Supramolecular Assembly of Nanostructured Conducting Polymer Hydrogels by Hydrotropic Agents for Outstanding Supercapacitive Energy Storage

Conducting polymer hydrogels (CPHs) are relevant to energy storage due to their micro-nanoscale three-dimensional network combined with a high electronic conductivity and electrochemical activity. The successful implementation of CPHs as an energy storage material requires solving two barriers: (1) low capacitance and electronic conductivity of current CPHs and (2) the lack of simple and scalable chemical synthesis routes. In this work, we propose a different approach for the synthesis of CPHs based on a supramolecular self-assembly induced by hydrotropic agents. The proposed synthesis method induces the formation of networks with superior electronic conductivity which does not require the addition of costly additives. Herein, para-toluene sulfonic acid (p-TSA) was proposed to produce CPHs of polypyrrole (PPy). The method was further extended to other polymer and hydrotropic agents as polyaniline and camphor sulfonic acid, demonstrating the versatility of the synthesis method. It was found that morphology and physical–chemical and electrochemical properties of PPy-CPHs can be fine-tuned with the amount of doping agents. The optimized PPy-CPHs sample possesses a high specific gravimetric capacitance of 560 F g–1 and an areal capacitance of 695 mF cm–2 at 0.75 A g–1 in addition to a capacitance retention of 72% at 10 A g–1, significantly higher than most state of the art PPy electrodes. Characterization suggests that CPH's faster charge transfer and enhanced ionic and electronic conductivity are due to the higher degree of conjugation, porosity, and size of polymer clusters. Moreover, the symmetric supercapacitor devices with liquid and solid electrolytes exhibit an excellent energy storage performance with a maximum energy density of 13 W h kg–1 and power density of 3.6 kW kg–1. These devices also exhibit a capacitance retention of 82% after 5000 cycles at 5 A g–1.