Silicon Nanotubes Outperform Carbon Nanotubes for Hydrogen Storage

With the help of Chemical Technology have determined that silicon nanotubes can store hydrogen more efficiently than carbon nanotubes. Dapeng Cao used a multiscale theoretical method, combining first-principle calculation and a grand canonical Monte Carlo (GCMC) simulation, to predict the adsorption capacity of hydrogen in silicon nanotube (SiNT) arrays at 298 K (24.85°C, 76.73°F) under pressures ranging from 1 to 10 MPa. In the multiscale method, the binding energy obtained from the first-principle calculation is used as an input in the GCMC simulation. From the first-principle calculation, they found that the SiNT arrays exhibit much stronger attraction to hydrogen both inside and outside SiNTs, compared to isodiameter carbon nanotubes (CNTs). The subsequent GCMC simulations indicated that gravimetric adsorption capacities of hydrogen in the SiNT arrays reach up to 1.30, 2.33, and 2.88 wt% at 2, 6, and 10 MPa, respectively. This represent improvements of 106%, 65%, and 52% in the gravimetric adsorption capacity of hydrogen at P = 2, 6, and 10 MPa, respectively, compared to the isodiameter CNTs

Calculations at the density functional level of theory (DFT) showed an increase of 20% in the binding energy of H₂ in SiCNTs compared with pure carbon nanotubes (CNTs). Classical Monte Carlo simulation of the nanotube bundles showed an even larger increase of the storage capacity in SiCNTs, especially in low temperature and high-pressure conditions.

At 1, 5 and 10 MPa at 175 K (-98°C, -145°F), the SiCNT bundles showed 1.18, 2.82 and 3.68 wt% respectively, compared to 0.53, 1.92 and 3.03 wt% respectively for the CNT bundles.

Modeled snspshots and gravimetric adsorption

capacities of hydrogen in the silicon nanotube

arrayas (SiNT),top; and carbon nanotubes (CNT)

bottom. T=298 K and P=2,6, and 10 MPa.

Gravimetric adsorption isotherms of hydrogen.

This technology synthesized SiCNTs from multiwalled carbon nanotubes (MWCNTs) via chemical vapor reaction (CVR) and purification. The SiCNTs were characterized by XRD, SEM and TEM. Hydrogen storage capacities measurements indicated that SiCNTs were superior to MWCNTs.