Electrochimica Acta 52 (2007) 7278–7285 Investigation of carbon-supported Pt nanocatalyst preparation by the polyol process for fuel cell applications Hyung-Suk Oh, Jong-Gil Oh, Youn-Gi Hong, Hansung Kim ∗ Department of Chemical Engineering, Yonsei University, 134 Shinchon-Dong, Seodaemun-gu, 120-749 Seoul, Republic of Korea Received 10 March 2007; received in revised form 18 May 2007; accepted 29 May 2007 Available online 17 June 2007 Abstract Parametric investigation of the polyol process for the preparation of carbon-supported Pt nanoparticles as catalysts for fuel cells was carried out. It was found that the concentration of glycolate anion, which is a function of pH, plays an important role in controlling Pt particle size and loading on carbon. It was observed that Pt loading decreased with increasing alkalinity of the solution. As evidenced by zeta potential measurement, this was mainly due to poor adsorption or repulsive forces between the metal colloids and the supports. In order to modify the conventional polyol process, the effect of the gas purging conditions on the characteristics of Pt/C was examined. By the optimization of the gas environment during the reaction, it was possible to obtain high loading of 39.5 wt% with a 2.8 nm size of Pt particle. From the single cell test, it was found that operating in ambient O 2 at 70 ◦ C can deliver high performance of more than 0.6 V at 1.44 A cm -2 . © 2007 Elsevier Ltd. All rights reserved. Keywords: Polyol process; Ethylene glycol; Zeta potential; PEM fuel cells 1. Introduction There is tremendous interest in the preparation of carbon- supported electro-catalysts for fuel cell applications [1–4]. It is well known that the performance of catalysts can be improved by achieving nanosized particles, uniform distribution and high loading of catalysts over large surface area carbons [5–7]. Con- ventional preparation techniques used for the preparation of supported catalysts are based on the wet impregnation followed by reduction in a hydrogen atmosphere at high temperatures or the chemical reduction of the metal precursors using reducing agents. However, these methods do not provide adequate control of particle size and distribution. Many studies have shown the difficulty of high metal loadings without a significant increase in the particle size [8,9]. Extensive investigations have been carried out to develop alternate routes for preparing supported Pt catalysts by the col- loidal method using diverse stabilizing agents. In those attempts, a stabilizing agent was used to prevent the aggregation of metal particles during the nucleation and growth steps. Boennemann et ∗ Corresponding author. Tel.: +82 2 2123 5753; fax: +82 2 312 6401. E-mail address: elchem@yonsei.ac.kr (H. Kim). al. developed organoaluminum-stabilized colloids with a parti- cle size smaller than 2 nm at room temperature [10]. Organic stabilizers such as polyvinyl pirrolidone (PVP) and the sur- factant dodecyldimethyl (3-sulfo-propyl) ammonium hydroxide (SB12) are widely used in the preparation of metal colloids [2,11,12]. The intrinsic problem underlying this process is that the stabilizing organic material remains on the surface of metal colloids. This should be removed prior to the application of metal particles for electrocatalysis. Removal of the organic material is important as it hinders the access of fuel to the catalyst sites. In general, the removal of stabilizer involves heat treatment. Conse- quently, due to the sintering effect, the phase separation and the distribution of metal particles are affected, resulting in lowered catalytic performance. In this respect, preparation via the polyol process is preferred due to several advantages. The polyol process is a technique in which a polyol such as ethylene glycol is used as both solvent and reducing agent. The polyol method has been used for the preparation of nanometal powder [13,14] and nanowires [15,16]. A unique property of the polyol process is that it does not require any type of polymer stabilizer. In the polyol process using ethy- lene glycol, metal ions are reduced to form a metal colloid by receiving the electrons from the oxidation of ethylene glycol to glycolic acid. Glycolic acid is present in its deprotonated 0013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2007.05.080