A new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide（AAO） template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano...A new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide（AAO） template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano-particles are nucleated along the AAO pipe wall together with the formation of MgO and Mg17Al12 as byproducts. The flow rate of argon gas, the temperature of the AAO template and the transporting distance between the Mg vapour source and the AAO template were optimized to achieve the confinement of Mg nano-particles with larger loading rate. Under optimized deposition conditions, the particle size of the loaded Mg is less than 100 nm and the effective filling factor is about 35 wt%. The confined Mg/MgH2 even after 10 de-/hydrogenation cycles still shows favourable kinetics. Furthermore, the slight reduction in hydrogen desorption enthalpy and entropy of MgH2 from（74.42 ± 0.12） to（73.21 ± 0.04） k J·mol^-1 and（130.98 ±0.05） to（130.11 ± 0.24） Jámol^-1·K^-1 is also found in the present nano-confinement.展开更多
Efficient technical strategies to synthesize hydrides with high capacity and favorable reversibility are significant for the development of novel energy materials.Herein,nano Mg-based borohydride,Mg(BH_(4))_(2),with r...Efficient technical strategies to synthesize hydrides with high capacity and favorable reversibility are significant for the development of novel energy materials.Herein,nano Mg-based borohydride,Mg(BH_(4))_(2),with robust architecture was designed and prepared by confining on graphene through a solution selfconfinement method.The Mg(BH_(4))_(2) confined on graphene displays a wrinkled 2D nano layer morphology within 8.8 nm thickness.Such 2D nano Mg(BH_(4))_(2) can start dehydrogenation at 67.9℃ with a high capacity of 12.0 wt.%,which is 190.5℃ lower than pristine Mg(BH_(4))_(2).The isothermal dehydrogenation tests and kinetics fitting results indicate the 2D nano Mg(BH_(4))_(2) possesses much-enhanced dehydrogenation kinetics of 31.3 kJ/mol activation energy,which is only half of pristine Mg(BH_(4))_(2).The thermodynamics of the 2D nano Mg(BH_(4))_(2) is also verified by PCT tests,of which Gibbs free energy value for the confined 2D nano Mg(BH_(4))_(2) is estimated to be-18.01 kJ/mol H_(2),lower than-16.36 kJ/mol H_(2) of pristine Mg(BH_(4))_(2).Importantly,the reversibility of the confined 2D nano Mg(BH_(4))_(2) is significantly enhanced to over 90%capacity retention with relatively kinetics stability during 10 cycles.The mechanism analyses manifest that Mg(BH_(4))_(2) exhibits stable 2D nano morphology during 10 cyclic tests,resulting in the greatly reduced H diffusion path and the improved de/rehydrogenation kinetics of the 2D nano Mg(BH_(4))_(2).Based on theoretical calculations of Mg(BH_(4))_(2) and the intermediate MgB12H12 confined on graphene,the charge transfer status of both samples is modified to facilitate de/rehydrogenation,thus leading to the significant thermodynamic improvements of the reversible hydrogen storage performances for 2D nano Mg(BH_(4))_(2).Such investigation of the Mg-based borohydride will illuminate prospective technical research of energy storage materials.展开更多
Hydrogen holds the advantages of high energy density,great natural abundance and zero emission,making it suitable for large scale and long term energy storage,while its safe and efficient storage is still challenging....Hydrogen holds the advantages of high energy density,great natural abundance and zero emission,making it suitable for large scale and long term energy storage,while its safe and efficient storage is still challenging.Among various solid state hydrogen storage materials,MgH_(2) is promising for industrial applications due to its high gravimetric and volumetric hydrogen densities and the abundance of Mg on earth.However,the practical application of MgH_(2) has been limited by its stable thermodynamics and slow hydrogen desorption kinetics.Nanocatalysis is considered as a promising approach for improving the hydrogen storage performance of MgH_(2) and bringing it closer to the requirements of commercial applications.It is worth mentioning that the recently emerging two-dimensional material,MXene,has showcased exceptional catalytic abilities in modifying the hydrogen storage properties of MgH_(2).Besides,MXene possesses a high surface area,excellent chemical/physical stability,and negatively charged terminating groups,making it an ideal support for the"nanoconfinement"of MgH_(2) or highly active catalysts.Herein,we endeavor to provide a comprehensive overview of recent investigations on MXene-based catalysts and MXene supports for improving the hydrogen sorption properties of Mg/MgH_(2).The mechanisms of hydrogen sorption involved in Mg-MXene based composites are highlighted with special emphases on thermodynamics,kinetics,and catalytic behaviors.The aim of this work is to provide a comprehensive and objective review of researches on the development of high-performance catalysts/supports to improve hydrogen storage performances of Mg/MgH_(2) and to identify the opportunities and challenges for future applications.展开更多
Carbon has been widely utilized as electrode in electrochemical energy storage,relying on the interaction between ions and electrode.The performance of a carbon electrode is determined by a variety of factors includin...Carbon has been widely utilized as electrode in electrochemical energy storage,relying on the interaction between ions and electrode.The performance of a carbon electrode is determined by a variety of factors including the structural features of carbon material and the behavior of ions adsorbed on the carbon surface in the specific environment.As the fundamental unit of graphitic carbons,graphene has been employed as a model to understand the energy storage mechanism of carbon materials through various experimental and computational methods,ex‐situ or in‐situ.In this article,we provide a succinct overview of the state‐of‐the‐art proceedings on the ion storage mechanism on graphene.Topics include the structure engineering of carbons,electric gating effect of ions,ion dynamics on the interface or in the confined space,and specifically lithium‐ion storage/reaction on graphene.Our aim is to facilitate the understanding of electrochemistry on carbon electrodes.展开更多
Molecular dynamics simulations have been used to investigate the confinement packing characteristics of small hydrophilic （N-acetyl-glycine-methylamide, Nagma） and hydrophobic （N-acetyl-leucine-methylamide, Nalma）...Molecular dynamics simulations have been used to investigate the confinement packing characteristics of small hydrophilic （N-acetyl-glycine-methylamide, Nagma） and hydrophobic （N-acetyl-leucine-methylamide, Nalma） biomolecules in large diameter single-wall carbon nanotubes （SWCNTs）. We find that hydrophilic biomolecules easily fill the nanotube and self organize into a geometrical configuration which reminds the water structural organization under SWCNT confinement. The packing of hydrophilic biomolecules inside the cylinder confines all water molecules in its core, which enhances their mobility. Conversely, hydrophobic biomolecules accommodate into the nanotubes with a trend for homogeneous filling, which generate unstable small pockets of water and drive toward a state of dehydration. These results shed light on key parameters important for the encapsulation of biomolecules with direct relevance for long-term storage and prevention of degradation.展开更多
We describe the synthesis of even-dispersed palladium nanoparticles(Pd NPs)confined within a cellulose nanofiber(CNF)matrix for developing a high-performance and recyclable catalyst.The CNF matrix was composed of CNF-...We describe the synthesis of even-dispersed palladium nanoparticles(Pd NPs)confined within a cellulose nanofiber(CNF)matrix for developing a high-performance and recyclable catalyst.The CNF matrix was composed of CNF-assembled mesoporous nanosheets and appeared as soft and hydrophilic foam.Ultrafine Pd NPs(∼6 nm)with high-loading(9.6 wt%)were in situ grown on these mesoporous nanosheets,and their dense spatial distributions were likely to generate nano-confinement catalytic effects on the reactants.Consequently,the CNF-confined Pd NPs(CNF-Pd)exhibited an enhanced room-temperature catalytic activity on the model reaction of 4-nitrophenol hydrogenation with a highest rate constant of 8.8×10^−3 s^−1 and turnover frequency of 2640 h The CNF Pd catalyst possessed good chemical stability and recyclability in aqueous media which could be reused for at least six cycles without losing activity.Moreover,chemoselective reduction of 3 nitrostyrene was achieved with high yield(80%–98%)of 3-aminostyrene in alcohol/water cosolvent.Overall,this work demonstrates a positive nanoconfinement effect of CNFs for developing stable and recyclable metal NP catalysts.展开更多
An essential technology of carbon capture, utilization and storage-enhanced oil recovery (CCUS-EOR) for tight oil reservoirs is CO_(2) huff-puff followed by associated produced gas reinjection. In this paper, the effe...An essential technology of carbon capture, utilization and storage-enhanced oil recovery (CCUS-EOR) for tight oil reservoirs is CO_(2) huff-puff followed by associated produced gas reinjection. In this paper, the effects of multi-component gas on the properties and components of tight oil are studied. First, the core displacement experiments using the CH_(4)/CO_(2) multi-component gas are conducted to determine the oil displacement efficiency under different CO_(2) and CH_(4) ratios. Then, a viscometer and a liquid density balance are used to investigate the change characteristics of oil viscosity and density after multi-component gas displacement with different CO_(2) and CH_(4) ratios. In addition, a laboratory scale numerical model is established to validate the experimental results. Finally, a composition model of multi-stage fractured horizontal well in tight oil reservoir considering nano-confinement effects is established to investigate the effects of multi-component gas on the components of produced dead oil and formation crude oil. The experimental results show that the oil displacement efficiency of multi-component gas displacement is greater than that of single-component gas displacement. The CH_(4) decreases the viscosity and density of light oil, while CO_(2) decreases the viscosity but increases the density. And the numerical simulation results show that CO_(2) extracts more heavy components from the liquid phase into the vapor phase, while CH_(4) extracts more light components from the liquid phase into the vapor phase during cyclic gas injection. The multi-component gas can extract both the light components and the heavy components from oil, and the balanced production of each component can be achieved by using multi-component gas huff-puff.展开更多
The presence of a capillary bridge between solid surfaces is ubiquitous under ambient conditions.Usually,it leads to a continuous decrease of friction as a function of bridge height.Here,using molecular dynamics we sh...The presence of a capillary bridge between solid surfaces is ubiquitous under ambient conditions.Usually,it leads to a continuous decrease of friction as a function of bridge height.Here,using molecular dynamics we show that for a capillary bridge with a small radius confined between two hydrophilic elastic solid surfaces,the friction oscillates greatly when decreasing the bridge height.The underlying mechanism is revealed to be a periodic ordered-disordered transition at the liquid–solid interfaces.This transition is caused by the balance between the surface tension of the liquid–vapor interface and the elasticity of the surface.This balance introduces a critical size below which the friction oscillates.Based on the mechanism revealed,a parameter-free analytical model for the oscillating friction was derived and found to be in excellent agreement with the simulation results.Our results describe an interesting frictional phenomenon at the nanoscale,which is most prominent for layered materials.展开更多
基金financially supported by the Ministry of Science and Technology under Project of ‘‘Key Fundamental Research on Novel High-Capacity Hydrogen Storage Materials’’ (No. 2010CB631302)the National Natural Science Foundation of China (No. 50971061)
文摘A new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide（AAO） template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano-particles are nucleated along the AAO pipe wall together with the formation of MgO and Mg17Al12 as byproducts. The flow rate of argon gas, the temperature of the AAO template and the transporting distance between the Mg vapour source and the AAO template were optimized to achieve the confinement of Mg nano-particles with larger loading rate. Under optimized deposition conditions, the particle size of the loaded Mg is less than 100 nm and the effective filling factor is about 35 wt%. The confined Mg/MgH2 even after 10 de-/hydrogenation cycles still shows favourable kinetics. Furthermore, the slight reduction in hydrogen desorption enthalpy and entropy of MgH2 from（74.42 ± 0.12） to（73.21 ± 0.04） k J·mol^-1 and（130.98 ±0.05） to（130.11 ± 0.24） Jámol^-1·K^-1 is also found in the present nano-confinement.
基金supported by the National Natural Science Foundation of China(Nos.52171223 and U20A20237)the Zhejiang Provincial Natural Science Foundation of China(No.LZ21E010002).
文摘Efficient technical strategies to synthesize hydrides with high capacity and favorable reversibility are significant for the development of novel energy materials.Herein,nano Mg-based borohydride,Mg(BH_(4))_(2),with robust architecture was designed and prepared by confining on graphene through a solution selfconfinement method.The Mg(BH_(4))_(2) confined on graphene displays a wrinkled 2D nano layer morphology within 8.8 nm thickness.Such 2D nano Mg(BH_(4))_(2) can start dehydrogenation at 67.9℃ with a high capacity of 12.0 wt.%,which is 190.5℃ lower than pristine Mg(BH_(4))_(2).The isothermal dehydrogenation tests and kinetics fitting results indicate the 2D nano Mg(BH_(4))_(2) possesses much-enhanced dehydrogenation kinetics of 31.3 kJ/mol activation energy,which is only half of pristine Mg(BH_(4))_(2).The thermodynamics of the 2D nano Mg(BH_(4))_(2) is also verified by PCT tests,of which Gibbs free energy value for the confined 2D nano Mg(BH_(4))_(2) is estimated to be-18.01 kJ/mol H_(2),lower than-16.36 kJ/mol H_(2) of pristine Mg(BH_(4))_(2).Importantly,the reversibility of the confined 2D nano Mg(BH_(4))_(2) is significantly enhanced to over 90%capacity retention with relatively kinetics stability during 10 cycles.The mechanism analyses manifest that Mg(BH_(4))_(2) exhibits stable 2D nano morphology during 10 cyclic tests,resulting in the greatly reduced H diffusion path and the improved de/rehydrogenation kinetics of the 2D nano Mg(BH_(4))_(2).Based on theoretical calculations of Mg(BH_(4))_(2) and the intermediate MgB12H12 confined on graphene,the charge transfer status of both samples is modified to facilitate de/rehydrogenation,thus leading to the significant thermodynamic improvements of the reversible hydrogen storage performances for 2D nano Mg(BH_(4))_(2).Such investigation of the Mg-based borohydride will illuminate prospective technical research of energy storage materials.
基金the support from the National Natural Science Foundation(No.52171186)National Key Research&Development Program(2022YFB3803700)of China.
文摘Hydrogen holds the advantages of high energy density,great natural abundance and zero emission,making it suitable for large scale and long term energy storage,while its safe and efficient storage is still challenging.Among various solid state hydrogen storage materials,MgH_(2) is promising for industrial applications due to its high gravimetric and volumetric hydrogen densities and the abundance of Mg on earth.However,the practical application of MgH_(2) has been limited by its stable thermodynamics and slow hydrogen desorption kinetics.Nanocatalysis is considered as a promising approach for improving the hydrogen storage performance of MgH_(2) and bringing it closer to the requirements of commercial applications.It is worth mentioning that the recently emerging two-dimensional material,MXene,has showcased exceptional catalytic abilities in modifying the hydrogen storage properties of MgH_(2).Besides,MXene possesses a high surface area,excellent chemical/physical stability,and negatively charged terminating groups,making it an ideal support for the"nanoconfinement"of MgH_(2) or highly active catalysts.Herein,we endeavor to provide a comprehensive overview of recent investigations on MXene-based catalysts and MXene supports for improving the hydrogen sorption properties of Mg/MgH_(2).The mechanisms of hydrogen sorption involved in Mg-MXene based composites are highlighted with special emphases on thermodynamics,kinetics,and catalytic behaviors.The aim of this work is to provide a comprehensive and objective review of researches on the development of high-performance catalysts/supports to improve hydrogen storage performances of Mg/MgH_(2) and to identify the opportunities and challenges for future applications.
基金National Key Research and Development Program of China,Grant/Award Number:2020YFA0711502National Natural Science Foundation of China,Grant/Award Numbers:52273234,52273239,52325202。
文摘Carbon has been widely utilized as electrode in electrochemical energy storage,relying on the interaction between ions and electrode.The performance of a carbon electrode is determined by a variety of factors including the structural features of carbon material and the behavior of ions adsorbed on the carbon surface in the specific environment.As the fundamental unit of graphitic carbons,graphene has been employed as a model to understand the energy storage mechanism of carbon materials through various experimental and computational methods,ex‐situ or in‐situ.In this article,we provide a succinct overview of the state‐of‐the‐art proceedings on the ion storage mechanism on graphene.Topics include the structure engineering of carbons,electric gating effect of ions,ion dynamics on the interface or in the confined space,and specifically lithium‐ion storage/reaction on graphene.Our aim is to facilitate the understanding of electrochemistry on carbon electrodes.
文摘Molecular dynamics simulations have been used to investigate the confinement packing characteristics of small hydrophilic （N-acetyl-glycine-methylamide, Nagma） and hydrophobic （N-acetyl-leucine-methylamide, Nalma） biomolecules in large diameter single-wall carbon nanotubes （SWCNTs）. We find that hydrophilic biomolecules easily fill the nanotube and self organize into a geometrical configuration which reminds the water structural organization under SWCNT confinement. The packing of hydrophilic biomolecules inside the cylinder confines all water molecules in its core, which enhances their mobility. Conversely, hydrophobic biomolecules accommodate into the nanotubes with a trend for homogeneous filling, which generate unstable small pockets of water and drive toward a state of dehydration. These results shed light on key parameters important for the encapsulation of biomolecules with direct relevance for long-term storage and prevention of degradation.
基金the National Natural Science Foundation of China(31925028 and 31670583)the Special Project for Double First-Class-Cultivation of Innovative Talents(000/41113102)。
文摘We describe the synthesis of even-dispersed palladium nanoparticles(Pd NPs)confined within a cellulose nanofiber(CNF)matrix for developing a high-performance and recyclable catalyst.The CNF matrix was composed of CNF-assembled mesoporous nanosheets and appeared as soft and hydrophilic foam.Ultrafine Pd NPs(∼6 nm)with high-loading(9.6 wt%)were in situ grown on these mesoporous nanosheets,and their dense spatial distributions were likely to generate nano-confinement catalytic effects on the reactants.Consequently,the CNF-confined Pd NPs(CNF-Pd)exhibited an enhanced room-temperature catalytic activity on the model reaction of 4-nitrophenol hydrogenation with a highest rate constant of 8.8×10^−3 s^−1 and turnover frequency of 2640 h The CNF Pd catalyst possessed good chemical stability and recyclability in aqueous media which could be reused for at least six cycles without losing activity.Moreover,chemoselective reduction of 3 nitrostyrene was achieved with high yield(80%–98%)of 3-aminostyrene in alcohol/water cosolvent.Overall,this work demonstrates a positive nanoconfinement effect of CNFs for developing stable and recyclable metal NP catalysts.
基金supported by the National Natural Science Foundation of China(No.52174038 and No.52004307)China Petroleum Science and Technology Project-major project-Research on tight oil-shale oil reservoir engineering methods and key technologies in Ordos Basin(ZLZX2020-02-04)Science Foundation of China University of Petroleum,Beijing(No.2462018YJRC015).
文摘An essential technology of carbon capture, utilization and storage-enhanced oil recovery (CCUS-EOR) for tight oil reservoirs is CO_(2) huff-puff followed by associated produced gas reinjection. In this paper, the effects of multi-component gas on the properties and components of tight oil are studied. First, the core displacement experiments using the CH_(4)/CO_(2) multi-component gas are conducted to determine the oil displacement efficiency under different CO_(2) and CH_(4) ratios. Then, a viscometer and a liquid density balance are used to investigate the change characteristics of oil viscosity and density after multi-component gas displacement with different CO_(2) and CH_(4) ratios. In addition, a laboratory scale numerical model is established to validate the experimental results. Finally, a composition model of multi-stage fractured horizontal well in tight oil reservoir considering nano-confinement effects is established to investigate the effects of multi-component gas on the components of produced dead oil and formation crude oil. The experimental results show that the oil displacement efficiency of multi-component gas displacement is greater than that of single-component gas displacement. The CH_(4) decreases the viscosity and density of light oil, while CO_(2) decreases the viscosity but increases the density. And the numerical simulation results show that CO_(2) extracts more heavy components from the liquid phase into the vapor phase, while CH_(4) extracts more light components from the liquid phase into the vapor phase during cyclic gas injection. The multi-component gas can extract both the light components and the heavy components from oil, and the balanced production of each component can be achieved by using multi-component gas huff-puff.
文摘The presence of a capillary bridge between solid surfaces is ubiquitous under ambient conditions.Usually,it leads to a continuous decrease of friction as a function of bridge height.Here,using molecular dynamics we show that for a capillary bridge with a small radius confined between two hydrophilic elastic solid surfaces,the friction oscillates greatly when decreasing the bridge height.The underlying mechanism is revealed to be a periodic ordered-disordered transition at the liquid–solid interfaces.This transition is caused by the balance between the surface tension of the liquid–vapor interface and the elasticity of the surface.This balance introduces a critical size below which the friction oscillates.Based on the mechanism revealed,a parameter-free analytical model for the oscillating friction was derived and found to be in excellent agreement with the simulation results.Our results describe an interesting frictional phenomenon at the nanoscale,which is most prominent for layered materials.
