| Combined with other clean energy power generation technologies,hydrogen production through water splitting can achieve completely pollution-free conversion of other clean energy into hydrogen energy for storage.The cheap and efficient electrocatalyst is the key to realize the industrialization of this technology.Because more intermediate products,steps and transferred electrons are involved in the process,the kinetics of oxygen evolution reaction is slower than that of hydrogen evolution reaction.Therefore,it is very important to develop electrocatalysts with high catalytic activity and stability by using cheap and easily available materials.The porous carbon based metals and their compounds derived from the modified metal-organic frameworks(MOF)at high temperature can have good dispersion,conductivity,catalytic activity and stability.It is very suitable to be used as electrocatalyst material for oxygen evolution reaction.Based on the above purpose,In chapter 3 and chapter 4,the organic framework of nickel based metals was modified by heteropoly acid doping and double MOF hybridization respectively.The effects of these two methods on morphology,structure and electrochemical properties were investigated.Then,the two methods were combined in Chapter 5,The advantages of the two methods were successfully combined and the defects were made up by the reasonable design.Finally,the materials with excellent oxygen evolution catalytic properties were prepared based on the nickel based MOF.The details are as follows.(1)The precursors were prepared by doping phosphomolybdate into a nickel based metal-organic framework by solvent heat method,and then heat treat them to form NiMoO4 hollow microspheres.The results show that the addition of appropriate amount of phosphomolybdate can help to form bimetallic oxide NiMoO4 in the derivatives.The results show that the addition of appropriate amount of phosphomolybdate is helpful to the formation of Ni and Mo bimetallic oxides.The combination of Mo can adjust the electronic structure of Ni as the active site,thus greatly improving its catalytic activity.However,the overall charge transfer performance will be weakened,and the particle size will also change.(2)I prepared double MOF hybrid structure Ni-BTCO@ZIF-67 precursors by doping Co2+on the surface of nickel based MOF and coordinating them with 2methylimidazole,which could be converted into the corresponding derivatives NiOCo3O4@NC hybrid material by heat treating in air at high temperature.The NiO octahedron derived from Ni based MOF is a good substrate to alleviate the aggregation of Co3O4@NC derived form ZIF-67,which can promote the exposure of active sites.However,the effect of this hybrid depends on the size and morphology matching between the two metal-organic frameworks,otherwise the growth will be extremely uneven.(3)Combined with the modification methods in the previous two chapters,I synthesized nickel based metal-organic framework hollow microspheres doped with ammonium molybdate tetrahydrate by one-step solvothermal method,and then immersed them in potassium ferricyanide solution as nickel source to grow NiFe PBA in situ for preparing the precursor NiMoBTC@PBA,which was heat treated at different temperatures in reducing atmosphere to synthesis three metal oxygen evolution reaction catalysts NiMoFe@NC.The results show that the derived NiMoFe@NC600 shows great oxygen evolution reaetion-eatalytic performance at low current density,which only needs an overpotential of 254 mV to achieve a current density of 10 mA·cm-2,but NiMoFe@NC700 shows better at high current density(only needs an overpotential of 360 mV to achieve a current density of 50 mA·cm-2),and the Tafel slope is only 65 mV dec-1,which is better than that of IrO2.At the same time,NiMoFe@NC700 also shows good stability,the current density almost does not decrease after constant voltage test for 11 h. |
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