SnO2 is a promising material for both Li-ion and Na-ion batteries owing to its high theoretical capacities. Unfortunately, the electrochemical performance of SnO2 is unsatisfactory because of the large volume change t...SnO2 is a promising material for both Li-ion and Na-ion batteries owing to its high theoretical capacities. Unfortunately, the electrochemical performance of SnO2 is unsatisfactory because of the large volume change that occurs during cycling, low electronic conductivity of inactive oxide matrix, and poor kinetics, which are particularly severe in Na-ion batteries. Herein, ultra-fine SnO2 nanocrystals anchored on a unique three-dimensional （3D） porous reduced graphene oxide （rGO） matrix are described as promising bifunctional electrodes for Li-ion and Na-ion batteries with excellent rate capability and long cycle life. Ultra-fine SnO2 nanocrystals of size -6 nm are well-coordinated to the graphene sheets that comprise the 3D macro-porous structure. Notably, superior rate capability was obtained up to 3 C （1In C is a measure of the rate that allows the cell to be charged/discharged in n h） for both batteries. In situ X-ray diffractometry measurements during lithiation （or sodiation） and delithiation （or desodiation） were combined with various electrochemical techniques to reveal the real-time phase evolution. This critical information was linked with the internal resistance, ion diffusivity （DLi＋ and DNa＋）, and the unique structure of the composite electrode materials to explain their excellent electrochemical performance. The improved capacity and superior rate capabilities demonstrated in this work can be ascribed to the enhanced transport kinetics of both electrons and ions within the electrode structure because of the well-interconnected, 3D macro-porous rGO matrix. The porous rGO matrix appears to play a more important role in sodium-ion batteries （SIBs）, where the larger mass/radius of Na-ions are marked concerns.展开更多
Understanding of fundamental processes and prediction of optimal parameters during the horizontal drilling and hydraulic fracturing process results in economically effective improvement of oil and natural gas extracti...Understanding of fundamental processes and prediction of optimal parameters during the horizontal drilling and hydraulic fracturing process results in economically effective improvement of oil and natural gas extraction. Although modern analytical and computational models can capture fracture growth, there is a lack of experimental data on spontaneous imbibition and wettability in oil and gas reservoirs for the validation of further model development. In this work, we used neutron im- aging to measure the spontaneous imbibition of water into fractures of Eagle Ford shale with known geometries and fracture orientations. An analytical solution for a set of nonlinear second-order diffe- rential equations was applied to the measured imbibition data to determine effective contact angles. The analytical solution fit the measured imbibition data reasonably well and determined effective con- tact angles that were slightly higher than static contact angles due to effects of in-situ changes in veloci- ty, surface roughness, and heterogeneity of mineral surfaces on the fracture surface. Additionally, small fracture widths may have retarded imbibition and affected model fits, which suggests that aver- age fracture widths are not satisfactory for modeling imbibition in natural systems.展开更多
文摘SnO2 is a promising material for both Li-ion and Na-ion batteries owing to its high theoretical capacities. Unfortunately, the electrochemical performance of SnO2 is unsatisfactory because of the large volume change that occurs during cycling, low electronic conductivity of inactive oxide matrix, and poor kinetics, which are particularly severe in Na-ion batteries. Herein, ultra-fine SnO2 nanocrystals anchored on a unique three-dimensional （3D） porous reduced graphene oxide （rGO） matrix are described as promising bifunctional electrodes for Li-ion and Na-ion batteries with excellent rate capability and long cycle life. Ultra-fine SnO2 nanocrystals of size -6 nm are well-coordinated to the graphene sheets that comprise the 3D macro-porous structure. Notably, superior rate capability was obtained up to 3 C （1In C is a measure of the rate that allows the cell to be charged/discharged in n h） for both batteries. In situ X-ray diffractometry measurements during lithiation （or sodiation） and delithiation （or desodiation） were combined with various electrochemical techniques to reveal the real-time phase evolution. This critical information was linked with the internal resistance, ion diffusivity （DLi＋ and DNa＋）, and the unique structure of the composite electrode materials to explain their excellent electrochemical performance. The improved capacity and superior rate capabilities demonstrated in this work can be ascribed to the enhanced transport kinetics of both electrons and ions within the electrode structure because of the well-interconnected, 3D macro-porous rGO matrix. The porous rGO matrix appears to play a more important role in sodium-ion batteries （SIBs）, where the larger mass/radius of Na-ions are marked concerns.
基金supported as part of the Center for Nanoscale Controls on Geologic CO_2 (NCGC)an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (No. DE-AC0205CH11231)+2 种基金a graduate fellowship through the Bredesen Center for Interdisciplinary Research at the University of Tennesseesupported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences DivisionEdmund Perfect ’s research was sponsored by the Army Research Laboratory (No.W911NF-16-1-0043)
文摘Understanding of fundamental processes and prediction of optimal parameters during the horizontal drilling and hydraulic fracturing process results in economically effective improvement of oil and natural gas extraction. Although modern analytical and computational models can capture fracture growth, there is a lack of experimental data on spontaneous imbibition and wettability in oil and gas reservoirs for the validation of further model development. In this work, we used neutron im- aging to measure the spontaneous imbibition of water into fractures of Eagle Ford shale with known geometries and fracture orientations. An analytical solution for a set of nonlinear second-order diffe- rential equations was applied to the measured imbibition data to determine effective contact angles. The analytical solution fit the measured imbibition data reasonably well and determined effective con- tact angles that were slightly higher than static contact angles due to effects of in-situ changes in veloci- ty, surface roughness, and heterogeneity of mineral surfaces on the fracture surface. Additionally, small fracture widths may have retarded imbibition and affected model fits, which suggests that aver- age fracture widths are not satisfactory for modeling imbibition in natural systems.
