Preparation and characterization of Pt-CeO2 and Pt-Pd electrocatalysts for the oxygen reduction reaction in the absence and presence of methanol in alkaline medium

In this work, we report the synthesis and characterization of unsupported Pt-CeO2 (1:1 wt. % Pt:CeO2 ratio) and Pt-Pd (1:1 wt. % Pt:Pd ratio) electrocatalysts as candidate cathodes for alkaline direct methanol fuel cells (A-DMFCs). The catalytic activity of the cathodes for the oxygen reduction reaction (ORR) in the absence and presence of methanol, in KOH as electrolyte, was evaluated at room temperature. The materials were prepared by chemical reduction with NaBH4, and pyrolysis at 300 and 600 °C under a H2/N2 atmosphere. The XRD results indicated the formation of polycrystalline materials with particle sizes ranging from 9 to 19 nm. Analysis by HRTEM showed the formation of nanostructures with lattice fringes corresponding to Pt, Pd (i.e., the Pt-Pd cathode), or CeO2 (i.e., the Pt-CeO2 material). The electrochemical characterization in 0.1 mol L−1 KOH showed that the Pt-Pd is highly active for the ORR in alkaline medium, delivering higher onset potential and mass activity than Pt-alone. Meanwhile, the Pt-CeO2 material showed slightly lower ORR mass activity than Pt. However, in the presence of methanol, the Pt-CeO2 nanocatalyst demonstrated significantly higher selectivity and tolerance capability to the alcohol than Pt and Pt-Pd.

► Pt-Pd and Pt-CeO2 synthesized by chemical reduction and pyrolysis. ► Higher catalytic activity of Pt-Pd for the ORR in alkaline medium related to Pt. ► The Pt-CeO2 nanostructures showed high selectivity and tolerance to methanol in KOH.