Fabrication Of TiN/TiO₂@Ti Composite Nano-electrode And Its Electrochemical Behavior In Metaborate Solution

Sodium borohydride?NaBH₄?,a typical coordination-type hydride,commonly used as a reductant,and also recognized as excellent hydrogen storage material,has become the preferential hydrogen source in fuel cell system,but its high cost restricts the rapid application and development to a great extent.The present preparation technology of NaBH₄ is mainly based on the principle of chemical synthesis,in which there are still some bugbears to be solved,such as expensive raw material price,complex process,harsh conditions and intricate separating procedures.Moreover,the by-product,sodium metaborate?NaBO₂?,produced during hydrolysis of NaBH₄ for releasing hydrogen has yet to find high value-added application way,but its regeneration,as a boron source,to be converted to NaBH₄ has become a research hotspot in recent years.By regulating the scientific and reasonable process conditions,realizing electrochemical conversion from Na BO₂ to Na BH₄ on the cathode surface is advantageous to the boron resource recycling,but more importantly,is expected to implement high-efficient and low-cost production of NaBH₄ under mild conditions.In electrochemical process,electrode behavior plays a key role in achieving the target chemical process,so it is of great significance to extensively study electrode materials and electrode construction.As the main part of research content of the national natural science foundation project?No.21576073?,this work has carried out the controllable preparation of titanium?Ti?-based compounds,i.e,titanium dioxide?TiO₂?and titanium nitride?Ti N?with various morphologies,and construction of nano composite cathode electrode;the electrode process and electrochemical behavior for metaborate solution under different conditions have also been systematically investigated.The major research contents in this academic dissertation are as follows:?1?The content of BH₄^-in solution was determined by using linear voltammetry peak current route and iodimetry,and the measuring method of low concentration for BH₄^-has been established.On the Au electrode,the electrochemical behavior of NaBH₄ was studied by cyclic voltammetry,and the clear and stable characteristic oxidation peak?-0.473 V?of anion BH₄^-was found,and the qualitative criterion about the anion was ascertained.The linear volt-ampere scan results verified the satisfactory linear relationship between peak current and BH₄^-ion concentration in the range from1.0×10^-4 mol/L to 9.0×10^-3 mol/L of NaBH₄ content;the parallel measuring results for two different concentrations of NaBH₄ alkaline solution reveals the average relative error of less than 3.18%,with the higher accuracy and better reproducibility.In view of the lower concentration of BH₄^-ion formed in the electrolytic process,which requires to establish the determination method for trace BH₄^-concentration,the different concentration gradient of NaBH₄ alkaline solution(i.e.,1.00×10^-1mol/L¹.00×10^-5 mol/L)were accurately prepared.By adding excessive amounts of KIO₃ and KI,the content of BH₄^-in acidic solution can be determined via Na₂S₂O₃standard titration method.The test results from the tagged recovery and precision experiments confirmed that precise measurement range of iodine quantity method is in the range from 1.00×10^-1 to 1.00×10^-3 mol/L;the higher the concentration is,the more accurate measurement results are;otherwise,the error is bigger.The ions OH^-and BO₂^-with suitable concentration existing in the solution do not evidently interfere the analysis results of BH₄^-.?2?Based on the metal titanium sheet,the Ti O₂ nanowires were first fabricated via hydrothermal route,and then the Ti N porous nanotube array was also prepared by the ammonia reduction process.In titanium nitride crystal microstructure,N element inserting into the lattice of metal Ti increases the d-band holes,which can reduce the Fermi level.The physicochemical properties of TiN are similar with some elements of platine group,which endows TiN with excellent conductivity and catalytic activities.The phase composition,morphology and microstructure of Ti O₂ nanowires as well as TiN nanotubes were characterized by means of XRD,SEM,TEM and EDS techniques.Studying results show that the diameter of Ti O₂ was 20⁵0 nm with aspect ratio of 100,and average diameter of 80 nm of Ti N.Moreover,the porous surface of the TiN nano tubes with a higher porosity is helpful to improve the catalytic activity.?3?The electrode process and electrochemical behavior of the alkaline NaBO₂solution system were investigated by means of Ti N/Ti O₂@Ti nano composite cathode.For comparison's sake,by selecting different metal electrode as cathode,the electrochemical process and behavior for BO₂^-were systemically studied,confirming the indirect electrochemical reduction mechanism for BO₂^-.Then,using Ti O₂NWs@Ti and Ti N NTs@Ti electrode as cathode respectively,the electrochemical behavior of the Na BO₂ alkaline solution is investigated in detail through adjusting power supply,solution concentration,electrolytic time,adding additives,and so on.The scientific evaluation of electrochemical catalytic ability for the Ti-based composite electrode under different conditions achieves a lot of electrochemical basic research data,and the reasons causing the experimental phenomena are analyzed via reliable theoretical explanation.