Au nanowires in 4H crystalline phase(4H Au NWs)are synthesized by colloid solution methods.The crys-talline phase and surface structure as well as its performance toward electrochemical oxidation of CO be-fore and aft...Au nanowires in 4H crystalline phase(4H Au NWs)are synthesized by colloid solution methods.The crys-talline phase and surface structure as well as its performance toward electrochemical oxidation of CO be-fore and after removing adsorbed oleylamine molecules(OAs)intro-duced from its synthesis are evaluat-ed by high-resolution transmission electron microscopy(HR-TEM),X-ray diffraction(XRD),underpoten-tial deposition of Pb(Pb-upd)and cyclic voltammetry.Different methods,i.e.acetic acid cleaning,electrochemical oxidation cleaning,and diethylamine replacement,have been tried to remove the adsorbed OAs.For all methods,upon the removal of the adsorbed OAs,the morphology of 4H gold nanoparticles is found to gradually change from nanowires to large dumbbell-shaped nanoparticles,accompanying with a transition from the 4H phase to the face-centered cubic phase.On the other hand,the Pb-upd results show that the sample sur-faces have almost the same facet composition before and after removal of the adsorbed OAs.After electrochemical cleaning with continuous potential scans up to 1.3 V,CO electro-oxida-tion activity of the 4H Au sample is significantly improved.The CO electro-oxidation activi-ty is compared with results on the three basel Au single crystalline surfaces reported in the lit-erature,possible origins for its enhancement are discussed.展开更多
The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of mate...The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of materials, e.g., metal cyanides, oxometallates, and metalorganic frameworks, but has not been reported in the family of metal hydrides. Herein, a colossal and continuous negative thermal expansion is firstly developed in the low-temperature phases of LT1-and LT2-Mg_(2)NiH_(4) between 488 K and 733 K from in-situ transmission electron microscope(TEM) video, with the volume contraction reaching 18.7% and 11.3%, respectively. The mechanisms for volume contraction of LT1 and LT2 phases are elucidated from the viewpoints of phase transformation, magnetic transition, and dehydrogenation, which is different from common NTE materials containing flexible polyhedra units in the structure. The linear volume shrinkage of LT2 in the temperature of 488-553 K corresponds to the phase transition of LT2→HT with a thermal expansion coefficient of -799.7 × 10^(-6) K^(-1) revealed by in-situ synchrotron powder X-ray diffraction. The sudden volume contraction in LT1 between 488 and 493 K may be caused by the rapid dehydrogenation of LT1 to Mg_(2)Ni. The revealed phenomenon in single composite material with different structures would be significant for preparing zero thermal expansion materials by tuning the fraction of LT1 and LT2 phases.展开更多
基金supported by the National Natural Science Foundation of China(No.22172151 and 21972131).
文摘Au nanowires in 4H crystalline phase(4H Au NWs)are synthesized by colloid solution methods.The crys-talline phase and surface structure as well as its performance toward electrochemical oxidation of CO be-fore and after removing adsorbed oleylamine molecules(OAs)intro-duced from its synthesis are evaluat-ed by high-resolution transmission electron microscopy(HR-TEM),X-ray diffraction(XRD),underpoten-tial deposition of Pb(Pb-upd)and cyclic voltammetry.Different methods,i.e.acetic acid cleaning,electrochemical oxidation cleaning,and diethylamine replacement,have been tried to remove the adsorbed OAs.For all methods,upon the removal of the adsorbed OAs,the morphology of 4H gold nanoparticles is found to gradually change from nanowires to large dumbbell-shaped nanoparticles,accompanying with a transition from the 4H phase to the face-centered cubic phase.On the other hand,the Pb-upd results show that the sample sur-faces have almost the same facet composition before and after removal of the adsorbed OAs.After electrochemical cleaning with continuous potential scans up to 1.3 V,CO electro-oxida-tion activity of the 4H Au sample is significantly improved.The CO electro-oxidation activi-ty is compared with results on the three basel Au single crystalline surfaces reported in the lit-erature,possible origins for its enhancement are discussed.
基金supported by the National Key Research and Development Program of China (2021YFB3701001)the National Natural Science Foundation of China (51871143)+1 种基金Shanghai Engineering Research Center for Metal Parts Green Remanufacture (No.19DZ2252900) from Shanghai Engineering Research Center Construction ProjectShanghai Rising-Star Program (21QA1403200)。
文摘The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of materials, e.g., metal cyanides, oxometallates, and metalorganic frameworks, but has not been reported in the family of metal hydrides. Herein, a colossal and continuous negative thermal expansion is firstly developed in the low-temperature phases of LT1-and LT2-Mg_(2)NiH_(4) between 488 K and 733 K from in-situ transmission electron microscope(TEM) video, with the volume contraction reaching 18.7% and 11.3%, respectively. The mechanisms for volume contraction of LT1 and LT2 phases are elucidated from the viewpoints of phase transformation, magnetic transition, and dehydrogenation, which is different from common NTE materials containing flexible polyhedra units in the structure. The linear volume shrinkage of LT2 in the temperature of 488-553 K corresponds to the phase transition of LT2→HT with a thermal expansion coefficient of -799.7 × 10^(-6) K^(-1) revealed by in-situ synchrotron powder X-ray diffraction. The sudden volume contraction in LT1 between 488 and 493 K may be caused by the rapid dehydrogenation of LT1 to Mg_(2)Ni. The revealed phenomenon in single composite material with different structures would be significant for preparing zero thermal expansion materials by tuning the fraction of LT1 and LT2 phases.
