Optimisation des performances d'une batterie rédox à flux à base fer

Details

Supervisors

Jacques, Pascal

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux

Abstract

enThe energy storage technologies will play an important role in the future because of the increasing use of intermittent sources of energy such as solar and wind. Their use is necessary to avoid instability of the grid but also to rebalance the load and the supply. Electrochemical cells are one way to store the excess produced energy. However, the challenge is to find batteries that would be reliable, widely available, effective and cost-attractive. An all-iron flow battery, subjet of this document, can be an interesting candidate particularly for its cheap and widely available electrolyte. The goal of this work is to optimize the performances of this technology. The system has been studied experimentally with an anion exchange membrane. Charge and discharge were tested separately before cycling of the battery. The main challenge of this system is the control of the parasitic reactions involving hydrogen evolution. These reactions have been identified and confirmed by experimental measurements. Sulfuric and hydrochloric acid have been investigated as electrolyte and the hydrochloric acid was found to give the best results. As the two main parasitic reactions involve the reduction of the hydrogen, the pH has been increased to 2 in the negative electrolyte. This increase improved significantly the faradaic efficiency of the battery. Thanks to the anionic membrane, it was possible to increase the pH of only one side of the cell. Even if it was possible to maintain a low pH of the positive electroyte, a crossover of the protons across the membrane has nevertheless been observed. In addition to the pH, other parameters of the electrolyte have been modified. Two supporting electrolytes, NaCl and KCl showed a decrease of the ohmic loss at the charge. Sodium chloride addition also decreased the overpotential at the charge. Cycling the all-iron flow battery with maximum faradaic, voltaic and energy efficiencies of 75, 61 and 41 \%, respectively, have been demonstrated. Carbon felt electrodes have been tested at the cathode and the anode. They did not achieve to decrease the overpotentials during the charge of the cell but were observed to increase the efficiency of the discharge by decreasing the ohmic losses. Finally, based on the best results of this master thesis, a cost model has been developed for a 10 kW/20 kWh flow battery. The anionic membrane of which the price is very expensive drastically increases the system cost. However, an increase of the performance and an expected diminution of the membrane cost can lead to a cheaper and more competitive battery. Perspectives as well as an optimization of the experimental cell are given as a conclusion of this document.