Carbon Materials as Positive Electrodes in Bromine‐Based Flow Batteries

Abstract

Bromine based redox flow batteries (RFBs) can provide sustainable energy storage due to the abundance of bromine. Such devices pair Br2/Br− at the positive electrode with complementary redox couples at the negative electrode. Due to the highly corrosive nature of bromine, electrode materials need to be corrosion resistant and durable. The positive electrode requires good electrochemical activity and reversibility for the Br2/Br− couple. Carbon materials enjoy the advantages of low cost, excellent electrical conductivity, chemical resistance, wide operational potential ranges, modifiable surface properties, and high surface area. Here carbon based materials for bromine electrodes are reviewed, with a focus on application in zinc‐bromine, hydrogen‐bromine, and polysulphide‐bromine RFB systems, aiming to provide an overview of carbon materials to be used for design and development of bromine electrodes with improved performance. Aspects deserving further R&D are highlighted.

A Zinc–Bromine Battery with Deep Eutectic Electrolytes

“…[ 40 ] This is demonstrated by the different dissociation constants for the polybromide anion ( K ) and the polyinterhalogen anion ( K 1 ), which are defined in the following equilibrium equations The equilibrium constant for the dissociation and association of Br 3− ( K , 16) is much higher than that of Br 2 Cl − ( K 1 , 1.14), implying that the formation of the polyinterhalogen anion increases the redox kinetics of bromine because the dissociation of polybromides, which is a prerequisite for the bromine reduction reaction, is facilitated. [ 41 , 42 ]…”

“…[ 40 ] This is demonstrated by the different dissociation constants for the polybromide anion ( K ) and the polyinterhalogen anion ( K 1 ), which are defined in the following equilibrium equations $$$$\begin{equation} \frac{{\left[{\mathrm{Br}}_{3}\right]}^{-}}{\left[{\mathrm{Br}}_{2}\right]\ensuremath{\times{}}{\left[\mathrm{Br}\right]}^{-}}=K \end{equation}$$$$ $$$$\begin{equation} \frac{{[{\mathrm{Br}}_{2}\mathrm{Cl}]}^{-}}{[{\mathrm{Br}}_{2}]\ensuremath{\times{}}{\left[\mathrm{Cl}\right]}^{-}}={K}_{1} \end{equation}$$$$The equilibrium constant for the dissociation and association of Br 3− ( K , 16) is much higher than that of Br 2 Cl − ( K 1 , 1.14), implying that the formation of the polyinterhalogen anion increases the redox kinetics of bromine because the dissociation of polybromides, which is a prerequisite for the bromine reduction reaction, is facilitated. [ 41,42 ]…”

“…The equilibrium constant for the dissociation and association of Br 3− (K, 16) is much higher than that of Br 2 Cl − (K 1 , 1.14), implying that the formation of the polyinterhalogen anion increases the redox kinetics of bromine because the dissociation of polybromides, which is a prerequisite for the bromine reduction reaction, is facilitated. [41,42] The effects of Cl − on the ZBB performances are summarized in Figure 5. This figure presents a comparison of the charge/discharge processes between the aqueous ZBB and the DES-ZBB without/with the Cl − anion.…”

Lignin-based porous junction for silver-silver chloride reference electrodes

“…Carbon materials are ideally suited for use in electrochemical systems due to various advantageous properties like high chemical and thermal resistance, good conductivity, controllable porosity etc. [14][15][16][17], with bio-based carbons offering additional benefits regarding low cost and sustainability aspects [18][19]. However, it is difficult to produce dimensionally stable carbon materials without the use of large amounts of additives that would affect the electrochemical measurement when using the carbon material as a salt bridge for a reference electrode.…”

A Mesoporous Tungsten Oxynitride Nanofibers/Graphite Felt Composite Electrode with High Catalytic Activity for the Cathode in Zn‐Br Flow Battery

“…In particular, bromine in the cathode has a lower reaction rate compared to zinc, which leads to electrochemical polarization, largely limiting the current and power density of the battery.Graphite felt (GF) is the most commonly used cathode material for the ZnBr flow battery owing to its porous structure with a high electronic conductivity, good chemical, and thermal stability. [12,13] Additionally, the self-standing structure of GF makes the material very useful as electrodes. However, its insufficient number of reaction sites and hydrophobic property that results in a low adsorption ability of bromine causes the high electrochemical polarization especially at high current density.…”