Novel synthesis of highly active Pt/C cathode electrocatalyst for direct methanol fuel cell

Abstract

A 40 wt% Pt/C cathode electrocatalyst with controlled Pt particle size of ~2.9 nm showing better performance than commercial catalyst for direct methanol fuel cell was prepared by a polyol process with water but without using stabilizing agent.Pt-based electrocatalysts with high loading are usually employed in direct methanol fuel cells (DMFC) as cathode electrocatalysts for oxygen reduction reaction at relatively low temperature. Synthesis of highly dispersed supported platinum with uniform nanoparticle size still remains a challenge, especially for high metal loading. The conventional methods for the synthesis of Pt and Pt alloy electrocatalysts are mainly impregnation 1 and colloid methods such as sulfite-complex route 2 and NR 4+ -stabilized metal colloids route. 3 The impregnation is limited because the average particle size is usually large and the size distribution is broad. Both colloidal routes produced well-homogenized ultrafine Pt electrocatalysts, but the complexity of these synthesis hinders its utilization. 4 Many investigators have contributed much endeavour to search for alternative routes. 5 In this paper, uniform platinum nanoparticles with an average diameter of about 2.9 nm supported on carbon with Pt loading up to 40 wt% were prepared by a modified polyol process. The modified polyol method exhibits the merits of impregnation and colloid procedures, i.e., the preparation method is simple but it is able to control the particle size and distribution. The as-synthesized Pt/C electrocatalyst shows better electrocatalytic activity for oxygen reduction reaction in DMFC than that of the commercial catalyst.The precursor, chloroplatinic acid, was dissolved into ethylene glycol (EG) and mixed with carbon black (Vulcan XC-72R, Cabot Corp., S BET = 236.8 m 2 g 21 ) suspended in distilled water. The mixture was maintained at 403 K in an oil bath for 3 h to ensure the complete reduction of Pt. A flow of argon was passed through the reaction system to remove oxygen and organic by-products. In the course of reaction, the evolved vapour was trapped and collected for GC-MS analysis. The resulting solid was filtered, washed with copious distilled water and dried at 343 K in vacuo. The obtained sample was denoted as 40 wt% Pt/C-EG. † The obtained electrocatalyst contains no stabilizing agent. This feature makes the modified process unique, because applications of the traditional polyol process 6 based on stabilizer such as polyvinyl pyrrolidone (PVP) were restricted in the area of electrocatalysis due to serious agglomeration of metal particles after removing the surfactant at relatively high temperature. Besides, the modified polyol process is carried out in a EG/H 2 O mixed solution, whereas, for the conventional polyol process, a strictly anhydrous organic solution is required. 6 The 40 wt% Pt/C-EG and the commercial 40 wt% Pt/C (Johnson Matthey Corp., denoted as 40 wt% Pt/C-JM) were comparatively tested as cathode electrocatalyst in DMFC. Fig. 1a shows the TEM image of the 40% Pt/C-EG sample. As the image ...

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Preparation of supported PtRu/C electrocatalyst for direct methanol fuel cells

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