Preparation And Investigation Of Fe-MOF-235 As Efficient Catalysts For Oxygen Evolution Reaction

Water splitting is an efficient,environmentally friendly and high product purity（～100%）hydrogen production method,which consists of hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.Compared with HER,OER has slow kinetics and high energy-consuming.The efficient OER catalyst can improve the reaction rate,reduce the energy consumption and raise the energy utilization rate.Ru O₂and Ir O₂are considered as the standard OER catalysts,which show excellent activity.However,the scarcity and high cost limit their large-scale applications.Therefore,it is important to develop non-precious metal catalysts with low cost,high activity and stability.In recent years,metal-organic frameworks（MOFs）have been applied in OER because of their tunable structure,large specific surface area and exceptional porosity.In the current studies,Ni,Co and Fe-based MOFs show high activity.To improve the activity of OER,most of MOFs are calcined,and then the MOFs-derived materials are used as the catalysts.However,the process is complicated,and the skeleton of MOFs collapse due to organic ligands lossing during the calcination.Hence,it is important for OER to find a high-efficiency MOFs catalysts,which will simplify the preparation process and reduce the experimental cost.In this thesis,Ni-MOF-74,Fe-MIL-88B and Co-ZIF-67 are synthesized;whereafter,the different topological structures of Fe-MIL-88B:Fe-MOF-235,Fe-MIL-101 and Fe-MIL-53are prepared using Fe³⁺and terephthalic acid;finally,the influnce of calcinatin is considered,which Fe-MOF-235 is calcined in N₂atmosphere.The main conclusions are as follows:（1）Among Ni-MOF-74,Fe-MIL-88B and Co-ZIF-67,Fe-MIL-88B exhibits the best activity for OER,the current density reaches 10 m A/cm²with an overpotential at 276 m V.（2）Among the four iron-based MOFs,Fe-MOF-235 shows the highest activity for OER,the current density reaches 10 m A/cm²with an overpotential at 255 m V,and the catalyst shows high stability during 70 h.（3）When Fe-MOF-235 is calcined in N₂atmosphere at 550 and 750℃,the activity of OER decreases.The reason is that the skeleton of MOFs are damaged.The more the loss of organic ligands,the higher the interfacial charge transfer resistance.Therefore,it is a key factor of the skeleton of Fe-MOF-235,which is beneficials of activity of OER.（4）The interfacial charge transfer resistance of MOFs is the key factor for OER activity.The interfacial charge transfer resistance of MOFs increases with the charge transfer ability decreasing,then the activity of OER decreases.