Poly(3,4-ethylenedioxythiophene)/nickel disulfide microspheres hybrid in energy storage and conversion cells

Mukkabla, R and M, Deepa and Srivastava, A K (2015) Poly(3,4-ethylenedioxythiophene)/nickel disulfide microspheres hybrid in energy storage and conversion cells. RSC Advances (5). pp. 99164-99178. ISSN 2046-2069

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Abstract

The redox pseudocapacitive response of a hybrid material made up of NiS2 microspheres embedded in a poly(3,4-ethylenedioxythiophene) or (PEDOT) layer is demonstrated for the first time. NiS2 microspheres of 2 to 3.5 μm dimensions were synthesized by a hydrothermal route and after electropolymerization with the monomer, EDOT, an assembly of the PEDOT/NiS2 hybrid was obtained on both rigid (stainless steel (SS) foil) and flexible (carbon (C)-fabric) current collectors. The synergy between NiS2 microspheres (electrically conductive, and composed of flaky nanoparticles thus ensuring good electrolyte penetration) when hybridized with PEDOT, (which provides a robust scaffold for the microspheres to adhere to, acts as a conductive glue and prevents their aggregation) allows charge storage and release by faradaic reactions. Symmetric supercapacitors on rigid and flexible supports were constructed using an ionic liquid electrolyte with pristine PEDOT, NiS2 and the PEDOT/NiS2 hybrid as the electroactive materials. The PEDOT/NiS2 hybrid based rigid cell delivered a high specific capacitance of 937.5 F g−1 compared to 517.5 F g−1, achieved for the PEDOT based cell at the same current density of 10 A g−1. The hybrid also showed excellent cycling stability with ∼81% capacitance retention relative to 50.5% capacitance retention at the end of 5000 cycles, obtained for the PEDOT based rigid cell. The energy and power densities achieved for the hybrid cell are: 154.16 W h kg−1 and 7.4 kW kg−1 respectively, greater by 47 and 4% compared to the PEDOT based cell. The flexible cell based on the PEDOT/NiS2 hybrid strikingly outperformed the pristine PEDOT or NiS2 cell, and it exhibited a remarkably large specific capacitance of 1540 F g−1 (at 10 A g−1) and showed good cycling stability as well. We also show the applicability of the hybrid as a counter electrode in photoelectrochemical solar cells. The foldability of the flexible cell, the high-rate capability, durability and capacitance of the cell based on the PEDOT/NiS2 hybrid, and the demonstration of a LED illumination with the same show that this approach of combining PEDOT with NiS2 can be extended to other redox active metal sulfides as well.

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