Hydrogen storage performance of sunflower stalk-derived activated carbons produced via ZnCl 2 and KOH activation

Abstract

In this study, the hydrogen storage capacities of activated carbons derived from sunflower stalk wastes were enhanced by initialchemical activation using different activating agents (ZnCl 2 or KOH) at biomass ratios of 1:1, 2:1, and 3:1 (w/w), followed bycarbonization at varying temperatures (600°C, 700°C, 800°C, and 900°C) based on their surface area performance. The optimi-zation and characterization of the prepared samples were systematically conducted using BET, FTIR, DTA/TG, and SEM/EDXtechniques. SEM/EDX analysis revealed a marked increase in porosity and notable alterations in the elemental composition ofthe activated carbon surfaces as a function of the activating agent and carbonization temperature. Hydrogen storage capacitiesof the optimized samples were measured as a function of pressure at both room and cryogenic temperatures. As a result of theoptimization process, the samples with the highest surface areas were identified as AC-Z2-700 and AC-K2-700, with AC-Z2-700exhibiting the highest hydrogen storage performance. Storage capacities increased with rising pressure and decreasing tempera-ture for both samples, while the isotherm profiles varied significantly between room and cryogenic conditions. The experimentaldata fitted well with the Henry and Freundlich isotherms at room temperature and with the Langmuir isotherm at cryogenictemperature. Furthermore, kinetic analyses indicated that the adsorption followed a pseudo-second-order model and that thedominant mechanism was intraparticle diffusion within the pores of the activated carbon. Overall, the findings demonstrate thatsunflower stalk is a promising and sustainable precursor for producing high-surface area activated carbons with competitivehydrogen storage capabilities, contributing to both clean energy applications and environmental sustainability.