Study On Electrochemical Hydrogen Storage Properties Of Transition Metal And Nitrogen Doped Porous Carbon Materials

The storage of hydrogen is the most critical link in the hydrogen energy industry chain.Because porous carbon materials have advantages such as high specific surface area and pore volume,tunable pore structure,high electrical conductivity and high chemical stability,many scholars have attached great importance to the mechanism and experimental exploration of its electrochemical hydrogen storage performance.In this thesis,porous carbon materials are modified by doped with transition metals and nitrogen to further improve their electrochemical hydrogen storage performance.The main research contents and results are as follows:1.Using metal phthalocyanine as the source of metal,nitrogen,and carbon,and ordered mesoporous silicon（SBA-15）as the template.The metal phthalocyanine is sublimated and deposited into the pores of the template by heating.It is carbonized at high temperature and the template is removed to obtain transition metals and nitrogen dual-doped ordered mesoporous carbon material（M-N@OMC）.The three-electrode test is performed in a 30 wt.%KOH solution of the working electrode,the platinum counter electrode,and the reference electrode（Hg-Hg O）.The hydrogen storage capacity of Fe-N@OMC,Co-N@OMC,Ni-N@OMC,Cu-N@OMC are 120,103,90,and 80 m Ah g^-1,respectively.When they are charged at a constant current of 100 m A g^-1 for 2 h,the capacity retention rates after resting for 24 h are 77%,78%,86%,and90%,respectively.In addition,the maximum adsorption energy of H atom on the metal surface is calculated by DFT theory.The results are Fe（-6.29 e V）,Co（-4.04 e V）,Ni（-3.97 e V）,Cu（-3.57 e V）.The spillover energy of the surface to the carbon layer is Fe（110）-305.18 e V、Co（111）-305.02 e V、Ni（110）-304.84 e V、Cu（111）-301.86 e V.2.The iron-nitrogen dual-doped carbon material（Fe-N@OMC）synthesized above is further treated with 6 M hydrochloric acid solution to obtain a nitrogen-doped carbon material（N@OMC）.By comparing the structural characterization and electrochemical performance of these two materials,the hydrogen storage capacity,rate performance,hydrogen storage stability and cycle performance of Fe-N@OMC have shown significant advantages.3.Activated carbon materials with different nitrogen contents and nitrogen functional groups are obtained by nitric acid treatment.Nitrogen doping can improve the chemical activity and hydrophilic properties of the carbon materials.The optimal nitric acid concentration,reaction temperature and reaction time of the nitric acid-treated carbon material were obtained through experiments,which are 0.15 g m L^-1HNO₃,50 ^oC and 4 h.Its hydrogen storage capacity is 148.4 m Ah g^-1,after 2 hours of constant current charging at a current density of 100 m A g^-1,the capacity retention rate after standing for 24 hours is 73.4%,the discharge capacity at a large current density of 1 A g^-1 is 84.3%of the discharge capacity at a current density of 100 m A g^-1.The DFT theoretical calculation is performed using a graphene with 12 carbon rings as the carbon substrate.After comparison,it is found that the H adsorption energy of the ortho C atom of pyridine oxide N and pyrrole N are the largest,and the H adsorption energy of the N atom of pyridine N is the largest.Graphite N has basically no advantage in increasing the H adsorption energy of carbon materials.