The Air/Platinum/Nafion Triple-Phase Boundary: Characteristics, Scaling, and Implications for Fuel Cells

Abstract

This contribution examines the heterogeneous kinetics of the oxygen reduction reaction (ORR) at the Pt/Nafion/air triple-phase boundary (TPB). This system is of particular interest for low-temperature polymer electrolyte membrane fuel cell applications. A focused ion beam system is used to prototype geometrically simple platinum microstructures directly on Nafion electrolyte membranes. By varying the size and shape of the platinum structures, the role and properties of the TPB are elucidated. Current-voltage and electrochemical impedance spectroscopy measurements reveal that the ORR kinetics scale with TPB length. A faradaic resistance per unit TPB length of 6×1096×109 Ω μm is extracted under short-circuit conditions at room temperature. Although this value is determined from microscopic measurements of geometrically simple platinum structures, it is successfully applied to predict the bulk performance of large-area sputtered platinum catalyst fuel cells. © 2004 The Electrochemical Society. All rights reserved.