Ni₂P active site ensembles tune electrocatalytic nitrate reduction selectivity

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Nitrate reduction reaction (NO3RR) is a key process for nitrogen management and chemical synthesis.
• Transition metal phosphides are promising electrocatalysts for NO3RR due to their tunable electronic properties.
• Understanding the reaction mechanism and selectivity is crucial for developing efficient catalysts.

Purpose of the Study:

• To investigate how active site ensembles on transition metal phosphides influence the selectivity of the nitrate reduction reaction.
• To elucidate the reaction mechanism of NO3RR on nickel phosphide (Ni2P) nanocrystals.
• To optimize conditions for selective nitrate reduction and ammonia production.

Main Methods:

• Electrochemical characterization of Ni2P nanocrystals.
• In situ spectroscopic studies to identify reaction intermediates.
• Computational modeling to understand adsorption energies and reaction pathways.

Main Results:

• Demonstrated that active site ensembles on Ni2P tune NO3RR selectivity.
• Reported a mechanism involving competitive co-adsorption of H* and nitrogen monoxide (NO*) intermediates.
• Achieved near 100% faradaic efficiency for nitrate reduction over hydrogen evolution at -0.4 V vs. RHE.
• Maximized ammonia (NH3) selectivity at -0.2 V vs. RHE.

Conclusions:

• Active site ensembles are critical for controlling NO3RR selectivity on transition metal phosphides.
• The competitive co-adsorption mechanism provides insights into catalyst design for selective nitrogen conversion.
• Ni2P nanocrystals show potential for efficient and selective electrochemical nitrate reduction to valuable products like ammonia.