Complementary Surface Motifs Enhance NO₃RR Performance in NiFe Alloys

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• First-row transition metals show a trade-off between Faradaic efficiency (FE) and NH₄⁺ selectivity in nitrate reduction reaction (NO₃RR).
• Understanding active sites is crucial for designing efficient electrocatalysts.

Purpose of the Study:

• To investigate NiFe alloys as electrocatalysts for NO₃RR.
• To identify descriptors that rationalize experimental trends and understand selectivity mechanisms.

Main Methods:

• Experimental synthesis and electrochemical testing of NiFe alloys.
• Computational studies including microkinetic modeling and DFT calculations of activation energies.
• Introduction of a "relative nitrate adsorption" descriptor.

Main Results:

• NiFe alloys exhibit high NO₃RR FE and superior NH₄⁺ selectivity compared to pure Ni or Fe.
• The "relative nitrate adsorption" descriptor correlates with reaction rate but not NH₄⁺ selectivity.
• NiFe alloys utilize local site diversity, with Ni-rich sites promoting NO₂* deoxygenation and Fe promoting NO* dissociation via a spillover mechanism.

Conclusions:

• NiFe alloys offer a promising strategy for efficient and selective NO₃RR.
• Performance is attributed to synergistic effects and local site diversity within the alloy, not a single active site.
• The findings provide insights into designing advanced electrocatalysts for nitrogen conversion.