TEMPO/Phenazine Combi-Molecule: A Redox-Active Material for Symmetric Aqueous Redox-Flow Batteries

Redox-active organic molecules are promising charge-storage materials for redox-flow batteries (RFBs), but material crossover between posolyte/negolyte and chemical degradation are limiting factors in the performance of all-organic RFBs. We demonstrate that the bipolar electrochemistry of 1,2,4-benzotriazin-4-yl (Blatter) radicals allows construction of batteries with symmetric electrolyte composition. Cyclic voltammetry shows that these radicals retain reversible bipolar electrochemistry also in the presence of water. The redox potentials of derivatives with a C(3)-CF3 substituent are least affected by water and, moreover, these compounds show >90% capacity retention after charge/discharge cycling in a static H-cell for seven days (ca. 100 cycles). Testing these materials in a flow regime at 0.1 M concentration of active material confirmed the high cycling stability under conditions relevant for RFB operation, and demonstrated that polarity inversion in a symmetric flow battery may be used to rebalance the cell. Chemical synthesis provides insight in the nature of the charged species by spectroscopy and (for the oxidized state) X-ray crystallography. The stability of these compounds in all three states of charge highlights the potential for application in symmetric organic redox-flow batteries.

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Theoretical Exploration of 2,2’-Bipyridines as Electro-Active Compounds in Flow Batteries

10.26434/chemrxiv.7995935.v2 ◽

2019 ◽

Author(s):

Mariano Sánchez-Castellanos ◽

Martha M. Flores-Leonar ◽

Zaahel Mata-Pinzón ◽

Humberto G. Laguna ◽

Karl García-Ruiz ◽

...

Keyword(s):

Redox Potential ◽

Active Material ◽

Chemical Properties ◽

Small Subset ◽

Solubility In Water ◽

Protonation Reaction ◽

Redox Active ◽

Physico Chemical ◽

Pka Value ◽

Flow Batteries

Compounds from the 2,2’-bipyridine molecular family were investigated for use as redox-active materials in organic flow batteries. For 156 2,2’-bipyridine derivatives reported in the academic literature, we calculated the redox potential, the pKa for the first protonation reaction, and the solubility in aqueous solutions. Using experimental data on a small subset of derivatives, we were able to calibrate our calculations. We find that functionalization with electron-withdrawing groups leads to an increase of the redox potential and to an increase of the molecular acidity (as expressed in a reduction of the pKa value for the first protonation step). Furthermore, calculations of solubility in water indicate that some of the studied derivatives have adequate solubility for flow battery applications. Based on an analysis of the physico-chemical properties of the 156 studied compounds, we down-select five molecules with carbonyl- and nitro-based functional groups, whose parameters are especially promising for potential application as negative redox-active material inorganic flow batteries.

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Theoretical Exploration of 2,2’-Bipyridines as Electro-Active Compounds in Flow Batteries

10.26434/chemrxiv.7995935 ◽

2019 ◽

Author(s):

Mariano Sánchez-Castellanos ◽

Martha M. Flores-Leonar ◽

Zaahel Mata-Pinzón ◽

Humberto G. Laguna ◽

Karl García-Ruiz ◽

...

Keyword(s):

Redox Potential ◽

Active Material ◽

Chemical Properties ◽

Small Subset ◽

Solubility In Water ◽

Protonation Reaction ◽

Redox Active ◽

Physico Chemical ◽

Pka Value ◽

Flow Batteries

Compounds from the 2,2’-bipyridine molecular family were investigated for use as redox-active materials in organic flow batteries. For 156 2,2’-bipyridine derivatives reported in the academic literature, we calculated the redox potential, the pKa for the first protonation reaction, and the solubility in aqueous solutions. Using experimental data on a small subset of derivatives, we were able to calibrate our calculations. We find that functionalization with electron-withdrawing groups leads to an increase of the redox potential and to an increase of the molecular acidity (as expressed in a reduction of the pKa value for the first protonation step). Furthermore, calculations of solubility in water indicate that some of the studied derivatives have adequate solubility for flow battery applications. Based on an analysis of the physico-chemical properties of the 156 studied compounds, we down-select five molecules with carbonyl- and nitro-based functional groups, whose parameters are especially promising for potential application as negative redox-active material inorganic flow batteries.

Download Full-text