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 physicien, à finalité spécialisée

Abstract

Due to recent considerations about the relations between climate change and greenhouse gases, there has been a continuous increase in renewable energy sources. Nevertheless, the intermittent nature of these power sources - such as wind turbines or photovoltaic panels - tends to weaken the electrical grid. Electrical storage systems could bring a solution to support the grid and pursue the deployment of greener power sources. Among the electrochemical storage systems, the All-Iron Flow Battery, introduced by L.W. Hruska and R.F. Savinell in 1981, represents a promising path for large-scale deployment : iron is abundant, low-cost, and relatively eco-friendly. The major limitation of this battery comes from the parasitic hydrogen evolution reaction that occurs at the negative pole during charging, which leads to battery capacity imbalance and iron (III) hydroxide precipitation (due to pH elevation). The eventual effect of these reactions is that the battery becomes unusable. The purpose of this work is to identify optimal conditions to improve iron deposition/dissolution reaction while suppressing the reaction of hydrogen evolution. It was shown that hydrochloridric acid seems more suitable than sulfuric acid and leads to higher coulombic efficiencies (near 85\% at 25°C). Chloride anions have also shown ability to cover the working electrode surface, so as to reduce the hydrogen evolution. An increase in the operating temperature improves the iron deposition kinetic as well : a coulombic efficiency higher that 90\% has been observed at 40°C. When the concentration of iron (II) chloride was increased, coulombic efficiencies higher than 98\% have been observed. All things considered, these latter excellent efficiencies have been observed by creating an environment incomparable to the real conditions of the practical cell of the battery. Even though great coulombic efficiencies have been observed, the evolution of hydrogen is still limiting and does not allow to operate the battery continuously over a high number of cycles. Therefore, the possibility to rebalance the battery by reusing the produced hydrogen was evaluated by multiple simulations. The encouraging results of these simulations suggest that a rebalancing system could be a solution to make the BRFF a feasible technology with a long and autonomous lifespan.