Preparation And Electrical Catalytic Properties Study Of Transition Metal Nanocomposites

The transition metal composite materials as electric catalytic electrode materials have received extensive attention. The goal of this dissertation is to synthesis of excellent Ni, Co, Fe nanocomposite materials such as hierarchical hydrotalcite nanoarrays, MOF-templated transition metal nanocomposite materials and transition metal/carbon nanocomposite materials. In addition, the electrochemical properties of these nanocomposite materials were studied. The details of this dissertation are summarized briefly as follows:1. By using a two-step hydrothermal method, Co/Ni hydrotalcite nanowire@ Co/Ni/Fe hydrotalcite nanosheet nanoarrays (H-LDH) was synthesized. We systematically researched the influence of the amount of Fe3+ on the morphology and the electrical catalytic properties of the nanoarrays. Then, the nanoarrays was used as electrocatalyst for oxygen evolution reaction (OER). Comparing to the Co/Ni hydrotalcite nanowires and NiCoFe LDH nanoparticles. The nanoarrays shows much better OER performance in KOH solution. When the Fe3+ was 1 mmol, H-LDH-1 nanoarrays shows the best OER performance with the lowest overpotential of 0.23 V, and the tafel slope of 53 mv/dec. The hierachical NiCoFe hydrotalcite nanoarrays shows better OER performance than Co/Ni hydrotalcite nanowires and NiCoFe LDH nanoparticles.2. A hybrid material consisting of Co and CoO nanoparticles distributed uniformly on hollow carbon (HC) nanocages as a high-performance catalyst for the oxygen reduction reaction (ORR) was prepared by using Co-imidazole based MOF (ZIF-67) as a precursor in different calcination temperature. In alkaline, the HC-700 exhibited superior performance towards oxygen reduction with an onset potential of 0.88 V, half-wave potential of 0.85 V, and nearly four electron selectivity (the electron transfer number is 4 at 0.3 V), which is comparable to commercial 20% Pt/C. The excellent electrocatalytic activity are mainly contributed to the high Co, N content and specific surface area. This work provides a new strategy for in situ synthesis of hollow nanostructure with metal-doped as high effective electrocatalysts for ORR in fuel cells.3. We successfully prepared higher performance ORR catalyst by appropriate content Zn doping to formation ZnxCo3-xO4 and Co loaded on graphitic carbon by using bimetallic organic frameworks as templates. The coprecipitation of Zn2+ and Co2+ ions derived from Zn(NO3)2-6H2O and Co(NO3)2-6H2O at an appropriate molar ratio in the presence of 2-methy- limidazolate to produce bimetallic zeolitic imidazolate frameworks (ZIFs) were prepared. The ZIFs were calcinated to get carbonized samples-Znx/Co3-x@C for ORR. The influence of the Zn content on ORR performance was investigated and the Zn0.5/Co2.5@C exhibited the best performance towards oxygen reduction compared to Co3@C without zinc doping in alkaline electrolyte and superior methanol tolerance in comparison to that of commercial 20% Pt/C. This work provides a new strategy for in situ synthesis of graphited carbon nanostructure with bimetal-doped as high effective electrocatalysts for ORR in fuel cells.