Novel battery produces electricity and hydrogen
The battery has been developed within a project that searched to answer the question which energy storage is best suited to buffer unstable energy generated by wind turbines and PV farms. One of the candidates for such an energy storage is the redox flow battery. While it has some drawbacks such as low energy density and a relatively poor energy efficiency of just 60 to 80 percent, it offers other benefits like easy scalability. In the case at hand, the scientists intended to generate hydrogen that in turn could be used to drive fuel cell vehicles. According to the Lausanne scientists, hydrogen could play an important role in future energy supply, because it enables emission-free operation of cars and buses.
The hydrogen is generated by a chemical reaction inside the battery. To initiate this reaction, a catalyzer is required, for example molybdenum carbide (MO2C). “The challenge was bringing the catalyzer into the desired shape”, explains Veronique Amstutz who oversaw the research project. After testing several approaches, the research team was successful with the idea to vapor deposit the molybdenum carbide in a thin layer onto small ceramics beads with a diameter of some 3 mm. Under these conditions, the catalyzer proved most efficient. The scientists also found out that they yielded good results when they implemented the battery as a vertical cylinder with eight sections which are switched in series.
The “hydrogen battery” however has a significant drawback: It can utilize only 50% of the the stored energy. The reason: Only one side of the redox flow battery, the negative electrolyte, generates hydrogen. The positive electrolyte generates oxygen, but oxygen bears no additional value in the energy storage system. In addition, the positive electrolyte that was used in the trials – Cerium – leads to corrosion problems in the battery. Therefore, the scientists agree that the development of such a battery requires significant further R&D efforts.
Nevertheless the redox flow battery offers several benefits. For example, it is possible to store the electric energy in the battery and later on tap the battery to produce hydrogen. Likewise it is possible to run the electrolyzer directly with electricity out of the grid.
More information: https://www.ee-news.ch/de/erneuerbare/pressemeldungen/article/33383/eth-lausanne-wasserstoff-aus-der-batterie (in German language)