Researchers have introduced a novel approach for the electroreduction of nitrate (NO3-) to ammonia (NH3) using layered double hydroxide (LDH) nanosheets. Their study, published in the journal Advanced Functional Materials, highlights how modulating surface-active hydrogen species (H*) enhances the efficiency of this process, which is crucial for sustainable nitrogen management and addressing environmental pollution.
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The findings offer a cleaner and efficient alternative to the traditional synthesis process, paving the way for environmentally friendly nitrogen fixation in agriculture and industry.
Challenges in Conventional Ammonia Production
NH3 is essential for agriculture, electronics, and pharmaceuticals. Traditionally, it has been produced through the Haber-Bosch (HB) process, which, although effective, is energy-intensive and produces significant carbon dioxide (CO2) emissions. This process emits about 1.8 tons of CO2 for every ton of NH3. This environmental challenge has intensified the need for cleaner, more sustainable alternatives. The conventional process consumes nearly 1-2% of the world’s total energy supply, highlighting the urgency for innovative solutions.
In this context, one promising method is the electrochemical reduction of NO3- to NH3, powered by renewable electricity. This process reduces the carbon footprint associated with conventional synthesis and mitigates nitrate pollution in water bodies. The nitrate reduction reaction (NitRR) converts harmful NO3- into valuable NH3 while contributing to the restoration of the nitrogen cycle. However, its efficiency heavily relies on the design of high-performance electrocatalysts, which determines reaction rates.
Development of Trimetallic LDH Catalysts for Electroreduction
Researchers synthesized and analyzed trimetallic NiCuFe (nickel (Ni), copper (Cu), and iron (Fe)) LDH nanosheets to enhance the electroreduction of NO3- to NH3. These nanosheets were fabricated using an electrodeposition technique, where nickel foam served as the substrate and a Ni, Cu, and Fe nitrate electrolyte was employed in a 1:1:1 molar ratio. The resulting 9.9 nm-thick nanosheets featured a large surface area of 127.4 m2/g and a three-dimensional structure that increased active site exposure and improved efficiency.
Characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) confirmed their uniform composition and morphology. Electrochemical tests conducted in a customized H-type electrochemical cell measured current density, Faradaic efficiency (FE), and NH3 yield rate under varying potentials and NO3- concentrations.
The NiCuFe-LDHs demonstrated superior catalytic activity and selectivity compared to bimetallic catalysts (CuFe-LDHs and NiFe-LDHs) due to the synergistic effects of Ni, Cu, and Fe. Notably, Ni played a critical role in promoting the adsorption of hydrogen species (H*), which is essential for facilitating NitRR.
Performance Metrics of NiCuFe-LDHs
The NiCuFe-LDHs nanosheets achieved an NH3 yield rate of 1.64 mmol h-1 cm-2 and a high FE of 94.8% at a potential of -0.4 V versus the reversible hydrogen electrode (RHE). This performance surpassed that of bimetallic catalysts, with the NH3 FE being 1.3 times higher than CuFe-LDHs and 2.7 times higher than NiFe-LDHs. These results highlight the strong interaction among Ni, Cu, and Fe in facilitating the NitRR while minimizing byproducts.
Operando electrochemical impedance spectroscopy (EIS) and differential electrochemical mass spectrometry (DEMS) demonstrated that Ni and Cu sites served as key active centers for the adsorption and activation of nitrate intermediates, accelerating reaction kinetics. The incorporation of Ni effectively suppressed competing hydrogen evolution reactions (HER), further improving selectivity toward NH3 production.
Durability tests over 15 consecutive cycles confirmed the long-term stability of the NiCuFe-LDHs, maintaining an NH3 yield above 90%. Additionally, the study highlighted that the catalyst retained structural integrity and performance even after extensive cycling. Researchers proposed integrating these nanosheets into a Zn-NO3- battery system, which could simultaneously treat nitrate pollutants, generate NH3, and provide energy output.
Applications for Sustainable Nitrogen Management
This research has significant implications for sustainable nitrogen management. The ability to efficiently convert NO3- into NH3 using renewable energy supports global goals to reduce carbon emissions and promote environmentally friendly agricultural practices.
The developed NiCuFe-LDHs can be implemented in future electrocatalyst designs to reduce nitrogenous compounds in wastewater treatment. Integrating this technology into energy storage systems, such as Zn-NO3—batteries, presents an innovative dual-function approach that enables pollutant remediation and power generation.
This research addresses environmental pollution and sustainable fertilizer production by transforming harmful nitrates into valuable NH3. It also demonstrates how renewable-powered systems can make chemical manufacturing cleaner and more efficient.
Conclusion and Future Directions
This study demonstrates the potential of trimetallic NiCuFe-LDHs nanosheets as efficient electrocatalysts for reducing NO3—to NH3. The nanosheets achieved high NH3 yield and FE, marking a significant step forward in sustainable NH3 production.
Future work should focus on optimizing the composition and structure of LDHs to enhance catalytic activity and selectivity. Additionally, scaling up the synthesis process and testing the catalysts under real-world conditions will be essential for industrial applications.
Overall, this research provides a strong foundation for developing next-generation clean technology solutions that simultaneously integrate renewable energy with efficient nitrogen conversion, paving the way for a more sustainable chemical industry.
Journal Reference
Liu, B., & et al. (2025). Modulating Surface-Active Hydrogen for Facilitating Nitrate-to-Ammonia Electroreduction on Layered Double Hydroxides Nanosheets. Advanced Functional Materials, e19238. DOI: 10.1002/adfm.202519238. https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202519238
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