Preparation And Electrocatalytic Properties Of Transition Metal Based Composites

In recent years,the search for inexpensive,environmentally friendly and efficient energy conversion catalysts has become a primary goal of research due to the growing demand for renewable and clean energy sources.Currently transition metal-based oxides are widely used in electrocatalysis due to their easy compounding with other materials and their inherently good catalytic properties,but further improvement of their catalytic activity remains a great challenge due to the poor electrical conductivity and selectivity of the materials.In the transition metal-based oxides,increasing the surface active area,the number of active sites on the material surface and the synergistic effect of bimetals were beneficial to the catalytic activity,which provided a new idea for the design and preparation of electrocatalysts with controllable surface morphology.In this paper,phosphorus-doped bimetallic oxides（P-Co Mo O₄@Ni）,core-shell structured oxides（HKUST-1@Cu₂O）with Cu₂O wrapped around HKUST-1 and metal oxides（Cu₂O@HKUST-1@CF）prepared by using three-dimensional porous materials as substrates were studied as inexpensive and efficient transition metals.The main studies are as follows:（1）The hydrothermal and reduction heat treatments were used to prepare phosphorus-doped P-Co Mo O₄@Ni composite electrocatalysts.The effects of different molar ratios of metal sources,solution concentrations,phosphorus atom doping,monometallic and different metal sources on the catalyst performance were investigated.The overpotential of P-Co Mo O₄@Ni-1 was only 98 m V at a current density of100 m A cm^-2under 1 M KOH electrolyte conditions.The catalyst exhibited negligible current decay and excellent stability over 24 hours.The modification of the catalytic activity of this catalyst material should be mainly attributed to the specific nanoflower morphology and the changed in the number of active sites of the composite catalyst.This work provided an experimental and theoretical basis for design and controlled synthesis of high-performance HER electrocatalysts.（2）Homogeneous nanosphere catalysts（HKUST-1@Cu₂O）consisting of HKUST-1 wrapped by Cu₂O were synthesized using HKUST-1 prepared by hydrothermal method as the core.The effects of the catalyst activity and selectivity were investigated before and after the composite,different loading amounts of HKUST-1 and different amounts of hydrophobic materials（PTFE）.The composite catalyst material showed excellent selectivity for ethylene with a Faraday efficiency（FE）of 46.08%（-1.0 V vs RHE）.And the current decay was negligible under the voltage of-1.0 V vs RHE condition for 3h continuous test,which showd excellent stability.The composite material possesses excellent catalytic activity of Cu₂O and high adsorption capacity of metal organic frameworks（MOFs）for CO₂gas,which further enhances the catalyst activity and selectivity to ethylene.These unique properties have provided opportunities in this work to design MOFs-based material catalysts with larger specific surface area,higher adsorption capacity,and more catalytic active sites.（3）On the basis of the second work,we prepared homogeneous HKUST-1 nanowire catalysts（Cu₂O@HKUST-1@CF）in situ on the surface of CF by hydrothermal method after the substrate was subjected to a redox process because of the complicated preparation procedure required for its electrode.The composite catalyst material showed excellent selectivity for carbon monoxide and methane,with a high Faraday efficiency（FE）of 59.38%for the C₁production（-1.1 V vs RHE）.By investigating the effect of adding different amounts of Cu（NO₃）₂and different amounts of PTFE on the catalytic performance before and after compounding.The effects of before and after compounding,the addition of different amounts of Cu（NO₃）₂and different amounts of hydrophobic material（PTFE）on the catalytic performance were investigated.The catalyst exhibited excellent stability（-1.1 V vs RHE）under continuous testing for 5 h.The addition of hydrophobic materials significantly suppressed the occurrence of HER and improved the selectivity for CO and CH₄.In this work,new strategies were provided to simplify the electrode preparation process and to suppress the occurrence of side reactions.