The Study Of Controlled Synthesis Of Supported Palladium Nanocatalysts And Their Electrocatalysis Performance

As a kind of new clean energy, fuel cells have advantages of high efficient, security, andenvironmental-benign, so they received considerable attention. However, there are still some majorimpediments that hinder their large-scale industrial applications, including the high cost of nobel metalcatalysts. Therefore, improving the utilize ratio of catalysts and reducing the doage of nobel metal havebecome one of the key research fields of many researchers. It is well known that the size, morphology anddispersion of metal nanoparticles are strongly related to the supports. So it is required to chooseappropriate supports. Carbon nanotubes (CNTs) are considered to be a good choice of supporting material,owing to the special surface structure, high electrical conductivity, good thermal and chemical stability.However, metal nanoparticles are hard to deposit on it directly because pristine CNTs are chemically inert,.Conventionally, CNTs are functionalized by introduction of functional groups on the surface via harshoxidative processes. But the structure and mechanical properties of CNTs are impaired during the harshoxidative processes, which would reduce the corrosion resistance and electrical conductivity. Thus,developing a new method to make nanoparticles deposit on the surface of supports and control metalparticle size at the same time that has no damage to the intrinsic structure has becoming the researchhotspot. In consideration of the negative effect of CO-like intermediate species on catalysts during theelectrooxidation of fuel, metal oxides are proved to be another choice because of their promoting effect onremoving intermediate species and releasing free active catalytic sites of catalysts.In this paper, methods and structures for controlling synthesis of supported Pd-based catalysts areinnovated, and their morphologies, structures and catalytic performance of formic acid or ethanolelectoxidation are also studied. The main contents are as follows: (1) We give an overview of the development profiles of fuel cell, and present the conventionalmethods of fuel cell catalysts, the general research progress, and introduce the selected topic basis,research content and methods.(2) Based on the theory of complexes and chelate effect, we used sodium oxalate as additive to controlthe synthsis of Pd nanoparticles via a facile chemical reduction approach at room temperature, thenMWCNTs supported Pd catalyst was obtained. The Pd nanoparticles with the average diameter of5.6nmwere well dispersed. The as-prepared catalyst showed higher current density of140mA/cm2thanPd/AO-MWCNTs (about90mA/cm2) obtained from the control experiment with performing harshoxidative treatments, and better stability as well towards formic acid electrooxidation.(3) Based on π-π conjugate effect and the theory of complexes, we used a series of aromaticbifunctional molecule (containing anthranllic acid, o-phenylendiamine, salicylic acid, catechol and phthalicacid) as additives to control the synthsis of Pd nanoparticles via a facile chemical reduction approach atroom temperature, then a series of MWCNTs supported Pd catalyst were obtained. The influence law ofdifferent bifunctional groups, such as–NH2,–OH,–COOH and their mixed groups, on the particle sizesand dispersities of Pd nanocrystals was intensively studied. Meanwhile, their catalytic performance law offormic acid electoxidation was also investigated. The two laws matched very well. The law was as follows:the good effect obeys the following order: NH2/COOH> NH2/NH2> COOH/OH> OH/OH>COOH/COOH. Pd nanoparticles controlled synthesis by anthranllic acid has highest dispersion, smallestsize and best catalytic performance towards formic acid electrooxidation.(4) Based on chelate effect, we used glutamate as additive to control the synthsis of Pd nanoparticlesvia a facile chemical reduction approach at room temperature, then dendritic Fe2O3supported Pd catalystwas obtained. The Pd nanoparticles with uniform size were well dispersed and had the average diameter of 4.6nm. In the preparation process, we decreased the dosage of palladium, What’s more, the resultingPd/Fe2O3hybrid catalyst still showed higher mass activity of450.8mA/mg Pd towards ethanolelectrooxidation due to the promoting effect of Fe2O3, superior to commercial JM20%Pt/C.The above results can conclude that these new methods for controlling synthesis of supportedPd-based catalysts not only have the character of mild conditions and no damage to the intrinsic structure ofthe supports, but also well control the dispersities and sizes of Pd nanoparticles. This paper not onlyprovides a reliable experiment basis for practical application of supported catalysts in fuel cell, but alsomakes estimable sense for cogniting the structure-activity relationship of catalysts.