Adsorption of hydrogen molecules on the alkali metal ion decorated boric acid clusters: A density functional theory investigation

摘要

The hydrogen storage capacity of alkali metal ion decorated boric acid (BA) based bowl, sheet and ball structures have been investigated using B3LYP method employing 6-31+G~(**) basis set. The maximum gravimetric density has been observed for the bowl shaped clusters. These values for Li~+, Na~+ and K~+ decorated clusters are 8.3, 8.8 and 7.8 wt.%, respectively. The range of the calculated binding energy per H_2 molecule (BE/H_2) for Li~+, Na~+ and K~+ decorated bowl shaped clusters are 2.57-3.59, 1.88-2.11 and 0.76-1.00 kcal/ mol, respectively. The same for the sheet clusters are 3.18-3.73, 1.68-2.40 and 0.73-0.97 kcal/mol, respectively. Similarly, BE/H_2 of Na~+ decorated ball clusters ranges from 1.88 kcal/mol to 2.62 kcal/mol. It has been shown in earlier studies that the BE/H2 should be in between the physisorption and chemisorption limits for realizing the practical applications of different class of materials. In this context, both BE/H_2 and gravimetric density of Na~+ decorated clusters indicate that these systems have appropriate properties. Hence Na~+ decorated (BA)_n structures are suitable for hydrogen storage applications.