Spatial Structure Regulation: A Rod‐Shaped Viologen Enables Long Lifetime in Aqueous Redox Flow Batteries

Abstract

As table rod-like sulfonated viologen (R-Vi) derivative is developed through as patial-structure-adjustment strategy for neutral aqueous organic redoxf lowb atteries (AORFBs). The obtained R-Vifeatures four individual methyl groups on the 2,2',6,6'-positions of the 4,4'-bipyridine core ring. The tethered methyls confine the movement of the alkylc hain as well as the sulfonic anion, thus driving the spatial structure from sigmoid to rod shape.T he R-Viw ith weak charge attraction and large molecular dimension displays an ultralow membrane permeability that is only 14.7 %o ft hat of typical sigmoid viologen. Moreover,t he electron-donating effect of methyls endows R-Viw ith the lowest redox potential of À0.55 Vv s. SHE among one-electron-storage viologen-based AORFBs.The AORFB with the R-Vianolyte and aK 4 Fe(CN) 6 catholyte exhibits an energy efficiency up to 87 %a nd extremely lowc apacity-fade rate of 0.007 %p er cycle in 3200 continuous cycles.

Conjugate‐Driven Electron Density Delocalization of Piperidine Nitroxyl Radical for Stable Aqueous Zinc Hybrid Flow Batteries

“…Accordingly, both the nucleophilic Fukui function (f − ) for the N−O⋅ form and the electrophilic Fukui function (f + ) for the + N=O form are in the same order of MIAcNH‐TEMPO<AcNH‐TEMPO, consistent with the order of chemical degradation rate. As known, a large Fukui function value represents the great possibility of electrophilic/nucleophilic attack [16b, 28] . For f − or f + , the largest values for AcNH‐TEMPO and MIAcNH‐TEMPO occur at O1 and N2 atoms (Figure 5B, Figure S27 and Table S1), therefore the N−O head is a favorable site for electrophilic/nucleophilic attack.…”

“…In agreement with their stable chemical stability and low capacity fade in batteries, the 1 H NMR and Raman spectra of cycled MIAcNH‐TEMPO catholytes display no observable chemical changes both in 0 % and 100 % SOCs (Figure S31). Subsequently, we screened and quantified the contribution of the membrane by an Ohmic‐compensated CV method [11b, 12d, 16b] . CV measurement of the cycled ZnCl 2 anolyte clearly presents the reversible redox behavior of TMAAcNH‐TEMPO, certifying the molecular impregnation from the catholyte to the anolyte (Figure S32).…”

Viologen Hydrothermal Synthesis and Structure-Property Relationships for Redox Flow Battery Optimization

“…As has been previously reported, sulfonated viologens form an inner salt sigmoid structure between the terminal alkyl sulfonate anion and the redox core pyridinium cation. 20 We hypothesize that this inner salt bonding is increased with shorter alkyl chains (i.e., EtS-Vi) and the presence of a secondary alcohol (i.e., SHOP-Vi) that prevents water molecules from solvating the species. Despite these inner salt dynamics, the asymmetric strategy improves the solubility of EtS-DiOH-Vi to 1.3 M -the average solubility of EtS-Vi and DiOH-Vi is 1.2 M -and rotational confinement approaches similar to those reported could be employed to potentially further enhance room temperature solubility.…”

Stable Operation of Aqueous Organic Redox Flow Batteries in Air Atmosphere

“…In following years, organic active species in anode side were coupled with various organics, [8b, 9] low‐cost metal‐based redox species [8c–e, 10] or other inorganics (metal‐free) [11] in cathode side to form different AORFBs, which have attracted extensive attention. However, most of these reported AORFBs were operated in an inert atmosphere (Table S1), which should be attributable to that the reduced states of organic active species in the anode side are sensitive to oxygen [8b–e, 9b–i, 10a–o, 11b,c] . For example, Aziz’ group recently demonstrated a highly stable AORFB (i.e., the 3,3′‐(9,10‐anthraquinone‐diyl)bis(3‐methylbutanoicacid) (DpivOHAQ)||Ferrocyanide (K 4 Fe(CN) 6 ) flow cell), and simultaneously Aziz et al.…”