Electrochemical Oxidation Of Ammonia Research Articles

Electro-nitrification coupled with biological denitrification achieves efficient nitrogen removal from rare earth mine ammonia-nitrate wastewater

Nowadays, ammonia-nitrate wastewater has been posed serious environmental hazards. Electrochemical ammonia oxidation (AOR) technology with environmentally friendly and easy-to-operate features has attracted much attention. In this work, a novel anode catalytic electrode (Ni1Cu1Fe0.5-S/Ti) is prepared by a one-step electrodeposition method for electro-nitrification, and coupled a biological denitrification device for the treatment of real ammonia-nitrate wastewater. The unique three-dimensional layered spherical structure of Ni1Cu1Fe0.5-S/Ti electrode has been verified through physical characterization, and electrochemical tests demonstrated that Ni1Cu1Fe0.5-S/Ti electrode gained an excellent current density of 54.48 mA·cm−2 toward to AOR at 0.65 V vs. Hg/HgO as well as good stability for four times repeated electro-nitrification experiments. The optimal experimental operating conditions were obtained by changing electrode spacing, initial NH4+-N concentration, current density and flow rate. Consequently, 97.7 % total nitrogen (TN) removal efficiency of real wastewater is achieved through electro-nitrification coupled with biological denitrification, providing a new perspective technology for ammonia-nitrate wastewater treatment.

Gasdiffusionselektroden für die Elektrokatalytische Oxidation von Gasförmigem Ammoniak: Das Überqueren des Thermodynamischen Tals der Stickstoffdreifachbindung

AbstractDa Ammoniak als vielversprechender Wasserstoffträger immer mehr an Interesse gewinnt, wird auch die elektrochemische Ammoniak‐Oxidationsreaktion (AmOR) immer interessanter. Um die Freisetzung von H2 in einer umgekehrten Haber–Bosch‐Reaktion unter Bildung des energetisch günstigeren N2 zu vermeiden, schlagen wir die Oxidation von Ammoniak zu Nitrit (NO2−) vor, das üblicherweise während des Ostwald‐Prozesses gewonnen wird. Wir untersuchten die anodische Oxidation von gasförmigem Ammoniak, der direkt einer Gasdiffusionselektrode (GDE) zugeführt wird, unter Verwendung verschiedener, in ihrer Zusammensetzung unterschiedlicher Multimetallkatalysatoren, die auf Ni‐Schaum abgeschieden sind, bei gleichzeitiger Bildung von H2 an der Kathode. Dadurch wird die H2‐Menge pro Ammoniakmolekül verdoppelt, während gleichzeitig ein niedrigeres Überpotential als bei der Wasserelektrolyse (1,4–1,8 V gegen RHE bei 50 mA cm−2) angelegt wird. Eine Selektivitätsstudie zeigte, dass einige der Katalysatorzusammensetzungen in der Lage waren, erhebliche Mengen an NO2− zu produzieren. Weitere Untersuchungen mit dem vielversprechendsten Katalysator Nif_AlCoCrCuFe, der in eine GDE integriert ist, zeigten eine Faraday‐Effizienz von bis zu 88 % für NO2− an der Anode, gekoppelt mit einer Faraday‐Effizienz von nahezu 100 % für die kathodische H2‐Produktion.

Gas Diffusion Electrodes for Electrocatalytic Oxidation of Gaseous Ammonia: Stepping Over the Nitrogen Energy Canyon.

As ammonia continues to gain more and more interest as a promising hydrogen carrier compound, so does the electrochemical ammonia oxidation reaction (AmOR). To avoid the liberation of H2 in a reverse Haber-Bosch reaction under release of the energetically more favorable N2, we propose the oxidation of ammonia to value-added nitrite (NO2 -), which is usually obtained during the Ostwald process. We investigated the anodic oxidation of gaseous ammonia directly supplied to a gas diffusion electrode (GDE) using a variety of compositionally different multi-metal catalysts coated on Ni foam under the simultaneous formation of H2 at the cathode. This will double the amount of H2 per ammonia molecule while applying a lower overpotential than that required for water electrolysis (1.4-1.8 V vs. RHE at 50 mA ⋅ cm-2). A selectivity study demonstrated that some of the catalyst compositions were able to produce significant amounts of NO2 -, and further investigations using the most promising catalyst composition Nif_AlCoCrCuFe integrated within a GDE demonstrated up to 88 % Faradaic efficiency for NO2 - at the anode coupled to close to 100 % Faradaic efficiency for the cathodic H2 production.

Correlative in situ analysis of the role of oxygen on ammonia electrooxidation selectivity on NiOOH surfaces

The electrochemical ammonia oxidation reaction (AOR) offers a promising pathway for environmental remediation, energy conversion, and the production of value-added chemicals. Although NiOOH shows potential as an efficient catalyst for AOR, the underlying mechanism and the influence of the concurrent oxygen evolution reaction (OER) are not yet fully understood. Here, the AOR mechanism on NiOOH is examined, emphasizing the influence of OER and dissolved O2. Using differential electrochemical mass spectrometry (DEMS), Raman spectroelectrochemistry, UV–vis spectroelectrochemistry, and attenuated total reflection infrared reflection (ATR-IR) spectroelectrochemistry, we reveal that the NiOOH formation, AOR activity, selectivity, and deactivation as well as the reaction intermediates are significantly modulated by OER and dissolved O2. AOR on NiOOH is potential-dependent: N2production starts with the onset of OER, while extensive NOx and NO2/3− species form at higher potentials. The OER competes with the AOR-to-N2 pathway but promotes AOR-to-NOx, where the presence of O2 mitigates OER deactivation on NiOOH. Our findings highlight the advantage of correlative in situ analysis in studying electrocatalytic processes and advance the current understanding of AOR pathways on NiOOH toward energy and environmental applications.

Multiple Strategies for Producing and Utilizing Ammonia Using Electrochemical Methods Using Transition Metal Based Electrocatalysts

Ammonia is one of the most important chemicals in fertilizer and industrial chemical production, stands as the world’s second-largest synthetic chemical (> 200 million tons). Additionally, its potential as a clean energy source is gaining attentions due to its carbon neutrality, high energy density, and ease of transport. Electrochemical ammonia production emerges as a 'green' method which minimize the carbon footprint. However, the development of effective systems to produce and utilize 'green' ammonia remains a significant challenge [1,2].To enhance the efficiency of electrochemical systems, modifications in both catalyst and system design are mandatory. This presentation will introduce the electrochemical nitrogen reduction reaction (eNRR) using Cu-based catalysts [3]. For catalyst modification, we addressed copper’s challenge of its low affinity and activation potential for stable dinitrogen (N2) molecules. This was achieved through phosphorus activation, which enhance the adsorption and activation of N2 by creating electron-deficient Cu sites on the catalyst surface. System-wise, the poor solubility of nitrogen in aqueous electrolytes limits it’s the performance of the system. Addressing this, we applied a gas diffusion electrode (GDE) coated with polytetrafluoroethylene (PTFE) into the eNRR system. This setup establishes an efficient three-phase boundary among liquid water, gaseous N2, and the solid catalyst, thus facilitating nitrogen access to the catalytic sites. Our novel catalyst in a flow-type cell attains a Faradaic efficiency of 13.15% and an ammonia production rate of 7.69 μg h-1 cm-2 at -0.2 VRHE. These figures represent 3.56- and 59.2-times improvements, respectively, over a pristine Cu electrode in a conventional electrolytic cell.Additionally, the presentation will provide a brief introduction to the amorphous Ni-Cu electrocatalyst for electrochemical ammonia oxidation, which is an essential reaction for ammonia utilization [4]. We highlight its doubled ammonia removal efficiency compared to the Ni-Cu LDH electrocatalyst, underlining the potential of these developments.[1] Y. Zeng, C. Priest, G. Wang, G. Wu, Restoring the Nitrogen Cycle by Electrochemical Reduction of Nitrate: Progress and Prospects, Small Methods, 4 (2020) 2000672.[2] B. Yang, W. Ding, H. Zhang, S. Zhang, Recent Progress in Electrochemical Synthesis of Ammonia from Nitrogen: Strategies to Improve the Catalytic Activity and Selectivity, Energy Environ. Sci., 14 (2021) 672-687.[3] J. Kim, C.H. Lee, Y.H. Moon, M.H. Lee, E.H. Kim, S.H. Choi, Y.J. Jang, J.S. Lee, Enhancing Ammonia Production Rates from Electrochemical Nitrogen Reduction by Engineering Three-Phase Boundary with Phosphorus-Activated Cu Catalysts, J. Energy Chem., 84 (2023) 394-401.[4] J.H. Jang, S.Y. Park, D.H. Youn, Y.J. Jang. Recent Advances in Electrocatalysts for Ammonia Oxidation Reaction.Catalysts., 13 (2023) 803.

Electrocatalytic Ammonia Oxidation to Nitrite and Nitrate with NiOOH‐Ni

AbstractAmmonia electrooxidation in aqueous solutions can be a highly energy‐efficient process in producing nitrate and nitrite while generating hydrogen under ambient conditions. However, the kinetics of this reaction are slow and the role of catalyst in facilitating ammonia electrooxidation is not well understood. In this study, a high‐performance NiOOH‐Ni catalyst is introduced for converting ammonia into nitrite with Faraday efficiency of up to 90.4% and nitrate production rate of 1 mg h−1 cm−2. By employing Operando techniques, the role of NiOOH catalyst is elucidated in the dynamic electrooxidation of ammonia. Density functional theory (DFT) calculations support experimental observations and reveal the mechanism of the electrochemical oxidation of ammonia to nitrite and nitrate. Overall, this research contributes to the development of a cost‐effective and highly efficient catalyst for large‐scale ammonia electrolysis, while shedding light on the underlying mechanism of the NiOOH catalyst in ammonia electrooxidation.

Novel Cu(200)/Ti cathode for the enhancement of N2 selectivity in direct ammonia electrolysis: The controls of Cu cathode facet orientation

Direct electrochemical ammonia oxidation reaction (AOR) using NiCu-based anodes is effective in removing ammonia from wastewater. However, this type of anode frequently produces undesired byproducts NO3−. Here, we investigated three configurations of novel Cu/Ti cathodes (Cu(111)/Ti, Cu(200)/Ti, Cu(220)/Ti) coupled with Cu/Ni foam (Cu/NF) anode to enhance N2 selectivity (SN2) in a direct ammonia electrolysis cell. Cu(200)/Ti cathode improved SN2 from 35 % (bare Ti cathode) to 60 % and it achieved 10–15 % higher SN2 compared to Cu(111)/Ti and Cu(220)/Ti. The improvement of SN2 on Cu(200) facet was ascribed to the high nitrate electroreduction activity and its conversion to N2. In real wastewater, Cu/NF anode-Cu(200)/Ti cathode paired electrolysis system demonstrated its excellent capability of 88 % NH3 removal with 95 % SN2. Our electrolysis system was capable to maintain the residual NH3-N and the NO3-N below 8 mg L−1, meeting effluent discharge standards. Our findings highlighted the importance of the control of Cu cathode facet orientations for an efficient elimination of NO3– and improvement of N2 production during direct ammonia electrolysis.

Dual Pathways in Catalytic Ammonia Oxidation by a Ruthenium Complex Bearing a Tetradentate Bipyridine-Bipyrazole Ligand: Isolation of a Diruthenium Intermediate with a μ-Hexazene Derivative.

We report herein chemical and electrochemical ammonia oxidation (AO) catalyzed by a Ru complex, [RuII(H2L)(pic)2]2+ [1, H2L = 6,6'-di(1H-pyrazol-3-yl)-2,2'-bipyridine, pic = 4-picoline], where H2L is a tetradentate ligand with a bipyridyl unit connected to two pyrazoles. 1 functions as an efficient electrocatalyst for the oxidation of NH3 to N2, with a low overpotential of 0.51 V vs Fc+/0 and a Faradaic efficiency of 96%. 1 also undergoes catalytic chemical AO using (4-BrPh)3N•+ as an oxidant, with a turnover number for N2 reaching 41. A novel binuclear complex, [RuIII(L)(pic)2(N2)RuIII(L)(pic)2]4+ (2), was isolated and structurally characterized in the catalytic chemical AO by 1. Complex 2 possesses a zigzag dianionic μ-hexazene unit where the N2 derived from ammonia oxidation is bonded to the pyrazoles, with an NN2-NN2 bond length of 1.3091(70) Å. 2 readily releases N2 upon treating with NH3. Based on experimental and DFT studies, in chemical AO the formation of an N-N bond is proposed to occur via bimolecular coupling of a ruthenium pyrazole imido intermediate to give 2; while in electrochemical AO the N-N bond is formed by nucleophilic attack of NH3 on the intermediate.

High-Rate, High-Selectivity Electrochemical Oxidation of Ammonia to Nitrite with a Silver-Based Catalyst

High-Rate, High-Selectivity Electrochemical Oxidation of Ammonia to Nitrite with a Silver-Based Catalyst

Nickel-based metal-organic-frameworks as electrocatalysts for electrochemical oxidation of ammonia

Electrochemical oxidation of ammonia can produce hydrogen by splitting the ammonia molecules, not merely facilitating the elimination of ammonia but also augmenting sustainable hydrogen-based technological systems. However, the anode reaction is sluggish and the development of novel electrocatalysts is the major method to overcome this demerit. Herein, three kinds of Ni-based MOFs (Ni-BDC, Ni-BTC, and Ni-NH2-BDC) were prepared and used as electrocatalysts towards electrochemical oxidation of ammonia for the first time. At optimized working condition (0.5 V), Ni-NH2-BDC presents the response current density of 2.12 mA/cm2 with the current efficiency of 92.6%, both of which are significantly higher than those of Ni-BDC and Ni-BTC, indicating the better performance of Ni-NH2-BDC. EIS tests and the measurement of conductivity revealed that the good performance of Ni-NH2-BDC could be attributed to the lower charge transfer resistance at the electrode/electrolyte interface and the significantly improved conductivity which is caused by the introduction of NH2 groups.This work shed lights on the development of MOFs electrocatalysts for ammonia oxidation as well as other electrochemical reactions.

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.

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.

Electrochemical ammonia oxidation on terephthalic acid framework (BDC-NH2) derived core-shell nickel oxide/nickel-enriched 2D carbon nanoflakes (NiO/Ni/CNF)

A terephthalic framework, Ni-BDC-NH2, was used to synthesize the nickel nanoparticles and nanoclusters on-site encapsulated within mesoporous carbon nanoflakes (NiO/Ni/CNF) for ammonia electrolysis. Ni2+ nodes recrystallized to form a core-shell oxide film covering the Ni metal, with the dispersity and particles size influenced by the pyrolysis temperature in a N2 atmosphere. Electrochemical characterization and Raman spectra identified the solid-state Ni(II)⇌Ni(III) transition as the electron mediator, while its lowered onset potential (+1.3 V vs. RHE), compared to that of oxygen evolution reaction (+1.7 V) enhanced the Faradaic efficiency. The performance of electrodes in ammonia oxidation was assessed, which revealed a N2 selectivity of at least 80 % under electrolytic conditions of current density = 0.5 – 1.5 mA cm−2, pH > 10, and initial NH3 level = 50–300 mg-N L−1 using NiO/Ni/CNF(700). An undivided cell equipped with NiO/Ni/CNF(700) anode and Cu/Ni cathode was utilized to treat a real wastewater (∼500 mg-N L−1, pH 4.5). Consequently, both the removal efficiency of NH3 and N2 selectivity surpassed 90 % in a continuous flow mode for 4 days, indicating the durability of electrode system.

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.

The Enhanced Performance of NiCuOOH/NiCu(OH)2 Electrode Using Pre-Conversion Treatment for the Electrochemical Oxidation of Ammonia.

Electrochemical oxidation of ammonia is an attractive process for wastewater treatment, hydrogen production, and ammonia fuel cells. However, the sluggish kinetics of the anode reaction has limited its applications, leading to a high demand for novel electrocatalysts. Herein, the electrode with the in situ growth of NiCu(OH)2 was partially transformed into the NiCuOOH phase by a pre-treatment using highly oxidative solutions. As revealed by SEM, XPS, and electrochemical analysis, such a strategy maintained the 3D structure, while inducing more active sites before the in situ generation of oxyhydroxide sites during the electrochemical reaction. The optimized NiCuOOH-1 sample exhibited the current density of 6.06 mA cm-2 at 0.5 V, which is 1.67 times higher than that of NiCu(OH)2 (3.63 mA cm-2). Moreover, the sample with a higher crystalline degree of the NiCuOOH phase exhibited lower performance, demonstrating the importance of a moderate treatment condition. In addition, the NiCuOOH-1 sample presented low selectivity (<20%) towards NO2- and stable activity during the long-term operation. The findings of this study would provide valuable insights into the development of transition metal electrocatalysts for ammonia oxidation.

Computational Analysis of Low Overpotential Ammonia Oxidation by Metal-Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts.

The catalyzed electrochemical oxidation of ammonia to nitrogen (AOR) is an important fuel-cell half-reaction that underpins a future nitrogen-based energy economy. Our laboratory has reported spontaneous chemical and electrochemical oxidation of ammonia to dinitrogen via reaction of ammonia with the metal-metal bonded diruthenium complex Ru2(chp)4OTf (chp- = 2-chloro-6-hydroxypyridinate, TfO- = trifluoromethanesulfonate). This complex facilitates electrocatalytic ammonia oxidation at mild applied potentials of -255 mV vs ferrocene, which is the [Ru2(chp)4(NH3)]0/+ redox potential. We now report a comprehensive computational investigation of possible mechanisms for this reaction and electronic structure analysis of key intermediates therein. We extend this analysis to proposed second-generation electrocatalysts bearing structurally similar fhp and hmp (2-fluoro-6-hydroxypyridinate and 2-hydroxy-6-methylpyridinate, respectively) equatorial ligands, and we further expand this study from Ru2 to analogous Os2 cores. Predicted M24+/5+ redox potentials, which we expect to correlate with experimental AOR overpotential, depend strongly on the identity of the metal center, and to a lesser degree on the nature of the equatorial supporting ligand. Os2 complexes are easier to oxidize than analogous Ru2 complexes by ∼640 mV, on average. In contrast to mono-Ru catalysts, which oxidize ammonia via a rate-limiting activation of the strong N-H bond, we find lowest-energy reaction pathways for Ru2 and Os2 complexes that involve direct N-N bond formation onto electrophilic intermediates having terminal amido, imido, or nitrido groups. While transition state energies for Os2 complexes are high, those for Ru2 complexes are moderate and notably lower than those for mono-Ru complexes. We attribute these lower barriers to enhanced electrophilicity of the Ru2 intermediates, which is a consequence of their metal-metal bonded structure. Os2 intermediates are found to be, surprisingly, less electrophilic, and we suggest that Os2 complexes may require access to oxidation states higher than Os25+ in order to perform AOR at reasonable reaction rates.

Selective electrocatalytic oxidation of ammonia to nitrogen by using titanium dioxide nanorod array decorated with ultrasmall Ir nanoparticles and non-noble metal Fe nanoparticles

Electrochemical ammonia oxidation process through active chlorine has been proposed as a potentially effective method for ammonia removal. Currently, most of the anodes require to use high-stable TiO2 loaded with large particles of noble metal Ru or Ir, which have low activity and high cost. Herein, we prepare ultrasmall and uniform metal nanoparticles of Ir on TiO2 to remove ammonia. Moreover, we use non-noble metal Fe to replace noble metals. The ammonia removal efficiency of Fe/TiO2 under 2 VVS Ag / AgCl during 2 h is 100 % and 94 % of ammonia is converted to N2. The Fe/TiO2 anodes not only have higher catalytic activity but also show excellent stability and reusability. Fe/TiO2 anodes still exhibit excellence activity and selectivity after 1 year. As a common metal, Fe will have more application space than iridium in ammonia removal for its low cost and selectively high efficiency.

Electrochemical oxidation of ammonia in a granular activated carbon/peroxymonosulfate/chlorine three-dimensional electrode system

The electrochemical conversion of ammonia into harmless nitrogen gas (N2) remains a significant challenge in wastewater treatment. This study explores the utilization of granular activated carbon (GAC) as three-dimensional particle electrodes within a peroxymonosulfate (PMS)/Cl−-PbO2/Ti electrochemical system to enhance ammonia oxidation and N2 transfer efficiency. In the observed experimental parameters designated as optimal, the system demonstrated a complete amelioration of ammonia within 45 min. The porous surface of GAC electrodes facilitates increased contact area, promoting better interaction with target compounds. This interaction leads to improved mass transfer efficiency, reduced chlorine overpotential, and enhanced current response. Quenching experiments reveal the substantial involvement of hydroxyl radicals (•OH), sulfate radicals (SO4•−), and chloride radicals (Cl•) in the oxidation process of NH4+-N, with Cl• generation through the oxidative process involving Cl− and SO4•− under electrical stimulation. After 90 min, a significant portion of NH4+-N is transformed into N2, achieving a conversion efficiency of 71.5 %. Additionally, the system demonstrates efficient removal of ammonia from practical aqueous environments. Three-dimensional fluorescence spectroscopic analysis confirms the system's effectiveness not only in removing ammonia but also in reducing organic substances resembling fulvic acid. These findings underscore the three-dimensional electrochemical GAC/PMS/Cl− system as a promising and efficient approach for ammonia removal in wastewater treatment applications.

Electrochemical oxidation of ammonia in water by Pt/NbC membrane-based catalytic nanofluid reactor

Electrochemical oxidation has garnered increasing attention for its potential in treating ammonia in wastewater. However, achieving both high conversion and high nitrogen selectivity simultaneously, while maintaining a short hydraulic retention time (HRT), remains a significant challenge. In this study, we constructed an efficient niobium carbide (NbC) nanoporous membrane reactor by incorporating metal platinum as a catalyst for the electrochemical oxidation of ammonia. The electrocatalytic oxidation process occurred within the nanochannels of the membrane. This design allowed for enhanced single-pass removal of ammonia due to the short diffusion distance on the nanometer scale, which subsequently increased the mass transfer efficiency. Remarkably, we achieved highly controllable pore sizes in the NbC membrane, ranging from 200 to 8.3 nm by dip-coating method. Without the addition of any oxidants, the single-pass removal of ammonia reached 100 % when the applied potential was set at 4 V vs. SCE on a membrane with a pore size of 8.3 nm, and an HRT of 249 s. The primary product obtained from this process was nitrogen, displaying a selectivity of 88.09 %, with a small percentage of nitrate production (selectivity of 11.91 %). By decreasing the applied potential or increasing the pore size, the selectivity of nitrogen can be further improved, reaching 100 %. However, this adjustment may lead to a decrease in the conversion of ammonia. DFT results have revealed that the production of nitrogen on the Pt (111) surface occurs through the NH4+→NH3 → NH2 → N → N2 pathway. This finding contributes to the understanding of the electrochemical process for ammonia removal in water, and provides a viable option for the design of efficient nanomembrane reactors.

Electrochemical ammonia oxidation catalyzed by ruthenium complexes: investigation of substituent effect of axial pyridine ligands

Abstract We have examined catalytic ammonia oxidation using ruthenium complexes bearing 2,2′-bipyridine-6,6′-dicarboxylate ligand and axial 3- and 4-substituted pyridine ligands under electrochemical conditions to study the substituent effect of the axial pyridine ligands. Ruthenium complex bearing 3,4-dibromopyridine ligands shows the highest catalytic activity to produce up to 145 equivalents of dinitrogen based on the catalyst.