Modulating Single-Atom Pt Coordination for Enhanced Low-Temperature Ammonia Fuel Cell Electrocatalysis.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Low-temperature direct ammonia fuel cells (DAFCs) offer on-demand clean electricity but suffer from low efficiency.
• This inefficiency stems from the slow kinetics of the ammonia oxidation reaction (AOR) and oxygen reduction reaction (ORR).
• High cost of traditional platinum (Pt)-based electrocatalysts necessitates reduced metal loading while improving activity.

Purpose of the Study:

• To design and synthesize a bifunctional platinum single-atom catalyst (SAC) with enhanced activity for both AOR and ORR.
• To investigate the structure-activity relationship of Pt SACs for DAFC applications.
• To demonstrate the efficacy of rationally designed SACs in improving DAFC performance.

Main Methods:

• Synthesis and characterization of a novel Pt SAC (Pt-DG-1) with modulated coordination.
• Electrochemical evaluation of Pt-DG-1 for AOR and ORR compared to commercial Pt/C.
• Integration of Pt-DG-1 into a DAFC to assess power density and Pt loading.
• In situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to probe reaction mechanisms.

Main Results:

• The optimized Pt SAC (Pt-DG-1) exhibited superior AOR (1.23 A mg_Pt^-1) and ORR (7.98 A mg_Pt^-1) mass activities.
• The DAFC utilizing Pt-DG-1 achieved a peak power density of 21.8 mW cm^-2 with a low Pt loading of 0.034 mg cm^-2.
• SHINERS revealed lower *OH coverage during ORR and suppressed *NO_x poisoning during AOR on Pt-DG-1.

Conclusions:

• Rationally designed Pt SACs can significantly enhance the catalytic activity for both AOR and ORR in DAFCs.
• The developed Pt-DG-1 catalyst offers a promising pathway for cost-effective and high-performance DAFCs.
• Understanding reaction intermediates and poisoning species is crucial for optimizing SAC design for fuel cell applications.