Understanding the Degradation Mechanisms of Conducting Polymer Supercapacitors.

Conducting polymers like polyaniline (PANI) are promising pseudocapacitive electrode materials, yet experience instability in cycling performance. Since polymers often degrade into oligomers, short chain length anilines have been developed to improve the cycling stability of PANI-based supercapacitors. However, the capacitance degradation mechanisms of aniline oligomer-based materials have not been systematically investigated and are little understood. Herein, two composite electrodes based on aniline trimers (AT) and carbon nanotubes (CNTs) are studied as model systems and evaluated at both pre-cycling and post-cycling states through physicochemical and electrochemical characterizations. The favorable effect of covalent bonding between AT and CNTs is confirmed to enhance cycling stability by preventing the detachment of aniline trimer and preserving the electrode microstructure throughout the charge/discharge cycling process. In addition, higher porosity has a positive effect on electron/ion transfer and the adaptation to volumetric changes, resulting in higher conductivity and extended cycle life. This work provides insights into the mechanism of enhanced cycling stability of aniline oligomers, indicating design features for aniline oligomer electrode materials to improve their electrochemical performance.

Molecular Engineering of Hierarchical Conducting Polymer Composites for Highly Stable Supercapacitors.

Long cycle life and high energy/power density are imperative to energy storage systems. Polyaniline (PANI) has shown great potential as an electrode material but is limited by poor cycling and rate performance. We present a molecular design approach of binding short-chain aniline trimers (ATs) and carbon nanotubes (CNTs) through the formation of amide covalent linkages enabled by a simple laser scribing technique. The covalently coupled AT/CNT (cc-AT/CNT) composite retains 80% of its original capacitance after 20 000 charge/discharge cycles, which readily outperforms long-chain PANI/CNT composites without covalent connections. The compact AT/CNT heterointerfaces produce fast charge/discharge kinetics and excellent rate capability. The flexible symmetric quasi-solid-state devices can be stably cycled beyond 50 000 cycles, at least 5 times longer than most PANI/CNT-based symmetric supercapacitors reported to date. This molecular design of durable conducting polymer-based electrode materials enabled by laser irradiation presents a feasible approach toward robust advanced energy storage devices.

Isomerism of the Aniline Trimer.

Weaker intermolecular forces expand the isomerization alternatives for molecular aggregation, as observed for the prototype models of the aniline trimer (An3 ) and the monohydrated aniline dimer (An2 -W) when compared to the phenol trimer. In this experiment the aniline clusters were generated in a jet-cooled expansion and probed using broadband (chirped-pulsed) microwave spectroscopy. Three isomers of the aniline trimer and two isomers of the hydrated dimer were detected and characterized in the rotational spectrum. In the homotrimer the weak N-H⋅⋅⋅N hydrogen bonds are assisted by subtle combinations of N-H⋅⋅⋅π and C-H⋅⋅⋅π interactions, producing several competing low-lying ring species in the gas phase. One of the aniline trimers is a symmetric top, topologically equivalent to the only observed phenol trimer. Conversely, addition of a water molecule to the aniline dimer introduces a leading O-H⋅⋅⋅N interaction, making water to behave as dominant hydrogen-bond pivot between the two aniline molecules. This combination of weak intermolecular interactions critically tests the performance of dispersion-corrected or parametrized density-functional methods. Evaluation of the B3LYP-D3(BJ) and M06-2X methods revealed deficiencies of the Truhlar functional to reproduce the experimental rotational data.

Biocompatible conductive hydrogels based on dextran and aniline trimer as electro-responsive drug delivery system for localized drug release.

Dextran with good biocompatibility and degradability shows great potentials for drug delivery and tissue engineering applications. Electro-responsive drug delivery system can provide on-demand and localized drug release. However, dextran-based conductive hydrogel with electrical stimuli responsiveness as drug delivery system has not been reported. Herein, we designed and fabricated a kind of biocompatible biodegradable conductive hydrogel system with the property of electro-responsiveness as a new smart drug delivery system for localized drug release. These series of hydrogels were synthesized by mixing dextran and electroactive aniline trimer with hexamethylene diisocyanate as crosslinker to form hydrogel network. These series of hydrogels exhibited stable rheological property and controllable swelling ratio. These hydrogels showed good conductivity and desirable electric stimuli ability to control drug release. Furthermore, this kind of hydrogel was controlled by external electrical stimuli to generate a kind of "on-off" precise drug release system. When extra voltage was applied, they released more drug intelligently and less drug molecule without external stimuli. The hydrogel showed good cytocompatibility and in vivo biocompatibility by using H&E staining and Toluidine blue staining. All together, these results indicated that these series of biocompatible conductive dextran-based hydrogels were promising candidates as smart drug delivery systems in future biomedical field.