A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Traditional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), such as noble metals and metal oxides, are expensive and environmentally detrimental.
• There is a need for cost-effective, stable, and efficient catalysts for ORR and OER to advance energy storage technologies like zinc-air batteries.

Purpose of the Study:

• To develop and characterize a novel, scalable, and sustainable electrocatalyst for both ORR and OER.
• To evaluate the performance of this new catalyst as an air electrode in primary and rechargeable zinc-air batteries.

Main Methods:

• Fabrication of a mesoporous carbon foam co-doped with nitrogen (N) and phosphorus (P) via a one-step pyrolysis of polyaniline aerogel in the presence of phytic acid.
• Characterization of the material's surface area and electrochemical properties.
• Testing the N,P-doped carbon foam in primary and rechargeable zinc-air batteries, and in a three-electrode configuration for independent OER/ORR activity assessment.
• Density functional theory (DFT) calculations to understand the origin of the catalytic activity.

Main Results:

• The synthesized N,P-doped carbon foam possesses a high surface area (∼1,663 m²/g) and exhibits excellent bifunctional electrocatalytic activity for both ORR and OER.
• Primary zinc-air batteries using the material achieved an open-circuit potential of 1.48 V, a specific capacity of 735 mAh/gZn, and an energy density of 835 Wh/kgZn.
• Rechargeable zinc-air batteries demonstrated stable cycling for 180 cycles at 2 mA/cm², and primary batteries operated stably for 240 h after mechanical recharging.
• DFT calculations confirmed that N,P co-doping and graphene edge effects are crucial for the observed bifunctional activity.

Conclusions:

• The developed N,P-doped carbon foam is a highly promising, cost-effective, and sustainable alternative to noble metal catalysts for ORR and OER.
• This material significantly enhances the performance and stability of zinc-air batteries, paving the way for their practical application.
• The study provides fundamental insights into the catalytic mechanisms, guiding future catalyst design for electrochemical energy conversion.