Yufeng Zhao | Corban University (original) (raw)
Papers by Yufeng Zhao
Applied Physics A: Materials Science & Processing, 1998
The Journal of Physical Chemistry C, 2012
ABSTRACT In recent years, carbon-based sorbents have been recognized for their potential applicat... more ABSTRACT In recent years, carbon-based sorbents have been recognized for their potential application within vehicular hydrogen storage applications. One method by which sorbents have been reported to store appreciable hydrogen at room temperature is via a spillover process: where molecular hydrogen is first dissociated by metal nanoparticle catalysts and atomic hydrogen subsequently migrates onto the carbon substrate. Many reports have invoked the spillover mechanism to explain enhancements in reversible room temperature hydrogen uptake for metal-decorated sorbents. However, there is a lack of experimental evidence for the proposed chemical species formed as well as several differing theoretical explanations describing the process. In this report, we utilize diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to identify the various chemical species formed upon room temperature H2 charging of ruthenium-decorated high surface area carbons. Room temperature H2 loading of a control sample with no ruthenium nanoparticles (Ru NPs) leads to broad reversible peaks in the DRIFTS spectrum that correspond to the vibration–rotation transitions of weakly bound physisorbed hydrogen molecules. In contrast, the sample modified with Ru NPs shows a variety of reversible and irreversible peaks in addition to the physisorbed H2 peaks. Rigorous experimental and theoretical analysis enables the assignment of the peaks to ruthenium-mediated formation of water, surface hydroxyl groups (R–OH, where R = carbon or ruthenium), and C–H bonds. The low-energy DRIFTS peaks assigned to spillover C–H bonds were additionally confirmed using inelastic neutron spectroscopy. Reversible vibrational peaks consistent with ruthenium-mediated formation of C–H bonds provide much-needed spectroscopic evidence for the spillover process. The results demonstrated here should facilitate future mechanistic investigations of hydrogen sorption on transition metal nanoparticles and high surface area activated carbons.
Physical Review B, 2011
Based on Density Functional Theory simulations, we have predicted a series of stable magnesium bo... more Based on Density Functional Theory simulations, we have predicted a series of stable magnesium borides MgB x with a broad range of stoichiometries, 2 < x ≤ 16, by removing magnesium atoms from MgB 2. The layered boron structures are preserved through an in-plane topological transformation between the hexagonal lattice domains and triangular domains. The process can be reversibly switched as the charge transfer changes with Mg insertion/extraction. The mechanism of such a chargedriven transformation originates from the versatile valence state of boron in its planar form. The discovery of these new physical phenomena suggests the design of a high-capacity magnesium boron battery. The complexity of boron chemistry has already been demonstrated in boron clusters [1-8] and polymorphs [9] that display peculiar hybridization [10] and bonding behavior [11]. Recently, boron chemistry has been further enriched with the discovery of planar, tubular, and cage-like boron [12-18] as well as the prediction of metal boride nanotubes [19] and diamond-like boron [20], in which three-center (3-c) bonding has been shown to stabilize the two-center (2-c) backbone bonding analogous to carbon [14,
The Journal of Physical Chemistry Letters, 2011
Chemical Physics Letters, 2010
Diamond-like boron crystal structures are predicted employing a decoration scheme, in which the n... more Diamond-like boron crystal structures are predicted employing a decoration scheme, in which the normal and hexagonal diamond frameworks are decorated with extra atoms across the basal plane. The predicted boron crystals can be viewed as isomorphs of a Ga structured boron, but have a much higher density of states (DOS) near the Fermi levels. This study may provide a more plausible explanation for the nonmetal-metal transition and the anomalous superconductivity of boron under high pressure.
Applied Physics Letters, 2012
We demonstrate the reversible lithiation of SiO2 up to 2/3 Li per Si, and propose a mechanism for... more We demonstrate the reversible lithiation of SiO2 up to 2/3 Li per Si, and propose a mechanism for it based on molecular dynamics and density functional theory simulations. Our calculations show that neither interstitial Li (no reduction), nor the formation of Li2O clusters and Si–Si bonds (full reduction) are energetically favorable. Rather, two Li effectively break a Si–O bond and become stabilized by oxygen, thus partially reducing the SiO2 anode: this leads to increased anode capacity when the reduction occurs at the Si/SiO2 interface. The resulting LixSiO2 (x<2/3) compounds have band-gaps in the range of 2.0–3.4 eV.
The Journal of Chemical Physics, 2013
The reduction of NiO in hydrogen, a reaction with many industrial applications, has not received ... more The reduction of NiO in hydrogen, a reaction with many industrial applications, has not received sufficient attention from theoretical standpoint because the complexity of the material properties and the process present considerable computational challenges. We report here the results of a systematic study on the hydrogen reduction of an ideal NiO(100) surface that produces a water molecule and an NiO(100) surface with an oxygen vacancy, using the Hubbard U corrected density functional theory method, with some of the key results verified by the hybrid density functional method. The major findings are: (1) the O vacancy in the NiO(100) surface slab is stabilized in the subsurface layer, although the vacancy is likely to remain on the outermost surface layer because the barrier for O vacancy migration from the surface to the second layer is as high as 3.02 eV; (2) regarding the energetics of hydrogen interaction with the ideal NiO(100) surface, water formation, and concomitant reducti...
Applied Physics A: Materials Science & Processing, 1998
The Journal of Physical Chemistry C, 2012
ABSTRACT In recent years, carbon-based sorbents have been recognized for their potential applicat... more ABSTRACT In recent years, carbon-based sorbents have been recognized for their potential application within vehicular hydrogen storage applications. One method by which sorbents have been reported to store appreciable hydrogen at room temperature is via a spillover process: where molecular hydrogen is first dissociated by metal nanoparticle catalysts and atomic hydrogen subsequently migrates onto the carbon substrate. Many reports have invoked the spillover mechanism to explain enhancements in reversible room temperature hydrogen uptake for metal-decorated sorbents. However, there is a lack of experimental evidence for the proposed chemical species formed as well as several differing theoretical explanations describing the process. In this report, we utilize diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to identify the various chemical species formed upon room temperature H2 charging of ruthenium-decorated high surface area carbons. Room temperature H2 loading of a control sample with no ruthenium nanoparticles (Ru NPs) leads to broad reversible peaks in the DRIFTS spectrum that correspond to the vibration–rotation transitions of weakly bound physisorbed hydrogen molecules. In contrast, the sample modified with Ru NPs shows a variety of reversible and irreversible peaks in addition to the physisorbed H2 peaks. Rigorous experimental and theoretical analysis enables the assignment of the peaks to ruthenium-mediated formation of water, surface hydroxyl groups (R–OH, where R = carbon or ruthenium), and C–H bonds. The low-energy DRIFTS peaks assigned to spillover C–H bonds were additionally confirmed using inelastic neutron spectroscopy. Reversible vibrational peaks consistent with ruthenium-mediated formation of C–H bonds provide much-needed spectroscopic evidence for the spillover process. The results demonstrated here should facilitate future mechanistic investigations of hydrogen sorption on transition metal nanoparticles and high surface area activated carbons.
Physical Review B, 2011
Based on Density Functional Theory simulations, we have predicted a series of stable magnesium bo... more Based on Density Functional Theory simulations, we have predicted a series of stable magnesium borides MgB x with a broad range of stoichiometries, 2 < x ≤ 16, by removing magnesium atoms from MgB 2. The layered boron structures are preserved through an in-plane topological transformation between the hexagonal lattice domains and triangular domains. The process can be reversibly switched as the charge transfer changes with Mg insertion/extraction. The mechanism of such a chargedriven transformation originates from the versatile valence state of boron in its planar form. The discovery of these new physical phenomena suggests the design of a high-capacity magnesium boron battery. The complexity of boron chemistry has already been demonstrated in boron clusters [1-8] and polymorphs [9] that display peculiar hybridization [10] and bonding behavior [11]. Recently, boron chemistry has been further enriched with the discovery of planar, tubular, and cage-like boron [12-18] as well as the prediction of metal boride nanotubes [19] and diamond-like boron [20], in which three-center (3-c) bonding has been shown to stabilize the two-center (2-c) backbone bonding analogous to carbon [14,
The Journal of Physical Chemistry Letters, 2011
Chemical Physics Letters, 2010
Diamond-like boron crystal structures are predicted employing a decoration scheme, in which the n... more Diamond-like boron crystal structures are predicted employing a decoration scheme, in which the normal and hexagonal diamond frameworks are decorated with extra atoms across the basal plane. The predicted boron crystals can be viewed as isomorphs of a Ga structured boron, but have a much higher density of states (DOS) near the Fermi levels. This study may provide a more plausible explanation for the nonmetal-metal transition and the anomalous superconductivity of boron under high pressure.
Applied Physics Letters, 2012
We demonstrate the reversible lithiation of SiO2 up to 2/3 Li per Si, and propose a mechanism for... more We demonstrate the reversible lithiation of SiO2 up to 2/3 Li per Si, and propose a mechanism for it based on molecular dynamics and density functional theory simulations. Our calculations show that neither interstitial Li (no reduction), nor the formation of Li2O clusters and Si–Si bonds (full reduction) are energetically favorable. Rather, two Li effectively break a Si–O bond and become stabilized by oxygen, thus partially reducing the SiO2 anode: this leads to increased anode capacity when the reduction occurs at the Si/SiO2 interface. The resulting LixSiO2 (x<2/3) compounds have band-gaps in the range of 2.0–3.4 eV.
The Journal of Chemical Physics, 2013
The reduction of NiO in hydrogen, a reaction with many industrial applications, has not received ... more The reduction of NiO in hydrogen, a reaction with many industrial applications, has not received sufficient attention from theoretical standpoint because the complexity of the material properties and the process present considerable computational challenges. We report here the results of a systematic study on the hydrogen reduction of an ideal NiO(100) surface that produces a water molecule and an NiO(100) surface with an oxygen vacancy, using the Hubbard U corrected density functional theory method, with some of the key results verified by the hybrid density functional method. The major findings are: (1) the O vacancy in the NiO(100) surface slab is stabilized in the subsurface layer, although the vacancy is likely to remain on the outermost surface layer because the barrier for O vacancy migration from the surface to the second layer is as high as 3.02 eV; (2) regarding the energetics of hydrogen interaction with the ideal NiO(100) surface, water formation, and concomitant reducti...