Theory of Flow Batteries with Fast Homogeneous Chemical Reactions

Abstract

Redox flow batteries are widely investigated toward cost-effective storage of energy generated via intermittent renewable sources. Many redox chemistries have been proposed for flow batteries, possessing various attractive features such as low-cost reactants, fast electrochemical reaction kinetics without precious metal catalysts, negligible thermal runaway risk, and low toxicity. While all flow batteries rely on heterogeneous electrochemical reactions occurring at electrode surfaces, in a subset of chemistries homogeneous chemical reactions occur in the electrolyte. A prominent example are batteries employing halogen-based catholytes, where halogen molecules complex with halide ions in the catholyte, forming redox-active polyhalide ions. However, state-of-the-art models capturing flow battery performance for halogen systems typically neglect the presence of such homogeneous reactions and polyhalide ions. The latter assumption allows for simpler models, but at the cost of accurately predicting battery chemical state and performance. We here present a generalized flow battery theory extended to include fast homogeneous reactions, which employs a technique known as the method of families to simplify the governing equations. We then apply and solve the model for the specific case of a membraneless hydrogen-bromine flow battery, illustrating the predicted effect of the homogeneous complexation reaction in the catholyte on flow battery performance.

Exploring the thermodynamics of the bromine electrode in concentrated solutions for improved parametrisation of hydrogen–bromine flow battery models

“…6% was reported. A more recent study [5] briefly discusses the consequence of complexation phenomena on the electrode potential as well as the electrode kinetics in the bromine-bromide-water system.…”

“…In one of the early papers analysing the performance of a hydrogen-bromine flow battery (HBFB) cell [4], the authors used a complicated empirical expression in order to model the cell voltage. In a modern paper by Ronen et al [5], the HBFB electrolyte was used as an example to derive a theory of a cell in which a fast homogeneous reaction, such as complex formation, takes place. It was pointed out that a presence of thermodynamic effects such as ionic equilibria influences also electrode kinetics and transport processes.…”

Estimation of activity coefficients for aqueous organic redox flow batteries: Theoretical basis and equations

“…(A) Papers using the dilute solution hypothesis without mentioning it; 2000–2010: [6] Sukkar and Skyllas-Kazacos (2003) , [7] Li and Hikihara (2008) , [8] You et al (2009) ; 2010–2015: [11] Tang et al (2011) , [12] Qiu et al (2012) , [13] Tang et al (2012) , [14] Badrinarayanan et al (2014) ; 2015-2018: [26] Zhou et al (2016) , [27] Nikonenko et al (2016) , [28] Yan et al (2016) , [29] Milshtein et al (2017) , [30] Bhattacharjee and Saha (2017) ; 2018-2022: [45] Lei et al (2018) , [46] Murali et al (2018) , [47] Chen et al (2019) [48] Xu et al (2020) [49] Chen et al (2021a) , [50] Chen et al (2021b) [51] Howard Amanda and Tartakovsky (2021) . (B) Papers mentioning the dilute solution hypothesis but not justifying it; 2000–2010: [9] Shah et al (2008) , [10] Al-Fetlawi et al (2009) ; 2010–2015: [15] Shah et al (2011) , [16] Vynnycky (2011) , [17] Knehr et al (2012) , [18] Yin et al (2014) [19] Chen et al (2014) ; 2015-2018: [31] Xu and Zhao (2015) , [32] Yang et al (2015) , [33] Boettcher et al (2015) , [34] Zhou et al (2015) , [35] Lei (2015) , [36] Gandomi et al (2016) , [37] Chu et al (2016) , [38] Chen et al (2017) , [39] Elgammal et al (2017) ; 2018-2022: [52] Ronen et al (2018) , [53] Oh et al (2019) , [54] Delgado et al (2020) , [55] Cacciuttolo et al (2021) . (C) Papers justifying or discussing the dilute solution hypothesis; 2010–2015: [20] Knehr and Kumbur (2011) , [21] Stephenson et al.…”

Activated Carbon‐Anchored 3D Carbon Network for Bromine Activity and its Enhanced Electrochemical Performance in Zn−Br2 Hybrid Redox Flow Battery

“…The modeling clearly depicted the homogenous complexation of the bromine/bromide redox reaction with the help of the membrane less hydrogen-bromide (H 2 /Br 2 ) redox flow system. [9] The electrode also plays a vital role to improve the reversibility and kinetics of the redox reaction. [3f] In general, graphite felt (GF) was used as electrode in both positive and negative side of the flow battery due to its high conductivity, good chemical stability, high surface area and high compressibility.…”

“…Recently, Roan et al, investigated the polyhalide complexation through modeling process in order to formulate the fast homogenous reaction kinetics of the poly bromide redox reaction. The modeling clearly depicted the homogenous complexation of the bromine/bromide redox reaction with the help of the membrane less hydrogen‐bromide (H 2 /Br 2 ) redox flow system . The electrode also plays a vital role to improve the reversibility and kinetics of the redox reaction .…”