hand, protons need to pass the membrane when the battery is charged or discharged. To allow efficient, commercial use of a redox flow batteries, the membrane needs to combine both these functions, which still remains a significant challenge for membrane developers so far.
The current benchmark is a Nafion membrane. This membrane is chemically stable and permeable for protons and is well known for H2 fuel cell applications. However, Nafion and similar polymers swell when exposed to water and loose their barrier function for vanadium ions. Polymer chemists try to prevent vanadium leakage by changing the molecular structure of such membranes.
The researchers from Aachen and Seoul came up with a completely different approach: “We use a hydrophobic membrane instead. This membrane keeps its barrier functions since it does not swell in water,” explains Prof. Dr.-Ing. Matthias Wessling. He is the vice scientific director at the Leibniz Institute for Interactive Materials and heads the chair of Chemical Process Engineering at RWTH Aachen University.
“We were pleasantly surprised when we discovered tiny pores and channels in the hydrophobic material and they appear to be filled with water. These water channels allow protons to travel through the membrane with high speed. The vanadium ions, however, are too large to pass the membrane.”
The diameter of the channels is less than two nanometers and the barrier function seems to be stable over time: Even after one week or 100 charging and discharging cycles vanadium ions could not pass the membrane. “We reached an energy efficiency of up to 99 percent, depending on the current. This shows that our membrane is a true barrier for the vanadium ions,” says Wessling. At all current densities tested, between 1 and 40 milliampere per square centimeter, the scientists reached 85 percent energy efficiency or more whereas conventional systems do not exceed 76 percent.
These results suggest a new transport model. Instead of swelling, the polymer with intrinsic microporosity, named PIM, condensed significantly. Water molecules that accumulate in the pores, but not in the polymer itself, might be the reason for this phenomenon. The researchers hope to initiate further studies to analyze this effect in detail.
While the phenomenon is puzzling, the scientists from Aachen and Seoul will perform additional application tests: Can they still improve the hydrophobic membrane for an application in a redox flow battery? And is the membrane stable in the long run? If this is the case, the hydrophobic membrane might indeed advance the practical use of redox flow batteries and similar energy storage systems. The researchers are highly motivated by the idea of a stable energy supply when using sustainable energy sources, by making a contribution to power system and frequency stability.
Chae, I. S., Luo, T., Moon, G. H., Ogieglo, W., Kang, Y. S., & Wessling, M. (2016). Ultra‐High Proton/Vanadium Selectivity for Hydrophobic Polymer Membranes with Intrinsic Nanopores for Redox Flow Battery. Advanced Energy Materials.
Dr. Janine Hillmer | idw - Informationsdienst Wissenschaft
Reliable molecular toggle switch developed
30.03.2017 | Karlsruher Institut für Technologie (KIT)
Researchers shoot for success with simulations of laser pulse-material interactions
29.03.2017 | DOE/Oak Ridge National Laboratory
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
30.03.2017 | Health and Medicine
30.03.2017 | Health and Medicine
30.03.2017 | Medical Engineering