A novel anodic nanostructure stainless steel-304L oxide as an emerging electrode material for high energy density asymmetric supercapacitor: Experimental and DFT Insights

Abstract

The electrodes material plays a significant role in the performance of supercapacitors. Therefore, the development of a novel electrode material for high energy density, high power density, and stable supercapacitor is highly desirable. Stainless steel 304L (SUS-304L) oxide nanostructure as an emerging electrode material provides an opportunity to explore its supercapacitive behavior. In the present study, a simple and facile technique of anodization was employed to synthesize nanostructured SUS-304L oxide (in powder form), which would otherwise impossible to achieve using the existing synthetic routes. The structural and microscopic results confirm the formation of multiple phases (Fe2O3, Fe3O4, and NiCr2O4), polycrystalline behavior, and nanoparticles (NPs) overlapping nanosheets (NSs) like morphology. As an electrode, the developed material demonstrated excellent electrochemical performance, achieving high specific capacitance of ~1226 F.g⁻¹ at 2A.g⁻¹ in KOH electrolyte. The fabricated asymmetric supercapacitor device (SUS-304L oxide//activated carbon) exhibited specific capacitance of ~ 209 F.g⁻¹, energy density of ~29 Whkg⁻¹ at power density of ~751 Wkg⁻¹. Additionally, the device retained ~89% of its initial capacitance over 8000 cycles. The outstanding performance is due to the synergetic effect of the multiple phases. To elucidate further the supercapacitive behavior, Ab-initio calculations based on density functional theory (DFT) was used to calculate the quantum capacitance. The observed large capacitance is mainly contributed by Fe-oxides, and can be ascribed to the large density of states of minority spin states of t2g and eg orbitals of Fe atoms at the octahedral sites. These findings demonstrate the potential of the prepared composite nanostructure (SUS-304L oxide) as a high-performance electrode material for practical asymmetric supercapacitor application.

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