Reversed I₁Cu₄ single-atom sites for superior neutral ammonia electrosynthesis with nitrate

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis
• Environmental Chemistry

Background:

• Electrochemical ammonia (NH₃) synthesis from nitrate reduction (NITRR) is a promising sustainable technology.
• Existing electrocatalysts often suffer from low NH₃ yields due to hydrogen (H*) byproduct formation via H*-mediated mechanisms.
• There is a need for novel electrocatalysts that can improve NH₃ selectivity and yield.

Purpose of the Study:

• To develop a novel electrocatalyst for enhanced NITRR.
• To investigate a new catalytic mechanism for NITRR beyond H*-mediated pathways.
• To demonstrate the practical application of the developed catalyst in a continuous flow system.

Main Methods:

• Preparation of reversed I₁Cu₄ single-atom sites by anchoring iodine on a copper surface.
• Electrochemical characterization of the catalyst's performance in NITRR under neutral conditions.
• Theoretical calculations (e.g., DFT) to elucidate the reaction mechanism and active site properties.
• Integration of the catalyst into a flow-through device for continuous ammonia synthesis and recovery.

Main Results:

• The I₁Cu₄ single-atom sites achieved a high NH₃ yield rate of 4.36 mg h^-1 cm^-2 and 98.5% Faradaic efficiency.
• Theoretical calculations confirmed a switch from H*-mediated reduction to a proton-coupled electron transfer (PCET) mechanism.
• The PCET mechanism suppresses H₂ evolution and enhances nitrate adsorption and reduction.
• In a flow-through device, the catalyst reached an industrial-level current density of 1 A cm^-2 with a NH₃ yield rate of 69.4 mg h^-1 cm^-2.

Conclusions:

• Reversed single-atom sites (I₁Cu₄) effectively promote NITRR via a PCET mechanism, overcoming limitations of H*-mediated pathways.
• This study highlights the importance of catalyst design in switching reaction mechanisms for improved electrochemical synthesis.
• The developed catalyst and system show significant potential for industrial-scale sustainable ammonia production from nitrate wastewater.