Multielectron Organic Redoxmers for Energy-Dense Redox Flow Batteries

Abstract

Redox flow battery is a highly promising stationary energy storage method, but the limited energy density and high chemical cost are among the main barriers for commercialization. Multielectron organic redoxmers represent a family of structurally tailorable candidates that can achieve multiplied energy density with decreased materials consumption, potentially resulting in a viable solution to address these challenges. Here, the recent development of organic molecules with reversible multiredox activities in both aqueous and nonaqueous electrolytes is reviewed. The major focus is on the fundamental correlation between the chemical structures and the functional properties of reported multielectron organic molecules. Valuable insights are offered on rational structural design strategies for improving the relevant physicochemical and electrochemical properties. Finally, the current challenges are discussed to suggest future research needs along the avenue of using the multielectron approach to achieve energy-dense, stable, cost-effective redox flow batteries.

Organic Four‐Electron Redox Systems Based on Bipyridine and Phenanthroline Carbene Architectures

“…Note, viologen anolyte materials are typically only cycled by one electron over the dication/radical cation oxidation states [40] . More recently there has been interest in harnessing two electrons from the viologen system, [41, 42] or finding other multi‐electron redox systems at highly negative or positive redox potentials [43–45] . Note, simple pyridinium/carbene hybrid molecules such as V (Figure 1) show significant decomposition after 25 cycles for two‐electron cycling in the symmetrical H‐cell [24a] …”

Exploring Carbonyl Chemistry in Non‐aqueous Mg Flow Batteries

“…The peak at 2.498 ppm corresponds to the chemical shift of H in the DMSOd 6 solvent, while the peak at 3.346 ppm corresponds to the chemical shift of HOD in the DMSOd 6 solvent. The 13 C NMR spectrum (Figure S2b) of NTCDA shows three peaks at 124.03 ppm, 127.78 ppm, and 131.03 ppm, corresponding to the three types of sp 2 carbons of the benzene ring structures, while the 13 C NMR peak at 158.85 ppm corresponds to sp 2 carbons in the anhydride groups (O=CÀ OÀ C=O). The septet peak centered at ~38 ppm corresponds to 13 C in the DMSOd 6 solvent.…”

“…In addition, the wide liquid range of organic solvents enables non‐aqueous RFBs capable of operating in extreme temperatures [5] . A large variety of organic and inorganic materials have been developed for non‐aqueous RFB [5–17] . Nevertheless, a lack of low potential anode materials limits its voltage to 2.5 V [18] .…”

“…[5] A large variety of organic and inorganic materials have been developed for non-aqueous RFB. [5][6][7][8][9][10][11][12][13][14][15][16][17] Nevertheless, a lack of low potential anode materials limits its voltage to 2.5 V. [18] As alternatives, non-aqueous hybrid RFBs with Li/Na metal anodes are able to fully utilize the high voltage potential of organic electrolytes due to the very low potentials of these alkali metals. [19] However, an Li/Na-ion conducting membrane is mandatory to separate the organic electrolytes from the very reactive alkali metal, which increases the overall cost and limits their performance.…”

Organische Vier‐Elektronen Redox‐Systeme basierend auf Bipyridin‐ und Phenanthrolin‐Carben‐Architekturen

“…Es sei darauf hingewiesen, dass im Fall von Viologen‐Anolyt‐Materialien in der Regel nur ein‐Elektron‐Transfer über die Oxidationsstufen Dikation/Radikalkation verwendet werden [40] . In jüngster Zeit ist das Interesse daran gewachsen, zwei Elektronen aus dem Viologensystem zu nutzen, [41, 42] oder andere Mehrelektronen‐Redoxsysteme mit stark negativen (oder positiven) Redoxpotentialen zu finden [43–45] . Es sei darauf hingewiesen, dass einfache Pyridinium/Carben‐Hybridmoleküle wie V (Abbildung 1) nach 25 Zyklen eine erhebliche Zersetzung für zwei‐Elektronen‐Zyklen in der symmetrischen H‐Zelle zeigen [24a] …”