NiCo-MOF, FeNi-MOF-5 And Phosphides Derived Form Them,the Synthesis,Characterization And Electrochemical Activity Of Water Splitting

Inorganic organic framework material(MOFs) is a kind of crystal composite with porous structure, which is built with metal ions and polyfunctional organic ligands. They have permanent pore structure, large surface area, adjusTable pore size and other properties. These properties make MOFs material to be ideal templates. In addition, because of the diversity of metal ions and organic groups, the MOFs have adjusTable structure and element composition.The organic functional groups are rich in C, N elements. According to the report, doping effect between different elements can improve catalytic properties of materials.Transition metal phosphides have been explored as highly efficient electrocatalysts, which have been widely used in OER and HER. In this study, MOFs have been used as ideal sacrificial templates for the generation of transition metal phosphides by thermal decomposition under controllable atmospheres.In this experiment, we use the hydrothermal method to synthesis the MOFs. Cobalt(Ⅱ) acetate tetrahydrate and nickel acetylacetonate are used as the metal ion source, terephthalic acid as polyfunctional organic ligands, PVP as surfactant.The mixed solution of DMF and water are solvent. NiCo-MOF and NaH2PO2 were placed in different porcelain crucibles, then the samples were heated at 350 ℃ for 180 min with a heating rate of 2 ℃.min-1 in N2 atmosphere. Finally, we get the bimetallic Phosphides Ni2P-CoP, which are coated with carbon film layer. The HER was evaluated in the solution of 0.5M H2SO4, the overpotentials and Tafel slope is -104 mV, 63 mV/dec, respectively. The OER was evaluated in the solution of 0.1M KOH, Ni2P-CoP only need overpotential of 320 mV,Tafel slope of 63 mV.dec-1. Both in the OER and HER activity test, the material all has excellent stability. EDX mapping shows that the elements Co, Ni and P are all well dispersed in the Ni2P-CoP. The HRTEM image of the Ni2P-CoP shows that Ni2P and CoP are together.Compared with Ni2P-CoP, Ni2P, CoP, mixture of Ni2P and CoP, we found Ni2P-CoP has the highest water electrolysis activity which can be attributed to the synergistic effects between the Ni2P and CoP.In this experiment, we also prepared MOF-5 containing Fe, Ni elements. Changing the molar ratio of Fe/Ni elements, we found that materials from cube structure into a cube 8 angle bar director structure,and the Fe/Ni value is bigger then the rod is thicker. The result of the BET test shows that the material with that Fe/Ni is 1:2 has the largest surface area and average pore diameter, respectively 507.3 m2.g-1 and 14 nm. The specific surface area and average pore size of the material decreased with Fe/Ni increased. After the reacton of FeNi-MOF-5 and NaH2P02 under 350℃ for 3 h, we got the bimetallic Phosphides of Fe,Ni. HER activity was test in solution of 0.5M H2SO4, When Fe/Ni was 1:2, the phosphides had the highest activity, the overpotential is -254 mV,Tafel slope is 96 mV/dec.