Abstract
In this work, African maize cobs (AMC) were used as a rich biomass precursor to synthesize carbon material through a chemical activation process for application in electrochemical energy storage devices. The carbonization and activation were carried out with concentrated Sulphuric acid at three different temperatures of 600, 700 and 800 °C, respectively. The activated carbon exhibited excellent microporous and mesoporous structure with a specific surface area that ranges between 30 and 254 m2·g−1 as measured by BET analysis. The morphology and structure of the produced materials are analyzed through Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Boehm titration, X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. X-ray photoelectron spectroscopy indicates that a considerable amount of oxygen is present in the materials. The functional groups in the activated carbon enhanced the electrochemical performance and improved the material’s double-layer capacitance. The carbonized composite activated at 700 °C exhibited excellent capacitance of 456 F g−1 at a specific current of 0.25 A g−1 in 6 M KOH electrolyte and showed excellent stability after 10,000 cycles. Besides being a low cost, the produced materials offer good stability and electrochemical properties, making them suitable for supercapacitor applications.
Highlights
Electrochemical capacitors have recently received significant scientific and technological attention because of their exciting possibilities as energy storage devices
The thermal degradation and stability of the raw maize cobs (MC) and activated carbon (AC) samples were performed with thermogravimetric analysis (TGA-DSC) at a temperature range of 28 to 1000 ◦ C
The second stage was due to the thermal degradation of organic compounds which corresponds to a weight loss range from 12–26% (Table S1) and may constitute loss of cellulose, hemicellulose and lignin compounds, which vaporize at that temperature range [51]
Summary
Electrochemical capacitors (supercapacitors) have recently received significant scientific and technological attention because of their exciting possibilities as energy storage devices. Materials 2020, 13, 5412 improve the energy density of supercapacitors by developing nanostructured active electrode materials with suitable surface area, porosity and morphology to increase energy density without sacrificing their intrinsic high-power density and cycle life [2]. This can be achieved by exploring electrolytes with large potential windows such as ionic or organic electrolytes. Depending on the charge storage mechanisms of the active materials used, the electrochemical systems (EC) can be generally classified into two types, namely electric double-layer capacitors based on ion adsorption (EDLCs mainly carbonaceous material with a high surface area) and pseudocapacitors (including redox material such as transition metal oxides and conducting polymers) [3]. Pseudocapacitors have been shown to exhibit much higher capacitance than the EDLCs and are either used to complement EDLCs to improve the power and energy densities [4]
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