Tailored Catalytic Microenvironments Enable Efficient Electrochemical Ammonia Production.

Area of Science:

• Catalysis
• Materials Science
• Electrochemistry

Background:

• Multi-electron hydrogenation reactions are crucial for sustainable energy and nitrogen cycling.
• Efficient catalysts require precise control over proton-coupled electron transfer (PCET) and reaction intermediates.
• Current catalysts often struggle with selectivity and efficiency in complex reactions like nitrate reduction.

Purpose of the Study:

• To design and investigate an integrated catalytic microenvironment (ICM) for efficient nitrate-to-ammonia reduction (NO3RR).
• To elucidate the mechanism of catalyst activation and intermediate stabilization using crystal field and Lewis acid-base principles.
• To develop a novel catalyst based on Co-substituted inverse spinel oxide (FeFeCoO4).

Main Methods:

• Synthesis of Co-substituted inverse spinel oxide (FeFeCoO4).
• Electrochemical characterization to evaluate catalytic performance (yield, Faradaic efficiency, energy efficiency).
• Analysis guided by crystal field theory and hard-soft acid-base principles to understand the ICM's function.

Main Results:

• FeFeCoO4 exhibits an integrated catalytic microenvironment (ICM) that enables efficient NO3RR.
• Co2+ substitution induces Jahn-Teller distortions, activating Fe3+ sites as H* donors.
• Decoupled dual-metal sites (Co2+ and Fe3+) facilitate PCET and stabilize nitrogen intermediates, suppressing hydrogen evolution.
• Achieved a peak NH3 yield of 1.89 × 10-6 mol s-1 cm-2 with 96.6% Faradaic efficiency and 30.5% energy efficiency.
• Demonstrated stable operation at 0.5 A cm-2 for 265 hours.

Conclusions:

• The developed FeFeCoO4 catalyst with an ICM effectively converts nitrate to ammonia.
• The catalyst design strategy, based on crystal field and Lewis acid-base principles, offers a blueprint for advanced multi-electron hydrogenation catalysts.
• This work advances sustainable energy solutions and nitrogen cycling technologies.