Preparation And Properties Of Carbon-supported Palladium, Silver And Binary-metal Nanoparticles Electrocatalysts

Direct alcohol fuel cell (DAFC) has broad application prospects because DAFC is environmentally friendly, affordable, safe and of high energy density. However, in terms of the current research status, many problems of Pt/C catalyst have greatly hindered its commercialization. First, the high price of precious metals Pt greatly raised the cost of DAFC. Second, for direct alcohol fuel cell, platinum-based anode catalysts is easily poisoned by the intermediates in the process of fuel oxidation, reducing catalytic activity. Therefore, current research focus on reducing the use of precious metals Pt and improve the catalytic performance. Among them it is proven that the alternative use of other metals of lower prices as catalysts and introducing other metals to improve the catalytic performance is an effective way.In this dissertation, Ag/C, Pd/C, PdAg/C and Pd-Ag/C electrocatalysts were prepared by microwave glycol one-step reduction method. Physicochemical characterization and electrochemical studies for oxygen reduction reaction (ORR) and methanol oxidation in alkaline media were performed. The main results obtained are as follows: 1. The Ag/C single-metal catalysts of pre-load rate 33wt.% was prepare with ammonia solution of silver as the silver source, carbon black (Vulcan XC-72,cabot) or acid-treated Vulcan-XC 72 carbon black as base. Physicochemical characterization evidenced Ag face-centered cubic structure, and the Ag particle had uniform size and dispersedly loaded on the surface of the acid-treated carbon black. Electrochemical studies indicated that the Ag/C had good catalytic performance for oxygen reduction reaction (ORR), but no catalytic activity for methanol oxidation reaction(MOR).2. The Pd/C single-metal catalysts of pre-load rate 33wt.% was prepare with ammonia, EDTA or NaCl as PdCl2 complexing agents, carbon black (Vulcan XC-7,cabot) as base. Physicochemical characterization evidenced Pd face-centered cubic structure, and the Pd particle had uniform smallest size and best dispersedly loaded on the surface of the carbon black with Pd-EDTA as Pd source. Electrochemical studies oxygen reduction and the methanol oxidation showed that the Pd/C from Pd-EDTA had the best catalytic activity for ORR and MOR, which would be attributed to the small partiele size(ca.5.6nm).3. The PdAg/C bimetallic catalysts of metal pre-load rate 33wt.% was prepared with ammonia, EDTA or NaCl as PdCl2 complexing agents,carbon black (Vulcan XC-7,cabot) as base. Physicochemical characterization showed two metals with face-centered cubic structure are loaded separately on the surface of cabon black, and the metal particles had uniform smallest size and best dispersedly loaded on the surface of carbon black with Pd-EDTA as Pd source. Electrochemical studies showed that the PdAg/C from Pd-EDTA had the best catalytic activity for ORR and MOR, and Pd:Ag= 1:1 is the best ratio for catalytic activity of AgPd/C bimetallic catalysts.4. The pre-prepared total metal loading 33 wt.% Ag-Pd/C alloy nanoparticles catalysts was prepared with NaCl as PdCl2 complexing agent in a pH=8.5 system. Physicochemical characterization confirmed the alloy structure,and the alloy nanoparticles with small particle size (ca. 11nm) dispersed on the suface of carbon. The electrochemical test results showed that the as-prepared Pd-Ag/C had better activity for ORR and MOR than Ag/C, Pd/C and PdAg/C, and Pd:Ag= 1:1 is the best ratio for catalytic activity of Ag-Pd/C alloy nanoparticles catalysts.