Nanoporous carbons from hydrothermally pre-treated avocado waste: experimental design, hydrogen storage behavior, and energy distribution analysis

Avocado waste, which includes the peel and seed, is a promising biomass source for highly porous materials crucial to establishing an economical and efficient hydrogen economy. Hydrothermally pre-treated avocado waste was explored as a precursor for biocarbon optimized for hydrogen storage, employing the design of experiment to vary activation temperature and impregnation ratio. The resulting optimized biocarbon, synthesized at 800 °C with a 1:3 impregnation ratio, exhibited appreciable hydrogen uptake at 77 K and 1 bar, surpassing some reported literature values. Notably, the optimized biocarbon (AC₂₀₀), hydrothermally pretreated at 200 °C, demonstrated a remarkable 3.07 wt% hydrogen uptake, attributed to its narrower micropores facilitating extensive adsorption. The study employed a modified Langmuir model incorporating homotattic patch approximation for a universal isotherm model, providing insights into the surface characteristics of the optimized biocarbon in terms of adsorption site availability and energy distribution. The modeling offers insight into the heterogeneous surface characteristics, specifically regarding the availability of adsorption sites, elucidating the distinct behavior exhibited by each optimized biocarbon.