Study On Controllable Preparation And Electrocatalytic Performence Of Silver And Palladium-silver Nanomaterials

Direct alcohol fuel cell (DAFC) is a new type of low-temperature fuel cellsusing small organic molecular (methanol and ethanol) as a fuel. DAFC is a greenenergy technology with non-polluting, high energy conversion efficiency and widefuel sourceeasily. But when alcohol oxidation reaction carried out in an acidicmedium, its performance is very low, which is a serious impediment to theapplications and development of DAFC. Moreover, Pt-based catalyst which isexpensive and susceptible to poisoning is often used in the alcohol oxidation in acidicmedia. Therefore, the research on alternative materials and improving catalyticactivity has become a hot public concern. Small molecular alcohol oxidation reactionin alkaline medium has some advantages. On one hand, it can reduce the oxidationpotential of the alcohol, which will make the oxidation easier. On the other hand,non-Pt transition metal can be used as a good catalyst for alcohol oxidation in alkalinemedia. In order to reduce the production cost of the catalyst and improve its catalyticactivity, the research on electro-catalyst in alkaline direct alcohol fuel cell (ADAFC)is of great significance.This dissertation focuses on the basic and applied research of silver andpalladium silver nanomaterials in ADAFC, exploring the controllable preparation andelectrocatalytic performance of silver and palladium silver nanomaterialsThe main contents are as follows:(1) Silver nanowires (SNWs) and silver nanoparticles (SNPs) are quickly andeasily prepared via polyol process through regulating the quantity of NaCl. Themorphology, composition, structure and size distribution of the nanomarerials werecharacterized by SEM, EDS, XRD and UV-Vis. The electro-catalytic performance of SNWs and SNPs toward oxygen reduction reaction (ORR) was studied in alkalineelectrolytes with or without alcohol by a linear sweep voltammetry (LSV)method.The results show that two kinds of silver nanomaterials with uniformmorphology are the face-centered cubic structure. The LSV results reveal that SNWsand SNPs have different electrocatalytic activity toward ORR under alkalinecondition. Compared to SNPs, SNWs’ onset potential and peak potential positivelyshifted70mV and50mV, respectively. The reduction peak current of SNWs is1.8times higher than that of SNPs. SNWs show better catalytic performance. The studyon alcohol resistance have shown that SNWs has good resistance toward methanoland SNPs has good resistance to ethanol. The isopropanol resistance of two kinds ofnanomaterials is poor.(2) PdAg nanomaterials with unique structure have been prepared using one-potprocess. The morphology, structure and composition of palladium-silvernanomaterials were characterized by SEM, TEM, XRD and EDS. The activity andstability of PdAg nanomaterials for catalytic oxidation of common alcohols underalkaline conditions are investigated by cyclic voltammetry and chronoamperometry.The main conclusions are as follows: the synthesized PdAg nanomaterials arenanoalloy particles with strawberry structure and wires with beaded structure,respectively; After Pd Ag alloy is formed a synergistic effect exist between Pd and Ag,which will enhance the catalytic performance of Pd. Compared with the commercialPd/C catalyst, the performance of methanol, ethanol, ethylene glycol and isopropylalcohol oxidation on PdAg nanomaterials were improved, especially for ethanoloxidation. It has high catalytic activity and stability and a wanderfull applicationprospect.(3) Reduced grapheme oxide (RGO) supported palladium-silver alloy(PdAg/RGO) nanomaterials with different composition have been prepared by hydrothermal method. The catalysts’ morphology, composition and structure werecharacterized by TEM, EDS, Raman and XRD. The electro-catalytic properties of thecatalysts were characterized by CV, CA, LSV and electrochemical impedancespectroscopy (EIS). The results showed that: PdAg nanoalloy has been successfullyloaded on the graphene surface, with dispersed and uniform morphology; PdAg/RGO(nPd: nAg=3:3) showed the best ethanol oxidation and oxygen reduction performance;silicates and carbonates as impurities in the electrolyte solution will decrease theperformance of ethanol oxidation and oxygen reduction.