Activated carbon from peanut shell and its molybdenum based nanocomposites for supercapacitor applications

Abstract

Synthesis of activated carbon from biomass waste has recently become the main focus for the majority of the scientific community. In this study, activated carbons derived from peanut shell waste and its molybdenum-based nanocomposites were explored as potential electrode materials for supercapacitor applications. Activated carbons and their composites were synthesized through atmospheric pressure chemical vapour deposition (AP-CVD) and characterized by various techniques such as N2 adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). This study aims on the enhancement of electrochemical performance of the activated carbons derived from peanut shell. To achieve this goal various directions have been adopted. First, the study is focused on the effect of the potassium-based activating agents (AAs) on the microstructure and electrochemical properties of the activated carbon from peanut shell materials. This approach contributes to the way to design and tune the properties of the porous carbon by selecting the appropriate AAs. The peanut shell waste (PSW) chemically activated carbon (APSW) with potassium hydroxide (KOH) exhibited a good electrochemical energy storage capability owing to their excellent structural and textural properties (2547 m2 g-1 specific surface area, and 1.2 cm3 g-1 pore volume). The second approach consists of enhancing the activated carbon derived from PSW by heteroatom-doping with nitrogen. Post nitrogen-doped activated carbon from PSW was synthesized by KOH activation of the PSW to produce peanut shell waste activated carbon (denoted as PAC) followed by post-doping with melamine (NPAC). The introduction of the nitrogen into the porous carbons enhances PAC physicochemical characteristics, surface chemistry, and provides more electrochemical active sites leading to an increase in supercapacitor performances. The last approach emphasizes on the incorporation of pseudocapacitive materials into PAC by making a composite. The ternary composite of PAC/molybdenum oxide/molybdenum carbide (PAC/MoO2/Mo2C) was prepared by one-step pyrolysis process of the PAC and ammonium molybdate precursor. The MoO2 and Mo2C nanostructures embedded into the PAC have led to a significant improvement on the performance with a specific capacitance of 253 F g-1 higher than the pristine PAC. This enhancement of the electrochemical performance is attributed to the synergistic effect of the merits of each component (PAC, MoO2, and Mo2C) in the ternary offering additional active sites, faster ions diffusion rate, greater electrical conductivity, and chemical stability. The electrochemical performance of the best as-synthesized electrodes materials have been tested in symmetric devices in 2.5 M KNO3 aqueous electrolyte: APSW-KOH4//APSW-KOH4, NPAC-1//NPAC-1 and PAC/MoO2/Mo2C-1//PAC/MoO2/Mo2C-1 in the wide cell potential in the range of 1.8 V to 2 V. In particular, the PAC/MoO2-1/Mo2C-1 electrode reveals the highest electrochemical performance with a specific energy and power of 51.8 W h kg-1 and 0.9 kW kg-1 at 1 A g-1, respectively as compared to 34.9 W h kg-1 and 1 kW kg-1 for NPAC -1 electrode and 25.2 W h kg-1 and 0.9 kW kg-1 for APSW-KOH4 electrode. This study highlights a sustainable and eco-friendly one-step pathway of synthesizing a ternary composite PAC/MoO2/Mo2C as advanced electrode material for high-performance energy storage. Moreover, this work also emphasized an efficient strategy to improve the electrochemical properties towards incorporating Mo-based components into the porous activated carbon materials.