Cryogenic hydrogen storage on peanut shell-derived-activated carbons: Isotherm, kinetics and mechanism

Abstract

This study investigates the cryogenic hydrogen storage performance of activated carbons synthesized from peanut shells via hydrothermal carbonization. Samples were prepared at 240 degrees C for 1, 3, and 6 h using ZnCl2 as the activating agent. Comprehensive characterization was conducted using BET, FTIR-ATR, XRD, SEM/EDX and TGA devices. The PS-ZnCl2-240-3 h sample exhibited the highest BET surface area (856 m(2)/g) and total pore volume (0.448 cm(3)/g), achieving a maximum hydrogen uptake of 2.1 wt% at 77 K and 30 bar. Adsorption behavior was analyzed using Langmuir, Freundlich, Dual-Langmuir, and Temkin isotherm models. The best fit was obtained with the Langmuir model (R-2 > 0.996), indicating monolayer physisorption. Kinetic data were fitted to pseudo-first-order and pseudo-second-order models; the latter showed superior correlation, particularly for the 3 h sample (R-2 = 0.9874). Boyd and Weber-Morris models revealed that intraparticle diffusion was the rate-limiting step. Comparative analysis confirmed that the 3 h activation condition yielded the most favorable combination of surface area, microporosity, and hydrogen storage capacity. These results demonstrate that peanut shell-derived activated carbons are promising, low-cost candidates for hydrogen storage applications under cryogenic conditions, offering competitive performance based on surface and pore structure optimization.