Study On Synthesis Of Metal-organic Framework Electrocatalytic Materials And Their Electrocatalytic Performance On Oxygen Evolution Reaction From Water Splitting

In recent years,with the rapid development of industrial production and the increment in population,the demand for fossil fuels has extremely increased,which has caused a huge negative impact on the environment.Environmental pollution and the greenhouse effect have driven the necessity of people looking for clean energy,and the plans of developing and using renewable energy are imperative.As a result,people’s interest in using sustainable and clean energy sources such as solar,wind and marine energy is increasing.However,in order to solve the intermittent problems of using these new energy sources,it is necessary to develop more efficient energy storage or conversion systems.Among them,hydrogen as a potential clean energy carrier has been widely used in batteries.Due to involving multiple reaction steps from water to O₂,the oxygen evolution reaction（OER）process has been considered as the bottleneck.Some noble-metal-based materials,such as Ru O₂ and Ir O₂,have relatively high electrocatalytic activity for the OER.However,their scarcity limits their largescale application.The search for OER electrocatalysts with high efficiency and low cost of nonprecious metal materials has become an important task.1)Fe₂Ni-MIL-88B MOF on nickel foam（Fe₂Ni MOF/NF）has been prepared through a one-pot method growth process.Compared with Fe MOF/NF and Ni MOF/NF,the interaction between Fe³⁺and Ni²⁺in Fe₂Ni MOF/NF accelerates the electron transfer through the oxygen of the ligand,leading to the increment of 3d orbital electron density of Ni,which enhances the activity of the OER.Fe₂Ni MOF/NF provides a current density of 10 m A cm^-2 at a low overpotential of 222 m V,and its Tafel slope is also very small,reaching 42.39 m V dec^-1.The great performance of the present Fe₂Ni MOF/NF catalyst is attributed to（1）the abundant active centers,（2）the bimetallic clusters Fe₂Ni-MIL-88B,（3）the positive coupling effect between Ni and Fe metal ions in the MOF,and synergistic effect between the MOF and NF.Besides,Fe₂Ni MOF/NF possesses excellent stability over 50 h of continuous operation,providing feasibility for commercial use.2)We prepared Fe₂Co-MIL-88B MOF on nickel foam（Fe₂Co MOF/NF）through a solvothermal process with terephthalic acid（TPA）.In this research,we report the synthesis and characterization of trimeric Fe₂Co（μ₃-O）clusters.The electrocatalytic performance dramatically benefits from the electron transfer of Fe and Co element,which is believed that this is related to the positive coupling effect between Co and Fe and the electronic structure change caused by Co replacing Fe metal ions in the MOF.Meanwhile,the introduction of Co destroys the inherent crystal structure and generates more active sites,improving OER performance.Meanwhile,density functional theory（DFT）calculations and post-OER characterization showed that Fe_0.67Co_0.33OOH were in situ formed during the OER active,where Fe_0.67Co_0.33OOH is confirmed as the real active species.These structures reveal that the OER proceeds via a Mars-van-Krevelen mechanism.The electrocatalysis shows superior OER activity with highcurrent density(10 m A cm^-2)at an overpotential of 224 m V,a Tafel slope of 45.3 m V dec^-1,and excellent stability for 50 hours in 1M KOH.This work provides a promising low-cost catalyst for practical applications.Our analysis provides a simple and effective strategy for the rational design of MOF-derived materials to achieve inexpensive and effective electrocatalysis.