Mechanism of magnesium based hydrogen storage enhanced by external microwave electric field based on internal nonmetallic element doping
Among numerous solid-state hydrogen storage materials,magnesium-based materials have been well recognized to be prosperous in application prospect,but its large-scale commercial application is hindered because of magnesium's poor dynamic performance(difficult hydrogen diffusion)and high reaction energy consumption in the process of hydrogen storage.External microwave field has been gradually applied to improve hydrogen storage process,for it can efficiently accelerate chemical reaction and decrease reaction temperature and energy consumption.At present,however,there are few reports on the studies of the internal non-metal doping synergistic with external microwave electric field enhanced magnesium based hydrogen storage.Based on the first-principles calculation,this paper investigates the mechanism of internal non-metal doping synergistic with external microwave electric field in improving magnesium based hydrogen storage,and analyzes the thermodynamic change mechanisms(e.g.adsorption energy,electronic behavior and transition state)of magnesium-hydrogen system doped with non-metal elements before and after the action of microwave electric field.And the following research results are obtained.First,microwave electric field alters the charge distribution on the surface of hydrogen molecule and magnesium and results in charge separation of hydrogen molecule(polarization),so as to change the interaction between hydrogen and magnesium.Second,state density calculation results also indicate that microwave electric field changes the electronic state distribution of H-s orbitals,causing H-s electrons to move towards the high-energy region,which enhances the hybridization of H-s orbitals with Mg-sp orbitals and improves the interaction between magnesium and hydrogen.Third,the synergistic modification of internal non-metallic element doping and external microwave electric field significantly reduces the reaction energy barrier of hydrogen absorption process from 0.94 eV to 0.77 eV.In conclusion,microwave electric field helps to polarize hydrogen gas,activate its reaction activity,and reduce reaction energy consumption;and the synergistic modification of internal non-metallic elements with external microwave electric field promotes the reaction process of hydrogen on the surface of magnesium,effectively improving the dynamic performance of magnesium hydrogen absorption process.
Solid-state hydrogen storageMagnesiumMicrowave electric fieldNon-metal dopingFirst-principles calculation
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