Preparation and Catalytic Properties of Bi-functional Transition Metal-based Nanomaterials for Water Electrolysis

Author:Li

Supervisor:shen yan

Database:Doctor

Degree Year:2019

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Pages:140

Size:15807K

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Environmental problems caused by the rapid development of economy and energy are becoming more and more serious.Therefore,more and more attention has been paid to the research and application of green and renewable energy.Hydrogen is considered as an ideal alternative to fossil fuels in the future due to its advantages of high efficiency,renewable energy and zero carbon emissions.Electrolysis of water is the main way to produce renewable and stable hydrogen.In order to improve the efficiency of water electrolysis and reduce its cost,the key is to develop efficient,low-cost,low overpotential and low Tafel slope electrocatalysts for hydrogen and oxygen evolution reactions.In recent years,people pay more and more attention to replacing noble metal catalyst with low-cost transition metal-based materials.However,the activity and stability of transition metal-based catalysts are still generally lower than those of noble metal-based catalysts.According to the above problems,based on the preparation of nanostructured arrays,the electrolytic water properties of transition metal-based electrocatalysts might be effectively enhanced by means of hybrid structure construction,ion doping and special composition.The main research contents are as follows:(1)By optimizing the content of Fe in Cox-Fey-P,the morphology and catalytic performance of Cox-Fey-P can be adjusted.An appropriate amount of Fe helps to increase the electrochemical activity surface area of the catalyst,accelerate the electron transfer rate,and the strong electron interaction between heterogeneous elements can also promote its excellent catalytic performance.(2)The synergistic effect of composite nanowire array NiCo2O4@NixCoy LDH/NF can improve the overall charge transfer rate and catalytic activity of the catalyst.In addition,by adjusting the molar ratio of Ni/Co in NixCoy LDH,the strong electron interaction between Ni and Co,the heterogeneous elements on the interface of NiCo2O4and NixCoy LDH will ultimately promote the overall catalytic performance of the composite catalyst.(3)The thickness of FeOOH shell in the NiCo2O4@FeOOH/NF composite nanowire is regulated by optimizing the electrodeposition time.The NiCo2O4@FeOOH/NF(500 s)with the thickness of FeOOH layer about 7 nm has good catalytic activity and stability for hydrogen evolution and oxygen evolution in the alkaline solution.The thickness of the FeOOH layer and the strong electron interaction between the NiCo2O4 and FeOOH interface are crucial to its excellent catalytic performance.(4)Three-dimensional nickel-cobalt phosphate nanowire arrays were grown vertically on carbon cloth in situ for the first time by an improved phosphating method.Experiments combined with density functional theory calculations show that the synergistic effects of three-dimensional morphology,[PO3]doping,conductive matrix and NiCo mixed phosphate enable catalysts to have superior electrocatalytic activity against OER and HER.(5)Cobalt phosphate nanowire arrays doped with Na were prepared for the first time,using electrodeposition and improved phosphating methods.The catalyst material shows strong catalytic activity for hydrogen and oxygen evolution reactions.In addition,the application of 2.62%Na-Co2P2O7/CC as a bifunctional catalyst in the two-electrode system has been proved to have significant performance and long-term stability.Moreover,2.62%Na-Co2P2O7/CC electrode was used to assemble the sodium ion battery,which can drive 2.62%Na-Co2P2O7/CC to serve as both the cathode and the anode for overall water splitting.