Advanced Hydrogen-Bromine Flow Batteries with Improved Efficiency, Durability and Cost

Abstract

The hydrogen/bromine flow battery is a promising candidate for large-scale energy storage due to fast kinetics, highly reversible reactions and low chemical costs. However, today's conventional hydrogen/bromine flow batteries use membrane materials (such as Nafion), platinum catalysts, and carbon-paper electrode materials that are expensive. In addition, platinum catalysts can be poisoned and corroded when exposed to HBr and Br 2, compromising system lifetime. To reduce the cost and increase the durability of H 2 /Br 2 flow batteries, new materials are developed. The new Nafion/ polyvinylidene fluoride electrospun composite membranes have high perm-selectivity at a fraction of the cost of Nafion membranes; the new nitrogen-functionalized platinum-iridium catalyst possesses excellent activity and durability in HBr/Br 2 environment; and the new carbon-nanotube-based Br 2 electrodes can achieve equal or better performance with less materials when compared to baseline electrode materials. Preliminary cost analysis shows that the new materials reduce H 2 /Br 2 flow-battery energy-storage system stack and system costs significantly. The resulting advanced H 2 /Br 2 flow batteries offer high power, high efficiency, substantially increased durability, and expected reduced cost. The active reactant material, hydrobromic acid (HBr) is also used as the supporting electrolyte. If the energy-storage system is commissioned in the discharged state, which is the most common case, HBr is the only chemical that is required. During charge, hydrobromic acid is electrolyzed to generate hydrogen and bromine, which are stored in separate tanks. Bromine has a moderate solubility in water which can be greatly enhanced by the presence of Br − via complexation to form Br 3 − or Br 5 − . 8,9 The gas phase H 2 electrode also simplifies the separation and recovery of crossover catholyte, which can be returned back to the catholyte tank.The H 2 /Br 2 flow battery technology has been under investigation since the 1960s. Brief literature reviews can be found in recent publications by Cho et al., 4 Kreutzer et al. 5 and Tolmachev. 6 H 2 /Br 2 flow batteries share the same cell architecture as proton-exchange-membrane fuel cells (PEMFCs). Therefore, H 2 /Br 2 flow batteries are also referred to as regenerative or reversible H 2 /Br 2 fuel cells. Similar to PEMFCs, * Electrochemical Society Active Member. * * Electrochemical Society Student Member. * * * Electrochemical Society Fellow.z E-mail: gygylin@gmail.com membrane-electrode assemblies (MEAs) are the most crucial components in the H 2 /Br 2 flow batteries. In today's state-of-the-art H 2 /Br 2 flow batteries, MEAs are commonly made of commercial perfluorosulfonic acid (PFSA) membranes such as Nafion, platinum catalysts, and plain carbon papers. The PFSA membrane in a H 2 /Br 2 flow battery is used to physically separate the positive and negative electrodes, and prevent mixing of hydrogen and bromine/bromides while allowing proton transport between the electrodes. The membrane resistance has ...

Advanced Redox-Flow Batteries: A Perspective

“…Therefore, in contrast to electrodes, a promising pathway here is to focus either on diluting the more expensive component with a filler or reinforcement 12,30 or on inherently lower-cost materials such as porous separators that are analogous to those used in some conventional batteries. A performance decrease is acceptable with these approaches, since the cost of these alternative materials can be on-the-order of 50 times lower (e.g., ≈$10 /m 2 ).…”

“…A good example of this approach has been the recent dramatic improvements in RFB power density (W/m 2 ) using the same basic set of materials utilized in previous RFB cells with improved flow-field and electrode designs. [7][8][9][10][11][12][13] The effectiveness of this approach is illustrated in Fig. 4, which illustrates how cell cost strongly depends on power density.…”

Evaluation of Electrospun Fibrous Mats Targeted for Use as Flow Battery Electrodes

“…Currently, the most commonly-used material for flow battery electrodes is commercially available carbon-fiber paper developed for use as the gas diffusion layer (GDL) of PEM fuel cells. Attempts to increase performance of these carbon papers include stacking multiple layers, [6][7][8] laser etching holes, 9 growing carbon nanotubes on fiber surfaces 10,11 and thermal activation. 12 These efforts to improve cell performance of flow batteries are driven by increasing the current density of the cell (A/m 2 ).…”

Effect of flow-field structure on discharging and charging behavior of hydrogen/bromine redox flow batteries

“…Recently, a high power density of 1.4 W•cm -2 and slow degradation of the RFB performance over 10,000 h were reported for 10−25 cm 2 lab-scale cells [1][2][3][4][5]. As shown in Fig.…”