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. 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.
Inspired by the humble cactus, a new type of membrane has the potential to significantly boost the performance of fuel cells and transform the electric vehicle industry.
The membrane, developed by scientists from CSIRO and Hanyang University in Korea, was described today in the journal Nature . The paper shows that in hot conditions the membrane, which features a water repellent skin, can improve the efficiency of fuel cells by a factor of four.
According to CSIRO researcher and co-author Dr Aaron Thornton, the skin works in a similar way to a cactus plant, which thrives by retaining water in harsh and arid environments.
“Fuel cells, like the ones used in electric vehicles, generate energy by mixing together simple gases, like hydrogen and oxygen. However, in order to maintain performance, proton exchange membrane fuel cells – or PEMFCs – need to stay constantly hydrated,” Dr Thornton said.
“At the moment this is achieved by placing the cells alongside a radiator, water reservoir and a humidifier. The downside is that when used in a vehicle, these occupy a large amount of space and consume significant power,” he said.
According to CSIRO researcher and co-author Dr Cara Doherty, the team’s new cactus-inspired solution offers an alternative
The main campus is in Seoul, and the second one, the Education Research Industry Cluster at Ansan, or ERICA campus, is located in Ansan. Hanyang (한양;漢陽) derives from the former name of the capital Seoul which was used during the Chosun Dynasty. Its motto and educational philosophy is Love in Deed and Truth.
The university established the nation’s first engineering institute (DongA Engineering Institute) in 1939 which became the founding facility of Hanyang University. It also established the first school of architecture and civil engineering in Korea.
Hanyang University has an alumni network of 300,000 that is not limited to the field of engineering but also to other fields. In 2015, Hanyang was ranked 1st for the number of CEO alumni of venture companies. In 2013, Times Higher Education ranked Hanyang University 76th for the number of alumni CEOs in the world’s top 500 companies.
The university enrolls over 2,000 foreign students each year and more than 3,000 students study abroad annually.HYU counts the Massachusetts Institute of Technology, University of Cambridge, and Tsinghua University among its 647 partner universities in 68 countries.