| 1. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Confinement dependence of electro-catalysts for hydrogen evolution from water splitting
- 2014
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Ingår i: Beilstein Journal of Nanotechnology. - : Beilstein Institut. - 2190-4286. ; 5:1, s. 195-201
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory is utilized to articulate a particular generic deconstruction of the electrode/electro-catalyst assembly for the cathode process during water splitting. A computational model was designed to determine how alloying elements control the fraction of H2 released during zirconium oxidation by water relative to the amount of hydrogen picked up by the corroding alloy. This model is utilized to determine the efficiencies of transition metals decorated with hydroxide interfaces in facilitating the electro-catalytic hydrogen evolution reaction. A computational strategy is developed to select an electro-catalyst for hydrogen evolution (HE), where the choice of a transition metal catalyst is guided by the confining environment. The latter may be recast into a nominal pressure experienced by the evolving H2 molecule. We arrived at a novel perspective on the uniqueness of oxide supported atomic Pt as a HE catalyst under ambient conditions.
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| 2. |
- Lindgren, Mikaela, 1987
(författare)
-
First Principles Approach to the Hydrogen Pick-up during Oxidation of Zirconium Alloys by Water
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zirconium alloys are widely used in nuclear power plants as cladding material to contain the fission fuel in the reactor cores. A limiting factor for fuel longevity is the corrosion property of the zirconium alloys. The main corrodent in the reactor core is water. Ideally, the oxidation process of zirconium alloys with water should be accompanied by molecular hydrogen release into the surrounding, but a significant amount of hydrogen is absorbed into the alloy. This process is called hydrogen pick-up, and is along with the oxidation rate decisive to the longevity of the fuel. The mechanisms controlling the hydrogen pick-up are to a large extent unknown.In this study, density functional theory, DFT, was used to gain insights into the mechanism for water induced corrosion of zirconium. The steady state process whereby Zr is oxidized by means of oxide ions at the metal/oxide interface comprises the anode process. This implies release of two electrons of the oxide ion. A sink for these electrons is offered by H+ ions, whereby H2 is formed or hydrogen picked up in the metal. These comprise the cathode processes. A detailed mechanism for electro-catalytic hydrogen evolution was explored. The mechanism comprises formation of a TM-H-Zr three-center hydride ion, followed by a hydride-proton recombination step forming H2. The efficiency of the system to utilize the overpotential for hydrogen evolution was found to be decisive for the fraction of hydrogen that is absorbed in the alloy. The ability of the anode process to sustain the cathode process was investigated, both by addressing the anode potential and its variations with respect to oxygen distribution. Diffusion barriers for redistribution of oxygen atoms in the α-Zr matrix were quantified, and the finding was taken to suggest the possible roles of meta-stable oxygen distributions to the change in hydrogen pick-up fraction. In addition, the drive for hydrogen pick-up by co-absorption with oxygen in α-Zr was studied and shown to be beneficial relative to H2 (g) for oxygen concentrations well above the oxygen solubility limit.
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| 3. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Impact of Additives on Zirconium Oxidation by Water: Mechanistic insights from first principles
- 2013
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Ingår i: RSC Advances. - 2046-2069. ; 3:44, s. 21613-21619
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Tidskriftsartikel (refereegranskat)abstract
- Zirconium alloys are widely used as cladding materials employed to contain the fission fuel in nuclear power plants. A limiting factor for fuel longevity is the corrosion property of the zirconium alloys. In the reactor, the main corrodent is water. The oxide forms thermodynamically during hydrogen evolution. Due to the corrosion mechanism, a fraction of the hydrogen is transferred to the alloy. It has long been known that the alloying elements actually control the hydrogen pick-up fraction, HPUF. A mechanism that explains these observations by means of density functional theory calculations is presented and validated. A hydroxylated grain boundary model decorated by various transition metal, TM, ions is employed to study the dependence of the hydrogen evolution reaction, HER, on the choice of TM ion and spin state along the hydride-proton recombination pathway. The efficiency of the system to utilize the overpotential for hydrogen evolution, originating from the overall corrosivity of the alloy, is found to be decisive for the HPUF. A dual origin of the detrimental effects of Co and Ni additives on the HPUF is identified.
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| 4. |
- Lindgren, Mikaela, 1987
(författare)
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Mechanistic Approach to Corrosion of Zirconium by Water - A First Principle Study
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zirconium and zirconium oxides are of major technological importance. There are broad applications for these materials, from fuel cell electrolyte to semiconductors and in hip-implants. In nuclear power plants, zirconium alloys are widely used as cladding material to contain the fission fuel in the reactor cores. A limiting factor for fuel longevity is the corrosion properties of the zirconium alloys. The main corrodent in the reactor core is water. The oxidation process of zirconium alloys with water should ideally be accompanied by molecular hydrogen release into the surrounding, but a significant amount of hydrogen is absorbed into the alloy. This process is called hydrogen pick-up, and is along with the oxidation rate decisive to the durability of the cladding. Mechanisms controlling hydrogen pick-up are to a large extent unknown. In this study density functional theory, DFT, is used to gain insights into the mechanism for water induced corrosion of zirconium. The purpose is to build understanding by deconstructing the corrosion phenomenon into computationally accessible and at the same time experimentally relevant quantum chemical modules. Anode and cathode reactions of the system are explored and a charge dependent oxygen vacancy transport through zirconia is identified. A detailed mechanism for electro-catalytic hydrogen evolution is articulated. It comprises formation of a transition metal associated hydride ion that recombines with a proton to form molecular hydrogen. The concentration dependence of the anode potential on absorbed oxygen in the alloy is examined along with the impact of co-absorption of oxygen and hydrogen in the α-Zr matrix. Two channels are taken to jointly constitute the oxidation process: one according to classical oxidation theory involving hydrogen evolution and the second reflected by inwards transport of protons causing hydrogen pick-up. Wagner theory and Tedmon kinetics are modified to include effects of oxide scale charging by augmenting the activation energy for diffusion of charged oxygen vacancies to also include the actual charging upon formation. Hydrogen assisted build-up of nano-porosity is also addressed.
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| 5. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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On the fate of hydrogen during zirconium oxidation by water: Effect of oxygen dissolution in α-Zr
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:22, s. 11050-11058
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Tidskriftsartikel (refereegranskat)abstract
- Zirconium oxidation by water is accompanied by hydrogen conversion, either H2 is released or hydrogen is picked up by the alloy. Strategies are sought to mitigate the detrimental hydrogen uptake into the metal. The corrosion phenomenon is subdivided into anode and cathode processes caused by electron release upon O2- oxidation at the metal/oxide interface in case of the former and electron-proton recombination resulting in hydrogen pick-up or H2 evolution in case of the latter. In a previous study, the additive dependence of the cathodic hydrogen evolution reaction was analysed. The present study contributes the oxygen concentration dependence of the anode potential, presents the impact of oxygen concentration on the co-absorption of hydrogen and merges the anode and cathode processes. The computational model is validated by semi-quantitatively reproducing the experimental solubility limit for oxygen in α-Zr. The impact of the emerging conceptual understanding for material development is discussed.
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| 6. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Oxygen Vacancy Formation, Mobility, and Hydrogen Pick-up during Oxidation of Zirconium by Water
- 2017
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 87:3-4, s. 355-365
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive first principles understanding of the oxidation of zirconium alloys by water was reiterated. Two channels were taken to jointly constitute to the oxidation process: one according to classical oxidation theory involving hydrogen evolution and the second reflected by inwards transport of protons causing hydrogen pick-up. The two were associated with charged and uncharged oxygen vacancies, respectively. The purpose of the present study was to clarify the nature of the effective anode during oxidation of zirconium as to the detailed role of the metal. Oxygen dissolution in the alloy resulted in a “pre-anodic” property associated with the formation of oxygen vacancy VO in the oxide, i.e., preceding VO2+/2e− separation. Atomistic perspective on the metal/oxide interface before nucleation of VO was provided. The rapid convergence of the model interface to bulk properties in spite of the local structural variability provided new insight as to the nature of an amorphous metal/oxide interface.
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| 7. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Possible origin and roles of nano-porosity in ZrO2 scales for hydrogen pick-up in Zr alloys
- 2017
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 492, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- A mechanistic understanding of Wagnerian build-up and subsequent non-Wagnerian break-down of barrier oxide upon oxidation of zirconium alloys by water is reiterated. Hydrogen assisted build-up of nano-porosity is addressed. Growth of sub-nanometer wide stalactitic pores owing to increasing aggregation of neutral oxygen vacancies offering a means to permeate hydrogen into the alloy is explored by density functional theory. The Wagnerian channel utilizes charge separation allowing charged oxygen vacancies and electrons to move separately from nominal anode to nominal cathode. This process becomes increasingly controlled by the charging of the barrier oxide resulting in sub-parabolic rate law for oxide growth. The break-down of the barrier oxide is understood to be preceded by avalanching hydrogen pick-up in the alloy. Pore mediated diffusion allows water to effectively short circuit the barrier oxide.
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| 8. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Toward a Comprehensive Mechanistic Understanding of Hydrogen Uptake in Zirconium Alloys by Combining Atom Probe Analysis With Electronic Structure Calculations
- 2015
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Ingår i: ASTM Special Technical Publication. - 0066-0558. - 9780803175297 ; STP 1543, s. 515-539
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Konferensbidrag (refereegranskat)abstract
- The ability of a zirconium alloy to resist corrosion relies on a compromise between two opposing strategies. Minimizing the hydrogen pickup fraction (HPUF) by invoking metallic electron conduction in the barrier oxide results in rapid parabolic oxide growth. On the other hand, slow sub-parabolic barrieroxide growth, as reflected in rate limiting electron transport, may result in a high HPUF. The objective of the present study is to offer mechanistic insights as to how low concentrations of different alloying elements become decisive for the overall corrosion behavior. Combining atomistic microanalysis with first principles modeling by means of density functional theory, the speciation and redox properties of Fe and Ni towards hydrogen evolution are firstly explored.Complementary atom probe microanalysis at the metal–oxide interface provides evidence for Fe and Ni segregation to grain boundaries in Zircaloy-2 that propagates into the ZrO2 scale. Descriptors for how alloying elements in ZrO2 control electron transport as well as catalytic electron-proton recombination ingrain boundaries to form H2 are determined by means of theory. The findings are generalized by further atomistic modeling, and are thus put in the context of early reports from autoclave experiments on HPUFs of zirconium with the alloying elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Nb. A shunting mechanism which combines inner and outer hydrogen evolution mechanisms is proposed. Properties of the transient zirconium sub-oxide are discussed. A plausible atomistic overall understanding emerges.
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