Session: Electrochemistry-enabled Catalysis for Energy, Chemicals, and Materials:

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^-2mA/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^-2mA/cm² with CeO₂addition, 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.

Lisandro Cunci

Appearances