Unusual Internal Electron Transfer in Conjugated Radical Polymers

Abstract

Nitroxide‐containing organic radical polymers (ORPs) have captured attention for their high power and fast redox kinetics. Yet a major challenge is the polymer's aliphatic backbone, resulting in a low electronic conductivity. Recent attempts that replace the aliphatic backbone with a conjugated one have not met with success. The reason for this is not understood until now. We examine a family of polythiophenes bearing nitroxide radical groups, showing that while both species are electrochemically active, there exists an internal electron transfer mechanism that interferes with stabilization of the polymer's fully oxidized form. This finding directs the future design of conjugated radical polymers in energy storage and electronics, where careful attention to the redox potential of the backbone relative to the organic radical species is needed.

Design of an n-type low glass transition temperature radical polymer

“…From a historical perspective, this is sensible as the majority of radical polymers are p-type in nature, and the most oft-used open-shell groups are those of the nitroxide class. [38][39][40][41][42][43][44][45][46][47] This draws a parallel to the conjugated polymer literature where hole-transporting macromolecules dominated the research landscape; however, it was clear in the conjugated polymer regime previously, and it is clear in the radical polymer community now, that developing preferentially-reduced (i.e., n-type) open-shell macromolecules will be of critical importance in the near future. 3,8,48,49 To address this gap, here we design, synthesize, and characterize the electronic and electrochemical properties of the first low glass transition temperature, n-type (i.e., preferentiallyreduced) radical polymer.…”

Tunable Conducting Polymers: Toward Sustainable and Versatile Batteries

“…90 Lutkenhaus et al recently synthesized a series of β-substituted PTh bearing TEMPO radicals with varying alkyl spacer groups (Figure 4d). 91 A specific capacity of 68 mAh g −1 was delivered with tetramethyl alkyl groups, corresponding to 38.2% of its theoretical capacity. By monitoring the open circuit potential decay via in situ spectroelectrochemistry, a rapid dedoping process was verified for the PTh backbone, which was caused by internal electron transfer from the nitroxide group to the PTh backbone (Figure 4e,f).…”

“…101 Zhou and co-workers fabricated Fe(CN) 6 4− -doped PPy cathodes. 91 The Fe(CN) 6 4− ions served as a redox mediator to improve the charge transfer between polymer and electrolyte, as its redox potential (∼ 3.0 V vs Li/Li + ) is close to the Fermi level of PPy (E F = +2.50 to +2.80 V vs. Li/Li + ). 102 The resulting PPy/FC cathodes delivered a significantly improved specific capacity of ∼145 mAh g −1 in sharp contrast to that ∼35 mAh g −1 from undoped PPy over a high potential range of 1.5−4.0 V (vs Li + /Li) at a current density of 50 mA g −1 .…”

N-Phenyl naphthalene diimide pendant polymer as a charge storage material with high rate capability and cyclability

“…There have been various efforts focused on increasing cyclability by introducing rigid aromatic groups, [3,4] insoluble salts, [5] and macromolecular materials. [6][7][8][9][10][11][12] Polymers can be designed to be insoluble in electrolyte solution while still retaining the high theoretical capacity (C theor ) of small molecules. As a result, polymer-based materials with carbonyl groups have gained popularity, such as anhydrides and quinones which have proven to achieve significant progress.…”