Triple Synergy Engineering via Metal-Free Dual-Atom Incorporation for Self-Sustaining Acidic Ammonia Electrosynthesis

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrochemical nitrate reduction reaction (NO₃RR) to ammonia offers advantages for fertilizer production but faces challenges.
• Existing metal catalysts suffer from instability, hydrogen evolution reaction (HER) competition, and proton depletion.
• Acidic conditions are desirable for direct ammonia synthesis and preventing volatilization.

Purpose of the Study:

• To develop a novel metal-free catalyst for efficient and stable electrochemical nitrate reduction in acidic media.
• To address catalyst instability, HER competition, and proton/species imbalance issues.
• To elucidate the atomic-level triple synergy mechanism for enhanced NO₃RR performance.

Main Methods:

• Fabrication of silicon-iodine dual-atom catalysts anchored on nickel oxide ultrathin nanosheets (Si/I-NiO@CC) using gradient-heating co-loading.
• Electrochemical characterization, including Faradaic efficiency and stability tests in acidic electrolyte.
• In situ spectroscopic analysis to investigate the catalytic mechanism and active sites.

Main Results:

• Achieved a record Faradaic efficiency of 96.8% for NO₃RR at -0.3 V vs. RHE.
• Demonstrated exceptional operational stability of 420 hours, surpassing all reported acid NO₃RR electrocatalysts.
• Identified a triple synergy mechanism involving electron-deficient Ni, oxygen vacancies, iodine-mediated proton reservoirs, and Si-O-Ni interfacial bonding.

Conclusions:

• The developed metal-free Si/I-NiO@CC catalyst effectively overcomes key challenges in acidic NO₃RR.
• Atomic-level triple synergy engineering provides a viable strategy for high-efficiency and stable ammonia synthesis.
• This work offers a constructive guideline for designing advanced electrocatalysts for selective nitrate reduction.