Capacitance enhancement of nitrogen-doped graphene oxide/magnetite with polyaniline or carbon dots under external magnetic field: Supported by theoretical estimation

The effect of conductive materials (polyaniline (PA) or carbon dots (Cdots)) added to supercapacitor consisting of nitrogen-doped graphene oxide (NG) and magnetic nanoparticles (magnetite, Fe3O4) was assessed. Small amounts (4 wt%) of Cdots in composites of NG and Fe3O4 nanoparticles have shown better supercapacitor performance than the addition of PA. When the external stimulating force (magnetic field, 8.98 mT) was coupled with the electrochemical system, the specific capacitance was highest (2213 F/g at a scan rate of 5 mV/s) and the cyclic retention was 91% after 5000 cycles for the NG/Cdots/Fe3\O4 composite electrode. These reports show that the adequate ternary composite materials effectively enhance the specific capacitance, increase the specific energy density and maintain the durability of supercapacitors under the magnet. The increase in the specific capacitance under the uniform magnetic field was proportional to the 3/5 power of bulk electrolyte concentration, although the power value was different from the theoretical estimation. The complex capacitance was almost double under the magnetic field due to the convection induced by the Lorentz force. It was also confirmed in comparison with the theoretical estimation that the Lorentz effect was responsible for the reduction of the charge transfer resistance, the increase of the relaxation time constant, the facilitation of the ion diffusion, and hence the increase of the double-layer capacitance. The present results will open a new window for the enhancement mechanisms on the capacitance efficiency under the magnetic field. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The study evaluated the effects of adding conductive materials (PA or Cdots) to supercapacitors made of nitrogen-doped graphene oxide (NG) and magnetic nanoparticles (Fe3O4). It was found that composites with a small amount of Cdots showed better performance compared to those with PA, especially when coupled with an external magnetic field. The results indicate that adequate ternary composite materials can effectively enhance specific capacitance and durability of supercapacitors under magnetic fields.