Carbon nanofiber-supported elongated square bipyramid-like MnWO4 composite electrodes for high-performance battery-type supercapacitors: Enhanced electrochemical performance via synergistic effect

Abstract

Battery-type electrode materials known for high electrochemical performance are commonly paired with carbon based materials, which have recently gained attention for their potential application in supercapacitors. These carbon-based materials offer the potential for comprehensive energy storage properties along with excellent cycle life. In this study, a carbon nanofiber (CNF)-based elongated square bipyramid-like manganese tungstate (MnWO4; MnW) composite was synthesized via a simple and cost-effective solid-state reaction followed by an impregnation method. The main objective was to understand the synergistic effects of varying the content of CNF in the reaction on the formation of two different composites (MnW-CNF@L and MnW-CNF@H) and their physicochemical and electrochemical properties were thoroughly examined and compared to those of the MnW. Pure composites have a high crystalline nature with bipyramid-shaped microstructures anchored on the onedimensional (1D) tubular CNF backbone, as confirmed by the structural and morphological analysis. In the context of the battery-type supercapacitor, the specific capacity is 2-fold higher for MnW-CNF@L (235.3 mAh g- 1/848.1 C g-1) and 4-fold higher for MnW-CNF@H (451.3 mAh g- 1/1624 C g-1) compared to the MnW (11.8 mAh g- 1/402.6 C g-1) electrode at a current density of 1 A g-1. In addition, the MnW-CNF@H composite electrode delivered 96% capacity retention when current density increased 20-fold and exhibited outstanding cyclic stability of 95% initial capacity retention after 5,000 cycles. A solid-state hybrid supercapacitor was fabricated using the battery-type MnW-CNF@H composite electrode as the cathode and activated carbon (AC) as the anode. The MnW-CNF@H//AC HSC device configuration resulted in remarkable performance metrics, displaying a high energy density of 48.9 Wh kg- 1 at 1018.2 W kg 1. The exceptional performance of this composite can be attributed to the synergistic effect among redox centres of Mn, W, and CNF. This work broadcasts a simple and cost-effective approach for designing high-performance supercapacitors, contributing to the development of sustainable energy storage systems.