# Complementary Surface Motifs Enhance NO3RR Performance in NiFe Alloys

## TL;DR

NiFe alloys improve nitrate reduction efficiency and ammonium selectivity by using complementary surface sites, outperforming pure Ni or Fe.

## Contribution

The study introduces a new descriptor for nitrate adsorption and identifies complementary surface motifs in NiFe alloys that enhance NO3RR performance.

## Key findings

- NiFe alloys show higher NO3RR Faradaic efficiency and NH4+ selectivity compared to pure Ni or Fe.
- NO2* deoxygenation is favored by Ni-rich sites, while NO* dissociation is supported by Fe atoms and the Fe lattice.
- Performance improvements are consistent across Ni/Fe ratios due to a spillover mechanism involving diverse active sites.

## Abstract

Elemental first row transition metal electrocatalysts typically exhibit a tradeoff between Faradaic efficiency (FE) for the nitrate reduction reaction (NO3RR) and selectivity toward NH4
+. Here, we find that NiFe alloys have high NO3RR FE and substantially higher NH4
+ selectivity than Ni or Fe. We introduce “relative nitrate adsorption,” a simple descriptor of the difference in NO3* and H* binding strength that rationalizes experimental trends in reaction rate order. This descriptor is consistent with competitive adsorption demonstrated in a microkinetic model that shows Fe inclusion promotes NO3* adsorption and increased NO3RR FE, but cannot describe the higher NH4
+ selectivity observed for NiFe alloys. In fact, calculated activation energies of subsequent reduction steps illustrate that no one active site motif can explain both improved FE and NH4
+ selectivity. Instead, our experimental and computational findings indicate NO2* deoxygenation is promoted by Ni‐rich active sites, whereas NO* dissociation is promoted by both surface Fe atoms and an underlying Fe lattice. These findings suggest that NiFe alloys leverage local site diversity via a spillover mechanism, explaining why the performance enhancements are similar regardless of the specific Ni/Fe ratio.

Mixed NiFe surface sites promote critical nitrate reduction reaction steps relative to pure Ni(111) and Fe(110), leveraging multiple adjacent sites to enhance ammonium selectivity and overall Faradaic efficiency.© 2026 WILEY‐VCH GmbH