Layer-by-Layer Electrode Fabrication for Improved Performance of Porous Polyimide-Based Supercapacitors

Nanoporous polymers are becoming increasingly interesting materials for electrochemical applications, as their large surface areas with redox-active sites allow efficient adsorption and diffusion of ions. However, their limited electrical conductivity remains a major obstacle in practical applications. The conventional approach that alleviates this problem is the hybridisation of the polymer with carbon-based additives, but this directly prevents the utilisation of the maximum capacity of the polymers. Here, we report a layer-by-layer fabrication technique where we separated the active (porous polymer, top) layer and the conductive (carbon, bottom) layer and used these “layered” electrodes in a supercapacitor (SC). Through this approach, direct contact with the electrolyte and polymer material is greatly enhanced. With extensive electrochemical characterisation techniques, we show that the layered electrodes allowed a significant contribution of fast faradic surface reactions to the overall capacitance. The electrochemical performance of the layered-electrode SC outperformed other reported porous polymer-based devices with a specific gravimetric capacitance of 388 F·g⁻¹ and an outstanding energy density of 65 Wh·kg⁻¹ at a current density of 0.4 A·g⁻¹. The device also showed outstanding cyclability with 90% of capacitance retention after 5000 cycles at 1.6 A·g⁻¹, comparable to the reported porous polymer-based SCs. Thus, the introduction of a layered electrode structure would pave the way for more effective utilisation of porous organic polymers in future energy storage/harvesting and sensing devices by exploiting their nanoporous architecture and limiting the negative effects of the carbon/binder matrix.

Zener-like electrical transport in polyaniline-graphene oxide nanocomposites

The present study includes the fabrication and characterization and an investigation of the electrical transport properties of nanocomposites of n-PANI and graphene oxide (GO). The samples were prepared by loading different weight percentages D of GO during the chemical oxidative in situ polymerization of aniline monomers. Structural characterization by XRD, FTIR, FESEM, etc. confirmed that the nanocomposites exhibited superior morphology and thermal stability. The transport properties were studied by measuring the variation of conductivity with temperature T, V–I characteristics and the fundamental response V_f at different temperatures T. The dc conductance Σ showed a transition from insulator type behavior to weakly temperature dependent behavior at temperature T_D, which decreased with increasing D. The V–I characteristics were generally nonlinear and the nonlinearity increased with decreasing temperature. Moreover, at temperatures T ≥ T_D, the characteristics showed saturation of voltage for higher values of current, similar to Zener diodes. At lower temperatures (T ≤ T_D), a voltage maximum occurred, similar to thyristors. This behavior leads to the possibility of fabricating devices containing these nanocomposites. We have tried to analyze these results using the framework of scaling theory and the concept of inter-chain hopping conduction and tunneling between conducting grains separated by insulating regimes in the nanocomposite.

The present study includes the fabrication and characterization and an investigation of the electrical transport properties of nanocomposites of n-PANI and graphene oxide (GO).

Three-dimensional conductive porous organic polymers based on tetrahedral polythiophene for high-performance supercapacitors

Three dimensional porous organic polymers with excellent electrochemical performance and good cyclic stability were constructed by introducing conductive polythiophene units into the frameworks with diamond topology.