Effect Of Electric Field On Hydrogen Adsorption Over Hydrogen Storage Materials

Energy crisis and worldwide environmental problem make hydrogen a prospective energy carrier. However, storage and transportation of hydrogen in large quantities at small volume is currently not practical. Lots of materials and devices have been developed for storage hydrogen, but to today none is able to meet the DOE targets.Activated carbon and MOF have been found to be good hydrogen adsorbents due to their high surface area. However, the weak van der Waals force between hydrogen and sorbent has limited the adsorption capacity. Previous studies have found that enhanced adsorption can be obtained with applied electric field. Stronger interaction between the polarized hydrogen and the charged sorbents under high voltage is considered as the reason.This study was initiated to investigate if the adsorption can be further enhanced when the activated carbon particles are separated with a dielectric TiO2. Hydrogen adsorption measurements on the TiO2-coated carbon materials, with or without an external electric field, were made. The results showed that the adsorption capacity increased with increasing amount of TiO2nanoparticles with an applied electric field. Behavior of hydrogen adsorption over TiO2-coated activated carbon under various electric potentials revealed that the hydrogen adsorption first increased and then decreased with the increase of electric field. The current leak detected at3000V was a sign of ionization of hydrogen.Percolative Metal-organic framework/Carbon (MOFAC) composites were synthesized by IRMOF8(isoreticular metal-organic frameworks) directly depositing on activated carbon via heterogeneous nucleation. Direct measurement of the amount of hydrogen adsorption was also carried out with MOFACs using the piezoelectric material PMN-PT as the charge supplier due to the pressure. The adsorption enhancement from the PMN-PT generated charges was remarkable. With help from the PMN-PT, the hydrogen uptake capability was increased about31.5%over the MOFAC3(MOF-Carbon composite with22.2%of carbon). The hydrogen adsorption isotherms of MOFACs under various electric potentials and hydrogen pressures were measured at ambient temperature. Results indicated that electric field strength enhanced hydrogen adsorption.The higher the applied electric potential, the higher the adsorption capacity of hydrogen. Meanwhile, rapid adsorption/desorption kinetics and total reversibility on the samples were observed in the present or absence of external electric field.Experiments were also carried out to examine the hydrogen adsorption performances over activated carbon separated by other dielectric materials, MgO, ZnO and BaTiO3, respectively. For the samples partitioned with MgO and ZnO, the measurements with and without an electric field indicated negligible differences. Electric field enhanced adsorption has been observed on the activated carbon separated with BaTiO3, a material with very high dielectric constant.Corresponding computational calculations using Density Functional Theory have been performed on hydrogen interaction with charged TiO2molcule as well as TiO2molcule, coronene, TiO2-doped coronene and MOF/carbon in the presence of an electric field. The simulated results were consistent with the observations from experiments, further confirming the proposed hypotheses.