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Now showing items 1 - 16 of 20

  • Catalytic activity of NiO cathode in molten carbonate fuel cells

    Czelej, Kamil   Cwieka, Karol   Colmenares, Juan C.   Kurzydlowski, Krzysztof J.  

    Molten carbonate fuel cells (MCFCs) have attracted significant attention because of their potential contribution to the development of a sustainable and clean-energy society. MCFC performance is governed by cathodic transformation of carbon dioxide to carbonate anion in complex: gas molten carbonate solid surface system. Based on our recently proposed reaction mechanism together with the density functional theory (DFT) calculated activation barriers we created a simplified microkinetic model to predict the catalytic activity of the NiO cathode. Under the MCFC operation condition the cathode surface in close proximity to the triple phase boundary (TPB) is highly active towards electro-reduction of oxygen and simultaneous formation of carbonate anion. Our results explain why, despite a great effort devoted to modify the chemical composition of the cathode, a substantial increase in the MCFC performance has not been observed, and the in-situ oxidized nickel remains state-of-the-art cathode material.
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  • Quantum behavior of hydrogen-vacancy complexes in diamond

    Czelej, Kamil   Zemła, Marcin Roland   Śpiewak, Piotr   Kurzydłowski, Krzysztof J.  

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  • Catalytic activity of NiO cathode in Molten Carbonate Fuel Cells

    Czelej, Kamil   Cwieka, Karol   Colmenares, Juan C.   Kurzydlowski, Krzysztof J.  

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  • Electronic Structure and N-Type Doping in Diamond from First Principles

    Czelej, Kamil   ?piewak, Piotr   Kurzyd?owski, Krzysztof J.  

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  • Titanium-related color centers in diamond:a density functional theory prediction

    Czelej, Kamil   Cwieka, Karol   Spiewak, Piotr   Kurzydlowski, Krzysztof Jan  

    Transition metal-related paramagnetic centers in diamond exhibiting bright photoluminescence are increasingly important defects for realizing high quality solid state single photon sources. Recently, advanced ab initio calculations of single nickel-related NE4 (nickel-vacancy) and NE8 (nickel-vacancy-nitrogen) complexes in nanodiamond provided an insight into the nature of optical transitions and demonstrated their potential for in vivo biomarker applications. For other transition metal-related defects in diamond, however, a comprehensive understanding of photoluminescence is rather scarce. Here we used first principles, hybrid density functional theory analysis to investigate the electronic structure and magneto-optical properties of titanium-related point defects in diamond. Our theoretical results including the paramagnetic S =3D 1/2 ground state, the calculated zero-phonon lines, quasi-local vibrational modes associated with Ti atoms, and hyperfine coupling parameters provide strong evidence that the neutral Ti-N and TiV-N complexes are indeed the experimentally observed N3 (titanium-nitrogen) and OK1 (titanium-vacancy-nitrogen) color centers. In addition, we predicted another low energy excitation in the spin minority channel of the TiV-N-0 defect that needs further experimental verification and might be an interesting candidate for a robust solid state single color emitter in the near IR region. In the case of a yet unobserved, neutral TiV (titanium-vacancy) defect we found a high symmetry D-3d configuration in the triplet E-3(u) ground state and we calculated the magneto-optical parameters to mediate its future identification. We emphasize the possibility of the dynamic Jahn-Teller effect for some centers and its impact on the experimentally observed hyperfine structure.
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  • Titanium related color centers in diamond: A density functional theory prediction

    Czelej, Kamil   Cwieka, Karol   ?piewak, Piotr   Kurzyd?owski, Krzysztof  

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  • Atomic-scale computational design of hydrophobic RE surface-doped Al2O3 and TiO2

    Czelej, Kamil   Zemla, Marcin Roland   Spiewak, Piotr   Wejrzanowski, Tomasz   Kurzydlowski, Krzysztof Jan  

    Intrinsically hydrophobic rare-earth oxides (REOs) have emerged as a robust class of ceramics for a variety of applications. Recently, the hydrophobicity of REOs has been observed experimentally and subsequently scrutinized using electronic structure density functional theory (DFT) calculations. In this work, we applied the DFT method to analyze the possibility of tuning the wettability of commonly used hydrophilic Al2O3 and TiO2 by surface doping with Ce. The calculations indicate that Ce can preferentially segregate to the surface of Al2O3 and TiO2 and form a Ce-rich oxide layer, which is stable under a wide range of oxygen chemical potentials. A remarkable increase in the water contact angle is predicted for Ce-doped Al2O3(0001), whereas the water contact angle calculated for Ce-doped TiO2(110) remains unchanged, regardless of the Ce concentration. The wetting properties of Ce-doped Al2O3 are governed by two factors: (1) the unique electronic structure of the rare-earth metal promotes hydrogen bond formation between H2O and surface oxygen; (2) significant relaxation of the surface Ce and O atoms hampers direct interaction between H2O and Al cations, preventing dissociative water adsorption. These results provide a valuable opportunity for Al2O3 surface modification, in terms of achieving hydrophobicity.
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  • CO2 stability on the Ni low-index surfaces: van der Waals corrected DFT analysis

    Czelej, Kamil   Cwieka, Karol   Kurzydlowski, Krzysztof Jan  

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  • Atomistic Insight into the Electrode Reaction Mechanism of Cathode in Molten Carbonate Fuel Cell

    Czelej, Kamil   Cwieka, Karol   Colmenares, Juan Carlos   Kurzyd?owski, Krzysztof  

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  • Atomistic insight into the electrode reaction mechanism of the cathode in molten carbonate fuel cells

    Czelej, Kamil   Cwieka, Karol   Colmenares, Juan C.   Kurzydlowski, Krzysztof J.  

    In an era of increasing energy demand challenges combined with simultaneous environmental protection, molten carbonate fuel cells (MCFCs) have emerged as an interesting candidate to overcome both of these issues. Although the macroscopic parameters of MCFCs have been successfully optimized, the microscopic understanding of the electrochemical catalytic reactions, which determine their performance, remains challenging due to their chemical complexity and high operation temperatures. In this paper, we propose a top-down approach to unravel the hitherto unreported electrode reaction mechanism of the cathode in MCFCs using density functional theory (DFT). The oxygen-terminated octopolar NiO(111) is predicted to facilitate cathodic transformation of carbon dioxide to carbonate anions through sequential Mars-van Krevelen (MvK) and Eley-Rideal (ER) mechanisms. This theoretical work opens up new prospects in the atomic scale computational design of the cathode material for MCFCs.
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  • Decomposition of activated CO2 species on Ni(110): Role of surface diffusion in the reaction mechanism

    Czelej, Kamil   Cwieka, Karol   Wejrzanowski, Tomasz   Spiewak, Piotr   Kurzydlowski, Krzysztof Jan  

    Highlights • Adsorption and decomposition of CO2 on Ni(110) was studied. • Possible reaction pathways were investigated. • Mechanism of CO2 decomposition on Ni(110) was clarified. Abstract Chemisorption and decomposition of CO2 on Ni(110) surface have been studied by means of spin-polarized density functional theory calculations. Several possible CO2/Ni(110) conformations with similar adsorption energies were found. The bonding nature of the adsorbed CO2 was further analyzed on the basis of partial density of states (PDOS) and effective bond order (EBO) results, indicating the enhanced charge transfer and significant activation of the C O bond. Climbing image nudged elastic bound calculations provide an insight into CO2/Ni(110) → CO/Ni(110) + O/Ni(110) reaction mechanism. All computed reaction pathways can be separated into two stages: 1) surface diffusion of CO2 to the one energetically favored conformation; 2) breakage of the coordinated C–O bond. The total reaction barrier (relative to the energy of CO2/Ni(110)) was found about 0.44 eV. Graphical abstract
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  • Hydrogen passivation of vacancies in diamond:Electronic structure and stability from ab initio calculations

    Czelej, Kamil   Spiewak, Piotr  

    Point defects in diamond such as vacancies act as a strong donor compensation center; therefore, remarkably reduce electron conductivity of diamond-based devices. Artificial synthesis methods of n-type diamond utilize the hydrogen-containing precursors enabling its diffusion into diamond crystal and subsequent formation of hydrogen-vacancy complexes. Here we employ spinpolarized, hybrid density functional theory calculations, in order to characterize the electronic properties and stability of hydrogen-passivated vacancies in diamond. We found strong thermodynamic preference for hydrogen passivation of four vacancy-related dangling bonds. An analysis of formation energy vs Fermi level diagrams indicate, that strong donor compensation effect associated with vacancies can be entirely neutralized by hydrogen incorporation. Thus, a careful control of hydrogen partial pressure in the growth process might be crucial to improve the electron conductivity of n-type diamond.
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  • Hydrogen passivation of vacancies in diamond: Electronic structure and stability from ab initio calculations

    Czelej, Kamil   ?piewak, Piotr  

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  • Ab initio prediction of strong interfacial bonding in the Fe vertical bar Al bimetallic composite system

    Czelej, Kamil   Kurzydlowski, Krzysztof J.  

    Atomic-scale calculations were used to investigate the formation of interfacial bonds in the Fe vertical bar Al bimetallic composite system. The results indicate that chemical bonds at pristine Fe vertical bar Al interface display more covalent character than constituent materials resulting in enhanced interface strength. Such an interface exhibits large cohesive energy exceeding significantly the value of bulk aluminum. The effect of two technologically relevant solute elements, i.e. carbon and magnesium on the interface strength was analyzed. Our robust yet simple computational model can be used to predict the most efficient combination of steels and aluminum alloys for cold pressure welding, leading to strong interfacial bonding. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • Electronic structure of substitutionally doped diamond: Spin-polarized, hybrid density functional theory analysis

    Czelej, Kamil   ?piewak, Piotr   Kurzyd?owski, Krzysztof J.  

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  • Inside the Interaction of Methanol Selective Oxidation Intermediates with Au- or/and Pd-containing Monometallic and Bimetallic Core@Shell Catalysts

    Czelej, Kamil   Cwieka, Karol   Colmenares, Juan Carlos   Kurzydlowski, Krzysztof J.  

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