| With the increasing of environmental problems such as atmosphere pollution, greenhouse effect, smog, etc caused by the consumption of fossil fuels, people have paid more attention on the development of clean, non-pollutant and renewable new energy resource. As a green and renewable energy carrier, hydrogen(H2) has been extensively studied. Water electrolysis is an important pathway for hydrogen production to meet the industrial requirement, but it needs to develop efficient cathode electrode with high activity and low overpotential toward hydrogen evolution reaction(HER) so as to save energy of electrolysis. In this thesis, nickel planar sheet and 3-dimensional(3D) porous nickel foam were used as the matrix/base material. By using electro-spark surface coating technology and double-glow plasma surface alloying technology, we have prepared a series of surface alloyed electrodes, respectively. Afterward, we have further prepared a novel kind of surface porous phosphide electrode via a phosphorization treatment. XRD, SEM, EDX and so forth were carried out to characterize the surface structure of these electrode materials. Meanwhile, linear sweep voltammetry(LSV), electrochemical impedance spectroscopy(EIS), potentiodynamic polarization and other electrochemical methods were conducted to analyze the catalytic performance of these modified electrode toward hydrogen evolution reaction in alkaline(1.0 mol/L KOH) and acid(0.5 mol/L H2SO4) medium.It can be found that some spots and craters structure with a certain amount of Mo element at a micron level was located on the surface of modified Ni@Ni-Mo electrode prepared by electro-spark surface coating technology. The micro-scale coarsening topography on the surface will increase the active surface area of the electrode, facilitating the decrease of overpotential for the hydrogen evolution reaction. Linear sweep voltammetry results revealed that surface modified Ni@Ni-Mo electrode possessed better catalytic activity and stability toward the HER, in good agreement with the results from the Tafel and EIS characterization.For the NF-W electrode system, which was prepared by double-glow plasma surface alloying technology, the catalytic activities toward the HER have been greatly improved. The NF-W sample obtained at 1000℃ exhibits better activity toward the HER than those obtained at other temperatures. With the extension of the treatment duration, tungsten content on the sample?s surface region was increased. The diameter of as-evolved particles attached on the surface of NF-W-2.5h and NF-W-3h was located at a nanometer range, undoubtedly contributing to a larger surface area. A relatively large size of the particles can be found on the surface of the other NF-W samples obtained. The electrochemical results indicate, the sample NF-W-3h has the best catalytic activity and good stability toward the HER. According to the Tafel curve, NF-W-3h alloy also reveals the lowest Tafel slope and onset overpotential value. With the increasing of potential, the charge transfer resistance Rct decreases rapidly, illustrating that the HER on the electrode surface has been greatly enhanced.For the phosphorization-treated electrode system, Ni-Mo-P obtained at 700℃, depicts a relatively uniform dendritic porous structure on the surface while a large number of fluffy structure was formed on the surface of NF-W-P. The existence of this porous or fluffy structure will increase the specific active surface area of the electrode accordingly, thereby reducing the onset overpotential for the HER. Linear sweep voltammetry showed that, the modified electrode phosphorized at 700℃ had the best catalytic activity for the HER compared with those obtained at the other temperatures. The phosphorized electrodes also reveal lower onset overpotential than those of non-phosphorized one. Meanwhile, the Ni-Mo-P and NF-W-P electrode obtained at 700℃ exhibit better stability and durability toward the HER, being well consistent with the Tafel and EIS results. |
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