Fabrication Of A-Si_1-xAg_x Films And Study On The Regulation Of Electrical Properties And Electrochemical Hydrogen Storage Properties

Electrochemical hydrogen storage is one of the effective hydrogen storage methods due to its ability to store hydrogen in situ at room temperature and pressure.Nickel hydrogen（Ni-MH）batteries have been widely used in fields such as portable electronic devices,emergency equipment,and new energy vehicles after commercialization due to their high power characteristics,environmental friendliness,and safety and stability.However,compared with lithium ion battery（LIB）,the energy density of Ni-MH battery is relatively low due to the low capacity of hydrogen storage alloy electrode and the low decomposition voltage of aqueous electrolyte,which seriously affects its application in new energy vehicles and energy storage.Research has shown that hydrogenated amorphous silicon thin film has an extremely high electrochemical discharge capacity(3635 m Ah·g^-1)in proton type ionic liquids,making it highly valuable for research and application in proton type batteries,including nickel hydrogen batteries.However,the cycling stability and rate performance of this material’s electrode are significantly different from practical applications.In order to explore and improve the conductivity and electrochemical hydrogen absorption and desorption performance of amorphous silicon film electrode,we prepared a-Si_1-xAg_x films with similar film thickness by Magnetron sputtering codeposition technology based on the analogy and reference of current research results of nano silicon in LIB battery field,and on the basis that Si-Ag binary alloy can form eutectic structure,and studied the influence of deposition process on film composition and structure,The electrical properties of a-Si_1-xAg_x thin films before and after gas hydrogenation treatment were compared and analyzed,as well as their electrochemical behavior and hydrogen storage performance in proton type ionic liquids.The main research findings are as follows:（1）The a-Si_1-xAg_x films with similar thickness were prepared by Magnetron sputtering technology by controlling the sputtering power of the silver target and co-sputtering time.The proportion of Si and Ag elements in the films was quantitatively analyzed by EPMA.The atomic percentage of Ag in the prepared films was 15.456%,19.893%and 30.481%,respectively.The microstructure,chemical composition,and state of a-Si_1-xAg_x were characterized by SEM,GIXRD,TEM,XPS,and Raman spectroscopy.The results showed that the film was composed of uniformly dispersed silver nanoparticles embedded in the amorphous silicon matrix;There is no composite form between Si and Ag,and they are all composed in the form of elemental compounds;With the increase of silver content,the crystallinity of silver nanocrystals in amorphous silicon matrix is improved,and their grain size increases accordingly;With the increase of silver content,the short and medium range disorder of amorphous silicon matrix also increases.Under the same charging test conditions,a-Si thin films exhibited a specific discharge capacity of 1335.1 m Ah·g^-1 and a capacity retention rate of 33.2%after 80 cycles of activation.As the silver content increases,the film with intermediate silver content（Ag at%=20%）exhibits a maximum film discharge specific capacity of 887.7 m Ah·g^-1（calculated based on the total mass of the film）and a maximum active material discharge specific capacity of 1681.9 m Ah·g^-1（discharge specific capacity of silicon in the film）,and achieves a capacity retention rate of 64.19%after 80 cycles of activation,achieving the optimal electrochemical charge discharge performance and capacity retention rate of silver containing films.In terms of a-Si_1-xAg_x:H thin films,hydrogenation treatment can generally improve the maximum discharge specific capacity of a-Si_1-xAg_x thin films,but it will have a negative impact on their cycling performance.Among them,a-Si:H thin films achieved the maximum discharge specific capacity(1753 m Ah·g^-1),but only had a capacity retention rate of 23.4%after capacity decay;The a-Si_0.8Ag_0.2:H film exhibits a maximum film discharge specific capacity of 953.2 m Ah·g^-1,an active material discharge specific capacity of 1805.9 m Ah·g^-1,and an optimal capacity retention rate of 51.59%.After gas state hydrogenation treatment,the a-Si_1-xAg_x thin film achieved higher discharge specific capacity,but it also intensified the polarization degree of the high silver content a-Si_1-xAg_x thin film,exacerbated the damage to its internal structure,and reduced its capacity retention rate in subsequent cycles.（2）This article characterizes the electrical properties of a-Si_1-xAg_x using a four probe tester and a KEITHLEY 2400 digital source meter.The results show that as the silver content increases from 0%to 30%,the resistivity of the thin film decreases from 110Ω·cm to 12.5Ω·cm,a total of 4 orders of magnitude;According to the Schottky diode principle model,test samples were prepared and the contact types at the silicon/nickel interface were qualitatively analyzed.The results showed that the two can form good ohmic contact.Through linear fitting,the actual interface contact resistance values of the test samples prepared using a-Si_1-xAg_x thin films with Ag atom percentages of 0%,2%,5%,7%,and 12%were 1.31622Ω,1.33525Ω,1.37041Ω,1.36323Ω,and 1.3491Ω,respectively.（3）The electrochemical activity and impedance of a-Si_1-xAg_x films were analyzed using cyclic voltammetry and electrochemical impedance spectroscopy（EIS）tests.T he results showed that a-Si_1-xAg_x films exhibited good electrochemical activity;The diffusion coefficient of hydrogen ions in a-Si_1-xAg_x thin films was calculated using cyclic voltammetry（CV）method.The a-Si_0.8Ag_0.2 thin film has the highest diffusion coefficient in silver containing thin films,among which the a-Si thin film has the highest diffusion coefficient;The electrochemical impedance spectroscopy（EIS）results show that a-Si thin films exhibit the highest electron transfer impedance,while silver containing thin films generally have lower electron transfer impedance.The introduction of silver can effectively improve the electron transfer rate within the film.Among them,a-Si_0.8Ag_0.2thin films exhibit the lowest electron transfer impedance and the smallest W_O-T value,indicating that medium-sized silver nanocrystals can maintain the integrity of the amorphous morphology of the substrate while reducing the electron transfer impedance,Improving the solid-phase diffusion efficiency of hydrogen ions also results in the lowest electrochemical polarization and highest coulombic efficiency in electrochemical cycling performance testing.