Microstructure And Hydrogen Transport Properties Of TiC/V Hydrogen Separation Composite Membranes By Ion Beam Sputtering

Pd and its alloy hydrogen separation membranes are used in the research of hydrogen separation and purification due to the characteristics of high hydrogen selectivity and high hydrogen permeability.However,due to the limitation of mineral resources,palladium has high production costs and is difficult to realize large-scale production applications.The crystal structure of the fifth subgroup metal materials（V,Nb,and Ta）is mostly body-centered cubic structure,with a gap size that is easy for hydrogen atoms to dissolve.While the solid solubility is relatively large,hydrogen atoms are more likely to be in the crystal Diffusion is an ideal material for hydrogen separation membranes.Due to the phase stability and mechanical integrity of the hydride of V,and the lower hydrogen embrittlement tendency of V compared to Nb and Ta,V foil was chosen as the substrate.Pure V does not have the ability to dissociate hydrogen molecules.Compared with other transition metal carbides,TiC has high exchange current density and neutral binding energy,which makes it have higher hydrogen dissociation/polymerization catalytic activity,and can To avoid high temperature mutual diffusion with V,this thesis selects TiC as the surface hydrogen dissociation/polymerization catalyst layer.Compared with traditional magnetron sputtering technology,the ion beam sputtering process is less likely to produce atomic clusters due to cascade collisions,which is beneficial to the formation of nano-scale films.At the same time,there is no argon plasma area involved in the magnetron sputtering process,which can avoid Defects such as film oxidation caused by gas inclusions.Therefore,this thesis uses ion beam sputtering technology to prepare TiC catalytic film,uses X-ray diffraction analysis,energy spectrometer to analyze the phase composition and composition of TiC film,and uses electrochemical workstation to perform linear scan voltammetry,AC impedance and Cyclic scanning voltammetry and other tests to explore the structure,composition and hydrogen evolution catalytic performance of TiC films under different ion beam sputtering process parameters.Hydrogen permeation experiments were carried out on films prepared with different process parameters to explore the hydrogen permeation performance and hydrogen permeation behavior mechanism of TiC/V composite films under different ion beam sputtering process parameters.Based on this,this thesis also selects the composite film prepared by the optimal process parameters.The hydrogen permeation tests of the mixed gas were carried out.By studying the phase structure,composition and hydrogen evolution catalytic performance of TiC film under different process parameters（substrate temperature,substrate bias voltage,beam intensity and film thickness）,the optimal ion beam sputtering process parameters were determined.There are onlyδ-TiC and bcc-V in the phases of TiC/V composite films prepared with different parameters.As the substrate temperature increases,the Ti/C atomic ratio gradually increases,and the（111）crystal plane diffraction peak intensity of the TiC film gradually increases.Increasing,the crystallinity gradually increases,which improves the catalytic performance of hydrogen evolution.The diffraction peak intensity of the（111）crystal plane of the TiC film decreases with the increase of the negative bias voltage of the substrate,the crystallinity also decreases,and the Ti/C atomic ratio gradually decreases.The adsorption process on the surface of the TiC film is the rate-limiting step of the hydrogen evolution reaction.As the bias voltage increases,to achieve the same current density,the required overpotential gradually increases.The diffraction peak intensity of the（111）crystal plane of the TiC film first increases and then decreases with the increase of the beam intensity.The Ti/C atomic ratio also first increases and then decreases,and the hydrogen evolution catalytic activity first increases and then decreases.The deposition rate of TiC film prepared by ion beam sputtering is 5 nm min^-1.With the increase of TiC thickness,the Ti/C atomic ratio first increases and then decreases,the number of surface active sites decreases,and the hydrogen evolution catalytic activity first increases and then decrease.It is finally determined that when the substrate temperature is 673 K,the substrate negative bias voltage is 0 V,the beam intensity is 15 m A,and the film thickness is 50nm,the TiC thin film prepared by ion beam sputtering is the best coating process for hydrogen evolution catalytic activity.The hydrogen evolution overpotential required at cm²is 501 m V,the Tafel slope is 156 m V/dec,the transfer resistance is 1.59 kΩ,and the electric double layer capacitance is 0.22 m F/cm².The hydrogen permeation performance of TiC/V composite film under different ion beam sputtering process parameters（substrate temperature,substrate bias voltage,beam intensity）was studied,and the hydrogen permeation behavior mechanism was determined.At the same time,the TiC/V under constant temperature and pressure was studied.Hydrogen permeation performance of composite membrane under mixed gas.The hydrogen permeation flow rate of TiC/V hydrogen separation composite membranes prepared at different substrate temperatures is positively correlated with the hydrogen permeation temperature and upstream hydrogen pressure.n is the pressure correction index,usually between 0.5 and 1,depending on the metal membrane permeation process.The speed limiting step.When the temperature is low,the value of n is close to 1,and the membrane surface dissociation is the rate limiting step of the hydrogen permeation process.When the temperature is higher,the value of n is close to0.5,and the bulk diffusion is the rate limiting step.When the hydrogen pressure is 0.8MPa and the hydrogen permeation temperature is 923 K,the hydrogen permeation flow rate J of the composite membrane prepared with the substrate temperature of 673 K is the highest,which is 0.57 mol H₂m^-2s^-1,which corresponds to the electrochemical performance test results.The hydrogen permeability is about four times that of pure Pd.With the increase of the negative bias of the substrate,the hydrogen permeability of the TiC/V hydrogen separation composite membrane first decreases and then increases.Its hydrogen permeability coefficient is only related to temperature and not to the upstream hydrogen pressure.At 923 K,the substrate is negatively biased.The hydrogen permeation flow rate of the composite membrane prepared at 0 V is 0.57 mol H₂m^-2s^-1,and the n value of the composite membrane prepared with several substrate negative bias voltages is close to 1 at 723 K.As the beam intensity increases,the hydrogen permeation flow rate of the TiC/V hydrogen separation composite membrane first increases and then decreases.When the beam current is low,the target is excited by fewer sputtering particles,and when the beam current is too high,it is located at The deeper atoms cannot escape,so when the beam intensity is moderate,the number of excited atoms is the largest,the peak intensity of the TiC（111）crystal plane is the highest,and the hydrogen permeability is the best.After 200 h of long-term hydrogen permeation test（130 h of pure H₂test and 70 h of 5%CO₂+95%H₂mixed gas test）at923 K,it is found that when 5%CO₂is present,the hydrogen of TiC/V composite film The reason for the significant decrease in the permeate flow rate is not only the decrease of the upstream hydrogen partial pressure,but also because of the competitive adsorption effect of CO₂on the membrane surface.When the feed gas is restored to pure hydrogen,the hydrogen permeation flow rate gradually recovers,indicating that CO₂is not correct.The composite film causes damage,and the TiC/V composite film has good stability.Finally,the process parameters for the optimal hydrogen permeation performance of the TiC/V hydrogen separation composite membrane prepared by ion beam sputtering were determined:the substrate temperature was 673 K,the substrate was unbiased,the beam intensity was 15 m A,and the composite membrane hydrogen was at923 K.The permeation flow rate is 0.57 mol H₂m^-2s^-1,and the hydrogen permeability coefficient is 9.9×10^-8mol H₂m^-1s^-1Pa^-0.5.Its hydrogen permeability is better than TiC/TiC prepared by magnetron sputtering in the literature.V and Mo₂C/V hydrogen separation composite membrane,when the hydrogen permeation temperature is 923 K,the hydrogen permeation flow is close to the pure V hydrogen separation membrane in the literature.TiC/V is an ideal material for hydrogen separation composite membrane.