Study On The Electrolysis Behavior Of MOFs And Its Derivative Phosphides Under The Magnetic Field

Environmental pollution and global energy crisis caused by the consumption of fossil fuels are currently one of the focuses of social attention.The development of new energy alternatives is particularly important.Clean,pollution-free and widely-sourced hydrogen energy has become the focus of scientific research.Electrolyzed aquatic hydrogen technology has become one of the most promising hydrogen production technologies due to its advantages in combining with renewable energy sources to obtain high-purity H₂.However,the current key problem is the lack of high-efficiency,low-cost,and long-life electrocatalysts that can provide high current density at low overpotentials.In this thesis,the cobalt and nickel bimetal MOF-74 and its derivative phosphides are synthesized as catalysts.The composition of the catalysts and the influence of the phosphating process on its electrocatalytic activity are studied,and the mechanism of the diplomatic variable magnetic field on the electrolytic water reaction is discussed.The main research work is summarized as follows:（1）Three-dimensional flower-like cobalt and nickel bimetal MOF-74 with different Co/Niratios were prepared by hydrothermal method.When the Co/Nimolar ratio is2/3(Co_0.4Ni_0.6-M),the corresponding catalyst presents a uniform nanoflower morphology.At 1 M KOH and a current density of 10 m A cm^-2,the overpotentials are280 m V（HER）and 313 m V（OER）,and the Tafel slopes are 109 m V dec^-1（HER）and79.39 m V dec^-1（OER）respectively.After 10 hours of operation,it can maintain good stability;（2）Using Co_xNi_1-x-M as the precursor,the metal phosphide Co_xNi_1-xP-M electrocatalyst was prepared by low-temperature phosphating method.Compared with the precursor Co_xNi_1-x-M,the HER and OER performance of the phosphide was greatly improved.Among them,the overpotentials of Co_0.4Ni_0.6P-M at 10 m A cm^-2 are 134 m V（HER）and 249 m V（OER）,respectively,and the Tafel slopes are 77.5 m V dec^-1（HER）and 66.64 m V dec^-1,respectively（OER）.At the same time,after 10 hours of i-t test,the Co_0.4Ni_0.6P-M still maintained 95%（HER）and 92.1%（OER）current densities,indicating that it has good stability;（3）Co_0.4Ni_0.6-MOF-74 was used to load magnetic nanoparticles NiFe₂O₄ to obtain a series of nanocomposites with different additions,and then the phosphides were prepared.When the addition of NiFe₂O₄ was 0.3g（NFO@M-4）,the overpotential of NFO@M-4 is 203 m V（HER）and 256 m V（OER）at the current density of 10 m A cm^-2,respectively,and the Tafel slopes are 86.88 m V dec^-1（HER）and 126.06 m V dec^-1（OER）,showing the best catalytic activity.After phosphating,the overpotential of NFO@M-P-4 is 99 m V and 192 m V,the Tafel slope is 46.2 m V dec^-1（HER）and 59.24m V dec^-1（OER）,and the current density can be maintained after 10 hours of operation83.2%and 94.78%,showing the good stability;（4）By introducing a diplomatic variable magnetic field in the electrocatalytic process,the Lorentz force generated by the external magnetic field can accelerate the liquid diffusion,and the magnetocaloric effect derived from the magnetic field can increase the temperature of the electrocatalytic system.The two mechanism together on the electrocatalytic system,making the current density of the catalysts are significantly improved under constant potential.