A Facile Route for Constructing Effective Cu-N_x Active Sites for Oxygen Reduction Reaction

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Copper/nitrogen electrocatalysts are crucial for the oxygen reduction reaction (ORR).
• Controlling copper-nitrogen coordination and comparing performance in similar matrices is challenging.
• Zeolitic imidazolate frameworks (ZIFs) offer a tunable platform for catalyst development.

Purpose of the Study:

• To develop a facile method for synthesizing distinct copper-nitrogen coordination structures.
• To investigate the influence of different copper-nitrogen sites on ORR activity.
• To evaluate the performance of the optimized catalyst in zinc-air batteries.

Main Methods:

• Pyrolysis of copper-doped zeolitic imidazolate framework nanoleaves (Cu-ZIF-L).
• Selective etching of Cu-ZIF-L using sulfuric acid (H2SO4) and nitric acid (HNO3) to generate different Cu-N sites.
• Characterization using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS).
• Electrochemical testing for oxygen reduction reaction (ORR) and zinc-air battery performance.

Main Results:

• Two distinct copper-nitrogen constructions, Cu+-N2 and Cu2+-N4, were successfully synthesized.
• XANES and EXAFS confirmed the different copper coordination environments.
• Cu+-N2 sites demonstrated higher ORR activity compared to Cu2+-N4 sites.
• The resulting Cu-N/C-H2SO4 catalyst exhibited excellent performance and stability as an air cathode in a zinc-air battery.

Conclusions:

• The acid-etching method provides a simple and effective route to tune copper-nitrogen coordination in electrocatalysts.
• Cu+-N2 active sites are superior to Cu2+-N4 sites for boosting ORR performance.
• The developed copper-nitrogen catalyst holds significant potential for applications in energy storage devices like zinc-air batteries.