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•ATR-SEIRAS is extended to study the AOR on Ir electrode in basic media.•NHx,ad species is attributed to the pivot intermediate.•N2Hx+y,ad species is identified as the key active ...intermediate to generate N2.•NO2− and NO3− byproducts arise from NOad oxidation.
Mechanistic understanding of electrochemical ammonia oxidation reaction (AOR) is important for designing efficient AOR catalysts. In this work, in situ attenuated total reflection surface-enhanced infrared spectroscopy (ATR-SEIRAS) is employed to study the AOR at varied potentials on an Ir electrode in alkaline media. The AOR on Ir contains two sequential oxidation peaks in the anodic voltammograms. The in situ ATR-SEIRAS results indicate that the small Peak I at a lower potential is mainly due to dehydrogenation of interfacial ammonia and dimerization of as-generated NHx,ad species to N2Hx+y,ad species. And the broad and intense Peak II at a higher potential mainly involves the N2 production from N2Hx+y,ad species, NOad species generation from NHx,ad species and further successive oxidation into the NO2− and NO3− by-products at higher potentials. It is thus inferred that NHx species are the pivotal intermediates for AOR on Ir electrode, and the N2Hx+y,ad and NOad species the key intermediates for the production of N2, NO2− and NO3−, respectively.
•Ammonia is successfully removed from model seawater by electrochemical oxidation.•The kinetic model combines chlorine electrogeneration and ammonia breakpoint chlorination.•The kinetic model is ...focused on designing ammonia removal in inland RAS marine fish farms.
This work reports a comprehensive kinetic analysis and modelling of the electrochemically assisted ammonia removal from marine aquaculture waters (RAS). The proposed model combines the kinetics of chlorine electrogeneration, experimentally determined, with the mechanism and kinetic parameters, taken from literature, of break point chlorination reactions involving aqueous chlorine (HClO and ClO−), total ammonia nitrogen (TAN as NH3 and NH4+), and the chlorinated derivatives of ammonia (monochloramine (NH2C1), dichloramine (NHC12), and nitrogen trichloride (NC13)). The model has been validated with laboratory experiments, obtained in an electrochemical cell provided with Ti/RuO2 anode and Ti cathode, and working with model sea water in the range of operating variables TAN0 = 10–60 mg L−1 and j = 5 – 20 A m−2; good agreement between simulated and experimental data for the progress of ammonia and combined chlorine concentrations assesses the validity and robustness of the kinetic model. Thus, this study provides the tools to analyse, predict and explain ammonia removal performance in the electrochemical treatment of marine RAS water.
Zn is introduced into Pt and PtIr electrodes by applying potential cycles to their corresponding polycrystalline microdisc electrodes in a ZnCl2-containing ionic liquid bath. Scanning-electron ...microscopy and energy-dispersive X-ray microanalysis studies show that nanostructured PtIrZn and PtZn layers created on the microdisc electrodes contain approximately 5wt% Zn. Cyclic voltammetric studies reveal that PtZn and PtIrZn are significantly more active towards electrochemical ammonia oxidation in alkaline media than virgin Pt and PtIr electrodes. The PtIrZn electrode demonstrates a low onset potential of 0.30V vs RHE and a high exchange current density of 4.3×10−8Acm−2, which is favorably comparable to state-of-the-art electrocatalyts for the same reaction. The catalytic activity promotion by the Zn modification may be related to the inhibition of the hydrogen electrochemistry. PtIrZn appears therefore to be a very promising anode catalyst for direct ammonia fuel cells and ammonia electrolysis.
Introduction of Zn into PtIr alloy efficiently decreases the onset potential of ammonia oxidation reaction in alkaline media by approximately 100mV. Display omitted
•Zn was introduced into PtIr and Pt through electro-deposition and dissolution.•Introducing Zn into PtIr and Pt promotes ammonia electrooxidation reaction.•PtIrZn demonstrates an onset potential of 0.30V vs RHE.•The onset potential of 0.30V is the lowest value reported so far.•Exchange current density of ammonia oxidation on PtIrZn exceeds 4×10−8Acm−2.
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•A kinetics model for NH3 electrooxidation on polycrystalline Pt was developed.•Kinetics parameters for NH3 electrooxidation were obtained for the first time.•Dimerization of NH2(ads) ...was identified as the rate determining step to form N2.•Kinetics of catalyst deactivation by stronger adsorbed intermediates was obtained.
A mathematical model for the ammonia electrooxidation kinetics, over polycrystalline Pt in alkaline media, was developed through the micro kinetics approach. Two different mechanisms were evaluated for the development of the model, a combined surface-diffusion controlled process and a surface confined process. Nonlinear multiple parameters estimation was implemented by direct comparison with experimental data, obtained in a rotating disk electrode system during linear sweep voltammetry, to calculate the kinetic parameters for the different elementary steps proposed in the mechanisms. It was demonstrated through modeling discrimination techniques that a surface confined process drives the oxidation of ammonia on the implemented electrode surface. The model validates that the formation of N2 is controlled by the catalytic dimerization of partially reduced ammonia adsorbates (i.e. NH2(ads)). Moreover, it confirms that the formation of stronger adsorbed intermediates at high overpotentials is the main cause for the catalyst deactivation.
Dendritic Pt nanostructures were prepared through electrodeposition on a substrate Pt electrode by applying square-wave potential method. It has been found that the as-prepared dendritic Pt ...nanostructure exhibited enhanced IR absorption with an enhancement factor up to 10 folds for adsorbed CO species. Such an enhanced in-situ FTIR spectroscopy (FTIRS) has been applied in studies of reaction mechanism of ammonia electrooxidation. From in-situ FTIR spectra recorded during ammonia electrooxidation, two characteristic IR bands at 1430cm−1 and between 1227 and 1250cm−1 were observed at low potential region (E<−0.50V vs. SCE), and are assigned to adsorbed NH2,ad and N2H4,ad, respectively. The assignment of the band between 1227 and 1250cm−1 has been also confirmed through studies by using isotopic 15NH3−NaOH and NH3−NaOH – D2O systems. Furthermore, in spectra collected at high electrode potential region (E>0.10V vs. SCE), two IR bands at 2231cm−1 and 1236cm−1 were observed and ascribed respectively to N2O and NO2− species, which are the ultimate oxidation products detected under present investigation conditions. In addition to in-situ FTIR spectroscopy, online electrochemical mass spectroscopy (OEMS) was used to detect volatile products. The clear OEMS signals of m/e=30 and m/e=46 measured at potentials above −0.5V and −0.30V, respectively, indicate the production of N2 (IR inactive) and confirm the generation of N2O. Based on results of cyclic voltammetry, in-situ FTIRS and OEMS, the reaction mechanism is therefore elucidated with molecular details of intermediates and products involved in ammonia electrooxidation in alkaline solutions.
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•Dendritic Pt nanostructures that possesses enhanced infrared effect for adsorbates are prepared by electrochemical method.•The adsorbed intermediates NH2, ad, N2H4, ad and ultimate products N2O and NO2− were determined clearly by In-situ FTIRS.•The volatile products N2 and the N2O were evidenced by OEMS during NH3 electrooxidation at different electrode potentials.•The reaction mechanism is proposed with molecular details for ammonia electrooxidation on Pt in alkaline solutions
•Pt nanoparticles supported on NiO and MnO2 were synthesized by sacrificial support method.•Shift in Pt4f photoemission electron spectra is found for Pt/NiO and Pt/MnO2.•Ammonia electrooxidation ...(AmER) is more favourable on Pt/NiO (vs. Pt/C and Pt/MnO2).•Electronic effect between Pt and NiO support is responsible for the higher catalytic activity for AmER.
In this study Pt nanoparticles supported on NiO, MnO2, and on carbon black were prepared and tested for the ammonia electrooxidation reaction (AmER) in alkaline media. The morphology and structure of the catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), nitrogen physisorption, and their surface properties were studied using synchrotron radiation photoelectron spectroscopy (SRPES). Cyclic voltammetry, chronoamperometry and Tafel plots were used to study the electrochemical behavior of ammonia on Pt/metal oxide catalysts. Pt/NiO showed the highest current density and the lowest onset potential for AmER (-0.48V vs. Hg/HgO) which increased in the order Eonset(Pt/NiO)<Eonset(Pt/MnO2)<Eonset(Pt/C). The reaction kinetic order with respect to the concentration of ammonia is close to zero, indicating fast surface adsorption of ammonia in agreement with previous studies on polycrystalline Pt electrodes, whereas the apparent Tafel slopes were found higher (56 − 69mVdec−1) than previously reported values for Pt (39mVdec−1). Our results show that the nature of the support strongly influences the size and electronic properties of the Pt nanoparticles, and as a result their electrocatalytic activity for AmER.
The governing mechanism of indirect ammonia electrooxidation has been often described similarly to breakpoint chlorination. However, comparison of the chloramine concentrations which develop in batch ...indirect ammonia electrolysis and classical breakpoint chlorination experiments (performed under similar conditions) suggests that the governing reactions are different. Three experimental sets were carried out with excess-ammonia solutions, with the aim of elucidating the mechanism of indirect electrochemical ammonia oxidation: (1) chloramination with Cl2(g) and NaOCl; (2) batch- and (3) single-pass electrolysis experiments.
Based on the results we propose a new mechanism for indirect ammonia electrooxidation, according to which trichloramine, rather than monochloramine, is the initial and primary product. NCl3 apparently forms from a reaction between NH4+ and Cl2(aq), which occurs in the near anode area where pH is <2 and the bulk Cl− concentration is high. At such conditions Cl2(aq) is the dominant active chlorine species in the anode vicinity. Upon formation in the near anode area NCl3 decomposes to N2, NH2Cl and NHCl2 in the bulk solution or/and close to the cathode surface area, where pH>12. Under batch operation and/or single-pass electrolysis characterized by long contact times both NH2Cl and NHCl2 that form in the bulk electrolyte are oxidized to NCl3 by Cl2(aq) upon return to the near-anode zone.
Electrochemical applications in RAS: A review Ben‐Asher, Raz; Gendel, Youri; Lahav, Ori
Reviews in aquaculture,
January 2024, 2024-01-00, 20240101, Letnik:
16, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Electrochemical water treatment for recirculating aquaculture systems (RAS) is a promising approach for replacing the biological water treatment methods and establishing a new RAS generation with ...improved cost‐effectiveness, lower environmental footprint, and no start‐up periods. On top of ammonia oxidation directly into N2(g), electrochemical oxidation results in effective disinfection, and in the removal of organic matter, including specific organic constituents such as off‐flavour agents. The paper provides an overview of incentives for the implementation of electrochemical methods in RAS. It covers the electrochemical principles relevant to aquaculture applications, the effects of physical and chemical parameters, as well as design considerations. In addition, the research performed to date for integrating electrochemical methods in RAS operation is reviewed and the variety of designs and operational configurations described. The electrochemical water treatment is perceived beneficial over biological water treatment especially in cold saline‐seawater aquaculture (e.g., Atlantic salmon), where large nitrification reactors are required and the large water consumption for purging processes can be curtailed. It is also beneficial for the culturing of nitrate‐sensitive species (e.g., L. vannamei). The paper points out the gaps to be overcome for allowing commercial breakthroughs based on electrochemical water treatment, including the need for expanding the practice and improving engineering practices by operating pilot systems for growing fish at both small and large scales; adjusting of electrochemical cell designs for reducing both capital and operational costs; developing full‐proof malfunction‐free dechlorination strategies, and evaluating and optimizing the disinfection abilities for inactivating typical pathogens in aquaculture.
The treatment of reject water containing concentrated ammonia and non-biodegradable organics is a challenging task in wastewater treatment plants. To address this problem, we propose a novel process ...consisting of a selective ammonium-exchange resin and an ammonia electrooxidation reaction (AmER-AOR). Because an alkaline condition is essential for direct ammonia oxidation, the use of a bipolar membrane (BPM) was helpful. Nonetheless, an initial pH of 13 and KOH addition were required to maintain a high alkalinity for the complete elimination of ammonia. The linear sweep voltammogram elucidated the high pH requirement and ammonia oxidation promotion. When the current density varied from 30 to 80 mA cm−2, 60 mA cm−2 showed the highest current efficiency (30.39%) and the lowest specific energy demand (95.3 kWh/kg-N), indicating the most energy-effective condition. Increasing the initial concentration of ammonia from 0.1 M to 0.5 M improved the current efficiency (51.57%), demonstrating an additional energy-effective strategy for the AmER-AOR. The energy efficiency of pure H2 production in the cathodic chamber was 30%. To estimate the viability for practical applications, reject water collected from a local wastewater treatment plant was applied in the AmER-AOR. Notably, no significant difference in the ammonia removal rate was observed with synthetic wastewater. To the best of our knowledge, this is the first study that employs a BPM as a separator and OH− supplier for direct ammonia oxidation. Our findings reveal that the AmER-AOR with a BPM has promising practical applicability in the treatment of reject water and energy production.
Small amounts of Pd served as a reducing agent to produce sub-100 nm polygonally-shaped Ni98Pd2 materials in ethylene glycol. As-synthesized particles were crystallized into fcc Ni with a fraction of ...I2-Ni(OH)2, and exhibited very low to no activity towards ammonia electrooxidation. Their catalytic activity has been significantly improved by building up a layer of Ni(OH)2 by cyclic voltammetry between a0.95 and 1.35 V vs. HgO/Hg in NaNO3 at pH 9. XPS analysis before and after the electrochemical treatment confirmed the transformation of Ni0 to higher state of oxidation. Ammonia electrooxidation on Ni(OH)2/NiPd occurred at around 1.28 V vs. HgO/Hg and was highly pH-dependent. At concentrations less than 100 mM, the direct electron transfer took place, whereas at higher ammonia concentrations it was the indirect electron transfer mechanism. A 9-h galvanostatic electrolysis at 20 mA cm-2 showed that 64% of the initial ammonia was degraded at 38% average current efficiency.
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