Synthesis And Electrocatalytic Properties Of Nickel-Based Organic Framework Materials

With the global energy demand expected to increase drastically over the next several decades,the development of a sustainable energy system to meet this increase is paramount.Renewable energy sources can be coupled with electrochemical conversion processes to store energy in chemical bonds.Among them,electrocatalytic oxygen production(OER)and electrocatalytic organic reactions are a type of reaction that effectively converts electrical energy into renewable clean energy.However,the slow kinetics of the OER reaction limits its efficient conversion.Based on the merits of high surface area,rich pore structure,diverse composition and well-defined metal centers,metal organic frameworks(MOFs)and their derivatives have been widely exploited as OER electrocatalysts.In addition,the recent development of conductive MOFs has led to several electrocatalytic MOFs that display activity comparable to that of the best-performing heterogeneous catalysts.Although many electrocatalytic MOFs exhibit low activity and stability,the few successful examples highlight the possibility of MOF electrocatalysts as replacements for noble-metal-based catalysts in commercial energy-converting devices.Based on this,this article mainly discusses the synthesis of nickel-based MOF materials and their high-efficiency electrocatalytic oxidation properties.1.Self-Supported Three-Dimensional Macroporous Amorphous NiFe Bimetallic-Organic Frameworks for Enhanced Water Oxidation.Amorphous materials are attractive for their "dangling bonds" and more active than the crystalline counterparts in many applications.Metal-organic frameworks(MOFs)have emerged as an exciting class of porous materials that received considerable interest in many research fields including electrocatalysis.However,amorphous MOFs have been rarely investigated directly as electrocatalysts compared with crystalline ones.In this study,amorphous bimetallic NiFe-MOF with a three-dimensional(3D)macroporous structure was successfully prepared on nickel foam via one-step bottom-up solvothermal reactions and exhibited the potential as efficient OER(oxygen evolution reaction)electrocatalysts.The prepared self-supporting electrode can provide a 10 mA cm-2 current density at an overpotential of 211 mV,as well as remarkable operational stability and nearly 100%Faraday efficiency.This performance is superior to most previously reported MOF electrocatalysts and well exceeds the corresponding crystalline NiFe-MOF.The greatly enhanced activity of amorphous NiFe-MOF 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 3D macroporous structure.This work will stimulate widespread interest in the study of amorphous MOF nanostructures with abundant active sites for improved electrocatalysts and beyond.2.In Situ Growth of 2D Fe-Doped Ni-BDC Nanosheets on Ni Foam For Efficient Electrocatalytic Water and Benzylamine Oxidation.Highly active and stable bifunctional electrocatalysts for overall water splitting are important for clean and renewable energy technologies.By replacing the slow oxygen release reaction(OER)with a thermodynamically favorable electrochemical oxidation(ECO)reaction,the production of high value-added chemicals has attracted more and more attention.Nitriles as one important class of intermediate in chemistry and biology are widely used in synthesis of agrochemicals,pharmaceuticals,and fine chemicals.Therefore,in this study,Fe-doped Ni-BDC nanosheets were synthesized in situ on the surface of nickel foam by hydrothermal method for efficient electrocatalytic oxidation of benzylamine instead of kinetic slow electrocatalytic oxygen evolution.Due to its inherent ultra-thin nanosheet structure and optimized NiFe bimetallic coupling catalytic effect,the prepared two-dimensional NiFeMOFns/NF exhibits excellent benzylamine(BA)electrooxidation performance.Especially,the Ni9Fel-MOFns/NF requires an ultralow potential of 1.304 V vs reversible hydrogen electrode(RHE)to achieve a 10 mA·cm-2 current density,which indicates the fastest reaction and the most favorable thermodynamic condition.Obviously,the anode electrocatalytic benzylamine reaction is beneficial to the rapid hydrogen production at the cathode,thereby increasing the rate of the total hydrolysis reaction.This work provides an effective way to explore total water decomposition.3.Ni-CAT@NiFe-BDC Nanosheet Composites for Enhanced Water Oxidation CatalysisThe design and construction of efficient electrode materials are significant for electrochemical energy conversion and storage technologies.The oxygen evolution reaction(OER)is a key process in water splitting devices and metal-air batteries.Here,NiFe-BDC modified with 2D conductive MOF nanorods were synthesized and used as a catalyst for water oxidation catalysis in alkaline media.Vertical growth of conductive 2D MOF nanorods on the surface of NiFe-MOF nanosheets can significantly improve the activity of electrocatalytic oxygen evolution reactions.In the case of active NiFe-BDC nanosheet(Ni-CAT@NiFe-BDC/NF),the overpotential is 178 mV to reach a current density of 10 mA cm-2 in 1 M KOH,which is lowered by?50 mV after hybridization due to the synergy of two-dimensional nanosheets and conductive MOF nanorods and the synergy of Ni active centers and Fe species.Specifically,the 2D conductive MOF nanorods can improve the conductivity of the composite material,and the nanorod array is perpendicular to the surface of the nanosheet,which facilitates the mutual transfer of charges,thereby reducing internal resistance.The mutual transfer of electrons between Ni and Fe in NiFe-BDCns itself is conducive to the production of high-valence Ni,thereby generating oxyhydroxide active species that are more conducive to oxygen evolution reactions.This work provides a new idea for studying the direct use of composite MOF materials as electrocatalysts.