Low-Temperature Pyrolysis: A Universal Route to High-Loading Single-Atom Catalysts for Fuel Cells

Area of Science:

• Materials Science
• Catalysis
• Electrochemistry

Background:

• High-temperature pyrolysis (HTP) is common for single-atom catalysts (SACs) but limited by Ostwald ripening at high temperatures (≥900°C).
• Achieving high single-atom loading is challenging due to aggregation and phase transformation issues at elevated synthesis temperatures.

Purpose of the Study:

• To develop a low-temperature synthesis strategy for high-loading single-atom catalysts.
• To investigate a trans-metalation approach for creating atomically dispersed M-N4 sites.
• To evaluate the catalytic performance of synthesized SACs in oxygen reduction reactions and fuel cells.

Main Methods:

• A low-temperature trans-metalation synthesis involving cation exchange between transition metal ions and Zn2+ on a nitrogen-doped carbon (NC) matrix.
• Utilizing a molten salt medium to facilitate cation exchange at reduced temperatures (450°C).
• Characterization and performance testing of the synthesized catalysts, including electrochemical evaluation in H2-O2 fuel cells.

Main Results:

• Successfully synthesized single-atom catalysts with high mass loading (3.7-4.7 wt.%) of atomically dispersed M-N4 sites.
• Demonstrated that cation exchange occurs effectively at 450°C, significantly lowering synthesis energy barriers.
• The Fe-SAC catalyst exhibited a peak power density of 1.12 W cm-2 in an H2-O2 fuel cell, showcasing excellent catalytic activity.

Conclusions:

• The developed low-temperature trans-metalation method is effective for synthesizing high-loading single-atom catalysts, mitigating Ostwald ripening.
• This approach offers a more energy-efficient pathway for producing advanced SACs for electrochemical applications.
• The synthesized Fe-based SACs demonstrate promising potential for efficient oxygen reduction reactions and fuel cell performance.