Authors:

Mark Merrill

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The onset of intermittent energy sources, e.g., wind and solar, requires a solution for energy storage that is both high in energy density and power density. While batteries are a reliable solution for high energy density, supercapacitors are at the forefront of research as a high power density energy storage solution. However, conventional supercapacitors still lack sufficient energy density for many off-grid applications. Here, we propose a framework utilizing agricultural waste to synthesize heteroatom (N and S) doped, MnO, functionalized, hierarchical porous carbon electrodes for high-performance supercapacitors. Biomass precursors including Spent Coffee Grounds (SCG) and Coconut Husks (CH) are pretreated with ZnCl, and undergo pyrolysis at 900°C. The resulting hierarchical porous carbon balances competing electrochemical pore functions: micropores maximize EDLC formation, while meso and macropores encourage ion transport. This explains why carbon-based supercapacitors exhibit extremely high electrical double layer capacitance (EDLC); nanoscale charge separation distances (~0.3-0.5 nm) and high surface areas enable specific capacitances approaching ~300 F/g. A key focus is identifying the threshold at which microporosity remains effective in improving capacitive performance. Following hydrothermal carbonization of the feedstock, Potentiostatic and Galvanostatic electrodeposition methods are actively being developed to deposit thin film MnO, coatings into the carbon structure. This approach utilizes both EDLC and pseudocapacitance from fast Mn**/Mn** redox reactions to maximize performance. Preliminary characterization of multiple feedstock-derived hierarchical porous carbon yielded a consistent specific surface area of ~1300 m?/g. Given that specific capacitance is fundamentally dependent on accessible surface area available for double layer formation, this result is a strong predictor of high specific capacitance in the final device. This approach will simultaneously divert waste from landfills and reduce emissions for a sustainable energy storage solution.

Source:

Illinois Institute of Technology

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Co-authors:

Mark Merrill