Biowaste-derived activated carbon from spent coffee grounds for volumetric hydrogen storage

Abstract

Nanoporous activated carbon materials were prepared from biowaste (spent coffee grounds) as a renewable and practical system for enhanced hydrogen storage at room temperature. Chemical charring and activation with potassium hydroxide (KOH) were performed to expand the pore network, increase the specific surface area, and improve the volumetric storage capacity. These materials were characterized using helium pycnometry, nitrogen adsorption, hydrogen adsorption, and scanning electron microscopy. The activation procedure resulted in a bimodal pore size distribution and a large fraction of nanopores of 7 Å pore widths that are optimal for hydrogen storage. Specific surface areas of 2595 m²/g were achieved with a crystalline volumetric storage capacity of 9.84 g/L at room temperature and 100 bar. This corresponds to an energy density around 1.18 MJ/L, which is a 28% improvement over compressed gas alone. This biowaste-derived material has the same volumetric storage capacity as the commercially available, petroleum-derived adsorbent, Maxsorb (MSC-30) produced by Kansai Coke. This demonstrates that reversible, physical adsorption of hydrogen on materials produced from biowaste may be used as a more ecologically friendly improvement for renewable energy storage. A similar performance can be achieved by engineering a range of biowaste-based adsorbent materials that involve cleaner precursors compared to the petroleum-based adsorbent materials currently offered on the market.