Synthesis And Electrochemical Properties Of Co,Ni-based MOFs

Metal-organic frameworks（MOFs）have been widely used in electrocatalysis,sensing,gas adsorption and separation,drug delivery and electrochemical energy storage,due to their ultra-high specific surface area,designed pores,and rich active sites.Here,a series of MOFs have been designed and synthesized with Co²⁺and Ni²⁺as metal sources,and their electrochemical energy storage and electrocatalysis properties have been investigated,aiming to obtain the MOF materials with potential electrochemical applications.As the following are the primary research contents:（1）TwonovelMOFs,[Co（HNTB）（bif）]·3H₂O·DMA（1）and[(Ni₂（μ₂-O）（HNTB）₂（bif）₂]·2H₂O·2H₃O·2DMA（2）,have been generated based on a tripod-type flexible carboxylic ligand（4,4’,4"-Nitrilotrisbenzoic acid,H₃NTB）and a rigid N-donor ligand（2,7-bis（1-imidazoly）fluorene,bif）by solvothermal method.The single-crystal X-ray diffraction results indicate that complex 1 exhibits a 2D layered structure and 2 is a 3D microporous structure with an anionic skeleton.Significantly,their electrochemical tests indicate that both of them own excellent capacitive performance at 1 A g^-1.Complex 1 has high specific capacitance(329.6 F g^-1)with cycling durability（retained73.2%over 8000 cycles）.Complex 2 has high specific capacitance(301.2 F g^-1)with cycling durability（retained 58.9%over 3000 cycles）.Additionally,an asymmetrical ultra-capacitor based on complex 1 and activated carbon（AC）delivers a maximum energy density of 20.9Wh kg^-1at 800.0 W kg^-1and a high cycle stability with 89.2%of the primary capacitance over 8000 cycles.Moreover,complex 2//AC owns an energy density of 19.3 Wh kg^-1at750.0 W kg^-1and a high cycle stability with 88.6%of the primary capacitance over 8000cycles.（2）Two novel MOFs,[Co（bcpp）（bbip）]·H₂O（3）and[Ni（bcpp）（bbip）]·H₂O（4）,have been generated based on a V-type flexible carboxylic ligand（3,5-bis（4-carboxyl phenoxy）pyridine,H₂bcpp）and a rigid N-donor ligand（1,1’-（1,4-phenylene）bis（1H-benzimidazole）,bbip）by solvothermal method.Moreover,a series of bimetallic Co_xNi_y-MOFs（x/y=1∶1,2.5∶1,2.75∶1,3∶1,3.25∶1 and 3.5∶1）are obtained by solvothermal technique.Their electrochemical tests indicate that Co_xNi_y-MOFs possess remarkable electrochemical storage properties.Significantly,the Co_2.75Ni₁-MOF has high specific capacitance(699 F g^-1)at 0.5 A g^-1and cycling durability（retained 72.7%over 3100 cycles）.Additionally,an asymmetrical ultra-capacitor based on Co_2.75Ni₁-MOF and AC delivers a maximum energy density of 20.44Wh kg^-1at 387.49 W kg^-1and a high cycle stability with 85.4%of the primary capacitance over 15,000 cycles.（3）The iridium（Ir）doped Ni-MOF nanoparticles（Ir@Ni-MOF-x/NF）were synthesized by a one-step solvothermal in situ grown on nickel foam（NF）.As a result,Ir@Ni-MOF-x/NF nanoparticles exhibit excellent hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）performances.With Ir loading of～2.75 at%,Ir@Ni-MOF-0.08/NF nanoparticles in 1 M KOH alkaline solution afford HER and OER current density of 100 m A cm^-2at an overpotential of 105 and 293 m V,respectively.When Ir@Ni-MOF-0.08/NF is used as both anodic and cathodic（pre-）catalyst,it enables overall water splitting at a current density of 50 m A cm^-2for a cell voltage of 1.666 V keeping 32 h without i R compensation,which is much superior to state-of-the-art Ru O₂-Pt/C-based electrolyzer.