Transforming breakfast bio-waste into hydrogen storage materials

Orange peels and tea leaves accumulate as everyday “breakfast bio-waste” all around the world. Through a simple thermo-chemical process, value from the waste can be obtained, turning it into high-quality products for energy storage applications. This study reports on the synthesis of bio-waste-derived nanoporous carbons and explores the effects of activation agents on the porous structures. Adding new value to different waste materials with an easy and fast synthesis method allows the exploration of those carbons as sophisticated hydrogen storage materials. Through detailed characterization, it was possible to link structural and chemical characteristics to the supercritical H₂ adsorption behavior up to pressures of 100 bar at 77K. The activation process leads to Quenched Solid Density Functional Theory (QSDFT) surface areas larger than 2100 m²/g and QSDFT pore volumes beyond 1.5 cm³/g. The H₂ uptake is strongly influenced by the pore structure characteristics leading to excess gravimetric capacities of up to 2.6 wt.% at low pressures (1 bar) and 5.3 wt.% at high pressures (30–40 bar). A statistical analysis of the influences of structural and chemical parameters on H₂ uptake was performed, highlighting the importance of specific surface area, specific pore volume and average pore size on the pressure-dependent H₂ uptake of the carbon materials.