Hydrogen storage performance of porous carbons from waste Cotton: Activation strategies, isotherm and kinetic analyses

Abstract

In this study, biomass-based carbon materials with high surface area were synthesized from cotton waste via different activation techniques for hydrogen storage applications. The effects of key process parameters—including pyrolysis temperatures (300–800 ◦ activation atmospheres (N 2 and CO 2 C), activation agent ratios (KOH/biomass = 1:10 or 1:20), and )—were systematically investigated. Characterization was performed using BET, FTIR, DTA/TG and SEM/EDX analyses. The highest surface area (1446 m 2 /g) and micropore volume (0.570 cc/g) were obtained for the sample pyrolyzed at 800 ◦ C and activated under CO 2 f low with KOH/biomass impregnation ratio of 1:10, resulting in a highly porous structure. Hydrogen adsorption experiments at 77 K and 17.4 bar revealed a maximum storage capacity of 2.79 wt% for the optimized carbon material, surpassing the theoretical prediction of Chahine’s rule. Adsorption isotherms were best described by the Langmuir model (R2 > 0.996), indicating monolayer coverage on a homogeneous surface. Kinetic modeling showed that the pseudo- second-order model best fit the experimental data. Additionally, Weber–Morris model demonstrated that intra-particle diffusion influenced the adsorption mechanism. Correlation analysis confirmed strong relationships between hydrogen storage capacity and both BET surface area (R = 0.87) and micropore volume (R = 0.86). These results highlight the potential of cotton-derived porous carbon material as low-cost, sustainable, and effective adsorbents for hydrogen storage systems. Importantly, the study demonstrates that combining chemical (KOH) and physical (CO 2 ) activation enables the production of high–surface-area carbons while substantially reducing KOH usage, representing a key novelty and a more sustainable alternative to traditional activation approaches.