Surface Structure Engineering of PtPd Nanoparticles for Boosting Ammonia Oxidation Electrocatalysis

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Direct ammonia fuel cells (DAFCs) require efficient catalysts for the ammonia oxidation reaction (AOR).
• Platinum-based catalysts face challenges due to high dehydrogenation energy barriers and deactivation by nitrogen intermediates during AOR.
• Optimizing catalyst structure and composition is crucial for improving AOR kinetics and DAFC performance.

Purpose of the Study:

• To develop highly active and stable Pt-based catalysts for the ammonia oxidation reaction (AOR) in direct ammonia fuel cells (DAFCs).
• To investigate the effect of alloying and surface modulation on the catalytic performance of Pt nanoparticles.
• To understand the reaction mechanism and identify factors limiting catalyst stability.

Main Methods:

• Synthesis of spherical PtM (M = Co, Ni, Cu, Pd) binary nanoparticles supported on reduced graphene oxide (rGO).
• Surface engineering of PtPd nanoparticles to achieve a cubic-dominant structure.
• Electrochemical characterization including onset potential, peak mass activity, and stability tests.
• Density functional theory (DFT) calculations to elucidate reaction mechanisms and energy barriers.

Main Results:

• Spherical PtPd nanoparticles exhibited superior catalytic activity compared to other PtM alloys and commercial Pt/C.
• The optimized cubic-dominant ⁽¹⁰⁰⁾Pt₈₅Pd₁₅/rGO showed a low onset potential (0.467 V vs RHE) and high peak mass activity (164.9 A g^-1).
• DFT calculations confirmed that alloying Pt with Pd reduces the dehydrogenation energy barrier of *NH₂ to *NH, enhancing AOR kinetics.
• Catalyst deactivation was observed due to Pd leaching, structural transformation, and nitrogen intermediate poisoning.

Conclusions:

• Alloying Pt with Pd and engineering a cubic-dominant surface structure are effective strategies to boost AOR performance in DAFCs.
• The optimized PtPd/rGO catalyst demonstrates significant potential for DAFC applications.
• Further research is needed to address catalyst stability issues related to metal leaching and intermediate poisoning for long-term DAFC operation.