Single-Atomic Co-N₄ Sites with CrCo Nanoparticles for Metal-Air Battery-Driven Hydrogen Evolution

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Developing earth-abundant trifunctional electrocatalysts for energy storage and conversion is crucial but challenging.
• Existing catalysts often lack the required activity and robustness for demanding applications.

Purpose of the Study:

• To design and synthesize a highly active and robust trifunctional electrocatalyst using earth-abundant materials.
• To investigate the electrocatalytic performance of the new catalyst for hydrogen evolution, oxygen evolution, and oxygen reduction reactions.
• To evaluate its application in rechargeable Zn-air batteries and self-driven water splitting systems.

Main Methods:

• Synthesis of a trifunctional electrocatalyst (CrCo/CoN₄@CNT-5) at a low calcination temperature (550 °C).
• Characterization of the catalyst comprising Co-N₄ single atoms and CrCo alloy nanoparticles.
• Electrochemical testing for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) in alkaline media.
• Assembly and testing of a liquid rechargeable Zn-air battery and a self-driven water splitting system.

Main Results:

• The CrCo/CoN₄@CNT-5 catalyst achieved a current density of 10 mA cm^-2 at a low cell voltage of ∼1.60 V for overall water splitting.
• In a Zn-air battery, the catalyst exhibited high open-circuit voltage and superior cycling durability compared to commercial Pt/C+IrO₂.
• The Zn-air battery powered water splitting system demonstrated a high H₂ evolution rate of 168 μmol h^-1.
• Theoretical calculations confirmed synergistic interactions between Co-N₄ sites and CrCo nanoparticles, enhancing H₂ evolution kinetics.

Conclusions:

• The synthesized CrCo/CoN₄@CNT-5 catalyst is a highly active and robust trifunctional electrocatalyst.
• The presence of a small amount of Cr significantly enhances catalytic activity and durability.
• This work provides a promising strategy for designing multifunctional electrocatalysts for efficient and long-term hydrogen evolution applications.