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This research aims to enhance ammonia synthesis from nitrate by optimizing Cu loading in NiFe-based catalysts.

July 24, 20260 citationsOpen Access

Cu-loading-modulated NiFe-based composite catalysts for high-efficiency nitrate electroreduction to ammonia

GWGuikang WengShantou University ZWZheling WangShantou University CZCe ZhouChangchun University of Science and Technology

Key Points

This research aims to enhance ammonia synthesis from nitrate by optimizing Cu loading in NiFe-based catalysts.
Synthesis of Cu2O/NiFeCu(OH)x composites via one-pot hydrothermal method with varying Cu nitrate loading.
Characterization using X-ray diffraction, electron microscopy techniques, and spectrometry.
Electrocatalytic performance evaluated in specific electrolyte conditions using multiple electrochemical techniques.
Optimized Cu2O/NiFeCu(OH)x achieves NH3 yield of 8.86 mg h−1 mgcat−1 and 94% Faradaic efficiency at −0.6 V vs. RHE.
Catalyst maintains activity for 12 h at −0.4 V vs. RHE with approximately 90% Faradaic efficiency over five cycles.
Performance enhancement attributed to composition modulation, not surface area change.

Abstract

Introduction: Electrocatalytic nitrate reduction reaction (NO3RR) is a sustainable route for ammonia (NH3) synthesis, yet it suffers from sluggish kinetics and low selectivity due to the eight-electron transfer process. Although Cu-based catalysts efficiently activate N O 3 − and mediate the deoxygenation step ( N O 3 − → N O 2 − ), while Ni/Fe-based hydroxides excel in water dissociation and N O 2 − hydrogenation, constructing a kinetically matched multimetallic tandem system remains challenging. Materials and methods: Here, a series of spherical Cu2O/NiFeCu(OH)x composites were synthesized via a one-pot hydrothermal method by tuning the Cu(NO3)2 loading (×0.17–×6 relative to the optimized recipe). The catalysts were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM)/high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES). Electrocatalytic performance was evaluated in 0.1 mol L−1 NaNO3/0.5 mol L−1 Na2SO4 using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry, with NH3 quantified by the indophenol blue method and 1H nuclear magnetic resonance (NMR). Results: The optimized Cu2O/NiFeCu(OH)x (1× Cu loading) delivers an NH3 yield of 8.86 mg h−1 mgcat−1 and a Faradaic efficiency (FE) of 94% at −0.6 V vs. reversible hydrogen electrode (RHE), outperforming control samples (NiFe(OH)x, NiCu(OH)x, FeCu(OH)x) and many reported NO3RR catalysts. The catalyst maintains stable activity for 12 h at −0.4 V vs. RHE and ~90% FE over five cycles. Excess Cu loading accelerates ( N O 3 − → N O 2 − but causes N O 2 − accumulation owing to kinetic mismatch, whereas insufficient Cu limits the deoxygenation step. Electrochemical active surface area (ECSA) and charge-transfer resistance (Rct) analyses confirm that performance enhancement originates from composition modulation rather than surface-area variation. Conclusions: This work demonstrates that precise Cu-loading modulation in NiFe-based architectures achieves kinetic matching between Cu-mediated deoxygenation and Ni/Fe-mediated hydrogenation, enabling efficient tandem NO3RR to NH3. The strategy provides a mechanistic guideline for designing multimetallic LDH-type electrocatalysts for nitrogen-cycle applications.

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