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.
Due to the lithium reserves for the growing sector of lithium-ion batteries (LIBs), there has been an increased interest in the development of new technologies based on the reactions with other ions, as Sodium (NIBs) and Potassium (KIBs) ion Batteries. Particularly, the intercalation potentials of NIBs are lower than LIBs, limiting their application, for this reason the KIBs are a promising option. Since lithium has a higher polarizing power than potassium, it is expected that the cation-structure interactions influence the intercalation potential. So, in this work we carefully evaluated the structural changes induced by the interactions of Li or K ions with an open framework structure (indium hexacyanoferrate) without water. The lack of water within the structure is important since new intra-interaction phenomena arise, which have not been previously analyzed, providing deeper insights of the importance of the various interactions in this kind of system. The intercalation potentials were evaluated by CV and galvanostatic experiments in a non-aqueous system using a mix of solvent, demonstrating a higher potassium intercalation voltage of 3.9 V vs K+/K in comparison to Lithium 3.3 V vs Li+/Li. The nature of such high potential is evaluated around the electronic structure alterations arising from internal structural modifications and intra structural interactions leading to changes in the way that the ion is interacting with the framework. The lowest formal potential shown in presence of lithium as intercalation ion, can be attributed to a noticeable anisotropy in the charge density on the Fe–(CN)6 octahedron provoking distortions of the molecular block FeCN6, as was confirmed by infrared analysis and Density Functional Theory calculations.
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