Electrochimica Acta 52 (2007) 4871–4877 A phenyl-sulfonic acid anchored carbon-supported platinum catalyst for polymer electrolyte fuel cell electrodes G. Selvarani a , A.K. Sahu a , N.A. Choudhury b , P. Sridhar a , S. Pitchumani a , A.K. Shukla a,b,∗ a Central Electrochemical Research Institute, Karaikudi 630006, India b Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India Received 11 November 2006; received in revised form 29 December 2006; accepted 30 December 2006 Available online 27 January 2007 Abstract A method, to anchor phenyl-sulfonic acid functional groups with the platinum catalyst supported onto a high surface-area carbon substrate, is reported. The use of the catalyst in the electrodes of a polymer electrolyte fuel cell (PEFC) helps enhancing its performance. Characterization of the catalyst by Fourier transform infra red (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and point-of-zero-charge (PZC) studies suggests that the improvement in performance of the PEFC is facilitated not only by enlarging the three-phase boundary in the catalyst layer but also by providing ionic-conduction paths as well as by imparting negative charge to platinum sites with concomitant oxidation of sulfur present in the carbon support. It is argued that the negatively charged platinum sites help repel water facilitating oxygen to access the catalyst sites. The PEFC with modified carbon-supported platinum catalyst electrodes exhibits 40% enhancement in its power density as compared to the one with unmodified carbon-supported platinum catalyst electrodes. © 2007 Elsevier Ltd. All rights reserved. Keywords: Polymer electrolyte fuel cell; X-ray photoelectron spectroscopy; Fourier transform infrared spectroscopy; Phenyl-sulfonic acid; Point-of-zero-charge 1. Introduction In the post-oil energy economy, hydrogen-based fuel cells are being perceived as a possible energy alternative. Hydrogen- based polymer electrolyte fuel cells (PEFCs) are most promising as they offer an order of magnitude higher power density than any other fuel cell system. A PEFC is fed with hydrogen, which is oxidized at the anode and oxygen that is reduced at the cath- ode. The protons released during the oxidation of hydrogen pass through the proton exchange membrane to the cathode. The electrons released during the oxidation of hydrogen travel through the external electric-circuit generating an electrical cur- rent. Owing to the high degree of irreversibility of the oxygen reduction, even under open-circuit conditions, the over potential of the oxygen electrode in a PEFC happens to be about 0.2V. This represents a loss of about 20% from the theoretical maxi- mum efficiency for a PEFC. Accordingly, at the heart of a PEFC is the electrocatalyst that has to fulfill several requirements, such ∗ Corresponding author. Tel.: +91 4565 227777; fax: +91 4565 227779. E-mail address: shukla@sscu.iisc.ernet.in (A.K. Shukla). as high intrinsic activities for the electrochemical oxidation of hydrogen at the anode and the reduction of oxygen at the cathode, to realize maximum efficiency of the PEFC [1–3]. Usually, the electrocatalyst is supported onto a porous carbon support in order to increase its contact area with the reactants. Since both the electrons and protons are involved in the elec- trochemical reactions, the porous catalyst layer must conduct both of these species optimally [4]. Furthermore, to extend the three-phase boundary in the catalyst layer, the electrocatalyst needs to be dispersed with a proton conducting substance, such as Nafion. This has been shown to improve the performance of the PEFCs [5–8], but the platinum in the catalyst layer remains yet not fully utilized. Uchida et al. [9,10] have studied the microstructure of the catalyst layer. During the catalyst preparation, nanometer-sized platinum particles are dispersed onto the surface of a 30–40 nm sized carbon support to enhance the platinum catalyst surface area. However, the small carbon particles tend to agglomerate due to the intermolecular interactions between their surfaces rendering the platinum sites within the agglomerate unutilized. This is because Nafion ionomer, generally added to the catalyst as a proton-conducting phase during the electrode fabrication 0013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2006.12.080