Design And Synthesis Of Hollow Layered Double Hydroxides For Oxygen Evolution Reaction

Due to the large specific surface area,low density and high porosity,hollow materials have been widely used for catalysis,adsorption,energy storage and conversion,and so on.In this thesis,we aim to design and synthesize hollow and multi-shelled hollow LDHs to improve its electrocatalytic performance for oxygen evolution reaction(OER).The main contents and conclusions are as follows:1.A method for synthesis of hollow NiCoFe-LDH by using metal-organic framework(MOF)as template was proposed.ZIF-67 was chosen as the template to fabricate the hollow NiCoFe-LDH through in-situ etching by the solution of Ni and Fe salt.Due to the existence of the cavity,the active sites inside the hollow material can be in sufficient contact with the electrolyte to improve the utilization rate of the active sites.Therefore,the prepared single-shelled hollow NiCoFe-LDH exhibits excellent OER performance,with an overpotential 276 mV to reach the current density of 10 mA cm-2,which is far smaller compared to the commercial IrO2 and the corresponding NiCoFe-LDH nanosheets synthesized by conventional methods.In addition,in the 12 h stability test,the current density did not significantly attenuate,demonstrating its excellent stability.The above results demonstrated that the construction of the hollow structure can effectively improve the OER activity and stability of the LDH material,which is important for guiding the synthesis of high performance LDH electrocatalysts.2.A method for synthesis of multilayer hollow NiCo-LDH by using multi-shelled MOF as a template is proposed.Compared with single-shelled hollow materials,multi-shelled hollow structures can make full use of the active sites inside each layer of materials,shorten the diffusion distance between layers,and reduce the diffusion resistance in the catalytic process,which are significant for further improving the OER performance.Herein,in this work,the multi-shelled ZIF-67@ZIF-8 was chosen as the template to synthesize the multi-shelled hollow NiCo-LDH through the selective etching and in-situ conversion process.Catalytic results show that the OER performance of multi-shelled NiCo-LDH is effectively improved with the increasing of the number of hollow layers.In addition,the obtained multi-shelled hollow NiCo-LDH can be successfully transformed to multi-shelled hollow NiCo metal oxide through a simple calcination treatment.Compared to the multi-shelled hollow NiCo-LDH,the OER performance of the multi-shelled NiCo metal oxide is further improved.The overpotential is only 273 mV at the current density of 10 mA cm-2,and can be stable working for more than 9 h,which is superior to commercial IrO2.