Electrocatalytic Performance Of Noble Metal Supported Ce O₂ Nanostructures For Methanol Electrooxidation

Direct methanol fuel cell(DMFC) has gained widespread attentions due to its environmentally friendly property, high power density and portability. DMFC uses methanol as fuel and usually Pt-based nanomaterial as anode catalyst. However, Pt-based catalysts are easily poisoned by the intermediates that are produced during the electrooxidation of methanol, which could reduce their performance. It has become a major obstacle to their commercial application. Thus developing high performance anode catalysts is an important task for DMFC.Nanosized CeO2 has been successfully synthesized with different morphologies by using hydrothermal method through controlling the concentration of reactants, pH of the solution, reaction temperature and other conditions. Then they were used as supports for Pt nanoparticles to generate a set of integrated Pt/CeO2 catalysts. The morphology and structure of the catalysts were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and energy dispersive spectroscopy(EDS). The electrocatalytic perfromance of the catalyts toward methanol electrooxidation were studied by cyclic voltammetry(CV) and chronoamperometry. The conclusions are as follow:(1) CeO2 spherical nanopolyhedra(NP), nanocubes(NC) and nanorods(NR) were synthesized. The corresponding exposed surface crystal planes are:(111),(100),(110)+(100). Pt nanoparticles were then loaded on those as-prepared CeO2 with 20 wt%. In methanol electrooxidation, a support shape induced variation of the cataltytic activity of Pt/CeO2 has been found. The trend is Pt/CeO2(NR) > Pt/CeO2(NP+NC) > Pt/CeO2(NC) > Pt/CeO2(NP). From the CV curves, we detected the highest oxdiation peak current density(6.29 mA cm?2) on Pt/CeO2(NR) catalyst, which is 7.1 times higher than that on Pt/CeO2(NP) catalyst(0.88 mA cm?2). Those(110) and(100) planes on CeO2 nanorods surface seemly have the greatest enhancement on the electrocatalytic activity of Pt nanoparticles toward methanol electrooxition, which is more suitable as a support for nanosized Pt.(2) Pt loading amount has a significantly influence on the catalytic performance of Pt/CeO2 catalysts for methanol electrooxidation. With the Pt loading amount increasing from 10 to 50 wt%, the catalytic activity of the four kinds of Pt/CeO2 catalysts presents a volcanic type trend. Both of the Pt/CeO2(NP+NC) and Pt/CeO2(NR) catalysts show the best catalytic performance with the loading of 20 wt% Pt, while it was 30 wt% Pt loading for both of the Pt/CeO2(NP) and Pt/CeO2(NC) catalysts.(3) The heat treatment on the catalytic performance of Pt/CeO2(NR) was also studied. The results show that with the increasing of the treatment temperature the aggregation of the catalyst increase, inducing an increased size of Pt particles and a reduced electrochemical real area. As a result, the electrocatalytic activity of Pt/CeO2(NR) toward methanol electrooxidation decreases. So the Pt/CeO2(NR) catalyst without heat treatment exhibits higher catalytic activity for methanol electrooxidation.