Study On The Electrooxidation Of Methanol By Tin Doped Titanium Dioxide Nanomaterials

Direct methanol fuel cell(DMFC) have attracted widely attention and been studied systematically, owing to their low temperature of operation, environmental benignity and high operational efficiency. However, Pt/C, which is commonly used anodic catalyst for DMFCs, still have several grand challenges need to be overcome. The challenges contain high price of Pt, weak resistance towards CO poisoning, low catalytic activity, and poor stability. In this work, Sn doped TiO2 solid solution(Sn-TiO2) have been introduced into the catalyst of DMFC which play the roles of co-catalysts and support, with the point to improve both catalytic activity and stability of the catalyst. The electrochemical activity of the new produced catalyst were tested by a CHI660 e. The promotion mechanism of oxide towards the catalysts was discussed in detail.(1) A solvothermal method was employed to prepare Sn-TiO2 with different Sn:Ti ratio(TiO2, Ti0.9Sn0.1O2, Ti0.8Sn0.2O2, and Ti0.7Sn0.3O2). The solid solution was then mixed with Vulcan XC-72 carbon black, the mixture was used as support for Pt catalysts. CV curves of Pt catalysts supported on Sn-TiO2–C with different Sn:Ti ratio and different oxide:C ratio were compared. Pt/Ti0.9Sn0.1O2–C70 was finally selected to undergo the further testing. Such as CV in different solution, CA, and CO-Stripping Voltammetry. Otherwise, the electronic structure of the oxide and catalysts were analyzed by XPS. The incorporation of Sn element improve the capacity of oxygen groups on the oxide surface, which further promote the “bifunctional mechanism” of the oxide. Moreover, a special structure called “three phase boundary” were formed more easily, which are benefical to both activity and stablity of the catalyst.(2) Anatase TiO2 particles were firstly dispersed in 10 mol L–1 NaOH solution. Sodium titanate nanotube could be obtained after a hydrothermal reaction. And followed by acid washing, water washing, Sn ion exchanging, and anneal. The obtained sample were Sn doped TiO2 nanotube(Sn-TNT). The oxide was then mixed with Vulcan XC-72 carbon black, the mixture was used as support for Pt catalysts, noted as Pt/Sn-TNT–C. And Pt/Sn-TNT–C catalyst show improved catalytic activity towards methanol oxidation reaction when to compare with Pt/ Ti0.9Sn0.1O2–C catalyst. The reason could be explained as followed. The electronic conductivity of the oxide was improved when TiO2(B) are partly existed in the oxide lattice. The water content on oxide surface are improved as well.(3) Sn doped TiO2 nanotube were further modified by HF solution. The modified oxide(Sn-F-TNT) were then mixed with carbon black, the mixture was used as support for Pt catalysts. The electrochemical activity of Pt/Sn-F-TNT/C catalyst were tested and compared to that of Pt/Sn-TNT/C catalyst. The result show that CO poison resistance of Pt/Sn-F-TNT/C catalyst are high than that of Pt/Sn-TNT/C, and the activity of catalytic towards MOR of Pt/Sn-F-TNT/C are slightly higher than that of Pt/Sn-TNT/C. The results of XPS show that F element were absorbing on the oxide surface rather than incorporation into the lattice. The absorbing state of F– improve the electronegativity of the oxide, which could further improve the oxygen groups content on oxide surface and homogeneous dispersion of Pt particles.