In situ Investigations of a Proton Trap Material: A PEDOT-Based Copolymer with Hydroquinone and Pyridine Side Groups Having Robust Cyclability in Organic Electrolytes and Ionic Liquids

Abstract

A conducting redox polymer based on PEDOT with hydroquinone and pyridine pendant groups is reported and characterized as a proton trap material. The proton trap functionality, where protons are transferred from the hydroquinone to the pyridine sites, allows for utilization of the inherently high redox potential of the hydroquinone pendant group (3.3 V versus Li0/+) and sustains this reaction by trapping the protons within the polymer, resulting in proton cycling in an aprotic electrolyte. By disconnecting the cycling ion of the anode from the cathode, the choice of anode and electrolyte can be extensively varied and the proton trap copolymer can be used as cathode material for all-organic or metal-organic batteries. In this study, a stable and nonvolatile ionic liquid was introduced as electrolyte media, leading to enhanced cycling stability of the proton trap compared to cycling in acetonitrile, which is attributed to the decreased basicity of the solvent. Various in situ methods allowed for in-depth characterization of the polymer’s properties based on its electronic transitions (UV–vis), temperature-dependent conductivity (bipotentiostatic CV-measurements), and mass change (EQCM) during the redox cycle. Furthermore, FTIR combined with quantum chemical calculations indicate that hydrogen bonding interactions are present for all the hydroquinone and quinone states, explaining the reversible behavior of the copolymer in aprotic electrolytes, both in three-electrode setup and in battery devices. These results demonstrate the proton trap concept as an interesting strategy for high potential organic energy storage materials.

Polyaniline-Lignin Interpenetrating Network for Supercapacitive Energy Storage

“…One limitation of conducting polymers, however, is their relatively low charge capacity. A variety of approaches have been considered to boost the charge capacity of conducting polymers, such as incorporating redox-active side groups, organic/inorganic species, and redox active dopants, or synthesizing nanostructured polymers to increase the effective surface area for efficient electrode–electrolyte contact. − Furthermore, morphological and structural characteristics and electrochemical behavior of conducting polymers is strongly dependent on the type of counterions compensating the positive charge of the conjugated polymer chains during synthesis. Small anionic dopants such as chloride, perchlorate, p-toluenesulfoante, and dodecylbenzenesulfonate are susceptible to migration out of the electrodes over time, whereas the use of large (bio)­polymers as dopants leads to more stable confinement of the redox moieties within the conductive polymer matrix …”

Electrochemical Characterization of Redox Probes Confined in 3D Conducting Polymer Networks

“…[9,10] Recent chemical approaches include also attaching redox units to conjugated polymer backbones yielding conjugated redox polymers. [11] A key feature of conducting polymers is the possibility to create homogenous films via solution processing. Particularly interesting is that as-deposited films can be further chemically modified by polymer-analogous reactions.…”

“…), [6] quinone derivatives, [7] stable radicals like 2,2,6,6‐tetramethylpiperidinyloxyl (TEMPO) [8] and aromatic systems like carbazole [9,10] . Recent chemical approaches include also attaching redox units to conjugated polymer backbones yielding conjugated redox polymers [11] …”

Proton trap effect on catechol–pyridine redox polymer nanoparticles as organic electrodes for lithium batteries

“…The proposed role for the pyridine acceptor was to assist the quinone/hydroquinone redox reaction by accommodating its protons during cycling in aprotic electrolytes. 19 Due to the chemical similarities between hydroxyquinone (1,4dihydroxybenzene) and catechol (1,2-hydroxybenzene), we hypothesized that the proton trap effect may take place also in catechol containing polymers. So, the main goal of this article is to investigate the effect of the presence of pyridine groups on the electrochemistry of catechol polymers.…”