Zintl phases with the nominal compositions Ca_(1-δ)Ce_(δ)Ag_(1-δ)Sb(RE=La,Ce,Pr,Nd,Sm;δ≈0.15)are interesting due to their unique crystal structures and potential as high temperature thermoelectrics.Their structur...Zintl phases with the nominal compositions Ca_(1-δ)Ce_(δ)Ag_(1-δ)Sb(RE=La,Ce,Pr,Nd,Sm;δ≈0.15)are interesting due to their unique crystal structures and potential as high temperature thermoelectrics.Their structures generally feature the LiGaGe type structure with substantial vacancies on the Ag sites.The formation of such defects can be explained by the electronic effects,with which 18 electrons are required to stabilize the CaAgSb Zintl system.Since the substitution of Ca^(2+)with RE^(3+)will lead to electron excess,the formation of Ag defects will be an intrinsic character of such compounds to maintain their electron precise nature.In this work,the material Ca_(0.85)Ce_(0.15)Ag_(0.85)Sb was selected for a detailed study on defect chemistry.In order to better understand the mechanism related to the defect formation and control in this system,we conducted a series of experiments aimed at controlling the point defects in Ca_(0.85)Ce_(0.15)Ag_(0.85)Sb.This strategy was realized by intentionally doping Nb,which resulted in the discovery of a series of low defect density materials Ca_(0.725+x)Nb_(0.1-x)Ce_(0.15)AgSb(0≤x≤0.05).In this work,an interesting defect controlling strategy on Zintl phases was demonstrated,which suggested the high flexibility of Ca_(1-δ)Ce_(δ)Ag_(1-δ)Sb in the optimization of thermoelectric properties.展开更多
Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulli...Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M （M=Ti, Al） and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAINb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%-12.5% （mole fraction）.展开更多
Selective hydrogenolysis of glycerol to 1,3‐propanediol（1,3‐PD） is an important yet challenging method for the transformation of biomass into value‐added chemicals due to steric hindrance and unfavorable thermody...Selective hydrogenolysis of glycerol to 1,3‐propanediol（1,3‐PD） is an important yet challenging method for the transformation of biomass into value‐added chemicals due to steric hindrance and unfavorable thermodynamics. In previous studies, chemoselective performances were found de‐manding and sensitive to H2 pressure. In this regard, we manipulate the chemical/physical charac‐teristics of the catalyst supports via doping Nb into WOx and prepared 1D needle‐, 2D flake‐, and 3D sphere‐stack mesoporous structured Nb‐WOx with increased surface acid sites. Moreover, Nb dop‐ing can successfully inhibit the over‐reduction of active W species during glycerol hydrogenolysis and substantially broaden the optimal H2 pressure from 1 to 5 MPa. When Nb doping is 2%, sup‐ported Pt catalysts showed promising performance for the selective hydrogenolysis of glycerol to 1,3‐PD over an unprecedentedly wide H2 pressure range, which will guarantee better catalyst sta‐bility in the long run, as well as expand their applications to other hydrogen‐related reactions.展开更多
Nb-Doped LiNi_(0.4)Co_(0.2)Mn_(0.4)O_(2)(Nb-NCM)nanobelts have been successfully fabricated for the first time through a facile electrospinning method by the delicate control of PAN pyrolysis and Nb-NCM formation(incl...Nb-Doped LiNi_(0.4)Co_(0.2)Mn_(0.4)O_(2)(Nb-NCM)nanobelts have been successfully fabricated for the first time through a facile electrospinning method by the delicate control of PAN pyrolysis and Nb-NCM formation(including nucleation and subsequent growth processes).According to the experimental evidence from temperature-dependent characterization and isolation of the intermediates,the formation of nanobelts undergoes a morphology evolution from nanofibres to nanotubes,and finally to the nanobelts composed of subunit nanoparticles.When used as a cathode for lithium-ion batteries,the as-electrospun Nb-NCM nanobelts exhibit superior electrochemical performances,which could be attributed to their unique features,such as their 1D nanostructure,well-crystallized nature and Nb-doping.These features can improve the ionic conductivity of Nb-NCM nanobelts and stabilize the electrode/electrolyte interface.Therefore,the 1D Nb-NCM nanobelts developed in this study not only provide an excellent model to investigate the fabrication of multi-element oxides using the electrospinning method,but also open up a facile route for designing 1D layered cathodes with a complex component for high performance lithium-ion batteries.展开更多
Developing highly efficient,Earth-abundant,and long-term stable electrocatalysts for the oxygen evolution reaction (OER) is of great importance for realizing industrial hydrogen generation from water splitting.Herein,...Developing highly efficient,Earth-abundant,and long-term stable electrocatalysts for the oxygen evolution reaction (OER) is of great importance for realizing industrial hydrogen generation from water splitting.Herein,a series of novel Fe and Nb co-doped β-Ni(OH)_(2)nanosheet arrays were successfully grown in situ on Ni foam via a chlorine etching method.The representative NiFe_(3)Nb_(2)-OH displayed outstanding OER performance with an overpotential of 294 mV to deliver 100 mA cm^(-2) in an alkaline electrolyte,outperforming other Ni related electrocatalysts.NiFe_(3)Nb_(2)-OH exhibited a stability of 90 h without obvious potential change at 50 mA cm^(-2).Significantly,the doped Fe and Nb effectively enhanced the electrochemical active area and electronic transfer capability of β-Ni(OH)_(2).Density functional theory (DFT) calculations indicated that the Gibbs free energy of the OER intermediates on the Fe,Nb co-doped β-Ni(OH)_(2)electrode was optimized.The tuned electronic interactions between Fe,Nb and Ni apparently boosted the OER performance of NiFe_(3)Nb_(2)-OH.These results demonstrated that Fe and Nb co-doped β-Ni(OH)_(2)is a highly efficient OER electrocatalyst in alkaline media.展开更多
The performance of a solid oxide fuel cell(SOFC)is strongly associated with the activity and durability of the cathode,where the oxygen reduction reaction occurs.In this study,we report our findings in the development...The performance of a solid oxide fuel cell(SOFC)is strongly associated with the activity and durability of the cathode,where the oxygen reduction reaction occurs.In this study,we report our findings in the development of an Nb-doped PrBa_(0.8)Ca_(0.2)Co_(2)O_(6-δ)(PrBa_(0.8)Ca_(0.2)Co_(2-x)Nb_(x)O_(6-δ),x=0,0.025,0.05,and 0.1,denoted as PBCCNx)perovskite composite as the SOFC cathode.Analyses of X-ray diffraction(XRD)patterns and energy-dispersive transmission electron microscopy(TEM-EDS)images suggest that after being treated at 950℃ in air,PBCCN0.05 mainly contains phases of Ca-and Nb-doped PrBaCo2O6-δdouble perovskite,PrCoO_(3) perovskite with Ca and Nb doping,and Ba_(3)Ca_(1.18)Nb_(1.82)O_(9-δ).When evaluated as an SOFC cathode,the PBCCN0.05 mixture has shown a low polarization resistance of 0.0074Ω·cm^(2)at 800℃ in La_(0.8)Sr0.2Ga_(0.8)Mg_(0.2)O_(3)electrolyte symmetrical cells.Accordingly,anode-supported single cells with a configuration of Ni-Zr_(0.84)Y_(0.16)O_(2-δ)(YSZ)/YSZ/Gd_(0.1)Ce0.9O_(2-δ)/PBCCN0.05 display high electrochemical performance,with a peak power density of 1.81 W·cm^(-2)and a reasonable durability of 100 h at 800℃.PBCCN_(0.05)possesses a higher concentration of oxygen vacancies,a faster oxygen surface adsorption-dissociation rate,and an increased mass ratio of PrCoO_(3) perovskite with Ca and Nb doping compared to PrBa_(0.8)Ca_(0.2)Co_(2)O_(6)-δwithout Nb doping.展开更多
Enhancing oxidation resistance of multicomponent carbides above 2000℃is critical for their thermal protection applications.For this purpose,novel Nb-and Ta-doped(Hf,Zr,Ti)C multicomponent carbides were designed to im...Enhancing oxidation resistance of multicomponent carbides above 2000℃is critical for their thermal protection applications.For this purpose,novel Nb-and Ta-doped(Hf,Zr,Ti)C multicomponent carbides were designed to improve their oxidation resistance at 2500℃.The results demonstrated that Nb and Ta doping reduced the oxidation rate constant by 16.67%and 25.17%,respectively,thereby significantly improving the oxidation resistance of(Hf,Zr,Ti)C.This enhancement was attributed to the changes in oxycarbide composition and distribution within the oxide layer by adding Nb and Ta.Owing to the different oxidation tendencies of the constituent elements,a distinctive structure was formed in which(Hf,Zr)O_(2)served as a skeleton,and various oxycarbides were dispersed throughout the oxide layer.The doped Nb and Ta were retained within oxycarbides,retarding the diffusion of oxygen into the lattice.More importantly,the addition of Nb and Ta reduced the size of oxycarbides,decreasing both size and quantity of the pores in the oxide layer and facilitating the formation of a more effective oxygen barrier.展开更多
基金the financial support from the National Natural Science Foundation of China(S.-Q.Xia:51271098,X.-T.Tao:51321091,T.-J.Zhu:11574267 and 51571177).
文摘Zintl phases with the nominal compositions Ca_(1-δ)Ce_(δ)Ag_(1-δ)Sb(RE=La,Ce,Pr,Nd,Sm;δ≈0.15)are interesting due to their unique crystal structures and potential as high temperature thermoelectrics.Their structures generally feature the LiGaGe type structure with substantial vacancies on the Ag sites.The formation of such defects can be explained by the electronic effects,with which 18 electrons are required to stabilize the CaAgSb Zintl system.Since the substitution of Ca^(2+)with RE^(3+)will lead to electron excess,the formation of Ag defects will be an intrinsic character of such compounds to maintain their electron precise nature.In this work,the material Ca_(0.85)Ce_(0.15)Ag_(0.85)Sb was selected for a detailed study on defect chemistry.In order to better understand the mechanism related to the defect formation and control in this system,we conducted a series of experiments aimed at controlling the point defects in Ca_(0.85)Ce_(0.15)Ag_(0.85)Sb.This strategy was realized by intentionally doping Nb,which resulted in the discovery of a series of low defect density materials Ca_(0.725+x)Nb_(0.1-x)Ce_(0.15)AgSb(0≤x≤0.05).In this work,an interesting defect controlling strategy on Zintl phases was demonstrated,which suggested the high flexibility of Ca_(1-δ)Ce_(δ)Ag_(1-δ)Sb in the optimization of thermoelectric properties.
基金Project(07JJ3102) supported by Hunan Provincial Natural Science Foundation,ChinaProject(k0902132-11) supported by Changsha Municipal Science and Technology,China
文摘Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M （M=Ti, Al） and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAINb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%-12.5% （mole fraction）.
基金supported by the National Natural Science Foundation of China (2169008, 21690084, 21673228, 21303187, 21403218)the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB17020100)+1 种基金DICP ZZBS 201612Key Projects for Fundamental Research and Development of China (2016YFA0202801)~~
文摘Selective hydrogenolysis of glycerol to 1,3‐propanediol（1,3‐PD） is an important yet challenging method for the transformation of biomass into value‐added chemicals due to steric hindrance and unfavorable thermodynamics. In previous studies, chemoselective performances were found de‐manding and sensitive to H2 pressure. In this regard, we manipulate the chemical/physical charac‐teristics of the catalyst supports via doping Nb into WOx and prepared 1D needle‐, 2D flake‐, and 3D sphere‐stack mesoporous structured Nb‐WOx with increased surface acid sites. Moreover, Nb dop‐ing can successfully inhibit the over‐reduction of active W species during glycerol hydrogenolysis and substantially broaden the optimal H2 pressure from 1 to 5 MPa. When Nb doping is 2%, sup‐ported Pt catalysts showed promising performance for the selective hydrogenolysis of glycerol to 1,3‐PD over an unprecedentedly wide H2 pressure range, which will guarantee better catalyst sta‐bility in the long run, as well as expand their applications to other hydrogen‐related reactions.
基金supported by the National Natural Science Foundation of China(grant no.21601148)the Natural Science Foundation of Fujian Province(grant no.2017J05090).
文摘Nb-Doped LiNi_(0.4)Co_(0.2)Mn_(0.4)O_(2)(Nb-NCM)nanobelts have been successfully fabricated for the first time through a facile electrospinning method by the delicate control of PAN pyrolysis and Nb-NCM formation(including nucleation and subsequent growth processes).According to the experimental evidence from temperature-dependent characterization and isolation of the intermediates,the formation of nanobelts undergoes a morphology evolution from nanofibres to nanotubes,and finally to the nanobelts composed of subunit nanoparticles.When used as a cathode for lithium-ion batteries,the as-electrospun Nb-NCM nanobelts exhibit superior electrochemical performances,which could be attributed to their unique features,such as their 1D nanostructure,well-crystallized nature and Nb-doping.These features can improve the ionic conductivity of Nb-NCM nanobelts and stabilize the electrode/electrolyte interface.Therefore,the 1D Nb-NCM nanobelts developed in this study not only provide an excellent model to investigate the fabrication of multi-element oxides using the electrospinning method,but also open up a facile route for designing 1D layered cathodes with a complex component for high performance lithium-ion batteries.
基金supported by the Natural Science Foundation of China(No.21776248 and 21676246)the Zhejiang Provincial Natural Science Foundation of China(No.LR17B060003)supported by the Fundamental Research Funds for the Central Universities.
文摘Developing highly efficient,Earth-abundant,and long-term stable electrocatalysts for the oxygen evolution reaction (OER) is of great importance for realizing industrial hydrogen generation from water splitting.Herein,a series of novel Fe and Nb co-doped β-Ni(OH)_(2)nanosheet arrays were successfully grown in situ on Ni foam via a chlorine etching method.The representative NiFe_(3)Nb_(2)-OH displayed outstanding OER performance with an overpotential of 294 mV to deliver 100 mA cm^(-2) in an alkaline electrolyte,outperforming other Ni related electrocatalysts.NiFe_(3)Nb_(2)-OH exhibited a stability of 90 h without obvious potential change at 50 mA cm^(-2).Significantly,the doped Fe and Nb effectively enhanced the electrochemical active area and electronic transfer capability of β-Ni(OH)_(2).Density functional theory (DFT) calculations indicated that the Gibbs free energy of the OER intermediates on the Fe,Nb co-doped β-Ni(OH)_(2)electrode was optimized.The tuned electronic interactions between Fe,Nb and Ni apparently boosted the OER performance of NiFe_(3)Nb_(2)-OH.These results demonstrated that Fe and Nb co-doped β-Ni(OH)_(2)is a highly efficient OER electrocatalyst in alkaline media.
基金supported by the Introduced Innovative R&D Team of Guangdong(No.2021ZT09L392)the National Natural Science Foundation of China(Nos.22179039 and 22005105)+1 种基金the Pearl River Talent Recruitment Program(No.2019QN01C693)the Natural Science Foundation of Guangdong Province(No.2021A1515010395).
文摘The performance of a solid oxide fuel cell(SOFC)is strongly associated with the activity and durability of the cathode,where the oxygen reduction reaction occurs.In this study,we report our findings in the development of an Nb-doped PrBa_(0.8)Ca_(0.2)Co_(2)O_(6-δ)(PrBa_(0.8)Ca_(0.2)Co_(2-x)Nb_(x)O_(6-δ),x=0,0.025,0.05,and 0.1,denoted as PBCCNx)perovskite composite as the SOFC cathode.Analyses of X-ray diffraction(XRD)patterns and energy-dispersive transmission electron microscopy(TEM-EDS)images suggest that after being treated at 950℃ in air,PBCCN0.05 mainly contains phases of Ca-and Nb-doped PrBaCo2O6-δdouble perovskite,PrCoO_(3) perovskite with Ca and Nb doping,and Ba_(3)Ca_(1.18)Nb_(1.82)O_(9-δ).When evaluated as an SOFC cathode,the PBCCN0.05 mixture has shown a low polarization resistance of 0.0074Ω·cm^(2)at 800℃ in La_(0.8)Sr0.2Ga_(0.8)Mg_(0.2)O_(3)electrolyte symmetrical cells.Accordingly,anode-supported single cells with a configuration of Ni-Zr_(0.84)Y_(0.16)O_(2-δ)(YSZ)/YSZ/Gd_(0.1)Ce0.9O_(2-δ)/PBCCN0.05 display high electrochemical performance,with a peak power density of 1.81 W·cm^(-2)and a reasonable durability of 100 h at 800℃.PBCCN_(0.05)possesses a higher concentration of oxygen vacancies,a faster oxygen surface adsorption-dissociation rate,and an increased mass ratio of PrCoO_(3) perovskite with Ca and Nb doping compared to PrBa_(0.8)Ca_(0.2)Co_(2)O_(6)-δwithout Nb doping.
基金This work was supported by the National Natural Science Foundation of China(No.52072410).
文摘Enhancing oxidation resistance of multicomponent carbides above 2000℃is critical for their thermal protection applications.For this purpose,novel Nb-and Ta-doped(Hf,Zr,Ti)C multicomponent carbides were designed to improve their oxidation resistance at 2500℃.The results demonstrated that Nb and Ta doping reduced the oxidation rate constant by 16.67%and 25.17%,respectively,thereby significantly improving the oxidation resistance of(Hf,Zr,Ti)C.This enhancement was attributed to the changes in oxycarbide composition and distribution within the oxide layer by adding Nb and Ta.Owing to the different oxidation tendencies of the constituent elements,a distinctive structure was formed in which(Hf,Zr)O_(2)served as a skeleton,and various oxycarbides were dispersed throughout the oxide layer.The doped Nb and Ta were retained within oxycarbides,retarding the diffusion of oxygen into the lattice.More importantly,the addition of Nb and Ta reduced the size of oxycarbides,decreasing both size and quantity of the pores in the oxide layer and facilitating the formation of a more effective oxygen barrier.
