Nanocarbons are of progressively increasing importance in energy electrocatalysis, including oxygen reduction, oxygen evolution, hydrogen evolution, COreduction, etc. Precious-metal-free or metal-free nanocarbon-based...Nanocarbons are of progressively increasing importance in energy electrocatalysis, including oxygen reduction, oxygen evolution, hydrogen evolution, COreduction, etc. Precious-metal-free or metal-free nanocarbon-based electrocatalysts have been revealed to potentially have effective activity and remarkable durability, which is promising to replace precious metals in some important energy technologies,such as fuel cells, metal–air batteries, and water splitting. In this review, rather than overviewing recent progress completely, we aim to give an in-depth digestion of present achievements, focusing on the different roles of nanocarbons and material design principles. The multifunctionalities of nanocarbon substrates(accelerating the electron and mass transport, regulating the incorporation of active components,manipulating electron structures, generating confinement effects, assembly into 3 D free-standing electrodes) and the intrinsic activity of nanocarbon catalysts(multi-heteroatom doping, hierarchical structure,topological defects) are discussed systematically, with perspectives on the further research in this rising research field. This review is inspiring for more insights and methodical research in mechanism understanding, material design, and device optimization, leading to a targeted and high-efficiency development of energy electrocatalysis.展开更多
The discovery that supported gold catalysts can promote CO/H2O-mediated reduction at ambient temperatures is important to chemoselective synthesis and has gained significant attention in recent years.Whether the alter...The discovery that supported gold catalysts can promote CO/H2O-mediated reduction at ambient temperatures is important to chemoselective synthesis and has gained significant attention in recent years.Whether the alternative Pt group metal （PGM） catalysts can exhibit such exceptional performance is thus an interesting research issue.So far,no PGM catalyst shows activity for CO/H2O-mediated reduction at ambient temperatures.Here,we demonstrate that it is possible to transform nonactive into highly active and selective catalysts for CO/H2O-mediated reduction by modulating the interfacial structure and electronic properties at the metal-support interfaces.Thus,highly active and chemoselective hydrogenation Pt,Ir,Rh and Pd catalysts can be prepared by decorating the exposed metal faces with partially reduced support species by means of a simple catalyst activation procedure.In this way,it has been possible to dramatically facilitate the previously unappreciated PGM-catalyzed activation of CO molecules under mild conditions,which can make a significant contribution not only to reveal the intrinsic catalytic potential of supported PGMs but also to establish a more sustainable and industrially-relevant process.展开更多
Pt/BaO/Al_2O_3 catalysts with different BaO loadings prepared from Al_2O_3 nanorods(Pt/BaO/Al_2O_3-nr) and irregular Al_2O_3 nanoparticles(Pt/BaO/Al_2O_3-np) were investigated for NOx storage and reduction(NSR). The P...Pt/BaO/Al_2O_3 catalysts with different BaO loadings prepared from Al_2O_3 nanorods(Pt/BaO/Al_2O_3-nr) and irregular Al_2O_3 nanoparticles(Pt/BaO/Al_2O_3-np) were investigated for NOx storage and reduction(NSR). The Pt/BaO/Al_2O_3 materials derived from Al_2O_3 nanorods always exhibited much higher NOx storage capacity(NSC) over the whole temperature range of 100–400°C than the corresponding Pt/BaO/Al_2O_3-np samples containing the same BaO loading, giving the maximum NSC value of 966.9 μmol/gcatat 400°C, 1.4 times higher than that of Pt/BaO/Al_2O_3-np. Higher catalytic performance of nanorod-supported NSR samples was also observed during lean-rich cyclic conditions(90 sec vs. 5 sec), giving more than 98% NOx conversion at 300–450°C over the Pt/BaO/Al_2O_3-nr sample with 15% BaO loading. To reveal this dependence on the shape of the support during the NSR process, a series of characterization techniques including the Brunauer–Emmett–Teller(BET) method,X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), H_2 temperature programmed reduction(H2-TPR), and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) were also conducted. It was found that intimate contact of Ba–Al and Ba–Pt sites was achieved over the Pt/BaO/Al_2O_3 surface when using Al_2O_3-nr as a support.This strong interaction among the multi-components of Pt/BaO/Al_2O_3-nr thus triggered the formation of surface nitrite and nitrate during the lean period, and also accelerated the reverse spillover of ad-NOxspecies onto the Pt surface, enhancing their reduction and leading to high NSR performance.展开更多
Developing exceptionally durable and efficient oxygen reduction reaction(ORR)catalysts is of paramount importance to the widespread commercialization of proton exchange membrane fuel cells(PEMFCs)but is still challeng...Developing exceptionally durable and efficient oxygen reduction reaction(ORR)catalysts is of paramount importance to the widespread commercialization of proton exchange membrane fuel cells(PEMFCs)but is still challenging.Herein,PtCu nanoalloys rooted on nitrogen-doped carbon nanosheets(PtCuNC-700)with fully exposed PtCu nanoalloys and strong metal–support interaction were developed.Benefiting from its structural and compositional merits,PtCuNC-700 showcases superior ORR activity and stability with a specific activity of 1.05mA cm^(−2)and mass activity of 0.45 A mgPt^(−1),4.2-fold and 3.7-fold higher than Pt/C(0.25 mA cm^(−2)and 0.12 A mgPt^(−1)),respectively.Moreover,PtCuNC-700 exhibits first-class performance in H2/air PEMFC assessment and delivers a peak power density of 929.7 mW cm^(−2)and excellent cycling stability up to 30,000 cycles.Theoretical calculations disclose that the synergistic effect of alloying Pt with Cu combined with the strong interaction between PtCu nanoalloys and nitrogen-doped carbon nanosheets can effectively modify the local electron configuration and density of states of Pt sites approaching the Fermi level.Hence,the PtCu-alloy catalysts realized here diminish the energy barrier for ORR and accelerate their reaction kinetics.This work provides a reliable and effective approach to boost the activity and stability of Pt alloy-based ORR electrocatalysts in PEMFCs.展开更多
We present examples of a controlled numerical experiment that contribute towards understanding of the physical phenomena that lead to the reduction of coherency of strong earthquake ground motion.We show examples for ...We present examples of a controlled numerical experiment that contribute towards understanding of the physical phenomena that lead to the reduction of coherency of strong earthquake ground motion.We show examples for separation distance of 100 m between the two points on the ground surface,which is in the range of engineering interest.Our examples illustrate the consequences of:(a)standing waves that result from interference of the incident and reflected waves from a near vertical contrast in material properties,(b)standing waves within a concave inhomogeneity(a semi-circular valley in our examples),and(c)smaller motions in the diffraction zone,behind the inhomogeneity.We show that it is possible to reduce coherency,to the extent observed for recorded strong earthquake ground motion,even by a single inclusion in a half space,for incident ground motion that is coherent.We also illustrate the combined effects of geometric spreading and finite fault width,superimposed on the otherwise dominating effects caused by interference.Our examples show reduction of coherence for specific angles of incident waves,while,for other angles of incidence,the coherence remains essentially equal to one.展开更多
基金supported by the National Key Research and Development Program (Nos. 2016YFA0202500 and 2016YFA0200102)the Natural Scientific Foundation of China (No. 21561130151)Royal Society for the award of a Newton Advanced Fellowship (Ref: NA140249)
文摘Nanocarbons are of progressively increasing importance in energy electrocatalysis, including oxygen reduction, oxygen evolution, hydrogen evolution, COreduction, etc. Precious-metal-free or metal-free nanocarbon-based electrocatalysts have been revealed to potentially have effective activity and remarkable durability, which is promising to replace precious metals in some important energy technologies,such as fuel cells, metal–air batteries, and water splitting. In this review, rather than overviewing recent progress completely, we aim to give an in-depth digestion of present achievements, focusing on the different roles of nanocarbons and material design principles. The multifunctionalities of nanocarbon substrates(accelerating the electron and mass transport, regulating the incorporation of active components,manipulating electron structures, generating confinement effects, assembly into 3 D free-standing electrodes) and the intrinsic activity of nanocarbon catalysts(multi-heteroatom doping, hierarchical structure,topological defects) are discussed systematically, with perspectives on the further research in this rising research field. This review is inspiring for more insights and methodical research in mechanism understanding, material design, and device optimization, leading to a targeted and high-efficiency development of energy electrocatalysis.
文摘The discovery that supported gold catalysts can promote CO/H2O-mediated reduction at ambient temperatures is important to chemoselective synthesis and has gained significant attention in recent years.Whether the alternative Pt group metal （PGM） catalysts can exhibit such exceptional performance is thus an interesting research issue.So far,no PGM catalyst shows activity for CO/H2O-mediated reduction at ambient temperatures.Here,we demonstrate that it is possible to transform nonactive into highly active and selective catalysts for CO/H2O-mediated reduction by modulating the interfacial structure and electronic properties at the metal-support interfaces.Thus,highly active and chemoselective hydrogenation Pt,Ir,Rh and Pd catalysts can be prepared by decorating the exposed metal faces with partially reduced support species by means of a simple catalyst activation procedure.In this way,it has been possible to dramatically facilitate the previously unappreciated PGM-catalyzed activation of CO molecules under mild conditions,which can make a significant contribution not only to reveal the intrinsic catalytic potential of supported PGMs but also to establish a more sustainable and industrially-relevant process.
基金supported by the National Natural Science Foundation of China (Nos.21673277 and 21637005)the National Key R&D Program of China (No.2017YFC0211105)+1 种基金the Science and Technology Program of Tianjin,China (No.16YFXTSF00290)the K.C.Wong Education Foundation
文摘Pt/BaO/Al_2O_3 catalysts with different BaO loadings prepared from Al_2O_3 nanorods(Pt/BaO/Al_2O_3-nr) and irregular Al_2O_3 nanoparticles(Pt/BaO/Al_2O_3-np) were investigated for NOx storage and reduction(NSR). The Pt/BaO/Al_2O_3 materials derived from Al_2O_3 nanorods always exhibited much higher NOx storage capacity(NSC) over the whole temperature range of 100–400°C than the corresponding Pt/BaO/Al_2O_3-np samples containing the same BaO loading, giving the maximum NSC value of 966.9 μmol/gcatat 400°C, 1.4 times higher than that of Pt/BaO/Al_2O_3-np. Higher catalytic performance of nanorod-supported NSR samples was also observed during lean-rich cyclic conditions(90 sec vs. 5 sec), giving more than 98% NOx conversion at 300–450°C over the Pt/BaO/Al_2O_3-nr sample with 15% BaO loading. To reveal this dependence on the shape of the support during the NSR process, a series of characterization techniques including the Brunauer–Emmett–Teller(BET) method,X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), H_2 temperature programmed reduction(H2-TPR), and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) were also conducted. It was found that intimate contact of Ba–Al and Ba–Pt sites was achieved over the Pt/BaO/Al_2O_3 surface when using Al_2O_3-nr as a support.This strong interaction among the multi-components of Pt/BaO/Al_2O_3-nr thus triggered the formation of surface nitrite and nitrate during the lean period, and also accelerated the reverse spillover of ad-NOxspecies onto the Pt surface, enhancing their reduction and leading to high NSR performance.
基金support from the National Natural Science Foundation of China(grant nos.52073137,51763018,U20A20246)the Fundamental Research Funds for the Central Universities(Innovation funded Projects,no.2022CXZZ104).
文摘Developing exceptionally durable and efficient oxygen reduction reaction(ORR)catalysts is of paramount importance to the widespread commercialization of proton exchange membrane fuel cells(PEMFCs)but is still challenging.Herein,PtCu nanoalloys rooted on nitrogen-doped carbon nanosheets(PtCuNC-700)with fully exposed PtCu nanoalloys and strong metal–support interaction were developed.Benefiting from its structural and compositional merits,PtCuNC-700 showcases superior ORR activity and stability with a specific activity of 1.05mA cm^(−2)and mass activity of 0.45 A mgPt^(−1),4.2-fold and 3.7-fold higher than Pt/C(0.25 mA cm^(−2)and 0.12 A mgPt^(−1)),respectively.Moreover,PtCuNC-700 exhibits first-class performance in H2/air PEMFC assessment and delivers a peak power density of 929.7 mW cm^(−2)and excellent cycling stability up to 30,000 cycles.Theoretical calculations disclose that the synergistic effect of alloying Pt with Cu combined with the strong interaction between PtCu nanoalloys and nitrogen-doped carbon nanosheets can effectively modify the local electron configuration and density of states of Pt sites approaching the Fermi level.Hence,the PtCu-alloy catalysts realized here diminish the energy barrier for ORR and accelerate their reaction kinetics.This work provides a reliable and effective approach to boost the activity and stability of Pt alloy-based ORR electrocatalysts in PEMFCs.
文摘We present examples of a controlled numerical experiment that contribute towards understanding of the physical phenomena that lead to the reduction of coherency of strong earthquake ground motion.We show examples for separation distance of 100 m between the two points on the ground surface,which is in the range of engineering interest.Our examples illustrate the consequences of:(a)standing waves that result from interference of the incident and reflected waves from a near vertical contrast in material properties,(b)standing waves within a concave inhomogeneity(a semi-circular valley in our examples),and(c)smaller motions in the diffraction zone,behind the inhomogeneity.We show that it is possible to reduce coherency,to the extent observed for recorded strong earthquake ground motion,even by a single inclusion in a half space,for incident ground motion that is coherent.We also illustrate the combined effects of geometric spreading and finite fault width,superimposed on the otherwise dominating effects caused by interference.Our examples show reduction of coherence for specific angles of incident waves,while,for other angles of incidence,the coherence remains essentially equal to one.
