Investigation of Two-Dimensional Structured Polyaniline for Supercapacitor Applications
Mass and charge transport within nanostructures, i.e., nanofluidic study, is essential to the mechanism understanding and further development of electrochemical systems. Two-dimensional (2D) nanofluidic materials featuring well-organized flat nanochannels, as well as adjustable structural and chemical properties have emerged as promising candidates for energy storage, and more importantly, established a perfect platform for ion transport study. The anion-dominated behaviour, which is absent in current EDL (electric double layer)- modulated systems, was comprehensively studied in the 2D structured tungstate anion linked polyaniline (TALP) using the gravimetric probe, electrochemical quartz crystal microbalance. It is revealed that the anion nature affects the movement of solvent molecules via modifying the built EDL. To be specific, the thicker EDL contributed by larger anion size and higher salt concentration leads to a counterflux of water molecules in the TALP interspace. The redox activity of polyaniline is then promoted to explore its effect on the ion behaviour and electrochemical performance of TALP. After introducing Faradaic processes in the 2D TALP system, the ion transport pattern would switch from an anion-dominated process to predominated proton transport mode. Meanwhile, except for extra charge contribution via redox reactions, the additive protons also serve as fast and effective charge carriers in 2D TALP channels, resulting in high capacitance retention at a high rate and for thick electrodes. After investigating the ion behaviours in TALP, this unique nanofluidic system is further explored to integrate with bio-systems. Endowing natural biomass with electroactivity other than carbonization is an appealing challenge in nanobiotechnology. By interfacial self-assembly, conformal TALP thin-film coating could be formed onto the surfaces of the plant stem, which enables the macroscopic electronic and ionic conductivity in the as-formed nanobioassembly. This nanofluid-integrated nanobioassembly holds the potential to be applicable with multiple functionalities beyond energy storage. In short, this study revealed the ion and solvent transport behaviour in 2D TALP nanochannels in response to varying electrolyte environments. Correlation between the ion behaviour with electrochemical performance was provided for TALP electrodes and its further employment in the energy storage system was explored with biomass system.
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