High-Efficiency Ammonia Electrosynthesis on Anatase TiO2-x Nanobelt Arrays with Oxygen Vacancies by Selective Reduction of Nitrite

A NiCo alloy particle-decorated TiO2 nanoarray as an efficient electrocatalyst for nitrite reduction to ammonia

Electrocatalytic nitrite (NO2-) reduction (NO2-RR) is a potential environmentally friendly method for producing NH3 efficiently. Herein, a hybrid catalyst with NiCo alloy particles uniformly decorated on a TiO2 nanograss array (NiCo-TiO2) is reported to display excellent NO2-RR performance. In alkaline media, NiCo-TiO2 possesses a large NH3 yield of 18 736.2 μg h-1 cm-2 at -0.4 V vs. RHE and a maximum FE of 97.5%. Utilizing NiCo-TiO2 as the cathode of a Zn-NO2- battery, it exhibits remarkable peak power density (6.49 mW cm-2) and a large NH3 yield (1911.4 g h-1 cm-2 at 20 mA cm-2). This work highlights the potential of catalysts based on alloy-metallic oxide hybrids for the electrochemical conversion of the NO2- pollutant into NH3.

Construction of a Heterostructured Alloy-Molybdenum Nitride Catalyst for Enhanced NH3 Production via Nitrate Electrolysis

Here, we reported a highly efficient nitrate electroreduction (NO3RR) electrocatalyst that integrated alloying and heterostructuring strategies comprising FeCo alloy and Mo0.82N (FeCo-Mo0.82N/NC). Notably, the maximum NH3 Faraday efficiency (FE) of 83.24%, NH3 yield of 12.28 mg h-1 mgcat.-1, and good stability were achieved over FeCo-Mo0.82N/NC. Moreover, a Zn-NO3- battery assembled with FeCo-Mo0.82N/NC exhibited a power density of 0.87 mW cm-2, an NH3 yield of 14.09 mg h-1 mgcat.-1, and a FE as high as 76.31%.

Valorization systems based on electrocatalytic nitrate/nitrite conversion for energy supply and valuable product synthesis

The excessive accumulation of nitrate/nitrite (NO x -) in surface and groundwater has severely disrupted the global nitrogen cycle and jeopardized public health. The electrochemical conversion of NO x - to ammonia (NH3) not only holds promise for ecofriendly NO x - removal, but also provides a green alternative to the energy-intensive Haber-Bosch process for NH3 production. Recently, in addition to the electrocatalyst design explosion in this field, many innovative valorization systems based on NO x --to-NH3 conversion have been developed for generating energy and expanding the range of value-added products. Collective knowledge of advanced conversion systems is indispensable for restoring the global nitrogen cycle and promoting a N-based economy. Herein, a timely and comprehensive review is provided on the important progress of valorization systems based on NO x - conversion, including waste treatment systems, novel electrolytic systems, and energy conversion and storage systems. Some mechanism explorations, device designs, key electrode developments and feasibility analyses are involved to gain deeper understanding of various systems and facilitate implementing these cleaning systems in industry. Finally, challenges and future prospects are outlined in the NO x - conversion field with an aim to promote large-scale electrocatalytic system development and prosperous N-based electrochemistry.

Facile Synthesis of a Cu3Mo2O9 Nanosheet Array for Electrochemical Reduction of Nitrite to Ammonia in Neutral Solution

Electrochemical nitrite (NO2-) is a promising technology for NO2- removal and a sustainable method for generating valuable ammonia (NH3), but this process is intricate and generates other byproducts. In this work, we propose a facile and low-cost method for the preparation of a Cu3Mo2O9 nanosheet array, which can serve as an efficient electrocatalyst for the reduction of NO2- to NH3. The morphology of Cu3Mo2O9 can be adjusted by controlling the synthesis conditions. In neutral solution, Cu3Mo2O9 achieves a high NH3 yield of 30.46 mg h-1 cm-2 and an outstanding faradaic efficiency of 98.6% with excellent long-term electrochemical stability for NO2- reduction. Density functional theory calculations further reveal the key role of the Cu3Mo2O9 (202) surface and its possible reaction pathways in the electrocatalytic reduction of nitrite.

Electrodegradation of nitrogenous pollutants in sewage: from reaction fundamentals to energy valorization applications

The excessive accumulation of nitrogen pollutants (mainly nitrate, nitrite, ammonia nitrogen, hydrazine, and urea) in water bodies seriously disrupts the natural nitrogen cycle and poses a significant threat to human life and health. Electrolysis is considered a promising method to degrade these nitrogenous pollutants in sewage, with the advantages of high efficiency, wide generality, easy operability, retrievability, and environmental friendliness. For particular energy devices, including metal-nitrate batteries, direct fuel cells, and hybrid water electrolyzers, the realization of energy valorization from sewage purification processes (e.g., valuable chemical generation, electricity output, and hydrogen production) becomes feasible. Despite the progress in the research on pollutant electrodegradation, the development of electrocatalysts with high activity, stability, and selectivity for pollutant removal, coupled with corresponding energy devices, remains a challenge. This review comprehensively provides advanced insights into the electrodegradation processes of nitrogenous pollutants and relevant energy valorization strategies, focusing on the reaction mechanisms, activity descriptors, electrocatalyst design, and actuated electrodes and operation parameters of tailored energy conversion devices. A feasibility analysis of electrodegradation on real wastewater samples from the perspective of pollutant concentration, pollutant accumulation, and electrolyte effects is provided. Challenges and prospects for the future development of electrodegradation systems are also discussed in detail to bridge the gap between experimental trials and commercial applications.

Recent progress on Ti-based catalysts in the electrochemical synthesis of ammonia

Electrochemical ammonia synthesis presents a sustainable alternative, offering the potential for enhanced energy efficiency and environmental benefits compared to the conventional Haber-Bosch process. In recent years, the electrocatalytic reduction of nitrate to ammonia (NO3-RR) has emerged as a crucial approach for achieving sustainable NH3 production. To enhance energy efficiency and successfully convert NO3- to NH3, it is essential to investigate cost-effective electrocatalysts that provide high Faraday efficiency and demonstrate adequate stability. Ti-based materials are considered ideal candidates as catalysts due to their environmental friendliness and robust stability. This review initially summarizes the nitrate reduction reaction pathway and concisely discusses the impact of the potential intermediates and reaction steps on the overall reaction efficiency and product selectivity. Subsequently, an overview of the fundamental characteristics of Ti and TiO2 is presented. Additionally, the research process on Ti-based electrocatalysts in the electrochemical reduction of nitrate for ammonia synthesis is summarized. Finally, the design strategies, such as heteroatom doping and the introduction of oxygen vacancies, to enhance catalytic efficiency and selectivity are presented. Through this comprehensive review, we endeavor to furnish researchers with the most recent insights into the application of titanium-based electrocatalysts in nitrate reduction reactions and to stimulate innovative thought processes on the electrocatalytic synthesis of ammonia.