The project aimed at the demonstration of a concept developed in the Laboratory of Physical and Analytical Electrochemistry (LEPA) in EPFL, called a dual-circuit redox flow battery. In brief, it is based on a redox flow battery (RFB), which can be dis-charged chemically to produce hydrogen or electrochemically to generate electricity. In the former case, the discharge occurs in a separate secondary circuit, in specific reactors. In RFBs, energy is typically stored in the electroactive species dissolved in the liquid electrolytes and the capacity of the battery is therefore determined by the volume of the electrolytes, the concentration of the active species in these electro-lytes and the cell potential of the battery during the discharge. In the present system, the capacity of the RFB can be increased on demand when surplus (renewable) en-ergy is available. This gain of capacity arises from the possibility to produce hydro-gen, which, in the compressed form, presents a higher energy density than a RFB.
As the bench-top prototype was successful, it became necessary to demonstrate its feasibility and its performances at a larger scale, and in real conditions of energy production and use. The results associated to the installation of a 10 kW/40kWh all-vanadium RFB, the design of the appended secondary circuit and the characterisa-tion of the overall dual-circuit RFB system are discussed in the present report. In particular, a characterisation of the commercial RFB was conducted. Moreover, the design of a catalyst and a catalytic bed reactor for the generation of hydrogen were essential in this project to generate hydrogen by chemically discharging the negative electrolyte of the RFB. Finally, various possibilities for the chemical discharge of the positive electrolyte were also investigated.
All in all, this project was successful and brought a strong knowledge related to commercially available RFBs, to the practical aspects related to the production and storage of hydrogen, and to the needs of electricity storage technologies. Moreover, the production of hydrogen directly from the RFB in a specifically built catalytic bed reactor could be repeatedly demonstrated. Therefore, further research on this sys-tem or similar systems is continuing at the laboratory-scale and at the demonstrator-scale in order to eventually bring this system to a commercial state.
