Electrochemical Ammonia Synthesis via NO Reduction on 2D-MOF

Novel magneto-electrocatalyst Cr2CO2-MXene for boosting nitrogen reduction to ammonia

Ammonia (NH3) plays important roles in chemistry, the environment, and energy; however, the synthesis of NH3 relies heavily on the Haber-Bosch process, causing serious environmental pollution and energy consumption. A clean and effective strategy for the synthesis of NH3 involves nitrogen (N2) being transformed to ammonia (NH3) using electrocatalysis. Adjusting the magnetism of electrocatalysts may improve their performance, and therefore, four magnetic states, nonmagnetic (NM), ferromagnetic (FM), interlayer antiferromagnetic (Inter-AFM), and intra-layer antiferromagnetic (Intra-AFM) Cr2CO2-MXene were designed to explore magnetoelectrocatalysis performance using well-defined density functional theory (DFT) calculations in this study. Upon comparing the nitrogen reduction limiting potentials of N2 molecules on the surface of the four different magnetic states in Cr2CO2-MXene, and the selectivity calculations of the hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR), the Inter-AFM Cr2CO2-MXene is shown to be a better NRR electrocatalyst than the other three cases. This study paves way to unravel the mystery of the spin-catalytic mechanism and will lay a solid foundation for eNRR electrocatalysts with magnetic materials for environmental and energy applications.

Nanoengineering Metal-Organic Frameworks and Derivatives for Electrosynthesis of Ammonia

Electrocatalytic synthesis under mild conditions has become increasingly important as one of the practical alternatives for industrial applications, especially for the green ammonia (NH3) industry. A properly engineered electrocatalyst plays a vital role in the realization of superior catalytic performance. Among various types of promising nanomaterials, metal-organic frameworks (MOFs) are competitive candidates for developing efficient electrocatalytic NH3 synthesis from simple nitrogen-containing molecules or ions, such as N2 and NO3-. In this review, recent advances in the development of electrocatalysts derived from MOFs for the electrosynthesis of NH3 are collected, categorized, and discussed, including their application in the N2 reduction reaction (NRR) and the NO3- reduction reaction (NO3RR). Firstly, the fundamental principles are illustrated, such as plausible mechanisms of NH3 generation from N2 and NO3-, the apparatus of corresponding electrocatalysis, parameters for evaluation of reaction efficiency, and detection methods of yielding NH3. Then, the electrocatalysts for NRR processes are discussed in detail, including pristine MOFs, MOF-hybrids, MOF-derived N-doped porous carbons, single atomic catalysts from pyrolysis of MOFs, and other MOF-related materials. Subsequently, MOF-related NO3RR processes are also listed and discussed. Finally, the existing challenges and prospects for the rational design and fabrication of electrocatalysts from MOFs for electrochemical NH3 synthesis are presented, such as the evolution of investigation methods with artificial intelligence, innovation in synthetic methods of MOF-related catalysts, advancement of characterization techniques, and extended electrocatalytic reactions.

Fundamentals, rational catalyst design, and remaining challenges in electrochemical NOx reduction reaction

Nitrogen oxides (NOx) emissions carry pernicious consequences on air quality and human health, prompting an upsurge of interest in eliminating them from the atmosphere. The electrochemical NOx reduction reaction (NOxRR) is among the promising techniques for NOx removal and potential conversion into valuable chemical feedstock with high conversion efficiency while benefiting energy conservation. However, developing efficient and stable electrocatalysts for NOxRR remains an arduous challenge. This review provides a comprehensive survey of recent advancements in NOxRR, encompassing the underlying fundamentals of the reaction mechanism and rationale behind the design of electrocatalysts using computational modeling and experimental efforts. The potential utilization of NOxRR in a Zn-NOx battery is also explored as a proof of concept for concurrent NOx abatement, NH3 synthesis, and decarbonizing energy generation. Despite significant strides in this domain, several hurdles still need to be resolved in developing efficient and long-lasting electrocatalysts for NOx reduction. These possible means are necessary to augment the catalytic activity and electrocatalyst selectivity and surmount the challenges of catalyst deactivation and corrosion. Furthermore, sustained research and development of NOxRR could offer a promising solution to the urgent issue of NOx pollution, culminating in a cleaner and healthier environment.

Efficient electrocatalytic reduction of NO to ammonia on BC3 nanosheets

Searching for an economical and highly efficient electrocatalytic reduction catalyst for ammonia synthesis under controllable conditions is a very attractive and challenging subject in chemistry. In this study, we systematically studied the electrocatalytic performance of BC₃ nanosheets as potential NO reduction reaction (NORR) electrocatalysts using density functional theory (DFT) calculations. It was found that BC₃ two-dimensional (2D) materials exhibit excellent catalytic activity with a very low limiting potential of -0.29/-0.11 V along three reaction paths. The total reaction is NO (g)+5H⁺+5e^-→NH₃(g)+ H₂O. The density of states of adsorbed NO, NH_3, and the corresponding crystal orbital hamiltonian population (COHP) analysis revealed the mechanism of NO being activated and the reasons for NH₃ adsorption/desorption on the surface of BC₃. The reaction path, limiting potential, and Gibbs free energy calculations of BC₃ catalyzed NO to ammonia synthesis revealed that for path 1, the potential-determining step is *NO+H⁺+e^-→*NOH, and for path 2/3 the potential-determining step is *NO+(H⁺+e^-)→*HNO. Calculation of the thermodynamic energy barriers for NO dissociation at the BC₃ surface and NO hydrogenation reveals that NO is more likely to be hydrogenated rather than dissociated. The influences of the proton-electron hydrogenation site on the process of ammonia synthesis in the key reduction step were analyzed by Bader charge analysis and charge density, it is pointed out that the electronic structure and affects the reaction process can be controlled by hydrogenation at different sites of intermediates. These results pave the way for using nitrogen oxides not just nitrogen as raw materials for ammonia synthesis with 2D materials.