In high-temperature proton exchange membrane fuel cells and phosphoric acid fuel cells, concentrated phosphoric acid is used as a proton-conducting medium. However, the use of phosphoric acid causes an adsorption problem onto Pt catalyst, which is known to impede the oxygen reduction reaction. To solve the problem, calixpyrrole is introduced as an electrode additive to block the adsorption of phosphate ion onto Pt catalyst. The introduction of calixpyrrole which can strongly interact with phosphate ion results in the enlargement of the available surface area of Pt catalyst and, accordingly, the enhancement of catalyst utilization in electrode. Among calix[n]pyrrole class, calix[4]pyrrole is synthesized and used as the electrode additive in this study. (c) 2008 Elsevier Ltd. All rights reserved.