Facile Synthesis of a Carbon-Encapsulated Pd Catalyst for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

The key to popularizing proton exchange fuel cells is developing highly active, stable, and cost-effective catalysts for oxygen reduction reaction. Pd is considered as an alternative to Pt due to its high tolerance to poisoning and electronic similarity with Pt, which is a robust but expensive catalyst. However, its vulnerability to dissolving in acidic media prevents the use of Pd as an oxygen reduction reaction catalyst. In this study, a facile synthesis method was developed to prepare a carbon-encapsulated Pd catalyst using aniline. The oxidative polymerization of aniline with a Pd precursor formed Pd nanoparticles embedded in a rod-shaped polyaniline matrix. The polyaniline matrix was carbonized using heat treatment, which then acted as a source of N-containing carbon layer that protects Pd nanoparticles from dissolution and improves oxygen reduction reaction activity. The stability and oxygen reduction reaction activity of the synthesized Pd catalyst were strongly dependent on the heat treatment temperature. The Pd catalysts heat-treated at 300 °C and 500 °C exhibited improved activity and stability as compared to commercial Pd/C. We envision that this method is suitable for mass production of active and stable oxygen reduction reaction catalysts in proton exchange fuel cells.