Pseudocapacitive Conjugated Polyelectrolyte/2D Electrolyte Hydrogels with Enhanced Physico‐Electrochemical Properties

Abstract

Conducting polymer hydrogels (CPHs) are an attractive class of materials that synergize the electrical properties of organic semiconductors with the physical properties of hydrogels. Of particular interest is the implementation of CPHs as electrode materials for electrochemical energy storage by taking advantage of redox‐tunable conjugated backbones and the large electroactive surface area. Herein, the use of 2D electrolytes as an effective post‐polymerization additive to enhance the pseudocapacitive performance of CPHs, is demonstrated. By using the self‐doped conjugated polyelectrolyte CPE‐K hydrogel as a model system, improvements in cycling stability, specific capacitance and working voltage window upon addition of the 2D electrolytes, are shown. Furthermore, positively charged 2D electrolytes to be more effective than their negatively charged counterparts are revealed. Rheology measurements and SEM imaging indicate that the 2D electrolytes serve as non‐covalent cross‐linkers that help in forming a mechanically more robust and highly percolated conducting network. These results provide a new and simple to execute post‐polymerization strategy to optimize the electrochemical performance of CPH‐based pseudocapacitors.

Ionic Tunability of Conjugated Polyelectrolyte Solutions

“…Given the structural differences between the counterions of different valency, there is an opportunity for stimulus-responsive sensing or actuation in response to small amounts of ion exchange. For example, small amounts of divalent Mg 2+ ions have recently been reported to change the operating mode of a biocomposite from electrical current generation to electrochemical energy storage, in part by changing the morphology of PCPDTBT-SO 3 – K + to sheet-like aggregates, similar to the pseudocapacitive behavior upon addition of a 2D electrolyte …”

“…For example, small amounts of divalent Mg 2+ ions have recently been reported to change the operating mode of a biocomposite from electrical current generation to electrochemical energy storage, in part by changing the morphology of PCPDTBT-SO 3 − K + to sheet-like aggregates, 65 similar to the pseudocapacitive behavior upon addition of a 2D electrolyte. 64 Moreover, the counterion affects the optoelectronic properties, independent of the structural differences, due to the way the counterion interacts with the π-conjugated backbone. 77,78,80 The absorbance for the PCPDTBT-SO 3 − M + polymers in dilute solution (3 mM in H 2 O) is shown in Figure 3c.…”

“…PCPDTBT-SO 3 – K + (poly­[2,6-(4,4-bis-potassium butanyl­sulfonate-4 H -cyclopenta-[2,1- b ;3,4- b ′]-dithiophene)- alt -4,7-(2,1,3-benzo­thiadiazole)], Figure ) is an anionic, narrow band gap conjugated polyelectrolyte that is a model system for surveying the design space of ionic interactions in CPEs due to its synthetic control, − well-characterized properties, − and high performance in optoelectronic − and bioelectrochemical devices. ,, Dilute, salt-free solutions of PCPDTBT-SO 3 – K + behave as polyelectrolyte solutions of isolated chains with the local chain rigidity determined by the conjugated backbone . However, at elevated concentrations in salt-free aqueous solutions (∼40 mg mL –1 ≈ 60 mM), PCPDTBT-SO 3 – K + aggregates into a percolated microgel network with a hierarchical structure illustrated in Figure , characterized by a microgel size ξ microgel ≈ 3–5 μm and a void size of ξ mesh ≈ 10–20 μm.…”

Increasing the molecular weight of conjugated polyelectrolytes improves the electrochemical stability of their pseudocapacitor gels

“…11,13 Of particular relevance is their implementation as pseudocapacitive hydrogels owing to their excellent ion conductivities, high degree of ionic–electronic coupling, water processability, self-doping properties, and large electrode/electrolyte interfacial areas. 11,14–17 Furthermore, their excellent shape adaptability and softness present them as attractive materials for flexible devices with sustained capacitive performance when bent or stretched. 18 Lastly, hydrogels can be designed to interface with living systems.…”

Enabling Electron Injection for Microbial Electrosynthesis with n‐Type Conjugated Polyelectrolytes

“…The degree of interchain connectivity in the CPEs (20 mg mL −1 in water) was probed via rheology measurements using a platecone geometry. [37] The materials were deposited onto the plate and a frequency sweep was carried out in the linear viscoelastic region at 23 °C and a constant strain of 0.01% (Figure 2c). Hydrogel-like behavior can be identified for both CPEs-the elastic modulus (G′) and loss modulus (G″) curves are linear and parallel with G′ greater than G″ across the measured frequency range.…”