Effect Of Metal Oxide On Electrooxidation Of Alcohols On Pt And Pd Catalysts

In today’s world, because of the excessive use of fossil energy and the serious pollution of the environment, the development of new clean energy have received broad attention. Fuel cell is a kind of energy device which can directly convert chemical energy to electrical energy. It is very important in the development of new energy because it is an environmentally-friendly technology. More importantly, it can show much higher energy conversion efficiency as compared with traditional engines because it is not subjected to the Kano cycles. Among all kinds of the fuel cells, the proton exchange membrane fuel cells(PEMFCs) with hydrogen and small molecular alcohols as anode fuel have been rapidly developed in recent years. Compared with hydrogen, liquid fuel has high energy density and is easy to transport and storage, so it has great application prospect. In the small molecular alcohols, methanol is cheap and easily obtained, and ethanol is non-toxic and can be obtained from the fermentation of biomass. Both of them are potential fuels for PEMFCs. Pt and Pd materials are the most important and indispensable anodic catalysts for direct alcohol fuel cells. However, whether it is Pt or Pd-based catalyst, there are some problems such as the high cost, poor stability, and easy to poisoning of catalyst. In order to reduce the cost, enhance the catalytic activity and stability and improve the anti-poisoning ability of catalysts, a series of metal oxide and composite metal oxides promoted Pt and Pd catalysts are designed and prepared in this work. The catalytic properties toward the oxidation of ethanol and methanol are investigated. The main results are as follows:1. Composite oxides(MoO3)mSnO2 are prepared through the liquid phase precipitation method and used as the promoter to Pt catalysts(Pt-(MoO3) mSnO2/C). XPS spectra show that Mo species in the as-prepared catalysts are characteristic of MoO3, and the contents of metallic Pt(0), Pt(II) and Pt(IV) species in the samples are dependent on the composition of the composite oxides. Among the series of Pt-(MoO3)mSnO2/C samples, Pt-(MoO3)0.2SnO2/C has the highest content of Pt(II and IV). The result of electrochemical test show that the catalytic performance of Pt with SnO2 or Mo-doped SnO2 as the promoter are higher than that of commercial Pt/C catalyst, moreover, the Mo-doped SnO2 exhibits much higher promotion effect than SnO2. Among the as-prepared catalysts, Pt-(MoO3)0.2SnO2/C exhibited the most negative onset potential of MOR, the highest MSA and IA. The onset potential of MOR(-0.50 V) is ca. 30 mV more negative as compared with that on Pt-SnO2/C or Pt/C catalysts. The MSA(4.44 A mg-1Pt) and IA(93.6 A m-2Pt) of Pt in Pt-(MoO3)0.2SnO2/C is ca. 1.4 and 1.2 times higher than that of Pt-SnO2/C, and 3.0 and 3.5 times higher than that on the Pt/C catalyst.2. CeO2 nanoparticles are prepared through the traditional hydrothermal methods by rationally tuning the reagents or the reaction temperature. The as-prepared three kinds of CeO2 nanoparticles are used as the promoter to Pt catalysts(Pt/CeO2/C-1, Pt/CeO2/C-2 and Pt/CeO2/C-3 catalysts). The catalytic activities of the catalysts for methanol electrooxidation reaction in alkaline electrolyte are comprehensively compared. Results show that CeO2 could show significant promotion effect to Pt toward MOR. Among the Pt/CeO2/C catalysts, Pt/CeO2/C-3 shows the most negative onset potential of MOR, the highest MSA and the highest stability. The MSA of Pt/CeO2/C-3(2.65 mA μg-1Pt) is 2、1.33、2.2 times higher than that of Pt/CeO2/C-1(1.35 mA μg-1Pt)、Pt/CeO2/C-2(2.00 m A μg-1Pt) and Pt/C-JM(1.2 mA μg-1Pt) catalyst.3. Sb doped Ce O2 nano-composite materials are synthesized by the hydrothermal method. The as-prepared composite oxides are used as the promoter and support to Pt catalysts. The catalytic activities of the catalysts for methanol electrooxidation reaction in alkaline electrolyte are comprehensively compared. Results show that the addition of CeO2 in the Pt catalysts could show significant promotion effect to Pt. And the catalysts promoted by the Sb-doped CeO2 show more enhanced catalytic properties as compared with the non-doped catalysts. Among the as-prepared catalysts, Pd/Sb-CeO2/C shows the most negative initial potential of MOR(negative shift about 20 mV), the highest mass-specific activity(MSA). The MSA of Pd/Sb-CeO2/C(9.86 mA μg-1Pd) is 1.43 and 2.43 times higher than that of Pd/CeO2/C(6.88 mA μg-1Pd) and Pd/C-JM(4.05 m A μg-1Pd) catalyst.