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Yimao Wan - One of the best experts on this subject based on the ideXlab platform.
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temperature and humidity stable alkali Alkaline Earth Metal carbonates as electron heterocontacts for silicon photovoltaics
Advanced Energy Materials, 2018Co-Authors: Yimao Wan, James Bullock, Mark Hettick, Chris Samundsett, Di Yan, Jun PengAbstract:Author(s): Wan, Y; Bullock, J; Hettick, M; Xu, Z; Samundsett, C; Yan, D; Peng, J; Ye, J; Javey, A; Cuevas, A | Abstract: © 2018 WILEY-VCH Verlag GmbH a Co. KGaA, Weinheim Nanometer scale interfacial layers between the Metal cathode and the n-type semiconductor play a critical role in enhancing the transport of charge carriers in and out of optoelectronic devices. Here, a range of nanoscale alkali and Alkaline Earth Metal carbonates (i.e., potassium, rubidium, caesium, calcium, strontium, and barium) are shown to function effectively as electron heterocontacts to lightly doped n-type crystalline silicon (c-Si), which is particularly challenging to contact with common Metals. These carbonate interlayers are shown to enhance the performance of n-type c-Si proof-of-concept solar cells up to a power conversion efficiency of ≈19%. Furthermore, these devices are thermally stable up to 350 °C and both the caesium and barium carbonates pass a standard 1000 h damp heat test, with g95% of their initial performance maintained. The temperature and humidity stable electron heterocontacts based on alkali and Alkaline Earth Metal carbonates show a high potential for industrial feasibility and longevity for deployment in the field.
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temperature and humidity stable alkali Alkaline Earth Metal carbonates as electron heterocontacts for silicon photovoltaics
Advanced Energy Materials, 2018Co-Authors: Yimao Wan, James Bullock, Mark Hettick, Chris Samundsett, Di Yan, Jun PengAbstract:Nanometer scale interfacial layers between the Metal cathode and the n-type semiconductor play a critical role in enhancing the transport of charge carriers in and out of optoelectronic devices. Here, a range of nanoscale alkali and Alkaline Earth Metal carbonates (i.e., potassium, rubidium, caesium, calcium, strontium, and barium) are shown to function effectively as electron heterocontacts to lightly doped n-type crystalline silicon (c-Si), which is particularly challenging to contact with common Metals. These carbonate interlayers are shown to enhance the performance of n-type c-Si proof-of-concept solar cells up to a power conversion efficiency of ≈19%. Furthermore, these devices are thermally stable up to 350 °C and both the caesium and barium carbonates pass a standard 1000 h damp heat test, with >95% of their initial performance maintained. The temperature and humidity stable electron heterocontacts based on alkali and Alkaline Earth Metal carbonates show a high potential for industrial feasibility and longevity for deployment in the field.
Jens K Norskov - One of the best experts on this subject based on the ideXlab platform.
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tuning methane activation chemistry on Alkaline Earth Metal oxides by doping
Journal of Physical Chemistry C, 2018Co-Authors: Hassan Aljama, Jens K Norskov, Frank AbildpedersenAbstract:We study oxidative coupling of methane (OCM) on Alkaline Earth Metal oxides (AEMOs) doped with either a transition Metal (TM) or an Alkaline Earth Metal (AEM) different from that of the host oxide. We assess whether doping can lead to new materials that are better than the pure oxides or deviate from the limitations of the scaling relations. Density functional theory (DFT) calculations show that doped AEMO surfaces follow similar linear scaling relations as observed on pure AEMO; however, doped surfaces bind the adsorbates, hydrogen, and methyl more strongly. Both TM- and AEM-doped AEMOs show that methane activation mostly occurs through a surface-mediated pathway, where at the transition state the methane C–H bond is stretched, and the methyl interacts mostly with the dopant atom and the hydrogen with the lattice oxygen. The stronger hydrogen binding in the doped surfaces leads to a lower methane activation barrier; however, in some cases, the catalyst surface binds the hydrogen too strongly, poisoning t...
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tuning methane activation chemistry on Alkaline Earth Metal oxides by doping
The Journal of Physical Chemistry, 2018Co-Authors: Hassan Aljama, Jens K Norskov, Frank AbildpedersenAbstract:We study oxidative coupling of methane (OCM) on Alkaline Earth Metal oxides (AEMOs) doped with either a transition Metal (TM) or an Alkaline Earth Metal (AEM) different from that of the host oxide. We assess whether doping can lead to new materials that are better than the pure oxides or deviate from the limitations of the scaling relations. Density functional theory (DFT) calculations show that doped AEMO surfaces follow similar linear scaling relations as observed on pure AEMO; however, doped surfaces bind the adsorbates, hydrogen, and methyl more strongly. Both TM- and AEM-doped AEMOs show that methane activation mostly occurs through a surface-mediated pathway, where at the transition state the methane C–H bond is stretched, and the methyl interacts mostly with the dopant atom and the hydrogen with the lattice oxygen. The stronger hydrogen binding in the doped surfaces leads to a lower methane activation barrier; however, in some cases, the catalyst surface binds the hydrogen too strongly, poisoning the active site and making the catalyst inactive. The doped systems are largely constrained by the scaling relations, but sites closer to the optimum of the volcano plot exist, suggesting room for improvement.
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surface energetics of Alkaline Earth Metal oxides trends in stability and adsorption of small molecules
Physical Review B, 2015Co-Authors: Michal Bajdich, Jens K Norskov, Aleksandra VojvodicAbstract:We present a systematic theoretical investigation of the surface properties, stability and reactivity, of rock-salt type Alkaline-Earth Metal oxides including MgO, CaO, SrO, and BaO. The accuracy of commonly used exchange-correlation density functionals (LDA, PBE, RPBE, PBEsol, BEEF-vdW and hybrid HSE) and random-phase approximation (RPA) is evaluated and compared to existing experimental values. Calculated surface energies of the four most stable surface facets under vacuum conditions: the (100) surface, the Metal and oxygen terminated octopolar (111), and the (110) surfaces exhibit a monotonic increase in stability from MgO to BaO. On the MgO(100) surface, adsorption of CO, NO, CH4 is characterized by physisorption while H2O chemisorbs, which is in agreement with experimental findings. We further use the on-top Metal adsorption of CO and NO molecules to map out the surface energetics of each Alkaline-Earth Metal oxide surface. The considered functionals all qualitatively predict similar adsorption energy trends. The ordering between the adsorption energies on different surface facets can be attributed to differences in the local geometrical surface structure and the electronic structure of the Metal constituent of the Alkaline-Earth Metal oxide. The striking observation that CO adsorption strength is weaker than NO adsorption on the (100) terraces as the period of the Alkaline-Earth Metal in the oxide increases, is analyzed in detail in terms of charge redistribution within the {\sigma} and {\pi} channels of adsorbates. Finally, we also present oxygen adsorption and oxygen vacancy formation energies in these oxide systems.
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surface energetics of Alkaline Earth Metal oxides trends in stability and adsorption of small molecules
Physical Review B, 2015Co-Authors: Michal Bajdich, Jens K Norskov, Aleksandra VojvodicAbstract:We present a systematic theoretical investigation of the surface properties, stability, and reactivity of rocksalt type Alkaline-Earth Metal oxides including MgO, CaO, SrO, and BaO. The accuracy of commonly used exchange-correlation density functionals (LDA, PBE, RPBE, PBEsol, BEEF-vdW, and hybrid HSE) and random-phase approximation (RPA) is evaluated and compared to existing experimental values. Calculated surface energies of the four most stable surface facets under vacuum conditions, the (100) surface, the Metal and oxygen terminated octopolar (111), and the (110) surfaces, exhibit a monotonic increase in stability from MgO to BaO. On the MgO(100) surface, adsorption of CO, NO, and ${\text{CH}}_{4}$ is characterized by physisorption while ${\text{H}}_{2}\text{O}$ chemisorbs, which is in agreement with experimental findings. We further use the on-top Metal adsorption of CO and NO molecules to map out the surface energetics of each Alkaline-Earth Metal oxide surface. The considered functionals all qualitatively predict similar adsorption energy trends. The ordering between the adsorption energies on different surface facets can be attributed to differences in the local geometrical surface structure and the electronic structure of the Metal constituent of the Alkaline-Earth Metal oxide. The striking observation that CO adsorption strength is weaker than NO adsorption on the (100) terraces as the period of the Alkaline-Earth Metal in the oxide increases is analyzed in detail in terms of charge redistribution within the $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ channels of adsorbates. Finally, we also present oxygen adsorption and oxygen vacancy formation energies in these oxide systems.
Frank Abildpedersen - One of the best experts on this subject based on the ideXlab platform.
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tuning methane activation chemistry on Alkaline Earth Metal oxides by doping
Journal of Physical Chemistry C, 2018Co-Authors: Hassan Aljama, Jens K Norskov, Frank AbildpedersenAbstract:We study oxidative coupling of methane (OCM) on Alkaline Earth Metal oxides (AEMOs) doped with either a transition Metal (TM) or an Alkaline Earth Metal (AEM) different from that of the host oxide. We assess whether doping can lead to new materials that are better than the pure oxides or deviate from the limitations of the scaling relations. Density functional theory (DFT) calculations show that doped AEMO surfaces follow similar linear scaling relations as observed on pure AEMO; however, doped surfaces bind the adsorbates, hydrogen, and methyl more strongly. Both TM- and AEM-doped AEMOs show that methane activation mostly occurs through a surface-mediated pathway, where at the transition state the methane C–H bond is stretched, and the methyl interacts mostly with the dopant atom and the hydrogen with the lattice oxygen. The stronger hydrogen binding in the doped surfaces leads to a lower methane activation barrier; however, in some cases, the catalyst surface binds the hydrogen too strongly, poisoning t...
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tuning methane activation chemistry on Alkaline Earth Metal oxides by doping
The Journal of Physical Chemistry, 2018Co-Authors: Hassan Aljama, Jens K Norskov, Frank AbildpedersenAbstract:We study oxidative coupling of methane (OCM) on Alkaline Earth Metal oxides (AEMOs) doped with either a transition Metal (TM) or an Alkaline Earth Metal (AEM) different from that of the host oxide. We assess whether doping can lead to new materials that are better than the pure oxides or deviate from the limitations of the scaling relations. Density functional theory (DFT) calculations show that doped AEMO surfaces follow similar linear scaling relations as observed on pure AEMO; however, doped surfaces bind the adsorbates, hydrogen, and methyl more strongly. Both TM- and AEM-doped AEMOs show that methane activation mostly occurs through a surface-mediated pathway, where at the transition state the methane C–H bond is stretched, and the methyl interacts mostly with the dopant atom and the hydrogen with the lattice oxygen. The stronger hydrogen binding in the doped surfaces leads to a lower methane activation barrier; however, in some cases, the catalyst surface binds the hydrogen too strongly, poisoning the active site and making the catalyst inactive. The doped systems are largely constrained by the scaling relations, but sites closer to the optimum of the volcano plot exist, suggesting room for improvement.
Jun Peng - One of the best experts on this subject based on the ideXlab platform.
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temperature and humidity stable alkali Alkaline Earth Metal carbonates as electron heterocontacts for silicon photovoltaics
Advanced Energy Materials, 2018Co-Authors: Yimao Wan, James Bullock, Mark Hettick, Chris Samundsett, Di Yan, Jun PengAbstract:Author(s): Wan, Y; Bullock, J; Hettick, M; Xu, Z; Samundsett, C; Yan, D; Peng, J; Ye, J; Javey, A; Cuevas, A | Abstract: © 2018 WILEY-VCH Verlag GmbH a Co. KGaA, Weinheim Nanometer scale interfacial layers between the Metal cathode and the n-type semiconductor play a critical role in enhancing the transport of charge carriers in and out of optoelectronic devices. Here, a range of nanoscale alkali and Alkaline Earth Metal carbonates (i.e., potassium, rubidium, caesium, calcium, strontium, and barium) are shown to function effectively as electron heterocontacts to lightly doped n-type crystalline silicon (c-Si), which is particularly challenging to contact with common Metals. These carbonate interlayers are shown to enhance the performance of n-type c-Si proof-of-concept solar cells up to a power conversion efficiency of ≈19%. Furthermore, these devices are thermally stable up to 350 °C and both the caesium and barium carbonates pass a standard 1000 h damp heat test, with g95% of their initial performance maintained. The temperature and humidity stable electron heterocontacts based on alkali and Alkaline Earth Metal carbonates show a high potential for industrial feasibility and longevity for deployment in the field.
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temperature and humidity stable alkali Alkaline Earth Metal carbonates as electron heterocontacts for silicon photovoltaics
Advanced Energy Materials, 2018Co-Authors: Yimao Wan, James Bullock, Mark Hettick, Chris Samundsett, Di Yan, Jun PengAbstract:Nanometer scale interfacial layers between the Metal cathode and the n-type semiconductor play a critical role in enhancing the transport of charge carriers in and out of optoelectronic devices. Here, a range of nanoscale alkali and Alkaline Earth Metal carbonates (i.e., potassium, rubidium, caesium, calcium, strontium, and barium) are shown to function effectively as electron heterocontacts to lightly doped n-type crystalline silicon (c-Si), which is particularly challenging to contact with common Metals. These carbonate interlayers are shown to enhance the performance of n-type c-Si proof-of-concept solar cells up to a power conversion efficiency of ≈19%. Furthermore, these devices are thermally stable up to 350 °C and both the caesium and barium carbonates pass a standard 1000 h damp heat test, with >95% of their initial performance maintained. The temperature and humidity stable electron heterocontacts based on alkali and Alkaline Earth Metal carbonates show a high potential for industrial feasibility and longevity for deployment in the field.
Eli Ruckenstein - One of the best experts on this subject based on the ideXlab platform.
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partial oxidation of methane to synthesis gas over Alkaline Earth Metal oxide supported cobalt catalysts
Journal of Catalysis, 2001Co-Authors: Haiyou Wang, Eli RuckensteinAbstract:Abstract The partial oxidation of methane to synthesis gas was investigated over the Alkaline Earth Metal oxide supported Co catalysts. Only MgO has proved to be a suitable support. The reaction behavior of the MgO-supported Co catalysts was significantly influenced by the calcination temperature (Tc) and Co loading. The 24 wt% Co/MgO catalyst precalcined at 800°C provided a high and stable activity; those precalcined at higher temperatures provided a lower stable activity and those precalcined at lower temperatures a lower stability. Because of the two oxidative states of Co, the structural characteristics of the Co catalysts are strongly affected by the nature of the support, calcination temperature, and Co loading. In the 24 wt% MgO-supported catalysts, only a solid solution of CoO and MgO was identified for Tc≥800°C, while one or two of the following compounds, Co3O4 and MgCo2O4, were additionally detected for Tc
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carbon dioxide reforming of methane over nickel Alkaline Earth Metal oxide catalysts
Applied Catalysis A-general, 1995Co-Authors: Eli RuckensteinAbstract:The CO2 reforming of CH4 over reduced NiO/Alkaline Earth Metal oxide catalysts was investigated. A CO yield of 95% was obtained from a stoichiometric feed mixture of CH4 and CO2, at high GHSV (60 000 cm3 g−1 h−1), over a reduced NiOMgO with a weight ratio of 0.2. In addition, the catalyst had excellent stability, since the CO yield remained unchanged during 120h. Compared to the reduced NiOMgO catalyst, the reduced NiOCaO,NiO SrO NiO BaO catalysts had low CO yields and very low stabilities. The TPD of CO over the reduced NiOMgO catalyst indicated a lower decomposition of CO to CO2 than over the other catalysts investigated, hence that MgO inhibits the disproportionation reaction 2CO → C + CO2 over Ni. The behavior of the reduced NiOMgO catalyst is probably due to the formation of a NiOMgO solution, as a result of the similar crystalline structures of NiO and MgO.