Electric charge and hydrogen storage

Hydrogen is a promising energy source for the future economy due to its environmental friendliness. One of the important obstacles for the utilization of hydrogen as a fuel source for applications such as fuel cells is the storage of hydrogen. Hydrogen has high gravimetric energy content but low volumetric energy density. It is desired to increase the volumetric energy density of hydrogen in a system to satisfy various applications. Adsorption of hydrogen on sorbents has been investigated. However, the weak interaction force between hydrogen molecules and the sorbents has resulted in low adsorption capacity. In this study, charge was introduced into the system. Several sorbents were investigated. The effects of charge on adsorption enhancement were determined. When NiO was embedded in a PMN-PT piezoelectric material, hydrogen adsorption increased from 0.08 to 0.11wt% at 135bar. For the activated carbon sorbent, hydrogen adsorption increased with both the increase in the applied voltage and the increase in the pressure. At 83bar, the adsorption capacity increases from 0.45wt% at 0V to 0.46, 0.49, 0.53, and 0.55wt% at 500, 1000, 2000 and 3000V, respectively. Preliminary modeling was carried out to explain the enhancement of adsorption. Modeling was conducted using the B3LYP/6-31G(d) method in the GAUSSIAN 03 software program. The results show that when the electrical field is applied, the hydrogen molecules are more perturbed and attracted closer to the nickel atom, indicating a stronger interaction. The effects increase consistently with the increasing electrical field strength. NiO is a dielectric material. The adsorption enhancement is through the polarization of the compound, which is represented by the Mulliken charge. Carbon is a conductive material. It receives charges on its surface. Although the charges on the sorbents are obtained through different mechanisms, enhancements are found for both materials. Copyright (c) 2011 John Wiley & Sons, Ltd.