2020 Fiscal Year Research-status Report
Quantum paradigms in hydrogen storage in nanostructures
| Project/Area Number |
19K15397
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| Research Institution | The University of Tokyo |
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Principal Investigator |
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| Project Period (FY) |
2019-04-01 – 2023-03-31
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| Keywords | nanostructure / graphene / ortho-para / hydrogen / DFT |
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| Outline of Annual Research Achievements |
This year, hydrogen adsorption on transition metal (TM) functionalized nanostructures has been investigated by means of first principles calculations based on the density functional theory (DFT). Previous investigation showed that Pd-graphene is stable relative to their isolated phases. After geometry optimization, it was found that Pd sits on top of a C atom of a graphene sheet at a distance of around 2 Angstroms. H was placed on different sites of Pd-graphene and optimized to determine the most stable adsorption site. The result show that H prefers to bond slightly off the top of the Pd atom. The bond length is around 1.5 Angstrom and H-Pd-C angle is around 105 degrees. The reference energy for H atom was chosen as half of an isolated H2 molecule. The corresponding adsorption energy is around -3 meV, showing stability relative to the gas phase H2.
The ortho-para (o-p) conversion of H2 was also investigated on a stepped Pd surface. The calculations could easily be extended to TM -functionalized nanostructures in the future. The perturbations were taken as the surface-H2 electrons coupling and Fermi-contact interactions. The o-p conversion probability was calculated using 2nd order perturbation theory. The relevant parameters such as the surface density of states (DOS), surface-molecule coupling potentials and surface wavefunctions were directly taken from DFT. The resulting o-p conversion time is around 2.99 seconds. In the future, the o-p conversion time for H2 adsorbing on TM-functionalized nanostructures will be investigated using the developed theory.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Transition metal functionalization of nanostructures relies on the stability of TM on the host nanostructures. In this study, graphene and graphitic carbon nitride (g-CN)were considered as host nanostructures for TMs. g-CN system however presented a challenge toward TM functionalization due to the instability of TMs on this host system. The study can proceed smoothly with TM-functionalized graphene and the rotational states and ortho-para conversion calculations are underway.
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| Strategy for Future Research Activity |
In the future research, the ortho-para conversion of TM-functionalized nanostructures will be investigated. The rotational states of H2 on these system will also be calculated and a new phase diagram with quantum effects of hydrogen storage in TM-functionaluzed nanostructures will be generated. To accelerate the search for candidate materials for TM-functionalized nanostructures, machine learning based on neural network potentials (NNPs) calculations will be performed.
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| Causes of Carryover |
Due to the emergence of corona virus, attendance to conferences locally and abroad was not possible. The intended funds for business trips were not used last year.
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