Thermodynamic trends for evaluating hydrogen storage density and energy flow on Maxsorb-III, HKUST-1 and UiO-66 (Zr) MOFs

Abstract

For CO2-free power generation in power plants or vehicles, hydrogen should be implemented as H2 possesses not only the highest energy density (120 MJ/kg) but also can be generated from the environment and reactions. However, H2 is difficult to store due to its low density at ambient conditions. To understand the efficacy of hydrogen interactions in porous materials including the randomness of hydrogen adsorption in terms of storage density, energy flow and dissipation, a thermodynamic study is required. This paper at first focuses on the study of H2 adsorption on various porous adsorbents such as activated carbons (AC types Maxsorb-III) and metal–organic frameworks (types UiO-66 (Zr) and HKUST-1 MOFs) and the results are presented in temperature-density co-ordinate system. Employing experimentally confirmed isotherms data of AC/MOFs + H2 systems, the density of H2 adsorbed phase, entropy flow and generation are evaluated. These results indicate the feasibility of hydrogen adsorption on functional adsorbents at various temperature and pressure. The simulation results show that the adsorbed phase densities of H2 on Maxsorb-III and HKUST-1 increase up to 18 kg/m3 and 20 kg/m3 at 5 bar and 77 K. The temperature-entropy diagram shows a close loop for the charging and discharging of hydrogen and ensures the storage of internal energy with less entropy dissipation under cryo-adsorption conditions.