Metal Oxide Inclusion in Polycrystalline Platinum Nanoparticles for Ammonia Electrooxidation

Abstract

The interest in platinum nanoparticles has increased due to their unique properties for applications as catalysts. However, platinum is not available for large-scale applications because of its elevated price and limited resources. Thus, efforts to optimize a cost-effective electrocatalyst that can enhance the ammonia oxidation reaction are of special interest for alkaline fuel cell applications. In this work, we synthesized Pt nanoparticles by colloidal methods using different precursors (K2PtCl6 or H2Pt(OH)6) and alloying them with different metal oxides (Fe2O3 or CeO2) in order to compare their electrocatalytic activities for ammonia oxidation. A colloidal synthesis is a reaction in solution of a metal precursor with a reduction agent in the presence of a capping agent to form colloidal nanoparticles. The Pt- Fe2O3 and Pt-CeO2 alloys were prepared by sonicating the metal oxide in solvent solution for 60 minutes with Pt nanoparticles. The Pt alloys were mixed with Nafion to coat a glassy carbon electrode for the electrochemical characterization and to measure their electrocatalytic potential for ammonia oxidation. The electrocatalytic activities for ammonia oxidation was studied by cyclic voltammetry at a low scan rate (20 mV/s). No significant difference in the onset potential (average onset potential value is -0.460 V) for the ammonia oxidation is observed based on the metal precursor. The highest current density was achieved by nanoparticles synthesized from the H2Pt(OH)6 precursor, with a value of 27.4 x 10-2 mA/cm2 (K2PtCl6 precursor had a value of 25.8 x 10-2 mA/cm2). The addition of metal oxides was found to not significantly change the onset potential for ammonia oxidation. However, current densities decreased with the addition of both metal oxides. Current densities of nanoparticles synthesized from the H2Pt(OH)6 precursor decreased to 24.9 x 10-2 mA/cm2 with CeO2 addition, but increased to 28.2 x 10-2 mA/cm-2 when Fe2O3 was added. In contrast, current densities of nanoparticles synthesized from the K2PtCl6 precursor had no significant different with CeO2 addition (25.7 x 10-2 mA/cm-2) but reduced significantly with Fe2O3 addition (16.7 x 10-2 mA/cm-2). Further characterization techniques such as scanning electron microscopy and X-ray diffraction are currently being analyzed.