Preparation And Electrocatalytic Properties Of Co(?)/Ni(?)-benzenecarboxylic Acid Metal-organic Frameworks

Electrochemical water splitting is one of important hydrogen production technologies.However,the high energy barrier in the oxygen evolution reaction(OER)limits the water electrolysis greatly.Though RuO2 and IrO2 are the most efficient electrocatalysts for OER,their high price and limited reserves make the industrial-level applications impossible.Metal-organic frameworks(MOFs)were widely applied in fields of chemical sensing,catalysis,and drug delivery due to the advantages of the uniform and abundant metal sites and cavities.Among them,transition metal-based MOFs with rich active sites,diverse structures and low price attract a lot of interest in electrocatalysis.Herein,with Co(?)or Ni(?)as the metal sources,a series of transition metal-based MOFs were prepared under ionothermal or hydrothermal conditions,whose electrocatalytic performances were investigated and compared to explore the influence of synthesis method on the electrocatalytic performances.1.Ionothermal synthesis of 4,4'-biphenyldicarboxylic acid(H2BPDC)with Co(?)or Ni(?)gave out three allomeric three-dimensional MOFs([RMI]2[M4.5(BPDC)3.5(HBPDC)2(OAc)2](M=Co,R=E,(1);M=Co,R=P,(2);M=Ni,R=P,(3)).Amino groups were grafted on the surface of Au nanoparticles to prepare ammoniated Au nanoparticles(AuNPs-NH2),which were assembled with compounds 1-3 to prepare MOF@AuNPs-NH2 composites.Three MOF@AuNPs-NH2 composites were utilized to catalyze the H2O2 reduction process.It indicated that compound 1 showed better catalytic performance.The electrochemical tests of H2O2 detection in 0.1 M NaOH with compound 1 as catalyst indicated that compound 1 showed its potential in H2O2 detection in alkaline solution(pH=13).2.Possibility of compound 1 applied in OER.Because compound 1 is not waterstable,our work tried to transfer compound 1 into an efficient OER electrocatalyst with high stability and efficient OER electrocatalyst.The transfer will follow the posttreatment to prepare derivatives and the synthesis to improve the catalytic ability.By the specific methods of oxygen-free sintering,medium-temperature phosphorization,electrostatic spinning,heterogeneous metals doping,self-sacrificing templates with metal oxide nanomaterials and a natural sedimentation,self-supporting electrodes were prepared to support the transfer.The results indicated compound 1 was micrometer-sized hexahedra with large size.It is difficult to embed compound 1 in one-dimensional polyacrylonitrile nanofibers to prepare Co-containing carbon-based material.High temperature destroyed the framework,leading to agglomeration.Furthermore,the high viscosity of the ionic liquid made the ligand hard to be deprotonated,resulting in metal oxide hardly reacting with ligand in synthetic process.In summary,it is a long way for us to go if applying compound 1 in OER considering there are many factors.3.A series of Co(NDC)(H20)4,Ni(NDC)(H2O)4,Co/Ni(NDC)(H2O)4(CoNi-NDC)were prepared under hydrothermal conditions with 2,6-naphthalene dicarboxylic acid dipotassium(K2NDC)as ligand and Co(II)and/or Ni(II)as the metal sources.With the hydrogen bindings forming between-NH2 groups of PANI and-COO-groups of NDC2in MOFs,self-supporting composite electrodes for OER can be prepared as MOFs loaded on foamed nickel(NF)coated with PANI.By optimizing the synthetic conditions of MOFs,the optimized self-supporting electrode CoNi-NDC/PANI-NF was obtained with an extraordinary OER electrocatalytic performance:low overpotential of 323 mV in 1.0 M KOH solution at a current density of 10 mA/cm2;Tafel slope of 73.3 mV/dec.Also,CoNi-NDC/PANI-NF exhibits excellent repeatability and stability.