The Study On Electrocatalytic Performance Of Metal-organic Framework Composite Platinum And Palladium Nanomaterials

Hydrogen-oxygen fuel cell is a new type of energy conversion device with high energy conversion efficiency and excellent environmental friendliness.Its electrode reactions include anodic hydrogen oxidation reaction（HOR）and cathodic oxygen reduction reaction（ORR）.The required raw materials,hydrogen and oxygen,can be obtained from hydrogen evolution reaction（HER）and the oxygen evolution reaction（OER）of electrolytic water.Electrocatalytic reactions mainly occur at the interface between electrodes and reactants,with high potential barriers and slow kinetics,which reduce the efficiency of electrode reactions.Designing and developing efficient electrocatalysts is an effective strategy to improve the efficiency of electrode reactions.Metal-organic frameworks（MOFs）are composed of transition metal ions and organic ligands,which can be in situ transformed into transition metal/carbon matrix composites with regular morphology after high temperature annealing treatment.The obtained composites have good electrical conductivity and abundant catalytic active sites,which can accelerate the electrode reaction rate.However,when MOFs-derived materials are used as supports to anchor noble metals on the premise of maintaining their morphology,it is still challenge to achieve the uniform distribution of noble metals in the support and enhance the synergistic effect of noble metals and transition metals in MOFs.In this thesis,the following studies have been carried out on the morphology control of Ni,Co and Zn-based MOFs and their effective compositing with Pt-group metals.（1）First,nanorod-like Ni-MOFs were prepared by liquid-phase self-assembly reaction using Ni Cl₂·6H₂O and 1,3,5-benzenetricarboxylic acid.The step-by-step annealing process was utilized to firstly realize the carbonization of the organic ligands in an argon atmosphere,then the Ni was in-situ reduction on the carbon-based carrier in argon-hydrogen mixture atmosphere,which prepared Ni/C series catalysts with Ni particles dispersed uniformly on on carbon supports.Compared with other samples obtained at different temperatures and atmospheres,Ni/C-H₂-700℃catalyst showed the best catalytic activity in water splitting reaction.This attributed to the synergistic effect between carbon-based supports with excellent electrical conductivity and Ni particles with high catalytic activity.（2）Based on the above-mentioned preparation process of MOFs precursor,zeolite imidazole framework（ZIF-67）with polyhedral structure was obtained through liquid-phase self-assembly reaction of Co（NO₃）₂·6H₂O and 2-methylimidazole.By adjusting the annealing temperature,cobalt oxide/carbon based porous framework were obtained retaining the polyhedral structure.The material has abundant sites and large specific surface area,which can anchor and disperse precious metal palladium.Then the Pd/Co₃O₄-N-C series catalysts was obtained with Pd uniformly attached inside the polyhedral framework,named Pd/Co₃O₄-N-C-280,Pd/Co₃O₄-N-C-300,Pd/Co₃O₄-N-C-350.Electrochemical test results showed that the Pd/Co₃O₄-N-C-300 catalyst exhibited the highest half-wave potential and catalytic performance toward ORR.Compared with Pd/C,the mass and area activity of Pd/Co₃O₄-N-C-300 were greatly improved,owing to the synergistic effect between Co₃O₄/carbon-based framework with abundant active sites and Pd nanoparticles.（3）Finally,the Zn/Co-ZIF precursor with higher dimensional stability was prepared by introducing Zn²⁺into the ZIF-67 precursor basing on the regular morphology of ZIF-8.The Zn/Co-containing carbon matrix was obtained by annealing treatment of Zn/Co-ZIF,which used for template to anchor precious metal platinum.Then,the ordered Pt₃Co intermetallic compound catalyst were prepared by the atomic rearrangement of platinum and cobalt under high-temperature calcination.Compared with the ZIF-67-derived Pt Co/C and ZIF-8-derived Pt Zn/C catalysts,the Pt₃Co/C catalysts exhibited better oxygen reduction catalytic activity and stability under both acidic and alkaline conditions.This benefitted from the ordered structure of Pt₃Co,the structural stability of Zn/Co-ZIF,and the synergistic effect of Pt₃Co and carbon matrix.