First Principles Study Of Potassium-doped PC₇₁BM For Hydrogen Storage

Hydrogen energy is considered as the "ultimate energy source" of the 21st century.The main factor affecting the large-scale application of hydrogen energy is its storage.In this thesis we use photoelectron spectroscopy(PES)and density functional theory(DFT)to explore the K-modified fullerene derivative PC71BM as a new solid-state hydrogen storage material.We use PES to study the reaction between PC71BM films and K atoms.The results reveal that the highest chemical ratio of K-intercalated PC71BM is K9PC71BM or K10PC71BM.The molecular structure of PC71BM is intact if the chemical ratio is not higher than K4PC71BM,and the 4s electrons of the K atoms are transferred to the lowest unoccupied orbits(LUMO)and LUMO+1 of the molecule.Higher chemical ratios KxPC71BM(x>4)lead to the detachment of the methyl group of PC71BM,and one or two K atoms are combined with the two O atoms of PC71BM.We then study the hydrogen storage property of K9PC71BM with DFT calculations.Hydrogen is adsorbed in molecular form(H2).The hydrogen storage capacity is at least 5.9 wt%even if only the first layer of the adsorbed H2 molecules are considered.The obtained storage capacity exceeds the U.S.Department of Energy 2025 weight ratio target for vehicle-mounted hydrogen storage materials.The averaged adsorption energy for the H2 molecules is 0.110 eV/H2,which means a desorption temperature near room temperature.Therefore,K9PC71BM is expected to be a new type of hydrogen storage material for vehicle usage.