Ammonia (NH₃) is an indispensable chemical in modern industry, serving as a core feedstock for fertilizers, pharmaceuticals, and numerous industrial products. However, the dominant industrial ammonia synthesis method, the Haber-Bosch process, relies on harsh high-temperature and high-pressure conditions and contributes over 1% of global greenhouse gas emissions, posing urgent environmental challenges. In contrast, the electrocatalytic nitrate reduction reaction (NITRR) emerges as a sustainable alternative: it converts environmentally abundant nitrate pollutants (from fossil fuel combustion, fertilizer use, and industrial wastewater) into high-value NH₃, simultaneously addressing nitrogen pollution and realizing nitrogen resource recycling. Nevertheless, NITRR involves a complex 8-electron/9-proton transfer process with sluggish kinetics, and the competitive hydrogen evolution reaction (HER) and formation of byproducts severely undermine the selectivity and efficiency of ammonia synthesis. Copper-based catalysts are promising for NITRR due to their unique 3d¹⁰ electron configuration, but their weak proton activation capability limits the generation of active hydrogen (*H)—a key intermediate for ammonia synthesis—hindering practical application.
Recently, a research team led by associateProf. Minghang Jiang from Xihua University developed a solution to this challenge. Their work, published in Chinese Journal of Catalysis (DOI: 10.1016/s1872-2067(25)64848-0 ), reports the synthesis of nano-dendritic Cu₂O/Cu heterojunction catalysts (Coₓ-Cu₂O/Cu, x=0.05, 0.10, 0.34) via a facile, energy-free, and environmentally friendly chemical replacement method.
The preparation of Coₓ-Cu₂O/Cu follows a straightforward three-step mechanism: First, Zn foil undergoes a displacement reaction with Cu²⁺ (from CuCl₂) to form dendritic copper. Second, the surface of dendritic copper reacts with oxygen in the solution or air to generate Cu₂O, constructing Cu₂O/Cu heterojunctions. Third, Co²⁺ (from CoCl₂) is reduced and doped onto the heterojunction interface, with its doping form (atomic or metallic) regulated by adjusting the Co²⁺ concentration in the precursor solution.
A critical insight is that the doping form of Co dictates its function: atomic Co enhances nitrate adsorption on the catalyst surface, while metallic Co promotes the activation of water molecules to produce *H. By optimizing the Co doping concentration (x=0.10), the team achieved a dynamic balance between *H production and consumption during NITRR—sufficient *H for nitrate hydrogenation while avoiding excessive *H that triggers HER. The Co₀.₁₀-Cu₂O/Cu catalyst exhibits exceptional performance: at −0.7 V vs. RHE, it achieves an NH₃ yield of 290.0 μmol·h⁻¹·mg⁻¹ cat and a Faradaic efficiency (FENH3) of 86.2%, far surpassing the pristine Cu₂O/Cu (51.0 μmol·h⁻¹·mg⁻¹ cat, 32.5% FENH3). Additionally, the catalyst demonstrates robust stability in cyclic and long-term tests, and maintains high activity in flow-type electrolytic cells, highlighting its potential for industrial application.
Theoretical calculations further confirm the mechanism: Co doping modulates the d-band center of the catalyst, strengthening nitrate adsorption and reducing the energy barrier of the rate-determining step (NO→NOH) in NITRR. Moderate Co doping inhibits excessive water molecule adsorption and HER, while optimizing *H generation kinetics. This work provides a novel strategy to regulate active hydrogen concentration via metal doping form, offering valuable guidance for the design of high-performance copper-based catalysts for sustainable ammonia synthesis.
About the Journal
Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 17.7. The Editors-in-Chief are Profs. Can Li and Tao Zhang.
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