Electronegative Phosphorus-Integrated Co²⁺ Active Sites for Enhanced Electrocatalytic Nitrogen Reduction

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Cobalt oxides are promising electrocatalysts for ammonia synthesis via electrocatalytic nitrogen reduction (ENRR).
• Undoped CoO suffers from declining ammonia yield due to electron loss from Co2+ active sites during ENRR.
• Maintaining the electronic stability of active sites is crucial for efficient and durable electrocatalysis.

Purpose of the Study:

• To improve the performance and stability of cobalt oxide electrocatalysts for ENRR.
• To investigate the effect of phosphorus (P) doping on the electronic structure and catalytic activity of CoO.
• To understand the mechanism of electron loss in CoO and how P doping mitigates this issue.

Main Methods:

• Synthesis of phosphorus-doped cobalt oxide (P-CoO) electrocatalysts.
• Electrochemical testing for ammonia yield and Faradaic efficiency (FE) measurements.
• Ex-situ characterization techniques and theoretical calculations to analyze electronic structure and reaction mechanisms.

Main Results:

• P-CoO exhibited a significantly enhanced ammonia yield (49.6 μg h⁻¹ mg⁻¹) and FE (9.6% at -0.2 V vs RHE) compared to undoped CoO.
• Undoped CoO showed a tendency to transition from Co2+ to Co3+ after ENRR, leading to performance degradation.
• P-doped CoO maintained its valence state, demonstrating improved catalytic activity and stability.

Conclusions:

• Phosphorus doping effectively stabilizes the Co active sites in CoO by preventing electron loss during ENRR.
• P-CoO presents a superior electrocatalyst for ammonia synthesis with enhanced yield and durability.
• This study provides insights into electronic modulation of active sites for improved electrocatalytic nitrogen reduction.