Medium-pressure hydrogen storage on activated carbon derived from biomass conversion

This study presents the utilization of activated carbons (ACs) derived from Polypodium vulgare, a commonly available feedstock, for effective medium-pressure H2 storage. For the ACs preparation, biomass was treated with KOH and then pyrolyzed at 700–900 °C. H2 adsorption was performed at 25–100 °C and pressures up to 45 bar; nine different models (Langmuir, Freundlich, Temkin, Redlich–Peterson, Toth, Hill, Koble–Corrigan, Sips, and Radke–Prausnitz) were used for adjusting experimental H2 adsorption isotherms. The micropore volume in the ranges 1.4–2 nm and 0.3–1.4 nm was determined by N2 and CO2 adsorption at −196 and 0 °C, respectively. The textural characteristics and the H2 storage capacity of ACs depended on the carbonization temperature. All samples exhibited a considerable specific surface area of 1234–1591 m2/g, and significant volume of micropores with size below 1.4 nm. The H2 adsorption capacity is related with the micropore volume determined by CO2 adsorption. The AC prepared at 800 °C (G-800) showed the highest H2 uptake and both the highest specific surface area and volume of micropores with size below 1.4 nm. G-800 adsorbs 13.63 mmol H2/g (2.73 wt%) at 25 °C and 45 bar. G-800 sample also showed exceptional cyclic stability, keeping its adsorption capabilities after undergoing multiple adsorption–desorption cycles. The isosteric heat of adsorption of ACs was determined using the Clausius-Clapeyron equation, yielding values ranging from 5.7 to 7.7 kJ/mol.