Abstract
Coffee is one of the largest agricultural products; however, the majority of the produced coffee is discarded as waste sludge by beverage manufacturers. Herein, we report the use of graphitic porous carbon materials that have been derived from waste coffee sludge for developing an energy storage electrode based on a hydrothermal recycling procedure. Waste coffee sludge is used as a carbonaceous precursor for energy storage due to its greater abundance, lower cost, and easier availability as compared to other carbon resources. The intrinsic fibrous structure of coffee sludge is based on cellulose and demonstrates enhanced ionic and electronic conductivities. The material is primarily composed of cellulose-based materials along with several heteroatoms; therefore, the waste sludge can be easily converted to functionalized carbon. The production of unique graphitic porous carbon by hydrothermal carbonization of coffee sludge is particularly attractive since it addresses waste handling issues, offers a cheaper recycling method, and reduces the requirement for landfills. Our investigations revealed that the graphitic porous carbon electrodes derived from coffee sludge provide a specific capacitance of 140 F g−1, with 97% retention of the charge storage capacity after 1500 cycles at current density of 0.3 A g−1.
Highlights
Coffee is one of the common agricultural products that are generally used for beverages
The graphitic porous carbon, which is derived from spent coffee sludge, was employed in electrical double-layer capacitor (EDLC) by manipulating its unique microstructure which has a high hierarchical porous nature and graphitic edges
Because of the high surface area (~1067 m2 g−1) and a hierarchical multiporous structure, activated hydrochar (AHC) gives easy pathways for ion and electron transport, which provides a higher electrochemical performance as an EDLC electrode than that demonstrated by the HC
Summary
Coffee is one of the common agricultural products that are generally used for beverages. Coffee Organization [1], which corresponds to an annual production of approximately eight million metric tons of coffee; coffee can be regarded as an important agricultural commodity [2]. Most of the produced coffee is discarded as waste sludge by beverage manufacturers. To prepare a cup of coffee, only 0.2% of the coffee beans are used and the remaining 99.8% is thrown away as waste coffee sludge; further, it is estimated that over 124,000 tons of waste are generated [3] annually. Coffee sludge is primarily composed of cellulose-based materials with many heteroatoms (e.g., nitrogen, oxygen, and sulfur), which are considered good precursors for the fabrication of functionalized carbon materials.
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