Browsing by Author "Boaks, Mawla"

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    Density Functional Theory (DFT) study of hydrogen storage in porous silicon
    (2018) Boaks, Mawla; Schubert, Peter
    Based on plane wave DFT calculation, we carried out micro level investigation of hydrogen storage in nanoporous silicon (npSi). One quarter of a hexagonal pore with Palladium catalyst placed at the surface has been studied for hydrogen dissociation, spillover, bond hopping, and diffusion for both single catalyst atom and small catalyst cluster consisting of multiple catalyst atoms. All the DFT computations were done in one of the biggest research supercomputer facilities of the world, Big Red II. We opted ABINIT, an open source DFT tool for our computations. Our calculation revealed low dissociation, spillover, and bond hoping energy barrier. The energy required to be provided from external sources to fully recharge the storage medium from a gaseous source at a completely empty state has also been evaluated. Hydrogen diffusion along the inner surface of the pore as a means of bond hopping and the possibility of quantum tunneling, a low temperature phenomena used to spontaneously go over an otherwise less likely high energy barrier have been studied as well. Using these micro level parameter values evaluated from the DFT study, the performance of any potential hydrogen storage material can be compared to a set of characteristics sought in an efficient storage media. Thus, the micro scale feasibility of this novel npSi material based hydrogen storage technology was studied as a part of a STTR Phase I project.
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    Kinetics of Hydrogen Storage on Catalytically-Modified Porous Silicon
    (Elsevier, 2019-03) Boaks, Mawla; Schubert, Peter J.; Electrical and Computer Engineering, School of Engineering and Technology
    Porous silicon has been demonstrated as a hydrogen storage media with surface-bound hydrogen content as high as 6.6% by weight. Hydrogenated porous silicon is readily synthesized by electrochemical etching in a solution of hydrofluoric acid. Hydrogen gas can be released thermally at temperatures starting at 280 °C. It has been proposed that a suitable catalyst at the pore mouth can both reduce the desorption temperature and facilitate gaseous recharge of the silicon matrix. This work presents a detailed kinetic study using density functional theory (DFT) of a reversible hydrogen storage system based on porous silicon via the mechanisms of dissociation, spillover, and bond-hopping of hydrogen atoms. For each of these steps, activation energy values and vibrational frequency has been determined. Using these activation energies along with vibrational frequency values evaluated from the micro level DFT study, the kinetic performance of catalytically-modified porous silicon as a potential hydrogen storage material has been completed for the first time. The energy difference between full and empty charge is computed at the atomic scale and compared to macroscopic calculations, showing close agreement. These results show the potential for rapid recharge at 8 bar at temperatures commensurate with waste heat from a proton-exchange membrane fuel cell.