Controlled Synthesis Of Amorphous FeNi Based Metal Organic Framework And Their Applications In Oxygen Evolution Reaction

The depletion of traditional fossil fuels and environmental degradation issues have exacerbated demand for renewable and clean energy.Hydrogen（H₂）with high gravimetric energy density,renewability,and environmentally friendly properties has been deemed as one of the ultimate green energy sources.Electrocatalytic water splitting is known as an effective route to produce high-purity hydrogen through two half-reactions:hydrogen evolution reaction（HER）at the cathode and oxygen evolution reaction（OER）at the anode.However,the 4-electron involved OER on the anodic electrode has limited the whole water electrolysis due to its slower kinetics than that of the cathodic HER.Although Ir O₂and Ru O₂ have been identified as the outstanding electrocatalysts for the OER,the exorbitant price and scarcity of these noble metals seriously restrict their largescale and widespread practical utilization.Therefore,it is highly desirable to design and develop an OER electrocatalyst with excellent catalytic activity and durability,which is efficient,low-cost,and has abundant reserves on the earth.In this work,we focus on amorphous metal organic frameworks,centering on target synthesis of Fe In-a MOF,Fe Ni-a MOF and Fe Ni（Fe）-a MOF/INF,and systematically exploring the applications of materials in OER.The main contents are in the following:1.Amorphous materials are attractive for their“dangling bonds”and more active than the crystalline counterparts in many applications.However,amorphous metal organic framewoks（a MOFs）have been rarely investigated directly as electrocatalysts compared with crystalline ones.Herein,a series of In_xFe_y-a MOF materials was prepared by one-step solvothermal method via inducing exotic metal ions.XRD,SEM,IR and N₂ adsorption results show that the introduction of Fe³⁺makes the original In-MOF lose its long-range ordered structure.The amorphous nanostructure possesses a high specific surface area and abundant exposed metal sites,which are beneficial for electrocatalytic reactions.In the electrocatalytic oxygen evolution reaction（OER）,the optimal Fe-a MOF can drive current densities of 10 m A/cm²at small overpotentials of 258.2 m V,along with a low Tafel slope of 45.45 m V/dec.In order to further improve the electrocatalytic performance of Fe-a MOF,we subsequently prepared bimetallic Fe Ni based a MOF.The overpotential of Fe₂Ni-a MOF at current density 10 m A/cm² is 238.1 m V,and the Tafel slope is 52.74 m V/dec,which is superior to Fe-a MOF and commercial Ir O₂.The excellent performance of Fe₂Ni₁-a MOF can be attributed to the structural control and electronic regulation of the bimetals,that is,1)the exposure of the active sites at electrocatalyst/electrolyte interfaces due to amorphous structure;2)the synergistic effect of nickel and iron metals for the OER.This work brings new insights for the development of next-generation high-efficiency electrocatalysts.2.Most metal organic frameworks（MOF）face the challenges of poor electrical conductivity and rare intrinsic active sites in electrocatalytic OER.In this study,amorphous bimetallic Ni Fe-a MOF nanosheets was successfully prepared on conductive iron-nickel foam（INF）via one-step bottom-up solvothermal reactions,and explored its application potential as OER electrocatalysts.The Fe Ni（Fe）-a MOF/INF presents superior OER activity in 1 M KOH,requiring overpotentials of 193.1 m V and 238.6 m V to deliver the current density of 10 and 50 m A/cm²,along with a low Tafel slope of 31.12 m V/dec.Moreover,the durability of the Fe Ni（Fe）-a MOF/INF catalyst is also outstanding,exhibiting only minor chronoamperometric decay after 24 h continuous operation at 10m A/cm².The greatly enhanced activity of amorphous Fe Ni（Fe）-a MOF/INF was originated from the abundant active metal sites and improved charge transfer due to unsaturated coordination as well as increased contact area with the electrolyte and good mass transfer benefitting from the unique 2D nanosheet morphology.This work will stimulate widespread interest in the study of amorphous MOF nanosheets with abundant active sites for improved electrocatalysts.