Application Of Ceramic Membrane With Straight-pore Structure In Hydrogen Production And Water Treatment

In recent years,the energy crisis and environmental pollution have gradually intensified,and it is urgent to find alternative energy sources and develop new environmental governance technologies.Ceramic membranes play an increasingly important role in these fields,mainly used in membrane separation fields,such as high temperature PM filtration,sewage treatment and membrane distillation.This is due to the high mechanical strength,strong corrosion resistance and adjustable pore structure of ceramic membranes,which can be used stably in harsh environments such as acid-base and high-temperature environments.Ceramic membrane structure is critical for applications.The ceramic membrane with straight-pore structure prepared by the phase inversion method has been widely used because of the large diameter straight-pores in the direction perpendicular to the membrane surface,which can reduce the mass transfer resistance and increase the specific surface area.This dissertation mainly studies the application of straight-pore ceramic membrane with unique structure in energy and water treatment.We propose to design a self-supported catalytic electrode using a conductive ceramic membrane with a straight-pore structure as the substrate for hydrogen production by electrolysis of water.The key research objective is to design self-supported electrodes for high current density applications,which are of most concern in industrial applications.High-performance and inexpensive separation membranes for membrane distillation and oil-water separation were also investigated.In the first part,according to the demand of high performance conductive electrode in water electrolysis hydrogen production process,we propose to design self-supported electrodes by utilizing the advantages of conductive ceramic membranes,such as hydrophilicity,high strength,erosion resistance,high conductivity,and easy generation of heterostructures.We selected tungsten carbide(WC)conductive ceramics with a platinum-like(Pt)electronic structure as the substrate to prepare robust ceramic membranes with open straight-pore structure,and further using CO2 oxidation and NH3 high temperature reduction,high catalytic activity of WO3-x nano whisker/WC heterojunction and nitrogen doped WC/W heterojunction were formed in-situ on the ceramic substrate,respectively.Thus,the self-supported electrode with high catalytic activity and stable application under high current density can be obtained,which has high industrial application value.In the second part,a stable and low-cost β-Sialon-mullite composite ceramic membrane was prepared for the preparation of fresh water resources and the treatment of oil-water pollution.By taking full advantages of its adjustable pore structure and low mass transfer resistance,excellent membrane distillation and oil-water separation performance were achieved.Further,the SiC ceramic membrane with 3D interconnected pore structure was prepared by combining foaming pore-forming and gel casting technology,which was applied in the field of high temperature PM filtration.In chapter 1,the characteristics of ceramic membrane and the preparation process of traditional ceramic membrane are introduced.Then the mechanism and application progress of preparing ceramic membrane with straight-pore structure by phase inversion are reviewed.Finally,the background and principle of electrolysis of water for hydrogen production and membrane separation applications such as water treatment are introduced.In chapter 2,the raw materials used in this paper and various testing methods are introduced.In chapter 3,the straight-pore structure WC ceramic membrane was prepared by combining phase inversion casting and pressureless sintering with a thickness of 0.6 mm,a flexural strength of 77.2 MPa,a porosity of 64.2%,and a straight pore diameter of 60 μm.A large number of nitrogen-doped WC/W(WC-N/W)heterojunctions were formed on the WC ceramic membrane after heat treatment in NH3,and a self-supported catalytic electrode for HER was obtained.The effects of heat treatment temperature on phase composition and electrochemical performance were systematically studied.The membrane electrode after NH3 reduction treatment at 1200℃ exhibits excellent HER performance,with overpotentials of 87 mV and 104 mV in acidic and alkaline solutions,respectively,and corresponding Tafel slopes of 44.9 mV/dec and 62.2 mV/dec.Moreover,it operates stably for 220 hours at multi-step current densities of 30-1000 mA cm-2 with excellent long-term stability.Combining the experimental and DFT calculation analysis,the excellent electrochemical performance is attributed to the WC-N/W heterointerface that modulates the electronic structure and promotes charge transfer.On the other hand,the straight-pore structure and superhydrophilic properties of the ceramic membrane facilitate the full contact between the electrolyte and the electrode,and also provide an escape channel for the generated hydrogen,which helps improve HER performance.In chapter 4,On the basis of the research in Chapter 3,the WC/WO3-x composite ceramic membrane self-supported catalytic electrode was prepared by heat-treating the straight-pore WC ceramic membrane in CO2 atmosphere and in-situ growth of WO3-x whiskers on the membrane surface and inside the finger hole.The effects of heat treatment temperature on the WO3-x whisker morphology,phase composition and HER performance were systematically investigated.The overpotentials of the membrane electrodes obtained by heat treatment at 900℃ are 107 mV and 123 mV in acidic and alkaline solutions,respectively,and the corresponding Tafel slopes are 59.3 mV/dec and 72.4 mV/dec.Moreover,excellent long-term stability is achieved by stable operation at 30-400 mA cm-2 multi-step current density for 180 hours in both acidic and alkaline solutions.Oxygen vacancies and WC/WO3-x heterointerfaces in membrane electrodes can modulate electronic structure and facilitate charge transfer.Moreover,the straight-pore structure and superhydrophilic properties of the ceramic membrane can also improve the HER reaction efficiency,so the prepared electrode can achieve excellent electrochemical performance.In chapter 5,β-Sialon-mullite ceramic membranes with high mechanical strength and rough surface were prepared by phase inversion casting and vapor phase growth.High oil droplet rejection(94%)can be achieved in oil-water separation experiments.The water contact angle of the ceramic membrane after PDMS hydrophobic modification is 165°,showing superhydrophobicity.In addition,in the membrane distillation experiment of 4 wt%NaCl solution,it was stable at 75℃ for 400 hours,showing excellent stability.In chapter 6,porous foamed mullite-bonded SiC ceramic membranes with 3D interconnected pore network were prepared by combining foaming pore-forming and gel casting technology.By adjusting the content of foaming agent,the morphology,strength,pore size distribution and porosity of the ceramic membrane can be adjusted.The ceramic membrane has high PM filtration efficiency(70.2%,90.1%,and 94.6%for PM 0.3,PM 2.5,and PM 10,respectively)and ultra-low pressure drop(27 Pa)in high temperature PM filtration experiment.Therefore,the prepared ceramic membrane has guiding significance in the fields of high-temperature PM filtration and air filtration.In chapter 7,all the research contents are summarized and puts forward the prospect.