Comparative study on the hydrogen storage capacity of crystalline and amorphous nanomaterials of MoO3: effect of a catalytic Pd capping

Abstract

Hydrogen storage capacities were investigated for two forms of MoO3 nanomaterial, amorphous of low crystallinity, and other highly crystalline, using the quartz crystal microbalance technique. Effect of a catalytic Pd capping on the nanomaterials was evaluated. MoO3 materials were grown using the gas condensation method, and both the amorphous and crystalline samples were composed of orthorhombic phases with Mo6+ oxidation state. For 4-min measurements, uncapped amorphous MoO3 achieved a higher storage capacity than its crystalline counterpart, while Pd-capped samples exhibited lower values due to slower kinetics. Then, Pd-capped samples were measured using longer H2 exposure times of 30 min, finding that Pd-capped crystalline MoO3 sample exhibited higher hydrogen storage capacity than its amorphous counterpart. Pd capping was found to affect the hydrogenation of the underlying oxide layer, mainly due to differences in long-range order and layered structure between crystalline and amorphous MoO3 samples.