Journal of Power Sources 162 (2006) 1023–1028 Research article Modification of carbon support to enhance performance of direct methanol fuel cell Chan Hee Park, M. Aulice Scibioh, Hyoung-Juhn Kim, In-Hwan Oh, Seong-Ahn Hong, Heung Yong Ha ∗ Fuel Cell Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Republic of Korea Received 25 April 2006; accepted 6 August 2006 Available online 11 October 2006 Abstract Carbon black powder is modified by applying a coating of a proton-conducting polymer electrolyte (ionomer), namely, perfluorosulfonic acid. The carbon is intended for use as a catalyst support in the preparation of Pt-Ru catalysts for direct methanol fuel cell. The aim is to extend the interfacial area between the catalytic metal particles and the proton-conducting ionomer. Ionomer incorporation is found to reduce the micropore volume and thus the BET surface-area of the carbon. Single-cell performance tests on a DMFC show that Pt-Ru catalyst supported on modified carbon exhibits superior performance to that on plain carbon. © 2006 Elsevier B.V. All rights reserved. Keywords: Direct methanol fuel cell; Ionomer-coated carbon support; Ionomer content; Active surface-area; Three-phase boundary; Platinum-ruthenium catalyst 1. Introduction In spite of intensive work on catalysts in recent years, car- bon supported and unsupported Pt–Ru alloys are still considered to be the best electrocatalysts for methanol oxidation in direct methanol fuel cells (DMFCs) [1–8]. Significant efforts have been made to find an appropriate synthesis procedure for production of these catalysts with suitable dispersions. The main require- ment of a good electrode is a three-phase boundary [9] between the supply of reactants on the one hand and the catalyst parti- cle and the protonic conductor on the other hand. The catalyst particles must be in direct contact with an electronic conductor to ensure that the electrons are supplied to, or taken away from, the reaction site. Electronic conductivity is usually provided by a carbon substrate on which the catalyst particles are supported. An effective reaction zone in a catalyst layer is made by impreg- nating the catalyst powder with some ionomeric binder before pressing the electrode onto a polymer electrolyte membrane to ensure good contact with the membrane. Usually, the catalyst powder is made into an ink with a solvent and then mixed with ∗ Corresponding author. Tel.: +82 2 958 5275; fax: +82 2 958 5199. E-mail address: hyha@kist.re.kr (H.Y. Ha). a binder material. The catalyst ink can be cast directly onto a membrane or a gas-diffusion medium. The effect of binder con- tent on the performance of the electrodes has been studied both for PTFE and ionomeric binders [10–12]. The ionomer (proton- conducting polymer electrolyte) was incorporated into a catalyst ink to increase the catalyst utilization [13–20]. In all studies, the platinum utilization, even in the best-performing electrodes, was very low (10–25%). Such attempts aimed at maximizing the cat- alyst utilization must also satisfy other criteria such as reactant access, product removal, and protonic and electronic path con- tinuity. In perfluorosulfonic acid (PFSA) ionomer, the sulfonic acid micelles have an approximate diameter of 4–200 nm [21] and hence would be excluded from carbon pores with diameters less than 4 nm. Accordingly, part of the platinum particles deposited within the micropores of the carbon support may be inaccessible to the polymer electrolyte in a catalyst layer. A diagrammatic representation of this aspect is given in Fig. 1(a). This shows that the interaction between the catalyst metal particles and the ionomer in the electrode is poor when plain carbon powder is employed as a support material. We have evolved a new technique to extend the three-phase boundary in a catalyst layer by coating carbon powder with ionomer followed by incorporation of catalyst metal particles. Fig. 1(b) shows the 0378-7753/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2006.08.030