Study On The Electrocatalytic Performance Of Derived Materials From Polyoxometalate-Coordinated Structure Composites

With the improvement of the world’s scientific and technological level,problems such as environmental destruction,insufficient energy supply,and deterioration of the ecological environment have gradually intensified.In this context,developing clean and efficient energy is of great significance.As a kind of efficient and clean energy,hydrogen has been widely concerned by the international and scientific community.Water electrolysis is a safe and pollution-free method for hydrogen production.The key technology is to develop highly efficient and stable catalyst.At present,the most effective electrocatalyst for hydrogen evolution is platinum-based noble metal catalysts.Due to the scarcity of precious metals,the development of highly efficient and low cost non-precious metal catalysts is of highly significance.polyoxometalate（POM）is a class of polymetallic anionic oxygen clusters,which have special redox properties,semiconductor-like characteristics and acidic properties.polyoxometalates can be used as candidate materials in energy related fields such as electrocatalysis,rechargeable batteries,photocatalysis and proton conduction.Due to the rich negative charges,POM can form various coordination structure materials through coordination bonds with metal cations and organic compounds.In this paper,polyoxometalate is used as template,and transition metal nickel is used for structural coordination with organic ligands melamine and triethylamine,obtained Polyoxometalate-based bimetallic complex materials.The morphology,coordination structure and the valence state of the catalyst were studied by PXRD,TEM,SEM,XPS,Raman and nitrogen adsorption.In addition,the electrocatalytic performance of the catalyst was also studied.The main work contents are as follows:（1）Nickel-molybdenum-based catalyst Ni/Mo₂C@NC was synthesized by one-step high-temperature calcination using polyoxometalate Mo₁₃₂,transition metal nickel ions and polyvinylimine to form coordinated precursor structures.The overpotentials of Ni/Mo₂C@NC at 0.5 M H₂SO₄ and 1.0 M KOH are 127 m V and 107 m V,respectively,and the slopes of Tafel are 118 m V dec^-1 and 88 m V dec^-1,respectively.In addition,Ni/Mo₂C@NC shows 48 h stability.Through a series of characterization and electrochemical performance studies,the synergistic effect of Mo₂C and Ni,and the interaction between the front and rear transition metals improves the adsorption capacity of Ni/Mo₂C@NC for hydrogen intermediates.In addition,the porous structure facilitates the full contact between the electrolyte and the active sites to improve the catalytic activity.（2）Using triethylamine and polyoxometalate Mo₁₃₂,introducing transition metal nickel as precursor,through one-step calcination at different temperatures to obtain bifocal catalyst.The nickel-molybdenum-based heterojunction catalyst Ni/Mo N@NC was obtained at 800℃,which displays excellent hydrogen evolution performance.When the current density is 10m A cm^-2 in 0.5 M H₂SO₄,the overpotential is 94 m V.The excellent hydrogen evolution results from the synergistic interaction between Ni and Mo N.Ni/Ni O@NC catalyst was obtained by calcination at 400℃.It has good UOR effect in 0.33 M urea and 1 M KOH,and the voltage is 1.41 V when the current density is 10 m A cm^-2.The higher electrolytic properties of urea are attributed to its controllable composition and hierarchical nanostructures.（3）Using melamine as carbon source,long-chain polyethylene glycol induced melamine to form two-dimensional layered precursor through hydrogen bonding in water.The amine group was combined with polyoxometalate and nickel ions through coordination effect.The nickel-molybdenum-based Ni/Mo₂C@NC was synthesized by one-step high-temperature calcination.The overpotential of Ni/Mo₂C@NC at 0.5 M H₂SO₄ and 1.0 M KOH are 170m V and 146 m V,and the Tafel slopes are 102 m V dec^-1 and 84 m V dec^-1,respectively.Ni/Mo₂C@NC shows good hydrogen evolution activity and stability.The good performance of Ni/Mo₂C@NC is attributed to the coordination structure of the precursor and the synergistic action of the bimetal,as well as the protection of the carbon shell can improve the stability of the catalyst.In this paper,through the synthesis of different molybdenum based polyoxometalate,organic ligands and transition metal nickel ions formed coordination structure precursors,and then through high temperature calcination,nickel-molybdenum based electrocatalysts are synthesized.The catalytic performance and reaction mechanism of these electrocatalysts were studied,which can provide a general for the design and synthesis of non-noble metal electrocatalysts.