Confinement of Zn-Mg-Al-layered double hydroxide and α-Fe2O3 nanorods on hollow porous carbon nanofibers: A free-standing electrode for solid-state symmetric supercapacitors

Abstract

Nano confinement of Layered double hydroxide (LDHs) nanosheets and metal oxide is a compelling way to develop new functional materials with unique physiochemical features for various energy storage devices with enhanced performance. Herein, ternary zinc-magnesium-aluminum layered double hydroxide (ZMA-LDH) nanosheets and hematite (α-Fe2O3) nanorods are confined in a hetero-interfacial orientation on electrospun three-dimensional hollow and porous carbon nanofibers (3DHPCNF) by a subsequent hydrothermal process, resulting in the formation of a multi-dimensional nanoarchitecture. Such a structure can incorporate a conductive matrix and eliminate the need of current collectors, thereby minimizing the dead mass in electrochemical energy storage materials. The amount of Zn significantly determines the structural, morphological, and electrochemical properties of ZMA-LDH nanostructures. ZMA-LDH@Fe2O3/3DHPCNF was used as a free-standing electrode material for supercapacitors and endowed high capacitive behavior at both positive and negative working potentials. With the well-arranged 1D-3D hollow and porous interconnection, increased terrestrial surface area, and superior electrical conductivity, the hierarchical composite electrode offers a high areal capacitance of 3437F cm−2 at 1 mA cm−2 and ultrahigh cyclic stability. This fascinating electrochemical performance is attributed to the synergistic effect of 1D/2D/3D hollow and porous nanostructures, bimetallic compositions, top-to-bottom utilization of electrode materials, and unique combinations of surface interfacial diffusion and faradaic reduction governed by carbon and LDH/Fe2O3, respectively. Furthermore, a flexible all solid-state ZMA-LDH@Fe2O3/3DHPCNF symmetric supercapacitor exhibited a high areal energy density at a high power density along with excellent cyclability. This result suggests new prospects to design highly efficient multi material based electrodes for energy storage devices.