Sergey Stolbov
University of Central Florida
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Featured researches published by Sergey Stolbov.
Journal of Chemical Physics | 2011
Sebastian Zuluaga; Sergey Stolbov
We report here results of our density functional theory based computational studies of the electronic structure of the Pd-Co alloy electrocatalysts and energetics of the oxygen reduction reaction (ORR) on their surfaces. The calculations have been performed for the (111) surfaces of pure Pd, Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) alloys, as well as of the surface segregated Pd/Pd(0.75)Co(0.25) alloy. We find the hybridization of dPd and dCo electronic states to be the main factor controlling the electrocatalytic properties of Pd/Pd(0.75)Co(0.25). Namely the dPd-dCo hybridization causes low energy shift of the surface Pd d-band with respect to that for Pd(111). This shift weakens chemical bonds between the ORR intermediates and the Pd/Pd(0.75)Co(0.25) surface, which is favorable for the reaction. Non-segregated Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) surfaces are found to be too reactive for ORR due to bonding of the intermediates to the surface Co atoms. Analysis of the ORR free energy diagrams, built for the Pd and Pd/Pd(0.75)Co(0.25), shows that the co-adsorption of the ORR intermediates and water changes the ORR energetics significantly and makes ORR more favorable. We find the onset ORR potential estimated for the configurations with the O-OH and OH-OH co-adsorption to be in very good agreement with experiment. The relevance of this finding to the real reaction environment is discussed.
Science | 2007
Kin L. Wong; Greg Pawin; Ki-Young Kwon; Xing Lin; T. Jiao; U. Solanki; R. H. J. Fawcett; Ludwig Bartels; Sergey Stolbov; Talat S. Rahman
We found that anthraquinone diffuses along a straight line across a flat, highly symmetric Cu(111) surface. It can also reversibly attach one or two CO2 molecules as “cargo” and act as a “molecule carrier,” thereby transforming the diffusive behavior of the CO2 molecules from isotropic to linear. Density functional theory calculations indicated a substrate-mediated attraction of ∼0.12 electron volt (eV). Scanning tunneling microscopy revealed individual steps of the molecular complex on its diffusion pathway, with increases of ∼0.03 and ∼0.02 eV in the diffusion barrier upon attachment of the first and second CO2 molecule, respectively.
Journal of Chemical Physics | 2005
Sergey Stolbov; Talat S. Rahman
Using the plane-wave pseudopotential method within the density-functional theory with the generalized gradient approximation for exchange and correlation potential, we have calculated adsorption energies (E(ad)), diffusion barrier, and the first dissociation barrier (E(1)) for NH(3) on Ni and Pd surfaces. While the top site is found to be preferred for NH(3) adsorption on both Ni(111) and Pd(111), its calculated diffusion barrier is substantially higher for Pd(111) than for Ni(111). We also find that during the first dissociation step (NH(3)-->NH(2)+H), NH(2) moves from the top site to the nearest hollow site on Ni(111) and Pd(111) and on the stepped surfaces, Ni(211) and Pd(211), it moves from the initial top site at the step edge to the bridge site in the same atomic chain. Meanwhile H is found to occupy the hollow sites on all four surfaces. On Ni(111), E(1) is found to be 0.23 eV higher than E(ad), while at the step of Ni(211), E(1) and E(ad) are almost equal, suggesting that the probability for the molecule to dissociate is much on the step of Ni(211). In the case of Pd(211), however, we find that the dissociation barrier is much higher than E(ad). These trends are in qualitative agreement with the experimental finding that ammonia decomposition rate is much lower on Pd than on Ni.
Journal of Physical Chemistry Letters | 2013
Sergey Stolbov; Sebastian Zuluaga
The focus of this work is on the Pt/MS structures (MS = Au, Ir, Ru, or Pt substrate), as promising electrocatalysts and a prototype for more general systems: (active element monolayer)/(metal substrate) (AE/MS). We evaluate from first principles the effects of AE monolayer strain and the interlayer AE-MS electronic state hybridization on surface reactivity and reveal rationale for the interlayer hybridization to dominate over the strain effect in determining the AE/MS surface reactivity. We find, however, that, if AE is weakly bound to MS, the surface electronic structure does not suffice to characterize the surface reactivity, because of involvement of other factors related to lattice response to adsorption of a reaction intermediate. Guided by our findings, we trace surface reactivity to a newly introduced hybridization parameter that reflects important features of the electronic structure of the AE/MS surface, which are not taken into account in the original d-band center model.
Physical Review B | 2005
Sergey Stolbov; Sampyo Hong; Abdelkader Kara; Talat S. Rahman
First principles calculations of the geometric and electronic structures have been performed for two coverages (0.25 ML and 0.5 ML) of C on Ni(001) to understand the mechanism of the Ni(001) reconstruction induced by carbon adsorption. The calculated structural behavior of the system is in a good agreement with experimental observations. The calculated path and energetics of the
Physical Review B | 2002
Sergey Stolbov; Abdelkader Kara; Talat S. Rahman
c(2\times 2)
Journal of Chemical Physics | 2015
Sergey Stolbov; Marisol Alcantara Ortigoza
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Journal of Chemical Physics | 2009
Sergey Stolbov; Marisol Alcantara Ortigoza; Radoslav R. Adzic; Talat S. Rahman
p4g
Journal of Chemical Physics | 2002
Sergey Stolbov; Talat S. Rahman
reconstruction in C
Journal of Physical Chemistry Letters | 2012
Sergey Stolbov; Alcántara Ortigoza M
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