Mechanism and Active Species in NH3 Dehydrogenation under an Electrochemical Environment: An Ab Initio Molecular Dynamics Study

Engineering the Local Electronic Configuration of Diatomic Iron-Nickel Site for Enhanced Nitrate and Ammonia Co-Electrolysis Activity

Anthropogenic activities have caused a significant rise in nitrate and ammonia nitrogen levels in natural water bodies, disrupting the balance of the nitrogen cycle. The electrocatalytic reduction of nitrate and the oxidation of ammonia are promising strategies for converting polyvalent nitrogen into nontoxic and harmless N2. Herein, a bifunctional electrode loaded with diatomic iron-nickel site on porous N-doped carbon (FeNi-NC) is designed and successfully applied for the co-electrolysis of nitrate and ammonia. The incorporation of the Fe atom shifts the partial density of states of Ni 3d away from the Fermi level and suppresses the 3d-2π* coupling between Ni sites and superficial N2, leading to the easy desorption of N2 intermediates. Consequently, the Faradaic efficiencies of FeNi-NC for N2 production at the cathode and anode are 90.3% and 99.4% at 1.8 V, respectively, and an electricity consumption saving of 19.4% is achieved. This work provides a feasible strategy to regulate the electronic configuration of atomically dispersed catalysts for sewage treatment.

Rational design of water splitting electrocatalysts through computational insights

Electrocatalytic water splitting is vital for the sustainable production of green hydrogen. Electrocatalysts, including those for the hydrogen evolution reaction at the cathode and the oxygen evolution reaction at the anode, are crucial in determining the overall performance of water splitting. Traditional methods for electrocatalyst development often rely on trial-and-error, which can be time-consuming and inefficient. Recent advancements in computational techniques provide more systematic and predictive strategies for catalyst design. This review article explores the role of computational insights in the development of water-splitting electrocatalysts. We start by giving an introduction of electrocatalytic water splitting mechanisms. Then, fundamental theories such as the Sabatier principle and scaling relationships are reviewed, which provide a theoretical basis for catalytic activity. We also discuss thermodynamic, electronic, and geometric descriptors used to guide catalyst design and provide an in-depth discussion of their applications and limitations. Advanced computational approaches, including high-throughput screening, machine learning, solvation models and Ab initio molecular dynamics, are also highlighted for their ability to accelerate catalyst discovery and simulate realistic reaction conditions. Finally, we propose future research directions aimed at searching universal descriptors, expanding data sets, and integrating developing interpretable models with catalyst design.

Towards superior CO2RR catalysts: Deciphering the selectivity puzzle over dual-atom catalyst

The electrocatalytic CO2 reduction reaction (CO2RR) is one of the most important electrocatalytic reactions. Starting from a well-defined *CO intermediate, the CO2RR can bifurcate into two pathways, either forming a hydrogenation product by *CO bond hydrogenation or leading to CO desorption by *C bond cleavage. However, it is perplexing why many dual-atom catalysts (DACs) exhibit high CO selectivity in experiments, despite previous theoretical studies arguing that the *CO bond hydrogenation is thermodynamically more favorable than the *C bond breaking. Furthermore, the selectivity is contingent upon the potential and is perturbed by the hydrogen evolution reaction (HER), which is far from clear. Using ab initio molecular dynamics and a "slow-growth" sampling method to evaluate the potential-dependent kinetics, we uncover the selectivity origin of CO2RR to CO on a typical NC-based DAC (CuFe-N6-C). Importantly, the results show that at higher CO* coverage, CO* desorption kinetics are accelerated, while the competing *CO bond hydrogenation reaction is inhibited at varying potentials. Furthermore, the selectivity of the HER is observed to increase as the potential decreases. However, at higher CO* coverage, the energy barrier for the *C bond cleavage is lower than that for HER, suggesting that HER is suppressed on CuFe-N6-C. Our work unlocks a long-standing puzzle about the selectivity of important DAC catalysts for CO2RR and provides insights for more effective catalyst design.

Molten-Salt-Mediated Chemical Looping Oxidative Dehydrogenation of Ethane with In-Situ Carbon Capture and Utilization

The molten-salt-mediated oxidative dehydrogenation (MM-ODH) of ethane (C2H6) via a chemical looping scheme represents an effective carbon capture and utilization (CCU) method for the valorization of ethane-rich shale gas and concurrent mitigation of carbon dioxide (CO2) emissions. Here, stepwise experimentation with Li2CO3-Na2CO3-K2CO3 (LNK) ternary salts (i) assessed how each component of the LNK mixture impacted ethane MM-ODH performance and (ii) explored physicochemical and thermodynamic mechanisms behind melt-induced changes to ethylene (C2H4) and carbon monoxide (CO) yields. Of fifteen screened LNK compositions, nine exhibited ethylene yields greater than 50 % at 800 °C while maintaining C2H4 selectivities of 85 % or higher. LNK salts rich in Li2CO3 content yielded more ethylene and CO on average than their counterparts, and net CO2 capture per cycle reached a maximum of ~75 %. Extended MM-ODH cycling also demonstrated long-term stability of a high-performing LNK medium. Density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations suggested that the molten salt does not directly activate C2H6. Meanwhile, an empirical model informed by experimental data and reaction thermodynamics adequately predicted overall MM-ODH performance from LNK composition and provided insights into the system's primary drivers.

Advances in designing efficient electrocatalysts for nitrate reduction from a theoretical perspective

Ammonia (NH3), an important raw material for producing fertilizers and useful chemicals, plays a crucial role in modern human society. As the Haber-Bosch process is energy- and emission-intensive, it is critical to develop a green and energy-efficient route for massive NH3 production under ambient conditions. The electrochemical nitrate reduction reaction to ammonia (eNO3-RR) is a potential way for producing NH3 while harmonizing the nitrogen cycle. In this feature article, we summarize the advances in designing eNO3-RR electrocatalysts from a theoretical perspective. First, the mechanisms and pathways of the eNO3-RR are summarized. Then, the recently developed electrocatalysts, including Cu-based catalysts, single-atom catalysts (SACs), dual-atom catalysts (DACs), and MXene catalysts, are categorically discussed. Finally, the challenges and prospects of designing highly efficient eNO3-RR catalysts through theoretical simulations are discussed. This feature article will provide valuable guidance for the future development of advanced eNO3-RR electrocatalysts for NH3 production.

Discovering Facet-Dependent Formation Kinetics of Key Intermediates in Electrochemical Ammonia Oxidation by a Electrochemiluminescence Active Probe

Facile evaluation of formation kinetics of key intermediate is crucial for a comprehensive understanding of electrochemical ammonia oxidation reaction (AOR) mechanisms and the design of efficient electrocatalysts. Currently, elucidating the formation kinetics of key intermediate associated with rate-determining step is still challenging. Herein, 4-phtalamide-N-(4'-methylcoumarin) naphthalimide (CF) is developed as a molecular probe to detect N2H4 intermediate during AOR via electrochemiluminescence (ECL) and further investigated the formation kinetics of N2H4 on Pt catalysts with different crystal planes. CF probe can selectively react with N2H4 to release ECL substance luminol. Thus, N2H4 intermediate as a key intermediate can be sensitively and selectively detected by ECL during AOR. For the first time, Pt(100) facet is discovered to exhibit faster N2H4 formation kinetics than Pt(111) facet, which is further confirmed by Density functional theory calculation and the finite element simulation. The AOR mechanism under the framework of Gerischer and Mauerer is further validated by examining N2H4 formation kinetics during the dimerization process (NH2 coupling). The developed ECL active probe and the discovered facet-dependent formation kinetics of key intermediates provide a promising new tool and strategy for the understanding of electrochemical AOR mechanisms and the design of efficient electrocatalysts.

Recent progress in energy-saving electrocatalytic hydrogen production via regulating the anodic oxidation reaction

Hydrogen energy with its advantages of high calorific value, renewable nature, and zero carbon emissions is considered an ideal candidate for clean energy in the future. The electrochemical decomposition of water, powered by renewable and clean energy sources, presents a sustainable and environmentally friendly approach to hydrogen production. However, the traditional electrochemical overall water-splitting reaction (OWSR) is limited by the anodic oxygen evolution reaction (OER) with sluggish kinetics. Although important advances have been made in efficient OER catalysts, the theoretical thermodynamic difficulty predetermines the inevitable large potential (1.23 V vs. RHE for the OER) and high energy consumption for the conventional water electrolysis to obtain H2. Besides, the generation of reactive oxygen species at high oxidation potentials can lead to equipment degradation and increase maintenance costs. Therefore, to address these challenges, thermodynamically favorable anodic oxidation reactions with lower oxidation potentials than the OER are used to couple with the cathodic hydrogen evolution reaction (HER) to construct new coupling hydrogen production systems. Meanwhile, a series of robust catalysts applied in these new coupled systems are exploited to improve the energy conversion efficiency of hydrogen production. Besides, the electrochemical neutralization energy (ENE) of the asymmetric electrolytes with a pH gradient can further promote the decrease in application voltage and energy consumption for hydrogen production. In this review, we aim to provide an overview of the advancements in electrochemical hydrogen production strategies with low energy consumption, including (1) the traditional electrochemical overall water splitting reaction (OWSR, HER-OER); (2) the small molecule sacrificial agent oxidation reaction (SAOR) and (3) the electrochemical oxidation synthesis reaction (EOSR) coupling with the HER (HER-SAOR, HER-EOSR), respectively; (4) regulating the pH gradient of the cathodic and anodic electrolytes. The operating principle, advantages, and the latest progress of these hydrogen production systems are analyzed in detail. In particular, the recent progress in the catalytic materials applied to these coupled systems and the corresponding catalytic mechanism are further discussed. Furthermore, we also provide a perspective on the potential challenges and future directions to foster advancements in electrocatalytic green sustainable hydrogen production.

In situ electro-generated Ni(OH)2 synergistic with Cu cathode to promote direct ammonia oxidation to nitrogen

To solve the problem of low removal rate and poor N2 selectivity in direct electrochemical ammonia oxidation (EAO), commercial Ni foam and Cu foam were used as anode and cathode of the EAO system, respectively. The coupling effect between the cathode and anode promoted nitrogen cycling during the reaction process, which improved N2 selectivity of the reaction system and promoted it to achieve a high ammonia removal rate. This study showed that the thin Ni(OH)2 with oxygen vacancy formed on the surface of Ni foam anode played an effective role in the dimerization of intermediate products in ammonia oxidation to form N2. This electrochemical system was used to treat real goose wastewater containing 422.5 mg/L NH4+-N and 94.5 mg/L total organic carbon (TOC). After treatment, this electrochemical system achieved good performance with an ammonia removal rate of 87%, N2 selectivity of 77%, and TOC removal rate of 72%. Therefore, this simple and efficient system with Ni foam anode and Cu foam cathode is a promising method for treating ammonia nitrogen wastewater.

Unraveling the Mechanism of Ammonia Electrooxidation by Coupled Differential Electrochemical Mass Spectrometry and Surface-Enhanced Infrared Absorption Spectroscopic Studies

Ammonia electrooxidation has received considerable attention in recent times due to its potential application in direct ammonia fuel cells, ammonia sensors, and denitrification of wastewater. In this work, we used differential electrochemical mass spectrometry (DEMS) coupled with attenuated total reflection-surface-enhanced infrared absorption (ATR-SEIRA) spectroscopy to study adsorbed species and solution products during the electrochemical ammonia oxidation reaction (AOR) on Pt in alkaline media, and to correlate the product distribution with the surface ad-species. Hydrazine electrooxidation, hydroxylamine electrooxidation/reduction, and nitrite electroreduction on Pt have also been studied to enhance the understanding of the AOR mechanism. NH3, NH2, NH, NO, and NO2 ad-species were identified on the Pt surface with ATR-SEIRA spectroscopy, while N2, N2O, and NO were detected with DEMS as products of the AOR. N2 is formed through the coupling of two NH ad-species and then subsequent further dehydrogenation, while the dimerization of HNOad leads to the formation of N2O. The NH-NH coupling is the rate-determining step (rds) at high potentials, while the first dehydrogenation step is the rds at low potentials. These new spectroscopic results about the AOR and insights could advance the search and design of more effective AOR catalysts.

Interface Engineering of PtZn Alloy and Nb2O5 for Promoting Ammonia Oxidation Reaction and Hydrogen Evolution Reaction

Ammonia electrolysis is a promising technology to obtain green hydrogen with zero-carbon emission, in which ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) occur at the anode and cathode, respectively. However, the lack of efficient catalysts hinders its practical application. Herein, PtZn alloy is combined with Nb2O5 to construct a bifunctional heterostructure catalyst (PtZn-Nb2O5/C). The optimal sample with Nb2O5 content of 7.05 wt % demonstrates the best performance with a peak current density of 304.1 mA mg-1Pt for AOR, and it is only reduced by 17.0% after 4000 cycles of durability tests. For HER, it has a low overpotential of 34 mV at -10 mA cm-2 under the alkaline condition. This can be ascribed to the interfacial interaction between the PtZn alloy and Nb2O5, which adjusts the adsorption behavior of OHad to concurrently promote AOR and HER activity. This work thus proposes a viable strategy to design an efficient bifunctional catalyst for hydrogen generation from ammonia electrolysis.

Aqueous pulsed electrochemistry promotes C-N bond formation via a one-pot cascade approach

Electrocatalytic C - N bond formation from inorganic nitrogen wastes is an emerging sustainable method for synthesizing organic amines but is limited in reaction scope. Integrating heterogeneous and homogeneous catalysis for one-pot reactions to construct C - N bonds is highly desirable. Herein, we report an aqueous pulsed electrochemistry-mediated transformation of nitrite and arylboronic acids to arylamines with high yields. The overall process involves nitrite electroreduction to ammonia over a Cu nanocoral cathode and subsequent coupling of NH3 with arylboronic acids catalyzed by in situ dissolved Cu(II) under a switched anodic potential. This pulsed protocol also promotes the migration of nucleophilic ArB(OH)3- and causes the consumption of OH- near the cathode surface, accelerating C - N formation and suppressing phenol byproducts. Cu(II) can be recycled via facile electroplating. The wide substrate scope, ready synthesis of 15N-labelled arylamines, and methodological expansion to cycloaddition and Click reactions highlight the great promise.

Cu-N4 in copper phthalocyanine@CFC catalyst for ammonia oxidation reaction catalysis

The high oxidation overpotential in the ammonia oxidation reaction (AOR) is a key factor restricting the fields of ammonia fuel cells, hydrogen production by electrochemical decomposition of ammonia, and treatment of ammonia-containing wastewater. Copper-based catalysts have been considered hopeless for AOR; however, in this research, copper phthalocyanine (CuPc) catalysts grown on carbon fiber cloth (CFC), CuPc@CFC, were investigated firstly for AOR catalysis, and the unique Cu-N₄ resulted in a peak potential of -0.29 V vs. Hg/HgO for AOR, which is superior to Pt/C. Density functional theory (DFT) calculations show that Cu-N₄ is the reactive center of AOR, and the LUMO of CuPc is distributed on the Cu site, which is favorable to gain electrons from NH₃ and thus adsorb NH₃; in contrast, the HOMO of C₁₀H₁₀CuN₈ is distributed on the Cu site, which tends to give electrons and is unfavorable to NH₃ adsorption. However, copper azide pyridine (C₁₀H₁₀CuN₈) was found in the samples after the AOR. Analysis of the comparison samples showed that changing the ethanol content has the effect of changing the grain size and inhibiting the generation of C₁₀H₁₀CuN₈ after the AOR process, as well as slightly changing the Cu-N₄, leading to the change of its Fermi energy level and d-orbital energy level center, thus providing new ideas for the future fabrication of catalysts in various fields of AOR.

Simulation on oily contamination removal by ozone using molecular dynamics

Ozone (O₃) is characteristic of high oxidative activity. It displays a high potential value in sterilization and decontamination. Although O₃ has been widely investigated for its efficiency and environmentally friendly effectiveness, the fundamental issue regarding the complicated microscopic interaction mechanism between O₃ and contaminant molecules remains largely unaddressed. We addressed this knowledge gap through molecular dynamics (MD) simulation at the molecular scale. Results indicated that five representative hydrocarbon molecules (n-hexadecane, phytane, terpane, naphthalin and acenaphthylene) on a rough silica (SiO₂) surface were almost removed after about 300 ps simulation. And the aromatic molecules were easier to be removed than aliphatic ones. The hydroxyl oxidation reaction was demonstrated as a predominant mechanism. As the large dose of O₃ was supplied by atmospheric air dielectric barrier discharge (DBD) plasma, this work provided an important theoretical reference for better using plasma technology for oily contaminant removal.

NiWO4 Microflowers on Multi-Walled Carbon Nanotubes for High-Performance NH3 Detection

NiWO4 microflowers with a large surface area up to 79.77 m2·g-1 are synthesized in situ via a facile coprecipitation method. The NiWO4 microflowers are further decorated with multi-walled carbon nanotubes (MWCNTs) and assembled to form composites for NH3 detection. The as-fabricated composite exhibits an excellent NH3 sensing response/recovery time (53 s/177 s) at a temperature of 460 °C, which is a 10-fold enhancement compared to that of pristine NiWO4. It also demonstrates a low detection limit of 50 ppm; the improved sensing performance is attributed to the porous structure of the material, the large specific surface area, and the p-n heterojunction formed between the MWNTs and NiWO4. The gas sensitivity of the sensor based on daisy-like NiWO4/MWCNTs shows that the sensor based on 10 mol % (MWN10) has the best gas sensitivity, with a sensitivity of 13.07 to 50 ppm NH3 at room temperature and a detection lower limit of 20 ppm. NH3, CO2, NO2, SO2, CO, and CH4 are used as typical target gases to construct the NiWO4/MWCNTs gas-sensitive material and study the research method combining density functional theory calculations and experiments. By calculating the morphology and structure of the gas-sensitive material NiWO4(110), the MWCNT load samples, the vacancy defects, and the influence law and internal mechanism of gas sensitivity were described.