Ammonia Species Research Articles

Investigating proton shuttling and electrochemical mechanisms of amines in integrated CO2 capture and utilization

Carbon capture and utilization (CCU) technologies present a promising solution for converting CO2 emissions into valuable products. Here we show how amines, such as monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP), influence the electrochemical CO2 reduction process in an integrated CCU system. Using in situ spectroscopic techniques, we identify the key roles of carbamate bond strength, proton shuttling, and amine structure in dictating reaction pathways on copper (Cu) and lead (Pb) electrodes. Our findings demonstrate that on Cu electrodes, surface blockage by ammonium species impedes CO₂ reduction, whereas on Pb electrodes, proton shuttling enhances the production of hydrocarbon products. This study provides additional insights into optimizing CCU systems by tailoring the choice of amines and electrode materials, advancing the selective conversion of CO₂ into valuable chemicals.

A Strategy for the Formal C−N Cross‐Coupling of Tertiary Amines

AbstractWe report a strategy for the formal C−N cross‐coupling of tertiary amines via the in situ generation and displacement of N‐acyl ammonium species. Specifically, treatment of diverse tertiary amines with TFAA or chloroformates in the presence of NaI leads to the efficient generation of alkyl iodides, which can be engaged directly in Ni‐catalyzed cross‐couplings. The protocol is applicable to acyclic and cyclic systems, including highly hindered variants. Applications to the late‐stage modification of complex heterocycles are presented.

Temperature-controlled shape transformation of PtCo alloy catalysts for enhanced ammonia oxidation in anion-exchange membrane direct ammonia fuel cells

Low-temperature anion-exchange membrane direct ammonia fuel cells (AEM-DAFCs) are emerging as attractive and environmentally friendly energy devices for small-scale transportation. However, challenges arise in the ammonia oxidation reaction (AOR) owing to the high activation energy required for direct ammonia modification and the issue of decreased activity in the AOR caused by the strong adsorption of ammonia and nitrogen species, necessitating solutions. In this study, we aimed to address the challenges related to the ammonia activation energy and ammonia adsorption capacity by alloying Pt and Co. Furthermore, during the fabrication of the PtCo catalysts, the synthesis process was controlled at different reaction temperatures to produce core–shell and hollow structures. In particular, the PtCo catalyst synthesized at 60 °C (PtCo-60), with a particle size of 7.65 nm in the hollow structure, exhibited the highest electrochemically active surface area among the PtCo catalysts produced (∼43.0 m2 g−1). This increase in the active surface area owing to structural changes was attributed to the increase in AOR activity. The onset potential of PtCo-60, adjusted for particle size and structure, was determined to be 0.454 V vs. RHE, with a mass activity of 128 A gPt−1, in cyclic voltammetry experiments using 1 M KOH +1 M NH4OH. Ultimately, in the AEM-DAFC unit cell test conducted at 80 °C, an output density of 11.33 mW cm−2 was achieved.

Transformation of waste thermocol into activated carbon for electrochemical detection of ammonia in an aqueous solution

In this study, waste thermocol sheets are used to synthesize activated carbon (AC) for the electrochemical detection of ammonia in an aqueous solution. The AC is characterized for its morphology, structure, and chemical composition via standard characterization techniques. AC shows promise for detecting ammonia in aqueous solutions due to its high adsorption capacity from large surface area and porosity. The electrochemical approach used to detect ammonia (NH3) in electrolyte solutions uses an AC electrode and is based mostly on the electro-oxidative conversion of ammonia species at the electrode's interface. AC electrodes fabricated on flexible conductive fabric (CF) are used for the electrochemical detection of ammonia at pH 6. The electrochemical sensing of ammonia in aqueous solutions involves its oxidation on the electrode's surface. Cyclic Voltammetry (CV) experiments were conducted over a pH range of 5 to 8, revealing optimal current responses at pH 6. Therefore, phosphate-buffered saline (PBS) at pH 6.0 was employed for all electrochemical analyses. Various concentrations of ammonia (10–100 ppm) were investigated within a voltage window of −0.3 V to 0.3 V, with current signals increasing proportionally with ammonia concentration. The limits of detection (LOD) and quantification (LOQ) were determined to be 28.55 ppm and 86.54 ppm, respectively. An incubation period of 3 min was observed for ammonia concentrations ranging from 0 to 40 ppm. Selectivity evaluations were conducted by assessing interference effects from ethanol (E), methanol (M), toluene (T), and uric acid (UA), revealing ammonia's distinctive peak, indicative of superior selectivity. Notably, the electrode exhibited remarkable stability, retaining approximately 95 % of the original signal over a 5-week duration. The reproducibility of the fabricated electrodes shows significant results. The repeatability was performed at room temperature in a buffer solution of pH 6 and at a 40-ppm concentration of ammonia and has shown almost similar results. Therefore, the fabricated AC sensing electrode has shown prominent stability, reproducibility, and repeatability. These sensing electrodes can be very beneficial for sensing applications.

A Strategy for the Formal C-N Cross-Coupling of Tertiary Amines.

We report a strategy for the C-N cross-coupling of tertiary amines via the in situ generation and displacement of N-acyl ammonium species. Specifically, treatment of diverse tertiary amines with TFAA or choroformates in the presence of NaI leads to the efficient generation of alkyl iodides, which can be engaged directly in Ni-catalyzed cross-couplings. The protocol is applicable to acyclic and cyclic systems, including highly hindered variants. Applications to the late-stage modification of complex heterocycles are presented.

Ammonia-induced constraints on butyrate degradation in anaerobic digestion: Impact of ammonia levels and pH conditions, and recovery behaviour

The accumulation of butyrate is a recurrent phenomenon in anaerobic digesters utilizing animal manure as the primary feedstock. Despite its prevalence, the factors governing the anaerobic degradation of butyrate remain inadequately explored. In this study, a series of experiments were carried out under different total ammonia concentrations (TAN, 0.18–20 g N/L) and pH conditions (7.0–8.0) to investigate the inhibition of butyrate anaerobic degradation by different ammonia species (NH4+ and NH3) and to assess the recoverability following severe ammonia inhibition. The findings indicate that at pH 7.5, butyrate degradation experienced remarkable inhibition when TAN exceeded 8.0 g N/L, while no discernible impact was observed at pH 7.0–8.0 and 4.0 g TAN/L. Additionally, the lag phase for butyrate degradation extended with increasing TAN concentration. Notably, the activity of butyrate-degrading bacteria exhibited full recovery from severe ammonia inhibition (TAN 20 g N/L or NH3 779.2 mg N/L), provided prolonged adaption time was allowed. The analysis using a modified Monod inhibition model highlighted that NH4+ contributed more to inhibition than NH3 at TAN concentrations of 2.0–20.0 g N/L. Therefore, simply reducing pH levels would not adequately counteract ammonia inhibition. Implementing an extended hydraulic retention time emerges as an effective measure to reduce butyrate accumulation in anaerobic digestion systems, particularly the feedstock being nitrogen-rich materials (e.g., animal manure).

The underestimated role of manganese in modulating the nutrient structure in a eutrophic seasonally-stratified reservoir

Accumulation and subsequent release of nutrients have great potential to trigger algal blooms in lakes and reservoirs. We conducted high vertical resolution (2 m interval) monitoring at ∼monthly intervals over a year for hydrological parameters, Chl-a, ammonium (NH4+), nitrate (NO3−) and different species of phosphorus (P) and manganese (Mn) in a 40-meter-deep subtropical reservoir (Shanmei Reservoir) in Fujian, southern China. In this seasonally stratified reservoir featured with high nutrient loading, the consistent trend in the ratio of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphorus (DIP) between the euphotic zone and the hypolimnion, coupled with its mirrored correlation with Chl-a concentration indicates that upward flux from the hypolimnion affects phytoplankton growth in the euphotic zone. The monthly variation of the depth-integrated multiple species of N and P indicates that during the stratification period in the hypoxic hypolimnion, approximately 80% of the DIP is removed, leading to a remarkable decoupling phenomenon between NH4+ and DIP. This process effectively increases the ratio of DIN to DIP in the hypolimnion, thereby significantly reducing the potential of algal blooms caused by the upward flux. A robust positive linear correlation between iron-manganese bound phosphorus (CBD-P) and particulate Mn was observed during stratification period implying that DIP was scavenged by sediment-released Mn throughout the water column. Vertical profiles during stratification showed that upward diffusion of Mn2+ facilitated the formation of Mn oxide zones near the oxycline. The most significant decrease in DIP inventory occurs when Mn oxide zones migrate either upwards from the bottom or downwards from the oxycline, indicating that the migration of Mn oxides on the vertical profile is a key factor in the decoupling of NH4+and DIP.Our findings underscore the importance of Mn cycling as an underappreciated DIP self-immobilization process in the water column of reservoirs characterized by high nutrient loading. Furthermore, we propose that denitrification and Mn cycling establish a consecutive feedback mechanism, preventing excessive nutrient accumulation in low oxygen bottom water. In the context of global changes, we anticipate a heightened prominence of this feedback mechanism.

Full spectroscopic model and trihybrid experimental-perturbative-variational line list for NH

ABSTRACT Imidogen (NH) is a reactive molecule whose presence in astrochemical environments is of interest due to its role in the formation of nitrogen-containing molecules and as a potential probe of nitrogen abundance. Spectroscopic NH monitoring is useful for Earth-based combustion and photolysis processes of ammonia and other nitrogen-containing species. NH is also relevant to ultracold molecular physics and plasma studies. To enable these diverse applications, high-quality molecular spectroscopic data are required. Here, a new line list with significant advantages over existing data is presented. Most notably, this line list models isotopologue spectroscopy and forbidden transitions (important for NH visible absorption), alongside some overall improvements to accuracy and completeness. This approach takes advantage of existing experimental data (from a previous MARVEL compilation) and perturbative line lists together with new MRCI ab initio electronic data. These are used to produce a novel variational spectroscopic model and trihybrid line list for the main 14N1H isotopologue, as well as isotopologue-extrapolated hybrid line lists for the 14N2H, 15N1H, and 15N2H isotopologues. The new 14N1H ExoMol-style trihybrid line list, kNigHt, comprises 4076 energy levels (1078 experimental) and 327 014 transitions up to 47 500 cm−1 (211 nm) between five low-lying electronic states (X 3Σ−, a 1Δ, b 1Σ+, A 3Π, and c 1Π). For most anticipated applications aside from far-infrared studies, this line list will be of sufficient quality; any improvements should focus on the b 1Σ+ energies, and the a 1Δ – A 3Π and b 1Σ+ – A 3Π spin–orbit couplings.

Nickel nitride-mediated nitric oxide generation for combating implant-associated infections

NiTi alloys are widely used in the fabrication of biomedical implants, and it is essential to endow them with selective antibacterial properties to avoid implant-associated infection. In this study, nickel nitride (Ni3N), as a promising new inorganic nitric oxide (NO) donor, was in situ constructed on the surface of NiTi alloys through a straightforward two-step plasma immersion ion implantation (PIII) strategy. Nickel sites were first exposed by physical bombardment with argon or metal plasma, followed by reaction with nitrogen plasma to form Ni3N. Ni3N can disrupt the transmembrane proton electrochemical gradient by capturing protons to produce ammonia species (NHx), resulting in the accumulation of reactive oxygen species (ROS) as a result of bacterial metabolic disruption. On the other hand, the generated NHx can further react with ROS to produce NO and reactive nitrogen species (RNS). As a result, the Ni3N films exhibited more than 99 % antibacterial efficiency against both gram-negative and gram-positive bacteria. They also demonstrated effective antibacterial properties in a rat subcutaneous implant model. In addition, the modified NiTi alloys exhibit good corrosion resistance and cytocompatibility. This study provides a green, safe, and inexpensive method for constructing metal nitride films on implant surfaces and offers new ideas for the clinical design and fabrication of novel antibacterial implants.

Aza-Diphosphido-Bridged Di-Iron Complexes Related to the [FeFe]-Hydrogenases

The reaction of the dianionic species [Fe2(CO)6(μ-PPh)2]2− with tBuN(CH2Cl)2 gives the di-iron carbonyl aza-diphosphido-bridged complex [Fe2(CO)6(µ-{P(Ph)CH2}2NtBu)] (1). Attempts to prepare 1 by click-chemistry by reacting [Fe2(CO)6(μ-PHPh)2] with CH2O and tBuNH2 afforded a bis-phosphido compound [Fe2(CO)6(µ-P(Ph)CH2NHtBu)2] (2) which exists as two, syn and anti, isolable isomers depending on the relative orientation of the groups carried by the phosphorus atoms. In the presence of HBF4.Et2O, in dichloromethane, 1 leads to the stabilized ammonium species [Fe2(CO)6(µ-{P(Ph)CH2}2NHtBu)](BF4) (3). The derivatives 1–3 were characterized by IR and 1H, 31P-{1H} NMR spectroscopies. Their structures in a solid state were determined by X-ray diffraction analyses, which accord with their spectroscopic characteristics.

Unravelling the distribution of three Ammonia species (Foraminifera, Rhizaria) in French Atlantic Coast estuaries using morphological and metabarcoding approaches

Assessing the distribution of species in natural environments is essential for their use in environmental surveys. Here, we investigate the distribution of three pseudo-cryptic species formerly lumped in the morphospecies Ammonia tepida (Cushman, 1926), commonly found on estuarine mudflats along the European coasts: Ammonia veneta Schultze, 1854 (T1), Ammonia aberdoveyensis Haynes, 1973 (T2) and Ammonia confertitesta Zheng, 1978 (T6). We studied their distribution at 51 sites located in seven estuaries of the French North Atlantic coast (Elorn, Aulne, Odet, Crac'h, Auray, Vilaine, Vie), using both morphological and molecular identification methods. Ammonia veneta was detected by both approaches at most of the stations. While A. aberdoveyensis was frequently identified by the morphological method but not detected with metabarcoding, the presence of A. confertitesta in the eDNA data often contrasted with its absence in the morphological analysis. The absence of A. aberdoveyensis in eDNA of sites where it was identified morphologically could be the consequence of its relative scarcity, and eventually a patchy distribution. Concerning A. confertitesta, we hypothesise that these contradictory results can be explained by the supposedly invasive character of this species. Despite the widespread presence of A. confertitesta genetic material (including adults, juveniles and propagules), a mature population has not yet fully developed everywhere. The seven investigated estuaries seem to represent different stages of replacement of the autochthonous species A. veneta and A. aberdoveyensis by A. confertitesta. Our study demonstrates that the combination of visual observations and molecular approaches is ideal for monitoring the progressive spreading of exotic species.

Effects of syngas and methanol fuel substitution on ammonia counterflow diffusion flames

Ammonia (NH3) is increasingly recognized as a promising alternative fuel. Various blending options have been proposed that are aimed at improving its flammability and applicability across diverse energy systems. This study conducts a comprehensive investigation, employing both experimental and numerical approaches, to understand the impact of blending ammonia with CH3OH or syngas, at various H2:CO ratios, on flame extinction limits, structure, and NOx emissions in counterflow laminar diffusion flames. Concentration profiles of ammonia and intermediate species (O2, CO, CO2, H2, NO, and N2O) were measured using Fourier-transformed infrared (FTIR) and gas chromatographic (GC) techniques. The findings indicate that increasing the H2:CO ratio in syngas-blended flames increases the extinction limits and reduces NO and N2O emissions. Compared with ammonia/methanol flames the ammonia/syngas flames exhibit higher extinction limits, flame temperatures, and lower NO and N2O emissions. Multiple kinetic models were found to underestimate the extinction strain limits, with Wang et al.’s 2021 model offering the closest predictions. Notably, discrepancies in ammonia dissociation and oxygen leakage to the rich side of stoichiometry impact reaction zone characteristics, extinction limits, and NOx predictions. Further kinetic analyses reveal that reactivity in syngas-blended flames is dominated by heat and radicals-producing reactions, while methanol-blended flames are sensitive to reactions involving ammonia fragments, resulting in decreased reactivity compared to syngas-blended flames. The results and findings from this study yield valuable insights into optimizing ammonia blends for enhanced flame stability and reduced emissions across various energy applications. It also provides data for chemical kinetics model validation in non-premixed diffusion environment where both species chemistry and transport are encountered.

The Crystal Chemistry of Voltaite-Group Minerals from Post-Volcanic and Anthropogenic Occurrences

Five samples of voltaite-group minerals from post-volcanic occurrences (geothermal fields and solfatara at pyroclastic flow) and from pseudofumaroles born by coal fires are characterized by single-crystal X-ray diffraction, scanning electron microscopy and electron microprobe analysis. The studied minerals include ammoniomagnesiovoltaite, ammoniovoltaite, voltaite and magnesiovoltaite. The quadrilateral of chemical compositions is determined by monovalent cations such as (NH4)+ and K+ and divalent cations such as Fe2+ and Mg2+. Minor Al can occur in the Fe3+ site. Minor amounts of P, V can occur in the S site. Ammonium members are described from geothermal fields, expanding the mineral potential of this type of geological environment. All minerals are cubic, space group Fd-3c, a = 27.18–27.29 Å, V = 20079–20331 Å3, Z = 16. No clear evidence of symmetry lowering (suggested for synthetic voltaites) is observed despite the chemical variation in the studied samples. Ammonium species tend to have a larger a lattice parameter than potassium ones due to longer <A–O> distances (A = N or K). The systematically shorter <Me2+–ϕ>obs (Me2+ = Fe, Mg; ϕ = O, H2O) in comparison to <Me2+–ϕ>calc bond lengths can be explained as a consequence of mean bond length variation due to significant bond length distortion in Me2+ϕ6 octahedra Me2–O2—2.039–2.055 Å; Me2–O4—2.085–2.115 Å; and Me2–Ow5—2.046–2.061 Å, with bond length distortion estimated as from 0.008 to 0.014 for different samples.

Ordered mesoporous phosphotungstate nanostructure loading dispersed iron oxide as a promising NH3-SCR catalyst: Synergistic effect of redox sites and acid centers

An ordered mesoporous phosphotungstate loading dispersed iron oxide is obtained as Fe/NPW catalyst for NH3-SCR. The Fe/NPW catalyst exhibits higher than 90 % NOx conversion at 250–475 °C and excellent SO2 tolerance since the ordered and uniform mesoporous structure favors the diffusion of reactants and dispersion of active ingredients. Moreover, the high dispersion enhances the interfacial interaction between Fe and W species on Fe/NPW catalyst, increasing the W5+/(W5++W6+) ratio to promote the formation of oxygen vacancies and surface adsorbed oxygen (Oα). Additionally, the synergistic effect of the redox sites and acid centers enabled by the dispersed iron oxide on the ordered mesoporous phosphotungstate provides moderate redox property and enhanced surface acidity. It improves the adsorption of NH3 and inhibits the over-oxidation of NH3 that occurs on Fe2O3 surface. Furthermore, the in-situ DRIFTS results show that the abundant surface acidity of phosphotungstate can suppress the formation of nitrate species. The introduction of Fe provides redox sites for reaction and enhances the thermal stability and activation of ammonia species adsorbed on Lewis acid sites, facilitating the Eley-Rideal pathway on Fe/NPW catalyst. The results of this work reveal that the synergistic effect of redox sites and acid centers on the ordered mesoporous Fe/NPW catalyst contributes to the excellent performance in the NH3-SCR process.

Insight into the transformation of 4-hydroxy-3-aminophenylarsonic acid (HAPA) and its mechanisms under simulated sunlight irradiation

Four-hydroxy-3-aminophenylarsonic acid (HAPA), the reduced product of roxarsone (4-hydroxy-3-nitro-phenylarsonic acid, ROX) under anaerobic conditions, is resistant to be biologically degraded under anaerobic/anoxic conditions. The transformation of HAPA in aquatic environment under sunlight irradiation is still unknown. In this study, the photodegradation of HAPA and the possible mechanism under simulated sunlight conditions were investigated. The result shows that under visible light irradiation, HAPA wasn’t degraded. Under UV254 and UV302 irradiation, about 60% and 30% HAPA were decomposed, while nearly no HAPA was degraded under UV365 irradiation over a period of 240 min. UVC light was the main wavelength for the degradation of HAPA under sunlight conditions. HCO3- and NO3- slightly enhanced the photodegradation, but Cl- and SO42- had a marginal influence on the photodegradation. During the photodegradation, HAPA was decomposed into organic intermediates, inorganic arsenics, ammonia and undetermined arsenic species. Arsenite (As(III)) was the dominant inorganic arsenic species from the photodegradation of HAPA. The mechanism analysis shows that singlet molecular oxygen (1O2) has little influence on the decomposition of HAPA under UV irradiation, but significantly enhanced the conversion of As(III) to arsenate (As(V)).

Preferential presence in harbours confirms the non-indigenous species status of Ammonia confertitesta (Foraminifera) in the English Channel

Though the morphological discrimination of the three pseudo-cryptic Ammonia species, A. aberdoveyensis, A. confertitesta and A. veneta, has been recently established, information on their ecology and habitats are still relatively scarce. This study aims to define distribution patterns of these species at eight sites scattered along the French coasts of the English Channel, over a total of 39 stations. These sites were classified into two habitats, either harbours (heavily modified sites) or less impacted (moderately influenced sites). The use of IndVal index (an index based on how a species is statistically specific to a habitat) clearly indicates that A. confertitesta is recorded preferentially in or close to harbours. Considering its non-indigenous species (NIS) status in Europe, we investigated its reported occurrences in Europe in the literature. It almost always showed a proximity to major European harbours. Sometimes, this species occurred relatively far away from these harbours, suggesting a secondary spread. Finally, this work interprets A. confertitesta being a NIS in the eastern English Channel with assumptions of being invasive regarding its dominance over the indigenous species A. aberdoveyensis and A. veneta. Complementary works such as retrospective core studies of fossil faunas are needed to quantitatively assess when and where A. confertitesta was introduced in Europe and potentially started to replace its congenerics A. veneta and A. aberdoveyensis.

A comparison of bifunctional MnOx catalysts prepared via different precipitants for simultaneous removal NO and CO

In this work, ammonium carbonate, sodium hydroxide, and ammonium hydroxide were selected as the precipitants to prepare bifunctional MnOx catalysts via the PEG-assisted co-precipitation method. SEM analysis revealed that MnOx catalysts prepared with ammonium carbonate (AC) displayed a spherical morphology with relatively large size, whereas the catalysts synthesized with sodium hydroxide (SH) and ammonium hydroxide (AH) exhibited polyhedron shapes with smaller size. The results demonstrated that Mn-AC catalyst presented superior catalytic activity for both NO reduction and CO oxidation, achieving 89% NO conversion at 100 ºC and over 80% CO conversion at 200 ºC, outperforming Mn-SH and Mn-AH catalysts. Mn-AC catalyst possessed more abundant Mn4+ species and surface chemisorbed oxygen than Mn-AH and Mn-SH catalysts, which served as a significant motivation for the difference in catalytic activity. Additionally, Mn-AC catalyst exhibited stronger surface acidity, which facilitated the adsorption and activation of ammonia species in the NH3-SCR reaction. Furthermore, in situ DRIFTS experiment suggested that the pre-desorption of CO promoted the adsorption and activation of NO. On this basis, the possible mechanism model of three precipitants on bifunctional MnOx catalysts was proposed.

Electrode-Supported Protonic Ceramic Electrolysis Cells for Ammonia Electrosynthesis at Intermediate Temperatures

Ammonia electrosynthesis, the electrochemical process of converting water and nitrogen into ammonia using renewable energy, has been the focus of attention in the search for a Haber-Bosch alternative. Ammonia produced using renewable energy can not only be used as a fertilizer, but also in its liquefied form as an energy-dense fuel (“energy carrier”). Protonic ceramic electrolysis cells (PCECs) are suitable for ammonia electrosynthesis at high temperatures due to their superior chemical and thermal stability and their ability to keep ammonia and water separate throughout the process, enabling efficient separation of pure ammonia after synthesis. However, on the system scale, high temperature conditions are less compatible with the fluctuating output of renewable energy generation. Additionally, as the temperature dependence of ammonia synthesis faces a trade-off between thermodynamic and kinetic favorability, intermediate temperatures, defined here as between 200-400˚C, are considered promising for ammonia electrosynthesis [1].We previously demonstrated that under a mixed cathodic gas feed of N2/H2, ammonia electrosynthesis using PCECs can be accelerated by cathodic polarization [2-3]. Non-Faradaic effects were observed; that is, the ammonia formation rate was not proportional to the current density. Our results demonstrated similar characteristics as those observed under the electrochemical promotion of catalysis (EPOC), first proposed by Stoukides et. al [4]. Recently, using electrolyte-supported PCECs operated at 600˚C, we showed that high ammonia formation rates on the order of 10-8 mol s-1 cm-2 can be attained in a single-chamber co-fed with N2 and H2 [5], which can eliminate gas sealing requirements.In this work, we aim to understand the factors needed to lower the operating temperature of ammonia electrosynthesis using PCECs co-fed with N2 and H2, from high temperatures between 500-600˚C to intermediate temperatures of 400˚C and below. Electrolyte-supported and electrode-supported cells were compared for their ammonia electrosynthesis rates and cell performances. Electrochemical testing was conducted in a single-chamber reactor co-fed with 50% H2/50% N2 at 300-600˚C. Ammonia formation rates were evaluated by bubbling the outlet gas into a dilute H2SO4 solution and measuring the resulting ammonium ion concentrations via high-performance liquid chromatography. We conducted electrochemical control tests in H2/Ar to validate that ammonia has been produced electrochemically from dinitrogen, rather than from potential traces of ammonia or NOx species (which are easier to reduce) found in the experimental environment.Preliminary experiments using electrode-supported cells with the configuration Fe|BaCe0.9Y0.1O3-δ (BCY)|Ni-BaZr0.8Y0.2O3-δ (Ni-BZY) have resulted in ammonia formation rates over 10-8 mol s-1 cm-2 at an applied voltage of -1 V, at just 400˚C, as shown in Fig. 1. This corresponds to a 150~200˚C reduction in temperature compared to that needed to obtain similar ammonia formation rates using electrolyte-supported cells of the configuration Pt|BCY|Fe. We further evaluate both types of cells in terms of their current density and electrochemical impedance, to understand how the effect of applied voltage varies with the different cell structures. The comparison suggests that Ohmic and anodic overpotentials are effectively limited in our electrode-supported cells, leading to an increased cathodic polarization that aids in accelerating ammonia formation even at intermediate temperatures. Acknowledgements This work was supported by JSPS KAKENHI Grant Numbers JP21H04938 and JP22J11546.

Atomic Ru coordinated by channel ammonia in V-doped tungsten bronze for highly efficient hydrogen-evolution reaction

Regulation of the atomic distribution is crucial for the development of atomically dispersed electrocatalysts. In this study, atomic Ru coordinated by channel ammonia in V-doped tungsten bronze (Ru/V-NHWO, Ru 0.44 wt%, V 0.45 wt%) was used as a high-performance catalyst for the hydrogen evolution reaction (HER), demonstrating remarkable mass activity in a wide pH range. Atomic Ru with a regulated spatial distribution and electronic structure was achieved owing to its unique coordination with the ammonia species in the hexagonal channels of V-NHWO. V doping in NHWO led to enhanced intrinsic activity and conductivity. Theoretical calculations revealed that the multichannel, vertically integrated Ru sites in the V-doped channels, as well as the coexisting Ru sites without multichannels or V-doping, improved the free energy of water dissociation and hydrogen sorption, which boosted the HER activity. Our study paves a new way for constructing atomically dispersed materials with a regulated spatial distribution for diverse applications.

Studies of NO Reduction with Ammonia Over Copper Species Deposited on MCM‐41 Nanospheres ‐ Experimental Evidence of Reaction Mechanism

AbstractNanospheres of MCM‐41 were modified with copper by template ion‐exchange (TIE) and cocondensation methods. In the samples modified by TIE, dispersion of copper was significantly improved by their post‐treatment in ammonia solutions. Highly dispersed copper species were significantly more active in low‐temperature NH3‐SCR than CuO aggregates. Copper dispersed on silica MCM‐41 catalytically operated at lower temperatures than copper deposited on silica‐alumina MCM‐41. The studies of reaction mechanism showed that ammonia and NOx species compete for these same adsorption sites (copper cations) and NH3 can remove NOx from such sites. Dispersed copper species are more active in NO to NO2 oxidation than CuO aggregates. Accumulation of oxidised NOx species in the absence of ammonia was more privileged on CuO aggregates. It is postulated that the main reaction pathway in the low‐temperature range is reaction of ammonia bounded to copper with NOx from gas phase or loosely bounded to the catalyst surface.