Direct ethanol fuel cell is a promising low temperature fuel cell,but its development is hindered by sluggish kinetics of anode catalysts for ethanol oxidation.Here a high efficient platinum/tin oxide/Graphene nanocom...Direct ethanol fuel cell is a promising low temperature fuel cell,but its development is hindered by sluggish kinetics of anode catalysts for ethanol oxidation.Here a high efficient platinum/tin oxide/Graphene nanocomposite is synthesized through a facile and environmentally benign method.The structure and morphology are carefully characterized by X-ray diffraction and Transmission electron microscopy,showing a clear platinum/tin oxide heterostructure uniformly dispersed on graphene support.This catalyst demonstrates the highest activity among the reported catalysts and much higher durability towards ethanol oxidation compared to conventional platinum nanocatalysts.The ultrahigh activity originates from promoted removal of poisoning carbon monoxide immediate species on platinum due to a strong electronic donating effect from both tin oxide and graphene,which is fully supported by carbon monoxide stripping and X-ray photoelectron spectroscopy analysis.Our platinum/tin oxide/Graphene appears to be a promising candidate for ethanol oxidation electrocatalysts.展开更多
Although polymer electrolyte membrane fuel cells （PEMFCs） have received broad attention due to their virtually zero emission, high power density, and high efficiency, at present the limited stability of the electroc...Although polymer electrolyte membrane fuel cells （PEMFCs） have received broad attention due to their virtually zero emission, high power density, and high efficiency, at present the limited stability of the electrocatalysts used in PEMFCs is a critical limitation to their large-scale commercialization. As a type of popularly used electrocatalyst material, carbon black supported platinum （Pt/C）--although highly efficient--undergoes corrosion of carbon, Pt dissolution, Ostwald ripening, and aggregation of Pt nanoparticles （NPs） under harsh chemical and electro- chemical oxidation conditions, which results in performance degradation of the electrocatalysts. In order to overcome these disadvantages, many groups have tried to improve the carbon support materials on which Pt is loaded. It has been found that some novel carbon nanomaterials and noncarbon materials with high surface areas, sufficient anchoring sites, high electrical conductivities, and high oxidation resistance under the strongly oxidizing condition in PEMFCs are ideal alternative supports. This review highlights the following aspects： （i） Recent advances in using novel carbon nanomaterials and noncarbon support materials to enhance the long-term durability of electrocatalysts; （ii） solutions to improve the electrical conductivity, surface area, and the strong interaction between metal and supports; and （iii） the synergistic effects in hybrid supports which help improve the stability of electrocatalysts.展开更多
The degradation of Pt nanoparticles （NPs） in fuel cell cathodes leads to the loss of the precious metal catalyst. While the effect of NP size on Pt dissolution has been studied extensively, the influence of NP shape...The degradation of Pt nanoparticles （NPs） in fuel cell cathodes leads to the loss of the precious metal catalyst. While the effect of NP size on Pt dissolution has been studied extensively, the influence of NP shape is largely unexplored. Because of the recent development of experimental methods to control the shape of metal NPs, rational guidelines/insights on the shape effects on NP stability are imperative. In this study, first-principles calculations based on density functional theory were conducted to determine the stability of 1-2 nm Pt NPs against Pt dissolution and coalescence with respect to NP shape. Toward dissolution, the stability of the Pt NPs increases in the following order： Hexagonal close-packed 〈 icosahedral 〈 cuboctahedral 〈 truncated octahedral. This trend is attributed to the synergy of the oxygen adsorption strength and the local coordination of the Pt atoms. With respect to coalescence, the size of a NP is related to its propensity to coalesce or detach/migrate to form larger particles. The stability of the Pt NPs was found to increase in the following order： Hexagonal close-packed 〈 truncated octahedral 〈 cuboctahedral 〈 icosahedral, and was correlated with the cohesive energies of the particles. By combining the characteristic stabilities of the shapes, new ＂metal-interfaced＂ Pt-based coreshell architectures were proposed that should be more stable than pure Pt nanoparticles with respect to both dissolution and coalescence.展开更多
To improve the contact between platinum catalyst and titanium substrate, a layer of TiO2 nanotube arrays has been synthesized before depositing Pt nanoflowers by pulse electrodeposition. Dramatic improvements in elect...To improve the contact between platinum catalyst and titanium substrate, a layer of TiO2 nanotube arrays has been synthesized before depositing Pt nanoflowers by pulse electrodeposition. Dramatic improvements in electrocatalytic activity （3x） and stability （60x） for methanol oxidation were found, suggesting promising applications in direct methanol fuel cells. The 3x and 60x improvements persist for Pt/Pd catalysts used to overcome the CO poisoning problem.展开更多
Oxide nanostructures grown on noble metal surfaces are often highly active in many reactions,in which the oxide/metal interfaces play an important role.In the present work,we studied the surface structures of Fe Ox-on...Oxide nanostructures grown on noble metal surfaces are often highly active in many reactions,in which the oxide/metal interfaces play an important role.In the present work,we studied the surface structures of Fe Ox-on-Pt and Ni Ox-on-Pt catalysts and their activity to CO oxidation reactions using both model catalysts and supported nanocatalysts.Although the active Fe O1x structure is stabilized on the Pt surface in a reductive reaction atmosphere,it is prone to change to an Fe O2x structure in oxidative reaction gases and becomes deactivated.In contrast,a Ni O1x surface structure supported on Pt is stable in both reductive and oxidative CO oxidation atmospheres.Consequently,CO oxidation over the Ni O1x-on-Pt catalyst is further enhanced in the CO oxidation atmosphere with an excess of O2.The present results demonstrate that the stability of the active oxide surface phases depends on the stabilization effect of the substrate surface and is also related to whether the oxide exhibits a variable oxidation state.展开更多
Developing high-efficient non-platinum （Pt） catalysts for oxygen reduction reaction （ORR） is the key to reduce the usage of Pt and the palladium （Pd）-based cata- lyst is a promising alternative. Here, we present...Developing high-efficient non-platinum （Pt） catalysts for oxygen reduction reaction （ORR） is the key to reduce the usage of Pt and the palladium （Pd）-based cata- lyst is a promising alternative. Here, we presented a facile approach to core/shell FePd/Pd nanoparticle （NP） catalyst with the FePd core in chemically ordered face-centered tetragonal （fct-） structure and the shell in controlled thickness from 0.32 to 0.81 nm via the thermal annealing of FePd NP followed by an electro-anodization process. With a 0.71 nm-thick Pd shell, the fct-FePd/Pd shows a robust catalytic activity and durability for ORR with the mass activities at 0.85 and 0.90 V reaching 453 and 96.7 A/mgpd, respectively, which are about 3.0 and 2.1 times higher than those of commercial Pt in alkaline media. This work presents a new class of non-Pt catalyst with superior performance to Pt for ORR catalysis, and the strategy demonstrated here can be extended to design highefficient catalysts for other chemical reactions.展开更多
Alloy nanocrystals （NCs） of Pt with 3d transition metals, especially Ni, are excellent catalysts for the oxygen reduction reaction （ORR）. In this work, we, for the first time, demonstrated the water phase colloida...Alloy nanocrystals （NCs） of Pt with 3d transition metals, especially Ni, are excellent catalysts for the oxygen reduction reaction （ORR）. In this work, we, for the first time, demonstrated the water phase colloidal synthesis of Pt-M （M = Ni, Co and Fe） alloy NCs with tunable composition and morphology through a facile hydrothermal method. Pt-Ni alloy NCs synthesized with this method presented better ORR activity than commercial Pt/C catalysts. The X-ray energy dispersive spectra （EDS） mapping technique revealed that Pt-enriched shells existed on the as-synthesized Pt-Ni alloy NCs. About two atom thick layered Pt-enriched shells formed on Pts0Nis0 NCs and the thickness of the Pt-enriched shells increased as the Ni content increased. Furthermore, X-ray photoelectron spectroscopy analysis revealed that the oxidation level of the surface Pt atoms on the Pt-Ni alloy NCs decreased compared with monometallic Pt NCs, implying a decrease in the oxophilicity of the surface Pt atoms. Pt-Ni alloy NCs with lower oxophilicity of the surface Pt atoms give higher ORR activity. The most active alloy sample showed 13 times higher specific activity and six times higher mass activity at 0.9 V vs. a reversible hydrogen electrode when compared with commercial Pt/C. Pt-Ni alloy NCs also showed better durability than commercial Pt/C in long term ORR tests.展开更多
Highly crystalline graphitic nanocarbons （GNC） have been prepared by the wet-air treatment of hydrothermally- derived graphitic porous carbon. The materials were characterized by scanning electron microscopy, X-ray ...Highly crystalline graphitic nanocarbons （GNC） have been prepared by the wet-air treatment of hydrothermally- derived graphitic porous carbon. The materials were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and electrochemical methods. The experimental results revealed that the treatment temperature has a significant effect on the morphology and degree of graphitic crystallinity. When GNC was treated at 450 ~C under a wet-air atmosphere, the product （GNC-450） consisted of aggregates of silkworm-shaped carbon nanoparticles with enhanced graphitic characteristics. GNC-450 was evaluated as a catalyst support in the electro-oxidation of methanol. The Pt/GNC-450 catalyst contained smaller Pt particles and had a higher electrochemically active surface area than a commercial carbon black-supported Pt catalyst. In the electro-oxidation of methanol, the Pt/GNC-450 catalyst showed the highest performance among the Pt catalysts examined in this study. The superior catalytic performance appears to be closely related to the enhanced graphitic characteristics with highly dispersed Pt nanoparticles on the graphitic layers, which have a positive effect on the electrochemical performance.展开更多
基金grateful to the financial support from the Key Research and Development Project of Tianjin(18ZXJMTG00180)the National Nature Science Foundation of China(21433003)~~
文摘Direct ethanol fuel cell is a promising low temperature fuel cell,but its development is hindered by sluggish kinetics of anode catalysts for ethanol oxidation.Here a high efficient platinum/tin oxide/Graphene nanocomposite is synthesized through a facile and environmentally benign method.The structure and morphology are carefully characterized by X-ray diffraction and Transmission electron microscopy,showing a clear platinum/tin oxide heterostructure uniformly dispersed on graphene support.This catalyst demonstrates the highest activity among the reported catalysts and much higher durability towards ethanol oxidation compared to conventional platinum nanocatalysts.The ultrahigh activity originates from promoted removal of poisoning carbon monoxide immediate species on platinum due to a strong electronic donating effect from both tin oxide and graphene,which is fully supported by carbon monoxide stripping and X-ray photoelectron spectroscopy analysis.Our platinum/tin oxide/Graphene appears to be a promising candidate for ethanol oxidation electrocatalysts.
文摘Although polymer electrolyte membrane fuel cells （PEMFCs） have received broad attention due to their virtually zero emission, high power density, and high efficiency, at present the limited stability of the electrocatalysts used in PEMFCs is a critical limitation to their large-scale commercialization. As a type of popularly used electrocatalyst material, carbon black supported platinum （Pt/C）--although highly efficient--undergoes corrosion of carbon, Pt dissolution, Ostwald ripening, and aggregation of Pt nanoparticles （NPs） under harsh chemical and electro- chemical oxidation conditions, which results in performance degradation of the electrocatalysts. In order to overcome these disadvantages, many groups have tried to improve the carbon support materials on which Pt is loaded. It has been found that some novel carbon nanomaterials and noncarbon materials with high surface areas, sufficient anchoring sites, high electrical conductivities, and high oxidation resistance under the strongly oxidizing condition in PEMFCs are ideal alternative supports. This review highlights the following aspects： （i） Recent advances in using novel carbon nanomaterials and noncarbon support materials to enhance the long-term durability of electrocatalysts; （ii） solutions to improve the electrical conductivity, surface area, and the strong interaction between metal and supports; and （iii） the synergistic effects in hybrid supports which help improve the stability of electrocatalysts.
文摘The degradation of Pt nanoparticles （NPs） in fuel cell cathodes leads to the loss of the precious metal catalyst. While the effect of NP size on Pt dissolution has been studied extensively, the influence of NP shape is largely unexplored. Because of the recent development of experimental methods to control the shape of metal NPs, rational guidelines/insights on the shape effects on NP stability are imperative. In this study, first-principles calculations based on density functional theory were conducted to determine the stability of 1-2 nm Pt NPs against Pt dissolution and coalescence with respect to NP shape. Toward dissolution, the stability of the Pt NPs increases in the following order： Hexagonal close-packed 〈 icosahedral 〈 cuboctahedral 〈 truncated octahedral. This trend is attributed to the synergy of the oxygen adsorption strength and the local coordination of the Pt atoms. With respect to coalescence, the size of a NP is related to its propensity to coalesce or detach/migrate to form larger particles. The stability of the Pt NPs was found to increase in the following order： Hexagonal close-packed 〈 truncated octahedral 〈 cuboctahedral 〈 icosahedral, and was correlated with the cohesive energies of the particles. By combining the characteristic stabilities of the shapes, new ＂metal-interfaced＂ Pt-based coreshell architectures were proposed that should be more stable than pure Pt nanoparticles with respect to both dissolution and coalescence.
文摘To improve the contact between platinum catalyst and titanium substrate, a layer of TiO2 nanotube arrays has been synthesized before depositing Pt nanoflowers by pulse electrodeposition. Dramatic improvements in electrocatalytic activity （3x） and stability （60x） for methanol oxidation were found, suggesting promising applications in direct methanol fuel cells. The 3x and 60x improvements persist for Pt/Pd catalysts used to overcome the CO poisoning problem.
基金financially supported by the National Natural Science Foundation of China(21222305,11079005,20923001)the National Basic Research Program of China(2011CBA00503,2013CB933100)
文摘Oxide nanostructures grown on noble metal surfaces are often highly active in many reactions,in which the oxide/metal interfaces play an important role.In the present work,we studied the surface structures of Fe Ox-on-Pt and Ni Ox-on-Pt catalysts and their activity to CO oxidation reactions using both model catalysts and supported nanocatalysts.Although the active Fe O1x structure is stabilized on the Pt surface in a reductive reaction atmosphere,it is prone to change to an Fe O2x structure in oxidative reaction gases and becomes deactivated.In contrast,a Ni O1x surface structure supported on Pt is stable in both reductive and oxidative CO oxidation atmospheres.Consequently,CO oxidation over the Ni O1x-on-Pt catalyst is further enhanced in the CO oxidation atmosphere with an excess of O2.The present results demonstrate that the stability of the active oxide surface phases depends on the stabilization effect of the substrate surface and is also related to whether the oxide exhibits a variable oxidation state.
基金Acknowledgments This work was supported by the Key Projects of Applied Technology Development in Chongqing （cstc2014yykfB900027, the Science and Technology Project of Chongqing Municipal Education Commission （KJI500601） and the Natural Science Foundation of Chongqing Science and Technology Commission （cstc2015jcyjA20007）.
文摘Developing high-efficient non-platinum （Pt） catalysts for oxygen reduction reaction （ORR） is the key to reduce the usage of Pt and the palladium （Pd）-based cata- lyst is a promising alternative. Here, we presented a facile approach to core/shell FePd/Pd nanoparticle （NP） catalyst with the FePd core in chemically ordered face-centered tetragonal （fct-） structure and the shell in controlled thickness from 0.32 to 0.81 nm via the thermal annealing of FePd NP followed by an electro-anodization process. With a 0.71 nm-thick Pd shell, the fct-FePd/Pd shows a robust catalytic activity and durability for ORR with the mass activities at 0.85 and 0.90 V reaching 453 and 96.7 A/mgpd, respectively, which are about 3.0 and 2.1 times higher than those of commercial Pt in alkaline media. This work presents a new class of non-Pt catalyst with superior performance to Pt for ORR catalysis, and the strategy demonstrated here can be extended to design highefficient catalysts for other chemical reactions.
基金We thank Prof. Dechun Zou and Mr. Ming Peng for their help with electrochemical characterization. This work was supported by the National Natural Science Foundation of China （Nos. 21025101, 21271011, and 21321001）. Y. W. Z. particularly appreciates the financial aid from the China National Funds for Distinguished Young Scientists from the National Natural Science Foundation of China （NSFC）. The work on micros- copy was partly carried out in the Center of Electron Microscopy of Zhejiang University, which was financially supported by the National Natural Science Foundation of China （No. 51222202）, the National Basic Research Program of China （No. 2014CB932500） and the Program for Innovative Research Teams in Universities of Ministry of Education of China （No. IRT13037） and the Fundamental Research Funds for the Central Universities （No. 2014XZZX003-07）.
文摘Alloy nanocrystals （NCs） of Pt with 3d transition metals, especially Ni, are excellent catalysts for the oxygen reduction reaction （ORR）. In this work, we, for the first time, demonstrated the water phase colloidal synthesis of Pt-M （M = Ni, Co and Fe） alloy NCs with tunable composition and morphology through a facile hydrothermal method. Pt-Ni alloy NCs synthesized with this method presented better ORR activity than commercial Pt/C catalysts. The X-ray energy dispersive spectra （EDS） mapping technique revealed that Pt-enriched shells existed on the as-synthesized Pt-Ni alloy NCs. About two atom thick layered Pt-enriched shells formed on Pts0Nis0 NCs and the thickness of the Pt-enriched shells increased as the Ni content increased. Furthermore, X-ray photoelectron spectroscopy analysis revealed that the oxidation level of the surface Pt atoms on the Pt-Ni alloy NCs decreased compared with monometallic Pt NCs, implying a decrease in the oxophilicity of the surface Pt atoms. Pt-Ni alloy NCs with lower oxophilicity of the surface Pt atoms give higher ORR activity. The most active alloy sample showed 13 times higher specific activity and six times higher mass activity at 0.9 V vs. a reversible hydrogen electrode when compared with commercial Pt/C. Pt-Ni alloy NCs also showed better durability than commercial Pt/C in long term ORR tests.
文摘Highly crystalline graphitic nanocarbons （GNC） have been prepared by the wet-air treatment of hydrothermally- derived graphitic porous carbon. The materials were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and electrochemical methods. The experimental results revealed that the treatment temperature has a significant effect on the morphology and degree of graphitic crystallinity. When GNC was treated at 450 ~C under a wet-air atmosphere, the product （GNC-450） consisted of aggregates of silkworm-shaped carbon nanoparticles with enhanced graphitic characteristics. GNC-450 was evaluated as a catalyst support in the electro-oxidation of methanol. The Pt/GNC-450 catalyst contained smaller Pt particles and had a higher electrochemically active surface area than a commercial carbon black-supported Pt catalyst. In the electro-oxidation of methanol, the Pt/GNC-450 catalyst showed the highest performance among the Pt catalysts examined in this study. The superior catalytic performance appears to be closely related to the enhanced graphitic characteristics with highly dispersed Pt nanoparticles on the graphitic layers, which have a positive effect on the electrochemical performance.
