Liquid Crystalline Phase Templated Platinum Catalyst for Oxygen Reduction

Abstract

The potentiostatic electrodeposition of platinum was carried out with a nonionic surfactant in the liquid crystalline phase acting as a templating agent. The electrochemically active surface area of 0.4 mg cm-2 unsupported Pt electrodeposited using a mixture of Brij 56 and n-heptane was increased by a factor of 2.7 compared to Pt deposited without structure-directing additives. The deposit morphology was studied by surface analysis (scanning electron microscopy, atomic force microscopy, and transmission electron microscopy). It was found that with the templating agent, the Pt nanoparticles with a 50 nm diameter had a mesoporous fine structure with pore diameters of 2-3 nm. Oxygen reduction experiments revealed a threefold increase in mass activity, and an improvement of the superficial current density at 0.9 V vs reversible hydrogen electrode (RHE) from 2× 10-4 to 6× 10-4 A cm geom -2 due to templating. The intrinsic specific activity of the templated Pt (i.e., current density normalized with respect to the active Pt area) was also improved at potentials more negative than 0.95 V vs RHE. The mesoporous structures studied in this work served as a model for the design of highly active polymer electrolyte membrane fuel cell cathode catalyst layers. © 2009 The Electrochemical Society.