ZIF-derived carbons as highly efficient and stable ORR catalyst.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Platinum/carbon (Pt/C) catalysts are standard for oxygen reduction reaction (ORR) but are expensive and scarce.
• Developing efficient, low-cost, non-precious metal alternatives for ORR is crucial for electrochemical applications.
• Metal-organic frameworks (MOFs) like ZIF-67 offer a promising precursor for advanced carbon-based catalysts.

Purpose of the Study:

• To synthesize highly efficient non-precious metal catalysts for oxygen reduction reaction (ORR).
• To investigate the synergistic effects of reduced graphene oxide (rGO) integration and KOH etching on ZIF-67 derived carbons.
• To evaluate catalyst performance and durability in both alkaline and acidic electrolytes compared to commercial Pt/C.

Main Methods:

• Fabrication of ZIF-67 derived carbons integrated with reduced graphene oxide (rGO).
• Post-synthesis treatment involving KOH etching to modify pore structure and active sites.
• Electrochemical characterization of oxygen reduction reaction (ORR) activity and durability in alkaline and acidic media.

Main Results:

• ZIF-67 derived carbon/rGO (ZIF-C/rGO) exhibited excellent ORR activity in alkaline media (onset potential: 1.00 V, half-wave potential: 0.87 V, limited current density: 5.92 mA cm-2), comparable or superior to Pt/C.
• ZIF-C/rGO demonstrated enhanced durability in both alkaline and acidic electrolytes compared to Pt/C, despite slightly lower ORR activity in acid media.
• KOH etching (ZIF-C/rGO-KOH) reduced ORR performance by decreasing active nitrogen sites and micropores, even with increased mesoporosity.

Conclusions:

• rGO integration significantly enhances ORR performance by improving charge transfer channels and micropore structure while preserving active N and Co sites.
• The synergistic effect between ZIF-67 derived carbon and rGO boosts ORR activity by mitigating over-polarization, aggregation, and mass transport limitations.
• ZIF-C/rGO presents a highly promising, durable, and cost-effective alternative to Pt/C for oxygen reduction reactions, particularly in alkaline environments.