Engineering vacancy and hydrophobicity of two-dimensional TaTe2 for efficient and stable electrocatalytic N2 reduction

Upgrading of nitrate to hydrazine through cascading electrocatalytic ammonia production with controllable N-N coupling

Nitrogen oxides (NOx) play important roles in the nitrogen cycle system and serve as renewable nitrogen sources for the synthesis of value-added chemicals driven by clean electricity. However, it is challenging to achieve selective conversion of NOx to multi-nitrogen products (e.g., N2H4) via precise construction of a single N-N bond. Herein, we propose a strategy for NOx-to-N2H4 under ambient conditions, involving electrochemical NOx upgrading to NH3, followed by ketone-mediated NH3 to N2H4. It can achieve an impressive overall NOx-to-N2H4 selectivity of 88.7%. We elucidate mechanistic insights into the ketone-mediated N-N coupling process. Diphenyl ketone (DPK) emerges as an optimal mediator, facilitating controlled N-N coupling, owing to its steric and conjugation effects. The acetonitrile solvent stabilizes and activates key imine intermediates through hydrogen bonding. Experimental results reveal that Ph2CN* intermediates formed on WO3 catalysts acted as pivotal monomers to drive controlled N-N coupling with high selectivity, facilitated by lattice-oxygen-mediated dehydrogenation. Additionally, both WO3 catalysts and DPK mediators exhibit favorable reusability, offering promise for green N2H4 synthesis.

In Situ Characterization Techniques for Electrochemical Nitrogen Reduction Reaction

The electrochemical reduction of nitrogen to produce ammonia is pivotal in modern society due to its environmental friendliness and the substantial influence that ammonia has on food, chemicals, and energy. However, the current electrochemical nitrogen reduction reaction (NRR) mechanism is still imperfect, which seriously impedes the development of NRR. In situ characterization techniques offer insight into the alterations taking place at the electrode/electrolyte interface throughout the NRR process, thereby helping us to explore the NRR mechanism in-depth and ultimately promote the development of efficient catalytic systems for NRR. Herein, we introduce the popular theories and mechanisms of the electrochemical NRR and provide an extensive overview on the application of various in situ characterization approaches for on-site detection of reaction intermediates and catalyst transformations during electrocatalytic NRR processes, including different optical techniques, X-ray-based techniques, electron microscopy, and scanning probe microscopy. Finally, some major challenges and future directions of these in situ techniques are proposed.

Electrocatalytic NO Reduction to NH3 on Mo2C Nanosheets

Electrocatalytic reduction of NO to NH₃ (NORR) emerges as a promising route for achieving harmful NO treatment and sustainable NH₃ generation. In this work, we first report that Mo₂C is an active and selective NORR catalyst. The developed Mo₂C nanosheets deliver a high NH₃ yield rate of 122.7 μmol h^-1 cm^-2 with an NH₃ Faradaic efficiency of 86.3% at -0.4 V. Theoretical computations unveil that the surface-terminated Mo atoms on Mo₂C can effectively activate NO, promote protonation energetics, and suppress proton adsorption, resulting in high NORR activity and selectivity of Mo₂C.

Sub-nm RuOx Clusters on Pd Metallene for Synergistically Enhanced Nitrate Electroreduction to Ammonia

The electrochemical nitrate reduction to ammonia reaction (NO3RR) has emerged as an appealing route for achieving both wastewater treatment and ammonia production. Herein, sub-nm RuOx clusters anchored on a Pd metallene (RuOx/Pd) are reported as a highly effective NO3RR catalyst, delivering a maximum NH3-Faradaic efficiency of 98.6% with a corresponding NH3 yield rate of 23.5 mg h-1 cm-2 and partial a current density of 296.3 mA cm-2 at -0.5 V vs RHE. Operando spectroscopic characterizations combined with theoretical computations unveil the synergy of RuOx and Pd to enhance the NO3RR energetics through a mechanism of hydrogen spillover and hydrogen-bond interactions. In detail, RuOx activates NO3- to form intermediates, while Pd dissociates H2O to generate *H, which spontaneously migrates to the RuOx/Pd interface via a hydrogen spillover process. Further hydrogen-bond interactions between spillovered *H and intermediates makes spillovered *H desorb from the RuOx/Pd interface and participate in the intermediate hydrogenation, contributing to the enhanced activity of RuOx/Pd for NO3--to-NH3 conversion.

Rigorous Assessment of Cl- -Based Anolytes on Electrochemical Ammonia Synthesis

Many challenges in the electrochemical synthesis of ammonia have been recognized with most effort focused on delineating false positives resulting from unidentified sources of nitrogen. However, the influence of oxidizing anolytes on the crossover and oxidization of ammonium during the electrolysis reaction remains unexplored. Here it is reported that the use of analytes containing halide ions (Cl- and Br- ) can rapidly convert the ammonium into N2 , which further intensifies the crossover of ammonium. Moreover, the extent of migration and oxidation of ammonium is found to be closely associated with external factors, such as applied potentials and the concentration of Cl- . These findings demonstrate the profound impact of oxidizing anolytes on the electrochemical synthesis of ammonia. Based on these results, many prior reported ammonia yield rates are calibrated. This work emphasizes the significance of avoiding selection of anolytes that can oxidize ammonium, which is believed to promote further progress in electrochemical nitrogen fixation.

Recent progress of photocatalysts based on tungsten and related metals for nitrogen reduction to ammonia

Photocatalytic nitrogen reduction reaction (NRR) to ammonia holds a great promise for substituting the traditional energy-intensive Haber–Bosch process, which entails sunlight as an inexhaustible resource and water as a hydrogen source under mild conditions. Remarkable progress has been achieved regarding the activation and solar conversion of N₂ to NH₃ with the rapid development of emerging photocatalysts, but it still suffers from low efficiency. A comprehensive review on photocatalysts covering tungsten and related metals as well as their broad ranges of alloys and compounds is lacking. This article aims to summarize recent advances in this regard, focusing on the strategies to enhance the photocatalytic performance of tungsten and related metal semiconductors for the NRR. The fundamentals of solar-to-NH₃ photocatalysis, reaction pathways, and NH₃ quantification methods are presented, and the concomitant challenges are also revealed. Finally, we cast insights into the future development of sustainable NH₃ production, and highlight some potential directions for further research in this vibrant field.

High-Efficiency N2 Electroreduction Enabled by Se-Vacancy-Rich WSe2-x in Water-in-Salt Electrolytes

Electrocatalytic nitrogen reduction reaction (NRR) is a promising approach for renewable NH₃ production, while developing the NRR electrocatalysis systems with both high activity and selectivity remains a significant challenge. Herein, we combine catalyst and electrolyte engineering to achieve a high-efficiency NRR enabled by a Se-vacancy-rich WSe_2-x catalyst in water-in-salt electrolyte (WISE). Extensive characterizations, theoretical calculations, and in situ X-ray photoelectron/Raman spectroscopy reveal that WISE ensures suppressed H₂ evolution, improved N₂ affinity on the catalyst surface, as well as an enhanced π-back-donation ability of active sites, thereby promoting both activity and selectivity for the NRR. As a result, an excellent faradaic efficiency of 62.5% and NH₃ yield of 181.3 μg h^-1 mg^-1 is achieved with WSe_2-x in 12 m LiClO₄, which is among the highest NRR performances reported to date.

Self-supported V-doped NiO electrocatalyst achieving a high ammonia yield of 30.55 μg h−1 cm−2 under ambient conditions

Vanadium doped nickel oxide grows on nickel foam exhibits a splendid NH3 yield and a high faradaic efficiency.