In Situ Structural Evolution and Activity Descriptor of Atomically Dispersed Catalysts During Nitrate...

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Single-atom catalysts (SACs) are promising for electrochemical nitrate reduction reaction (eNO3RR) and ammonia production.
• Understanding in situ structural and compositional evolution of SACs during electrocatalysis is crucial for catalyst design but remains unexplored.

Purpose of the Study:

• To investigate the in situ structural evolution and performance of metal-nitrogen-carbon (MNC) single-atom catalysts (SACs) for the electrochemical nitrate reduction reaction (eNO3RR).
• To establish structure-activity relationships and identify design principles for highly active eNO3RR catalysts.

Main Methods:

• Synthesized and electrochemically tested a series of MNC SACs (M = Cr, Fe, Co, Ni, Cu) for eNO3RR.
• Utilized in situ Synchrotron X-ray fluorescence (SXRF) mapping to probe structural evolution under various cathodic potentials.
• Generated structure-activity plots using experimental data and literature values.

Main Results:

• NiNC exhibited the highest ammonia Faradaic efficiency (78.0 ± 2.9%) and production rate, followed by CoNC.
• In situ SXRF revealed significant Ni and Co mobility, leading to the formation of metallic clusters from 0.0 V vs. RHE.
• A clear trend between OH binding energy and turnover frequency was observed, with metallic NiNC and CoNC showing stronger OH binding and higher activity.

Conclusions:

• The study reveals the in situ structural evolution of MNCs during eNO3RR, highlighting metal-ligand mobility and cluster formation.
• Stronger OH binding in the metallic phase of NiNC and CoNC explains their superior catalytic activity compared to SACs.
• This work provides a descriptor for identifying active eNO3RR catalysts and offers insights into their dynamic structural changes.