Hydrogen-Bromine RFB :Electrochemical Measurements and Cell Performance of a 40cm² H/Br-RFB System

Conventional redox flow batteries (RFB) use electrolyte solutions as energy storage media. For this reason the energy density is mainly limited by the solubility of the redox couples in the solutions. The kinetics of the reactions is mostly moderate so that cycling power densities can only reach max. 100 mW/cm². Depending on the energy / performance ratio the cost of the energy converter of RFBs clearly dominates the total investment costs. For longer storage periods the influence of the cost of the energy storage medium increases. For these reasons RFBs with redox pairs with high kinetics and thus a high power density are desirable. Hydrogen and bromine-based energy storage fulfill both requirements because the kinetics of the reactions are very fast and both elements are inexpensive and very abundant. In addition potentially high energy densities and efficiencies can be achieved.

Anode:                H₂ -> 2 H⁺ +2 e^-                 E⁰ = 0.00 V

Cathode:             Br₂ +2 e^- -> 2 Br^-               E⁰ = + 1.06 V

Cell:                     H₂ + Br₂ -> 2 HBr               E = 1.06 V

Although the first studies were made in the 80s of the last century [1], the research intensified due to these positive characteristics in the last years [2, 3]. For a viable use, hydrogen storage, bromine diffusion, bromine complexation and system behavior are the biggest challenges.

In this work we want to present the results of the development and the construction of an H/Br-RFB with an active area of 40 cm² and its behavior at different electrolyte compositions, temperatures and current densities. For better identification of the properties the half-cell potentials and impedances were also measured and evaluated. This research forms the basis for our future studies  involving the use of advanced bromine complexation agents (BCAs) and their impact on H/Br-RFB.

 [1] Yeo, R. S.; Chin, D. ‐T. (1980): A Hydrogen‐Bromine Cell for Energy Storage Applications. In: Journal of The Electrochemical Society 127 (3), S. 549–555. DOI: 10.1149/1.2129710.

[2] Cho, Kyu Taek; Albertus, Paul; Battaglia, Vincent; Kojic, Aleksandar; Srinivasan, Venkat; Weber, Adam Z. (2013): Optimization and Analysis of High-Power Hydrogen/Bromine-Flow Batteries for Grid-Scale Energy Storage. In: Energy Technology 1 (10), S. 596–608. DOI: 10.1002/ente.201300108.

[3] Cho, Kyu Taek; Tucker, Michael C.; Ding, Markus; Ridgway, Paul; Battaglia, Vincent S.; Srinivasan, Venkat; Weber, Adam Z. (2014): Cyclic Performance Analysis of Hydrogen/Bromine Flow Batteries for Grid-Scale Energy Storage. In: ChemPlusChem, S. n/a. DOI: 10.1002/cplu.201402043.