The donor ionization energies in a quantum well and quantum dot with finite and infinite barriers are estimated for different well dimensions. Using the effective mass (EM) approximation, calculations are presented with constant effective mass and position dependent effective masses that are different for finite and infinite cases. Our results reduce to an approximate form used by X. H. Qi et al., Phys. Rev. B58 (1998) 10578 in the finite barrier model and that of L. E. Oliveira and L. M. Falicov, Phys. Rev. B34 (1986) 8676 in the infinite barrier case. Results are presented by taking the GaAs quantum well as an example. The use of constant effective mass of 0.067m0 is justified for well dimensions ≥a* where a* is an effective Bohr radius which is about 100 Å. While Qi et al. found a maximum of 22% variation in the binding energies due to mass variation, we obtained nearly 100% variation when mass variations are included correctly.
a b s t r a c tHydrogen is considered as the most promising clean energy carrier because of its abundance, environmental friendliness and high conversion efficiency. However, developing safe, compact, light weight and cost-effective hydrogen storage materials is one of the most technically challenging barriers to the widespread use of hydrogen as fuel. The present work reports the hydrogen storage performance of multi-walled carbon nanotubes (MWCNT)/hexagonal boron nitride (h-BN) nanocomposites (MWCNT/h-BN), where ultrasonication method is adopted for the synthesis of the MWCNT/h-BN nanocomposites. Hydrogenation process was carried out using Seiverts-like hydrogenation setup. Characterization techniques such as X-ray Diffraction (XRD), Micro-Raman Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Nitrogen adsorptionedesorption isothermal studies (BET), CHN-elemental analysis and Thermogravimetric Analysis (TGA) were used to analyze the samples at various stages of the experiment. A maximum of 2.3 wt% hydrogen storage is achieved in the case of acid treated MWCNTs (A-MWCNT) with 5 wt% of h-BN nanoparticles compared to pure MWCNTs that could store 0.15 wt% only. Moreover the calculated binding energy (0.42 eV) of stored hydrogen of A-MWCNT with 5 wt% of h-BN nanocomposite lies in the recommended range of binding energy (0.2e0.6 eV) for fuel cell applications. The TG study shows that 100% desorption is achieved at the temperature range of 120e410 C and confirms that the prepared hydrogen storage medium will serve effectively in the realm of hydrogen fuel economy in near future.
The hydrogen storage performance of hybrid nanocomposites composed of reduced graphene oxide, acid treated halloysite nanotubes and hexagonal boron nitride nanoparticles (RGO/A-HNT/h-BN) was studied.
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