Fabrication Of Pd-based Catalysts And Investigation Of Their Electrochemical Ability For Formic Acid And Alcohols Oxidation

Due to the continuous depletion of fossil fuel, finding a new and sustainable fuel is very important and emergency. Direct liquid fuel cells attracted lots of attentions from researchers, because of their high efficient, security, clean, and can be operated at low temperature. However, there are some defects restricting their development, such as the high price and easily CO poisoned and deactivation of catalysts. In order to solve these problems and promote the development of fuel cells, new catalysts, with high catalytic activity and poisoning resistance, should be fabricated. Pd and Pt are in the same group, and have similar electrochemical capability. In addition, Pd is much cheaper and more abundant in the earth compared with Pt, and Pd shows great CO poisoning resistance. Therefore, Pd is regarded as a substitution of Pt catalysts. Unfortunately, naked Pd is prone to aggregate, which restricts its electrochemical activity. To solve these problems, we decided to fabricate Pd-based catalysts with high Pd dispersion, high catalytic activity, strong poisoning resistance and excellent durability.In this paper, we adopted a facile and simple chemical method to fabricate Pd/TiO2-MWCNTs and modified Pd/TiO2-MWCNTs catalysts. Modified TiO2 was applied as support material between Pd nanoparticles and MWCNTs template to improve the electrochemical capability of the catalysts. TEM, XRD, and XPS methods were applied to analysis the morphology of the catalysts. In addition, CV, I-t, and EIS methods were utilized to analysis the electrochemical ability of Pd-based catalysts. Major results are listed as follows:(1) A new model of catalyst was fabricated, which applied TiO2 as support material between Pd nanoparticles and MWCNTs template. TiO2 was utilized to enhance the Pd dispersion and promote the electron transfer in the catalysts. Therefore, the electro-catalytic activity of catalysts can be enhanced, and the price of catalysts can be decreased.(2) TiO2 is semiconductor with low conductivity, which restricts its application in the field of electrochemistry. In order to fabricate TiO2-based catalysts with high conductivity, HNO3 was adopted to modify TiO2 in order to increase its conductivity and surface activity. The research found that the application of modified TiO2 as support can fabricate TiO2-based catalysts with excellent conductivity.(3) The results of TEM, XRD, and XPS tests indicated that the application of HNO3 to modify TiO2 could improve its surfactivity, thus enhancing the integration between TiO2 and Pd, MWCNTs. In addition, the introduction TiO2 into catalysts could increase Pd dispersion and decrease Pd particle size. On the other hand, the results of electrochemical tests indicated that the application of TiO2 as support material in Pd/TiO2-MWCNTs could improve the catalyst’s catalytic activity and long-term cycle stability (durability) for formic acid oxidation. This might be due to the high Pd dispersion and the function of TiO2 which promote the electron transfer between Pd and MWCNTs.(4) To improve deactivation resistance of the catalysts, HF and HNO3 was adopted to modify TiO2 in order to further increase its conductivity and surfactivity. And by utilizing this modified TiO2, we successfully fabricated the modified Pd/TiO2-MWCNTs catalyst. The TEM, XRD, and XPS tests showed that the introduction of TiO2 which was modified by HF and HNO3 could increase Pd dispersion and loading, and decrease Pd particle size. Therefore, the availability of Pd was enhanced by this method.(5) The results of electrochemical tests for formic acid oxidation by different catalysts indicated that the modified Pd/TiO2-MWCNTs catalyst showed better electro-catalytic activity, long-term cycle stability (durability), and deactivation resistance compared to Pd/MWCNTs and Pd/TiO2-MWCNTs catalysts. This might be due to the conductivity and surfactivity of TiO2 were further enhanced by the pretreatment of HE In addition, the integration of TiO2 and Pd, MWCNTs was strengthened as well.(6) The results of electrochemical tests of alcohols oxidation by different catalysts indicated that the introduction of TiO2 which was modified by HF and HNO3 could enhance the electro-catalytic activity, long-term stability (durability), and deactivation resistance of the catalysts. The electro-catalytic activity for alcohols oxidation by modified Pd/TiO2-MWCNTs catalyst was:ethanol> methanol> isopropanol, and the long-term cycle stability (durability) for alcohols oxidation was: ethanol> isopropanol> methanol. And then ethanol was adopted to study the mechanism of alcohols oxidation. The results indicated that the alcohols electro-oxidation process is irreversible and diffusion controlled.Based on the above results, we found that the application of semiconductor oxide (TiO2) as support material between noble metal nanoparticles (Pd) and carbon-based template (MWCNTs) could enhance the electro-catalytic activity, durability and deactivation resistance of catalysts. These findings were expected to solve the problems which restrict the development of direct liquid fuel cell.