Preparation Of The Three-Dimensional Porous Ni Based Metal Nanoelectrodes And Their Study Of Electrocatalytic Properties

The limited reserves of fossil fuels and the increasing environmental degradation make it imperative for the development of clean and renewable energy and energy storage devices. Hydrogen and fuel cells are considered to be two viable alternatives to fossil fuels because of their advantages of high energy density, non pollution, sustainable utilization and so on. At present, the development of efficient, stable, low-cost electrocatalysts and electrode materials for hydrogen production and fuel cells has become a research hotspot. And three-dimensional (3D) porous structure is an ideal morphology of the efficient electrodes. Based on these, we designed a series of 3D porous Ni based metal nanoelectrodes with large holes and small holes, which can improve the efficiency of mass transfer, increase the surface area of small holes and the content of surface active atoms. Moreover, through the design of superaerophobic Ni nanoflower electrode, ultrathin non-precious Ni nanosheets array and ultrathin Ni-Co alloy nanosheets array, the improvement of structure and control of the composition of the electrode materials were realized. And the excellent performance of hydrazine oxidation reaction and hydrogen evolution reaction was obtained. Detailed experiments and conclusions are as follows:1) We prepared 3D porous Ni nanoflower electrodes by solvothermal reducing Ni(OH)2 nanosheets array grown on Ni foam substrate. The obtained Ni nanoflowers showed a uniform size and well crystallinity. There are a lot of small holes between the nanoflowers and their petals and big holes in Ni foam. So the 3D porous structure with large holes and small holes was designed. Meanwhile,3D porous electrodes showed a superaerophobic surface and low adhesion force for bubbles, which could promote the bubbles to leave the electrode surface quickly and expose more active sites in time. Compared to commercial Pt/C catalysts,3D porous Ni nanoflower electrodes showed a much higher electrocatalytic performance and stability towards hydrazine oxidation reaction and hydrogen evolution reaction. What is more, this experiment also provides a new method for the controllable design of non-noble metal nanostructures.2) We obtained ultrathin Ni nanosheets array by putting Ni(OH)2 nanosheets array into a mild reduction condition and reducing slowly. The prepared Ni nanosheets had a layered structure, exposed (111) crystal surface, and showed a thickness of only 2.2nm. Because of a slow kinetics conversion process, the porous structure of nickel hydroxide array was preserved. Because of a rough surface, Ni nanosheets array had no adhesion force and showed a superaerophobic characteristic. Because of a large number of active surface atoms and a single crystalline nanostructure,3D porous ultrathin Ni nanosheets array showed a much higher electrocatalytic performance of hydrazine oxidation reaction than Pt/C catalysts. After partially oxidized, Ni/NiO nanosheets array could be used as an active catalyst of hydrogen evolution reaction and oxygen evolution reaction due to a tunable surface. To the best of our knowledge, the single crystalline Ni nanosheet is the first report of ultrathin non-noble metal nanosheets, which can provide a simple and feasible method for the preparation of non-noble metal nanosheets.3) We synthesised ultrathin Ni-Co alloy nanosheets array by slowly reducing NixCo1-x(OH)2 nanosheets array. The obtained Ni-Co nanosheets exposed (111) crystal surface and showed a single crystalline structure. And the two elements could be evenly distributed in the ultrathin nanosheets. Nio.6Coo.4 alloy nanosheets array showed a much higher electrocatalytic performance of hydrazine oxidation reaction than the other NixCo1-x nanosheets arrays, Ni nanosheets array, and Pt/C catalysts. When as an anode of hydrazine fuel cell, the cell assembled by Ni0.6Co0.4 alloy nanosheets array showed a higher open-circuit voltage and power density than that of Ni nanosheets array and Pt/C catalysts. To the best of our knowledge, the single crystalline Ni-Co alloy nanosheet is the first report of ultrathin non-noble metal alloy nanosheets, which can provide a simple and feasible method for the preparation of non-noble metal alloy nanosheets.