Selective Electrocatalytic Oxidation of Nitrogen to Nitric Acid Using Manganese Phthalocyanine

Controlling electrocatalytic nitrate reduction efficiency by utilizing dπ-pπ interactions in parallel stacking molecular systems

Electrochemical reduction of nitrate to ammonia using electrocatalysts is a promising alternative strategy for both wastewater treatment and production of green ammonia. Numerous tactics have been developed to increase the electrocatalyst's NO3RR activity. Herein, we report a unique molecular alignment-dependent NO3RR performance using α-CuPc and β-CuPc nanostructures as effective electrocatalysts for the ambient synthesis of ammonia. The well-aligned β-CuPc demonstrated an impressive ammonia yield rate of 62 703 μg h-1 mgcat -1 and a Faradaic efficiency of 96%. In contrast, the less well-aligned α-CuPc exhibited a yield rate of 36 889 μg h-1 mgcat -1 and a Faradaic efficiency of 61% at -1.1 V vs. RHE under the same conditions. Scanning tunneling microscopy/spectroscopy (STM/S) confirms that the well-aligned β-CuPc exhibits superior transport properties due to optimal interaction of the Cu atom with the nitrogen atom of parallel molecules (dπ-pπ) in its one-dimensional nanostructure, which is clearly reflected in the electrocatalytic performance. Furthermore, theoretical research reveals that the NO3RR is the predominant process on the β-CuPc catalyst in comparison to the hydrogen evolution reaction, which is verified by gas chromatography, with β-CuPc exhibiting weaker binding of the *NO intermediate at the copper site and a lower overpotential, hence facilitating the NO3RR relative to α-CuPc.

Dynamic restructuring of electrocatalysts in the activation of small molecules: challenges and opportunities

Electrochemical activation of small molecules plays an essential role in sustainable electrosynthesis, environmental technologies, energy storage and conversion. The dynamic structural changes of catalysts during the course of electrochemical reactions pose challenges in the study of reaction kinetics and the design of potent catalysts. This short review aims to provide a balanced view of in situ restructuring of electrocatalysts, including its fundamental thermodynamic origins and how these compare to those in thermal and photocatalysis, and highlighting both the positive and negative impacts of in situ restructuring on the electrocatalyst performance. To this end, examples of in situ electrocatalyst restructuring within a focused scope of reactions (i.e. electrochemical CO2 reduction, hydrogen evolution, oxygen reduction and evolution, and dinitrogen and nitrate reduction) are used to demonstrate how restructuring can benefit or adversely affect the desired process outcome. Prospects of manipulating in situ restructuring towards an energy-efficient and durable electrocatalytic process are discussed. The practicality of pulse electrolysis on an industrial scale is questioned, and the need for genius schemes, such as self-healing catalysis, is emphasized.

Design Criteria for Active and Selective Catalysts in the Nitrogen Oxidation Reaction

The direct conversion of dinitrogen to nitrate is a dream reaction to combine the Haber-Bosch and Ostwald processes as well as steam reforming using electrochemistry in a single process. Regrettably, the corresponding nitrogen oxidation (NOR) reaction is hampered by a selectivity problem, since the oxygen evolution reaction (OER) is both thermodynamically and kinetically favored in the same potential range. This opens the search for the identification of active and selective NOR catalysts to enable nitrate production under anodic reaction conditions. While theoretical considerations using the computational hydrogen electrode approach have helped in identifying potential material motifs for electrocatalytic reactions over the last decades, the inherent complexity of the NOR, which consists of ten proton-coupled electron transfer steps and thus at least nine intermediate states, poses a challenge for electronic structure theory calculations in the realm of materials screening. To this end, we present a different strategy to capture the competing NOR and OER at the atomic scale. Using a data-driven method, we provide a framework to derive generalized design criteria for materials with selectivity toward NOR. This leads to a significant reduction of the computational costs, since only two free-energy changes need to be evaluated to draw a first conclusion on NOR selectivity.

Are transition metal phthalocyanines active for urea synthesis via electrocatalytic coupling of CO2 and N2?

Electrocatalytic coupling of CO2 and N2 to synthesize urea presents a promising approach to address global energy and environmental challenges. Despite the potential, developing an efficient catalyst capable of activating both CO2 and N2 while suppressing side reactions remains a significant challenge. Recent studies have indicated that CuPc and CoPc exhibit notable activity in this process. Herein, we report a theoretical analysis of the catalytic performance of 3d-5d transition metal phthalocyanines (MPcs) in the electrocatalytic urea synthesis reaction. Our findings reveal that MPcs generally exhibit limited activity due to the poor competitiveness of N2 for adsorption sites and the high energy barrier associated with CO-N2 coupling, which hinders their ability to compete with CO reduction and/or N2 reduction pathways. Furthermore, the coupling between CO and NH2* is either insufficient for N2 reduction or is outcompeted by ammonia formation. We propose that enhancing N2 adsorption could facilitate C-N coupling, offering a potential strategy for the design of single-atom catalysts aimed at improving urea synthesis efficiency.

Direct electrochemical N2 oxidation to nitrate on supportive Pt/CeO2

Here, we present the development of an efficient Pt/CeO2 catalyst for electrocatalytic N2 oxidation to nitrate. Characterization results indicate that highly dispersed Pt and oxygen vacancies from CeO2 nanocubes (NCs) exhibit strong interactions, which promote the N2 adsorption on the catalyst surface and suppress the competitive OER activity on oxygen vacancies, resulting in significantly enhanced e-NOR performance.

High-Entropy Perovskite Oxides as a Family of Electrocatalysts for Efficient and Selective Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) can convert nitrogen (N2) into nitrate (NO3-) under ambient conditions, providing an attractive approach for synthesis of NO3-, alternative to the current approach involving the harsh Haber-Bosch and Ostwald oxidation processes that necessitate high temperature, high pressure, and substantial carbon emission. Developing efficient NOR catalysts is a prerequisite, which remains a formidable challenge, owing to the weak activation/dissociation of N2. A variety of NOR electrocatalysts have been developed, but their NOR kinetics are still extremely sluggish, resulting in inferior Faradaic Efficiencies. Here, we report a high-entropy Ru-based perovskite oxide (denoted as Ru-HEP) that can function as a high-performance NOR catalyst and exhibit a high NO3- yield rate of 39.0 μmol mg-1 h-1 with a Faradaic Efficiency of 32.8%. Both our experimental results and theoretical calculations suggest that the high-entropy configuration of Ru-HEP perovskite oxide can markedly enhance the oxygen-vacancy concentration, where the Ru sites and their neighboring oxygen vacancies can serve as unsaturated centers and decrease the overall energy barrier for N2 electrooxidation, thereby leading to promoted NOR kinetics. This work presents an alternative avenue for promoting NOR catalysis on perovskite oxides through the high-entropy engineering strategy.

Enhancing Electrochemical Reactivity with Magnetic Fields: Unraveling the Role of Magneto-Electrochemistry

Electrocatalysis performs a vital role in numerous energy transformation and repository mechanics, including power cells, Electric field-assisted catalysis, and batteries. It is crucial to investigate new methods to improve electrocatalytic performance if effective and long-lasting power systems are developed. The modulation of catalytic activity and selectivity by external magnetic fields over electrochemical processes has received a lot of interest lately. How the use of various magnetic fields in electrocatalysis has great promise for building effective and selective catalysts, opening the door for the advancement of sophisticated energy conversion is discussed. Furthermore, the challenges and possibilities of incorporating magnetic fields into electrocatalytic systems and suggestions for future research areas are discussed.

Thermal-hydraulic characteristics of nitric acid: An experimental and numerical analysis

Nitric acid is one of the most important products in the chemical industry, ranking third globally in terms of acid production. Although nitric acid has many industrial applications, its primary function is the production of ammonium nitrate, which is used in the fertilizer industry. In this report, we propose a plan for an Ostwald process plant that will produce 1000 metric tons of nitric acid per day. Based on an effective energy analysis, we have concluded that using a single pressure method provides optimal results. First, ammonia is vaporized using process heat at 1000 kPa and 35 °C before being superheated using steam to a temperature of 80 °C. Filtered air is compressed by an axial compressor to a discharge pressure of approximately 740 kPa and a temperature of 155 °C. After conducting a site evaluation, three existing manufacturing sites are being considered for the acid production plant: Ogun State (Nigeria), Gwadar Seaport (Pakistan), and Ras-Alkhair Seaport (Saudi Arabia). Based on the results of the site assessment, Ras-Alkhair has been selected as the most suitable location for the nitric acid plant. About 65 % of all nitric acid produced worldwide is used in the production of ammonium nitrate, which is in turn used in the fertilizer and explosives industries. The synthetic nitric acid that will be produced from this plant will be used in the production of fertilizers.