Zero-carbon parks have broad prospects in carbon neutralization.As an energy hub,hydrogen energy storage plays an important role in zero-carbon parks.However,the nonlinear characteristics of hydrogen energy storage sy...Zero-carbon parks have broad prospects in carbon neutralization.As an energy hub,hydrogen energy storage plays an important role in zero-carbon parks.However,the nonlinear characteristics of hydrogen energy storage systems(HESSs)have a significant impact on the system economy.Therefore,considering the variable working condition characteristics of HESSs,a hybrid operation method is proposed for HESS,to support the efficient and economic operation of zero-carbon parks,By analyzing the operating principle of a zero-carbon park with HESS,the system structure framework and variable condition linearization model of the equipment in HESS are established.Moreover,considering the energy output characteristics of hydrogen energy storage equipment under variable working conditions,a multimodule hybrid operation strategy is proposed for electrolytic and fuel cells,effectively meeting the thermoelectric load demand of zero-carbon parks in different scenarios.Finally,the economy of the proposed hybrid operation strategy was verified in typical scenarios,using a zero-carbon park embedded with a HESS.展开更多
By collecting and organizing historical data and typical model characteristics,hydrogen energy storage system(HESS)-based power-to-gas(P2G)and gas-to-power systems are developed using Simulink.The energy transfer mech...By collecting and organizing historical data and typical model characteristics,hydrogen energy storage system(HESS)-based power-to-gas(P2G)and gas-to-power systems are developed using Simulink.The energy transfer mechanisms and numerical modeling methods of the proposed systems are studied in detail.The proposed integrated HESS model covers the following system components:alkaline electrolyzer(AE),highpressure hydrogen storage tank with compressor(CM&H_(2) tank),and proton-exchange membrane fuel cell(PEMFC)stack.The unit models in the HESS are established based on typical U-I curves and equivalent circuit models,which are used to analyze the operating characteristics and charging/discharging behaviors of a typical AE,an ideal CM&H_(2) tank,and a PEMFC stack.The validities of these models are simulated and verified in the MicroGrid system,which is equipped with a wind power generation system,a photovoltaic power generation system,and an auxiliary battery energy storage system(BESS)unit.Simulation results in MATLAB/Simulink show that electrolyzer stack,fuel cell stack and system integration model can operate in different cases.By testing the simulation results of the HESS under different working conditions,the hydrogen production flow,stack voltage,state of charge(SOC)of the BESS,state of hydrogen pressure(SOHP)of the HESS,and HESS energy flow paths are analyzed.The simulation results are consistent with expectations,showing that the integrated HESS model can effectively absorb wind and photovoltaic power.As the wind and photovoltaic power generations increase,the HESS current increases,thereby increasing the amount of hydrogen production to absorb the surplus power.The results show that the HESS responds faster than the traditional BESS in the microgrid,providing a solid theoretical foundation for later wind-photovoltaic-HESS-BESS integration.展开更多
In this paper,a typical-operation-curve generation method of a hydrogen energy storage system operating under the mode of stabilizing wind power fluctuations is proposed.This method is used to optimize the power and c...In this paper,a typical-operation-curve generation method of a hydrogen energy storage system operating under the mode of stabilizing wind power fluctuations is proposed.This method is used to optimize the power and capacity configuration of the energy storage system.The time series curves of the charging and discharging powers of the hydrogen energy storage are obtained by EMD decomposition,and the curves are classified according to the similarities and differences of the characteristic parameters in different time periods.After the classification,typical charging and discharging power values of each type of curve at each moment are obtained by a cloud model,and then,typical operation curves of each type are obtained by integration.On this basis,the power and capacity of the energy storage system are optimized with the objective of economic optimization through the MATLAB CPLEX toolbox.Combined with the measured data of a wind farm with an installed capacity of 400 MW in Northeast China,the validity and rationality of the typical operation curve generation method proposed in this paper are verified.展开更多
Nanocrystalline and amorphous LaMg_（12）-type LaMg_（11）Ni ＋ x wt% Ni（x = 100, 200） alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydroge...Nanocrystalline and amorphous LaMg_（12）-type LaMg_（11）Ni ＋ x wt% Ni（x = 100, 200） alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydrogen storage kinetics of as-milled alloys were investigated systematically. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. And the gaseous hydrogen storage properties were investigated by Sievert apparatus and a differential scanning calorimeter（DSC） connected with a H_2 detector. Hydrogen desorption activation energy of alloy hydrides was estimated by using Arrhenius and Kissinger methods. It is found that the increase of Ni content significantly improves the gaseous and electrochemical hydrogen storage kinetic performances of as-milled alloys. Furthermore, as ball milling time changes, the maximum of both high rate discharge ability（HRD） and the gaseous hydriding rate of as-milled alloys can be obtained. But the hydrogen desorption kinetics of alloys always increases with the extending of milling time. Moreover, the improved gaseous hydrogen storage kinetics of alloys are ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and milling time.展开更多
Energy storage is an effective way to address the instability of renewable energy generation modes,such as wind and solar,which are projected to play an important role in the sustainable and low-carbon society.Economi...Energy storage is an effective way to address the instability of renewable energy generation modes,such as wind and solar,which are projected to play an important role in the sustainable and low-carbon society.Economics and carbon emissions are important indicators that should be thoroughly considered for evaluating the feasibility of energy storage technologies(ESTs).In this study,we study two promising routes for large-scale renewable energy storage,electrochemical energy storage(EES)and hydrogen energy storage(HES),via technical analysis of the ESTs.The levelized cost of storage(LCOS),carbon emissions and uncertainty assessments for EESs and HESs over the life cycle are conducted with full consideration of the critical links for these routes.In order to reduce the evaluation error,we use the Monte Carlo method to derive a large number of data for estimating the economy and carbon emission level of ESTs based on the collected data.The results show that lithium ion(Li-ion)batteries show the lowest LCOS and carbon emissions,at 0.314 US$kWh-1 and 72.76 g CO_(2) e kWh^(-1),compared with other batteries for EES.Different HES routes,meaning different combinations of hydrogen production,delivery and refueling methods,show substantial differences in economics,and the lowest LCOS and carbon emissions,at 0.227 US$kWh^(-1) and 61.63 gCO_(2) e kWh^(-1),are achieved using HES routes that involve hydrogen production by alkaline electrolyzer(AE),delivery by hydrogen pipeline and corresponding refueling.The findings of this study suggest that HES and EES have comparable levels of economics and carbon emissions that should be both considered for large-scale renewable energy storage to achieve future decarbonization goals.展开更多
A hydrogen compressed air energy storage power plant with an integrated electrolyzer is ideal for large-scale,long-term energy storage because of the emission-free operation and the possibility to offer multiple ancil...A hydrogen compressed air energy storage power plant with an integrated electrolyzer is ideal for large-scale,long-term energy storage because of the emission-free operation and the possibility to offer multiple ancillary services on the German energy market.This paper defines analyzes such a storage concept and conducts an extensive comparison with four additional storage concepts based on various criteria.The results show that the combination of storing compressed air and hydrogen offers a higher efficiency than storing only hydrogen and lower specific investment costs than storing only compressed air.This result is confirmed with analysis of the optimal sizing of each power plant component for simultaneous participation on multiple energy markets with a linear optimization dispatch mode.The hydrogen compressed air energy storage(HCAES)power plant can utilize more revenue possibilities than a hydrogen energy storage because of the higher round-trip efficiency and the combination of the air compressor and the integrated electrolyzer during charging mode.The integration of the electrolyzer,however,offers a couple of challenges itself because of the highly flexible operation mode.A new concept for the controllable 24-pulse diode-thyristor rectifier of the electrolyzer is presented,that uses mostly common components while offering little to no grid harmonics and a long lifetime.The flexible integrated electrolyzer allows for the 4-quadrant operation of the storage power plant.展开更多
Hydrogen,as a secure,clean,efficient,and available energy source,will be successfully applied to reduce and eliminate greenhouse gas emissions.Hydrogen storage technology,which is one of the key challenges in developi...Hydrogen,as a secure,clean,efficient,and available energy source,will be successfully applied to reduce and eliminate greenhouse gas emissions.Hydrogen storage technology,which is one of the key challenges in developing hydrogen economy,will be solved through the unremitting efforts of scientists.The progress on hydrogen storage technology research and recent developments in hydrogen storage materials is reported.Commonly used storage methods,such as high-pressure gas or liquid,cannot satisfy future storage requirement.Hence,relatively advanced storage methods,such as the use of metal-organic framework hydrides and carbon materials,are being developed as promising alternatives.Combining chemical and physical hydrogen storage in certain materials has potential advantages among all storage methods.Intensive research has been conducted on metal hydrides to improve their electrochemical and gaseous hydrogen storage properties,including their hydrogen storage capacity,kinetics,cycle stability,pressure,and thermal response,which are dependent on the composition and structural feature of alloys.Efforts have been exerted on a group of magnesium-based hydrides,as promising candidates for competitive hydrogen storage,to decrease their desorption temperature and enhance their kinetics and cycle life.Further research is necessary to achieve the goal of practical application by adding an appropriate catalyst and through rapid quenching or ball milling.Improving the kinetics and cycle life of complex hydrides is also an important aspect for potential applications of hydrogen energy.展开更多
The nanocrystalline and amorphous LaMg11Ni ＋ x wt% Ni （x = 100, 200） composites were synthesized by the mechanical milling, and their gaseous and electrochemical hydrogen storage kinetics performance were systemati...The nanocrystalline and amorphous LaMg11Ni ＋ x wt% Ni （x = 100, 200） composites were synthesized by the mechanical milling, and their gaseous and electrochemical hydrogen storage kinetics performance were systematically investigated, The results indicate that the as-milled composites exhibit excellent hydrogen storage kinetic performances, and increasing Ni content significantly facilitates the improvement of the hydrogen storage kinetics properties of the composites. The gaseous and electrochemical hydrogen storage kinetics of the composites reaches a maximum value with the variation of milling time. Increasing Ni content and milling time both make the hydrogen desorption activation energy lower, which are responsible for the enhancement in the hydrogen storage kinetics properties of the composites. The diffusion coefficient of hydrogen atom and activation enthalpy of charge transfer on the surface of the as-milled composites were also calculated, which are considered to be the dominated factors for the electrochemical high rate discharge ability.展开更多
To improve the hydrogen storage performance of PrMg12-type alloys, Ni was adopted to replace partially Mg in the alloys. The PrMgllNi＋x wt.% Ni （x=100, 200） alloys were prepared via mechanical milling. The phase st...To improve the hydrogen storage performance of PrMg12-type alloys, Ni was adopted to replace partially Mg in the alloys. The PrMgllNi＋x wt.% Ni （x=100, 200） alloys were prepared via mechanical milling. The phase structures and morphology of the experimental alloys were in vestigated by X-ray diffraction and transmission electron microscopy. The results show that increasing milling time and Ni content accelerate the formation of nanocrystalline and amorphous structure. The gaseous hydrogen storage properties of the experimental alloys were determined by differential scanning calorimetry （DSC） and Sievert apparatus. In addition, increasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subsequently and the dehydrogenation rate always increases. The maximum capacity is 5. 572 wt. % for the x = 100 alloy and 5. 829 wt. % for the x = 200 alloy, respectively. The enthalpy change （ △H ）, entropy change （△S） and the dehydrogenation activation energy （Exde） markedly lower with increasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.展开更多
Nanocrystalline and amorphous Nd Mg_（12^-）type Nd Mg_（11）Ni＋ x wt% Ni（x=100, 200） hydrogen storage alloys were synthesized by mechanical milling. The effects of Ni content and milling time on hydrogen storage t...Nanocrystalline and amorphous Nd Mg_（12^-）type Nd Mg_（11）Ni＋ x wt% Ni（x=100, 200） hydrogen storage alloys were synthesized by mechanical milling. The effects of Ni content and milling time on hydrogen storage thermodynamics and dynamics of the alloys were systematically investigated. The gaseous hydrogen absorption and desorption properties were investigated by Sieverts apparatus and differential scanning calorimeter connected with a H_2 detector. Results show that increasing Ni content significantly improves hydrogen absorption and desorption kinetics of the alloys. Furthermore,varying milling time has an obvious effect on the hydrogen storage properties of the alloys. Hydrogen absorption saturation ratio（R^a_（10）; a ratio of the hydrogen absorption capacity in 10 min to the saturated hydrogen absorption capacity） of the alloys obtains the maximum value with varying milling time. Hydrogen desorption ratio（R^d_（20）, a ratio of the hydrogen desorption capacity in 20 min to the saturated hydrogen absorption capacity） of the alloys always increases with extending milling time. The improved hydrogen desorption kinetics of the alloys are considered to be ascribed to the decreased hydrogen desorption activation energy caused by increasing Ni content and milling time.展开更多
We use the ab initio density functional theory to calculate the band structure, density of states, charge transfer, charge density difference, binding energy and vibration frequency. We can see that the conduction ban...We use the ab initio density functional theory to calculate the band structure, density of states, charge transfer, charge density difference, binding energy and vibration frequency. We can see that the conduction band through the Fermi level include SWNT/H_2/Li, SWNT/H_2/Al and SWNT/H_2/Ca, which shows a kind of metallic character. The charge distribution and contour plots of charge difference density of ion/H_2/SWNT show charge transfer between ion and H_2 molecules rather than between H_2 and H_2. Meanwhile, the interaction between Al, Ca and H_2 is weaker than that of Li. We can also prove that the ion is the primary reason to the increase of adsorption energy of hydrogen molecule in SWNT. Finally, we calculate the vibration frequency and don＇t find any imaginary frequency, which proves that the（7,0） SWNT is more stable.展开更多
基金supported by Natural Science Foundation of China(no.72471087)Natural Science Foundation of Beijing Municipality(no.9242015).
文摘Zero-carbon parks have broad prospects in carbon neutralization.As an energy hub,hydrogen energy storage plays an important role in zero-carbon parks.However,the nonlinear characteristics of hydrogen energy storage systems(HESSs)have a significant impact on the system economy.Therefore,considering the variable working condition characteristics of HESSs,a hybrid operation method is proposed for HESS,to support the efficient and economic operation of zero-carbon parks,By analyzing the operating principle of a zero-carbon park with HESS,the system structure framework and variable condition linearization model of the equipment in HESS are established.Moreover,considering the energy output characteristics of hydrogen energy storage equipment under variable working conditions,a multimodule hybrid operation strategy is proposed for electrolytic and fuel cells,effectively meeting the thermoelectric load demand of zero-carbon parks in different scenarios.Finally,the economy of the proposed hybrid operation strategy was verified in typical scenarios,using a zero-carbon park embedded with a HESS.
基金supported by the State Grid Jiangxi Electric Power Co.,Ltd.(No.52182020008K)Beijing Millions of Talents Funding Project(No.2020A30).
文摘By collecting and organizing historical data and typical model characteristics,hydrogen energy storage system(HESS)-based power-to-gas(P2G)and gas-to-power systems are developed using Simulink.The energy transfer mechanisms and numerical modeling methods of the proposed systems are studied in detail.The proposed integrated HESS model covers the following system components:alkaline electrolyzer(AE),highpressure hydrogen storage tank with compressor(CM&H_(2) tank),and proton-exchange membrane fuel cell(PEMFC)stack.The unit models in the HESS are established based on typical U-I curves and equivalent circuit models,which are used to analyze the operating characteristics and charging/discharging behaviors of a typical AE,an ideal CM&H_(2) tank,and a PEMFC stack.The validities of these models are simulated and verified in the MicroGrid system,which is equipped with a wind power generation system,a photovoltaic power generation system,and an auxiliary battery energy storage system(BESS)unit.Simulation results in MATLAB/Simulink show that electrolyzer stack,fuel cell stack and system integration model can operate in different cases.By testing the simulation results of the HESS under different working conditions,the hydrogen production flow,stack voltage,state of charge(SOC)of the BESS,state of hydrogen pressure(SOHP)of the HESS,and HESS energy flow paths are analyzed.The simulation results are consistent with expectations,showing that the integrated HESS model can effectively absorb wind and photovoltaic power.As the wind and photovoltaic power generations increase,the HESS current increases,thereby increasing the amount of hydrogen production to absorb the surplus power.The results show that the HESS responds faster than the traditional BESS in the microgrid,providing a solid theoretical foundation for later wind-photovoltaic-HESS-BESS integration.
基金This work was supported by the National Key Research and Development Program of China(Materials and Process Basis of Electrolytic Hydrogen Production from Fluctuating Power Sources such as Photovoltaic/Wind Power,No.2021YFB4000100).
文摘In this paper,a typical-operation-curve generation method of a hydrogen energy storage system operating under the mode of stabilizing wind power fluctuations is proposed.This method is used to optimize the power and capacity configuration of the energy storage system.The time series curves of the charging and discharging powers of the hydrogen energy storage are obtained by EMD decomposition,and the curves are classified according to the similarities and differences of the characteristic parameters in different time periods.After the classification,typical charging and discharging power values of each type of curve at each moment are obtained by a cloud model,and then,typical operation curves of each type are obtained by integration.On this basis,the power and capacity of the energy storage system are optimized with the objective of economic optimization through the MATLAB CPLEX toolbox.Combined with the measured data of a wind farm with an installed capacity of 400 MW in Northeast China,the validity and rationality of the typical operation curve generation method proposed in this paper are verified.
基金Funded by the National Natural Science Foundation of China(Nos.51471054,51761032,and 51371094)the Natural Science Foundation of Inner Mongolia,China(No.2015MS0558)
文摘Nanocrystalline and amorphous LaMg_（12）-type LaMg_（11）Ni ＋ x wt% Ni（x = 100, 200） alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydrogen storage kinetics of as-milled alloys were investigated systematically. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. And the gaseous hydrogen storage properties were investigated by Sievert apparatus and a differential scanning calorimeter（DSC） connected with a H_2 detector. Hydrogen desorption activation energy of alloy hydrides was estimated by using Arrhenius and Kissinger methods. It is found that the increase of Ni content significantly improves the gaseous and electrochemical hydrogen storage kinetic performances of as-milled alloys. Furthermore, as ball milling time changes, the maximum of both high rate discharge ability（HRD） and the gaseous hydriding rate of as-milled alloys can be obtained. But the hydrogen desorption kinetics of alloys always increases with the extending of milling time. Moreover, the improved gaseous hydrogen storage kinetics of alloys are ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and milling time.
基金This research is supported by the National Natural Science Founda-tion of China(No.51921004)B.Wang thanks the funding support by Hong Kong Scholars Program(No.XJ2021033).
文摘Energy storage is an effective way to address the instability of renewable energy generation modes,such as wind and solar,which are projected to play an important role in the sustainable and low-carbon society.Economics and carbon emissions are important indicators that should be thoroughly considered for evaluating the feasibility of energy storage technologies(ESTs).In this study,we study two promising routes for large-scale renewable energy storage,electrochemical energy storage(EES)and hydrogen energy storage(HES),via technical analysis of the ESTs.The levelized cost of storage(LCOS),carbon emissions and uncertainty assessments for EESs and HESs over the life cycle are conducted with full consideration of the critical links for these routes.In order to reduce the evaluation error,we use the Monte Carlo method to derive a large number of data for estimating the economy and carbon emission level of ESTs based on the collected data.The results show that lithium ion(Li-ion)batteries show the lowest LCOS and carbon emissions,at 0.314 US$kWh-1 and 72.76 g CO_(2) e kWh^(-1),compared with other batteries for EES.Different HES routes,meaning different combinations of hydrogen production,delivery and refueling methods,show substantial differences in economics,and the lowest LCOS and carbon emissions,at 0.227 US$kWh^(-1) and 61.63 gCO_(2) e kWh^(-1),are achieved using HES routes that involve hydrogen production by alkaline electrolyzer(AE),delivery by hydrogen pipeline and corresponding refueling.The findings of this study suggest that HES and EES have comparable levels of economics and carbon emissions that should be both considered for large-scale renewable energy storage to achieve future decarbonization goals.
基金supported by the Lower Saxony State Ministry of Science and Culture and Volkswagen Stiftung within the innovation lab“Wasserstoffregion Nord-West-Niedersachsen(H2-ReNoWe)”.
文摘A hydrogen compressed air energy storage power plant with an integrated electrolyzer is ideal for large-scale,long-term energy storage because of the emission-free operation and the possibility to offer multiple ancillary services on the German energy market.This paper defines analyzes such a storage concept and conducts an extensive comparison with four additional storage concepts based on various criteria.The results show that the combination of storing compressed air and hydrogen offers a higher efficiency than storing only hydrogen and lower specific investment costs than storing only compressed air.This result is confirmed with analysis of the optimal sizing of each power plant component for simultaneous participation on multiple energy markets with a linear optimization dispatch mode.The hydrogen compressed air energy storage(HCAES)power plant can utilize more revenue possibilities than a hydrogen energy storage because of the higher round-trip efficiency and the combination of the air compressor and the integrated electrolyzer during charging mode.The integration of the electrolyzer,however,offers a couple of challenges itself because of the highly flexible operation mode.A new concept for the controllable 24-pulse diode-thyristor rectifier of the electrolyzer is presented,that uses mostly common components while offering little to no grid harmonics and a long lifetime.The flexible integrated electrolyzer allows for the 4-quadrant operation of the storage power plant.
基金Sponsored by National Natural Science Foundation of China(51161015,51371094)
文摘Hydrogen,as a secure,clean,efficient,and available energy source,will be successfully applied to reduce and eliminate greenhouse gas emissions.Hydrogen storage technology,which is one of the key challenges in developing hydrogen economy,will be solved through the unremitting efforts of scientists.The progress on hydrogen storage technology research and recent developments in hydrogen storage materials is reported.Commonly used storage methods,such as high-pressure gas or liquid,cannot satisfy future storage requirement.Hence,relatively advanced storage methods,such as the use of metal-organic framework hydrides and carbon materials,are being developed as promising alternatives.Combining chemical and physical hydrogen storage in certain materials has potential advantages among all storage methods.Intensive research has been conducted on metal hydrides to improve their electrochemical and gaseous hydrogen storage properties,including their hydrogen storage capacity,kinetics,cycle stability,pressure,and thermal response,which are dependent on the composition and structural feature of alloys.Efforts have been exerted on a group of magnesium-based hydrides,as promising candidates for competitive hydrogen storage,to decrease their desorption temperature and enhance their kinetics and cycle life.Further research is necessary to achieve the goal of practical application by adding an appropriate catalyst and through rapid quenching or ball milling.Improving the kinetics and cycle life of complex hydrides is also an important aspect for potential applications of hydrogen energy.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51161015 and 51371094)
文摘The nanocrystalline and amorphous LaMg11Ni ＋ x wt% Ni （x = 100, 200） composites were synthesized by the mechanical milling, and their gaseous and electrochemical hydrogen storage kinetics performance were systematically investigated, The results indicate that the as-milled composites exhibit excellent hydrogen storage kinetic performances, and increasing Ni content significantly facilitates the improvement of the hydrogen storage kinetics properties of the composites. The gaseous and electrochemical hydrogen storage kinetics of the composites reaches a maximum value with the variation of milling time. Increasing Ni content and milling time both make the hydrogen desorption activation energy lower, which are responsible for the enhancement in the hydrogen storage kinetics properties of the composites. The diffusion coefficient of hydrogen atom and activation enthalpy of charge transfer on the surface of the as-milled composites were also calculated, which are considered to be the dominated factors for the electrochemical high rate discharge ability.
基金financially sponsored by National Natural Science Foundation of China (51471054)
文摘To improve the hydrogen storage performance of PrMg12-type alloys, Ni was adopted to replace partially Mg in the alloys. The PrMgllNi＋x wt.% Ni （x=100, 200） alloys were prepared via mechanical milling. The phase structures and morphology of the experimental alloys were in vestigated by X-ray diffraction and transmission electron microscopy. The results show that increasing milling time and Ni content accelerate the formation of nanocrystalline and amorphous structure. The gaseous hydrogen storage properties of the experimental alloys were determined by differential scanning calorimetry （DSC） and Sievert apparatus. In addition, increasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subsequently and the dehydrogenation rate always increases. The maximum capacity is 5. 572 wt. % for the x = 100 alloy and 5. 829 wt. % for the x = 200 alloy, respectively. The enthalpy change （ △H ）, entropy change （△S） and the dehydrogenation activation energy （Exde） markedly lower with increasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.
基金financially supported by the National Natural Science Foundation of China(Nos.51371094 and 51471054)
文摘Nanocrystalline and amorphous Nd Mg_（12^-）type Nd Mg_（11）Ni＋ x wt% Ni（x=100, 200） hydrogen storage alloys were synthesized by mechanical milling. The effects of Ni content and milling time on hydrogen storage thermodynamics and dynamics of the alloys were systematically investigated. The gaseous hydrogen absorption and desorption properties were investigated by Sieverts apparatus and differential scanning calorimeter connected with a H_2 detector. Results show that increasing Ni content significantly improves hydrogen absorption and desorption kinetics of the alloys. Furthermore,varying milling time has an obvious effect on the hydrogen storage properties of the alloys. Hydrogen absorption saturation ratio（R^a_（10）; a ratio of the hydrogen absorption capacity in 10 min to the saturated hydrogen absorption capacity） of the alloys obtains the maximum value with varying milling time. Hydrogen desorption ratio（R^d_（20）, a ratio of the hydrogen desorption capacity in 20 min to the saturated hydrogen absorption capacity） of the alloys always increases with extending milling time. The improved hydrogen desorption kinetics of the alloys are considered to be ascribed to the decreased hydrogen desorption activation energy caused by increasing Ni content and milling time.
基金supported by the National Natural Science Foundation of China(11474207 and 11374217)
文摘We use the ab initio density functional theory to calculate the band structure, density of states, charge transfer, charge density difference, binding energy and vibration frequency. We can see that the conduction band through the Fermi level include SWNT/H_2/Li, SWNT/H_2/Al and SWNT/H_2/Ca, which shows a kind of metallic character. The charge distribution and contour plots of charge difference density of ion/H_2/SWNT show charge transfer between ion and H_2 molecules rather than between H_2 and H_2. Meanwhile, the interaction between Al, Ca and H_2 is weaker than that of Li. We can also prove that the ion is the primary reason to the increase of adsorption energy of hydrogen molecule in SWNT. Finally, we calculate the vibration frequency and don＇t find any imaginary frequency, which proves that the（7,0） SWNT is more stable.
