Synthesis And Electro-catalytic Performance Of Nickel Based Nanomaterials

With high surface areas, nanostructured materials can effectively improve the catalytic activity, thus have received widespread interest in electrocatalysis. Nowdays, with the tremendous growth of demand for energy, depletion of fossil fuels and worsened environmental pollution, it is urgent to develop renewable clean energy sources. Fuel cell and hydrogen, as high energy efficiency and environmentally friendly secondary energy, have been a hot topic in the field of energy research. Thus it is important to develop new type of nano electrocatalyst for electrochemical systems, such as direct methanol fuel cell and water splitting devices, which is a key step to promote commercial use of these clean energy. Earth-abundant transition metal nickel（Ni） and its compounds are an interesting non-noble-metal alternative, because of its cost effectiveness（global Ni reserves are just less than silicon, oxygen, iron and magnesium, ranking fifth） and high electrocatalytic activity. In this thesis, we describe the fabrication of Ni based nano self-supporting electrode and their application in electro-oxidation of methanol and electro-catalytic water splitting.The main research results are as following:1. We describe the first fabrication of nickel oxide nanosheet@nanowire arrays on Ni foam（Ni O NS@NW/NF） through a hydrothermal process followed by annealing treatment, thus obtain 3D self-supporting electrode. When directly used it as anode for electro-oxidation of methanol, the Ni O NS@NW/NF electrode exhibits high catalytic activity and stability, affording a current density of 89 m A cm^-2 at 1.62 V（vs. RHE） in 1 M KOH with 0.5 M methanol, which is 3 times higher than that of NF(30 m A cm^-2). In addition, the hierarchical architecture of Ni O and 3D self-supporting configuration of this electrode favors the exposure of more active sites and facilitates sufficient transport of reactants and products, resulting in high electrocatalytic activity.2. We develop a simple solvothermal method for configuration of Ni O/Ni, Ni3S2/Ni, Ni Se/Ni self-supporting electrodes. The electro-catalytic performance of nickel chalcogenides（Ni O, Ni3S2, Ni Se） nanowires is also systematic studied and the electro-catalytic activity is in the order of Ni Se > Ni3S2 > Ni O. When used as a 3D self-supporting anode for electro-catalytic oxidation of methanol, the Ni Se/Ni achieves a current density of 132 m A cm^-2 at 0.5 V（vs. SCE） in 1 M KOH with 0.5 M methanol, which is 4 times higher than that of NF(32 m A cm^-2).3. It is still a challenge to realize efficient electro-catalyic water splitting in the same electrolyte, including oxygen evolution reaction（OER） and hydrogen evolution reaction（HER）, which has been rarely reported so far. In this chapter, we report a 3D self-supporting electrode prepared by a versatile and one-step electrodeposition of Ni Fe nanosheets film on NF substrate（Ni Fe/NF）. The Ni Fe/NF shows high catalytic activity for both OER and HER in basic media, and it only needs overpotentials of 264 m V to afford 20 m A cm^-2 for OER and 139 m V to deliver 10 m A cm^-2 for HER in 1 M KOH. Inspired by the bifunctional activity of Ni Fe/NF, we constructed an alkaline water electrolyzer using Ni Fe/NF as catalyst for both anode and cathode. This electrolyzer splits water with a current density of 10 m A cm^-2 at 1.64 V, which is superior to that of Ni Fe LDH/NF（1.7 V）.