Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potential...Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potentials from 0.6 V to 1.0 V （vs. RHE） with the exchange current density of ca. 50 mA/cm^2 at 0.8 V, the fast kinetics of OHad desorption indicates that it should not be the rate determining step for ORR. In the kineticor kinetic-mass transport mix controlled potential region, ORR current at constant potential displays slight decrease with reaction time. ORR current in the positive-going potential scan is slightly larger than that in the subsequent negative-going scan with electrode rotation speed （〉800 r/min） and slow potential scan rate （〈100 mV/s）. The open circuit potential of Pt/0.1 mol/L HClO4 interface increases promptly from 0.9 V to 1.0 V after switch from O2 free- to O2-saturated solution. The increase of open circuit potential as well as ORR current decays under potential control due to the accumulation of OHad from dissociative adsorption of O2. It indicates that at Pt（111） the net rate for O2 decomposition to OHad is slightly faster than that for OHad removal, one cannot simply use the assumption of rate determining step to discuss ORR kinetics. Instead, the ORR kinetics is determined by both the kinetics for O2 decomposition to OHad as well as the thermo-equilibrium of OHad＋H^＋＋e→←H2O.展开更多
Nb-doped TiAl alloys exhibit excellent mechanical properties at high temperatures,and the underlying mechanism and optimal doping amount remain elusive.Molecular dynamics simulation is helpful to clarify these problem...Nb-doped TiAl alloys exhibit excellent mechanical properties at high temperatures,and the underlying mechanism and optimal doping amount remain elusive.Molecular dynamics simulation is helpful to clarify these problems,but most of the existing interatomic potentials are limited to the Ti-Al binary system and lack interatomic potentials for doped alloys.Here,an intera-tomic potential of Nb-Al-Ti ternary systems based on the modified embedded-atom method was developed.The ternary potential can accurately predict the structure and thermodynamic properties of the Nb-Al-Ti system.The potential shows that the optimal Nb content for high-temperature strength-ductility synergy of TiAl single crystals is 8%,consistent with the amount of miracle synthesis of TiAl single crystals.Tensile simulations further show that the developed potential can make an effective prediction at high temperatures,indicating the potential for the development and applications of high-temperature Nb-Al-Ti ternary systems.展开更多
基金V. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.20773116）, the National Instrumentation Program （No.2011YQ03012416）, and 973 Program from the Ministry of Science and Technology of China （No.2010CB923302）.
文摘Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potentials from 0.6 V to 1.0 V （vs. RHE） with the exchange current density of ca. 50 mA/cm^2 at 0.8 V, the fast kinetics of OHad desorption indicates that it should not be the rate determining step for ORR. In the kineticor kinetic-mass transport mix controlled potential region, ORR current at constant potential displays slight decrease with reaction time. ORR current in the positive-going potential scan is slightly larger than that in the subsequent negative-going scan with electrode rotation speed （〉800 r/min） and slow potential scan rate （〈100 mV/s）. The open circuit potential of Pt/0.1 mol/L HClO4 interface increases promptly from 0.9 V to 1.0 V after switch from O2 free- to O2-saturated solution. The increase of open circuit potential as well as ORR current decays under potential control due to the accumulation of OHad from dissociative adsorption of O2. It indicates that at Pt（111） the net rate for O2 decomposition to OHad is slightly faster than that for OHad removal, one cannot simply use the assumption of rate determining step to discuss ORR kinetics. Instead, the ORR kinetics is determined by both the kinetics for O2 decomposition to OHad as well as the thermo-equilibrium of OHad＋H^＋＋e→←H2O.
基金the National Key Research and Development Program of China(Grant No.2019YF40705400)National Natural Science Foundation of China(Grant Nos.51535005,51731006,and 51771093)+2 种基金the Research Fund of State Key Laboratory of Mechanics and Control of Me-chanical Structures(Grant Nos.MCMS-I-0418K01,MCMS-I-0419K01)the Fundamental Research Funds for the Central Universities(Grant Nos.NZ2020001,NC2018001,NP2019301,NJ20I 9002,and 30919011295)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Nb-doped TiAl alloys exhibit excellent mechanical properties at high temperatures,and the underlying mechanism and optimal doping amount remain elusive.Molecular dynamics simulation is helpful to clarify these problems,but most of the existing interatomic potentials are limited to the Ti-Al binary system and lack interatomic potentials for doped alloys.Here,an intera-tomic potential of Nb-Al-Ti ternary systems based on the modified embedded-atom method was developed.The ternary potential can accurately predict the structure and thermodynamic properties of the Nb-Al-Ti system.The potential shows that the optimal Nb content for high-temperature strength-ductility synergy of TiAl single crystals is 8%,consistent with the amount of miracle synthesis of TiAl single crystals.Tensile simulations further show that the developed potential can make an effective prediction at high temperatures,indicating the potential for the development and applications of high-temperature Nb-Al-Ti ternary systems.
