Electrochemical Oxidation Of Ammonia Research Articles

The Application of Functionalized Biomass Based Activated Carbon in Electrochemical Oxidation of Ammonia

The Application of Functionalized Biomass Based Activated Carbon in Electrochemical Oxidation of Ammonia

Effective performances of chronoamperometry on the passivation process of n-InP in acidic liquid ammonia (-55 °C)

Chronoamperometry has proven to be a useful in-situ technique to investigate on the anodic passivation mechanism on n-InP semiconductors in acidic liquid ammonia. From our preliminary work, we assumed that the phosphazene film results from parallel electrochemical reactions: InP dissolution and ammonia oxidation. The main question posed here was based on the involvement of bromide (Br−) from the conductive salt (NH4Br) in the anodic process. From chronoamperometry, the decrease in the current deviated from Cottrell behavior. No variation of the anodic charge and no shift of the anodic peak potential was found by using various ammonium halogenides (I-, Br-, Cl−). Contrary to ammoniacate solvent, the reduction of Br2 was never observed. These results suggested that the oxidation of Br− into Br2 apparently could not occur during the anodic process. Thanks to chronoamperometry, the passivation rate constant was determined for the first time on InP in liquid ammonia. This constant (–k≈ 10−2 s−1) was roughly similar to that described in the literature on Pt in aqueous alkaline solution during ammonia oxidation. As for on Pt, the deactivation of the surface could be interpreted as a partial electrochemical oxidation of ammonia on n-InP.

Electrochemical Oxidation of the Effluent from Coking Wastewater Treatment Plants Using Ti/RuO<sub>2</sub>-IrO<sub>2</sub> Electrode

This paper explored the electrochemical oxidation of coking wastewater with Ti/RuO2-IrO2 anode. The effects of electrodes connections, area-volume ratio and aeration on the removal efficiency were studied and the ammonia removal mechanism was investigated. The results show that the highest NH4+-N and COD removal efficiency and current efficiency are achieved at the area-volume ratio of 14.44m2/m3 and electrode distance of 0.5cm. Unipolar connection is better than bipolar connection. For electrochemical oxidation of ammonia, the chloride ion is the main factor affecting nitrogen removal. NH4+-N is removed mainly by the oxidation of hypochlorous.

Electrochemical Oxidation of Ammonia Using Electrodeposited Pt on Carbon Substrate As Catalyst in Ammonia Electrolysis

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Development of a direct ammonia-fueled molten hydroxide fuel cell

A fundamental study on direct ammonia fuel cells with a molten hydroxide electrolyte was conducted. The electrochemical oxidation of ammonia on Pt electrode in a molten NaOH–KOH electrolyte was investigated by cyclic voltammetry and mass spectrometry. Ammonia was proved to be oxidized to N2 on the Pt electrode during anodic polarization in the molten hydroxide electrolyte. Furthermore, the direct ammonia fuel cell, i.e., Pt gas diffusion electrode|molten NaOH–KOH electrolyte|Pt gas diffusion electrode, was assembled and operated at 200–220 °C. The cell achieved the maximum power density of ca. 16 mW cm−2 at 220 °C with the supply of NH3 and humidified O2 to the anode and cathode, respectively. The mechanism of ammonia oxidation over Pt electrodes in a molten hydroxide electrolyte was discussed based on the results obtained.

Electrochemical Oxidation of Ammonia on Graphene-Gold Composites

In this study, gold nanoparticles were modified on graphene surface to form the graphene-gold composites by one-pot reaction in aqueous solution. Electrochemical measurements indicated that the modification of the composites on electrode could efficiently enhance the voltammetric response. Moreover, our results also indicated that the electrocatalytic oxidation of ammonia could be observed on the graphene -gold composites modified glassy carbon electrode.

Study of the electrochemical oxidation of ammonia on platinum in alkaline solution: Effect of electrodeposition potential on the activity of platinum

Abstract The electrochemical activity for the oxidation of ammonia of Pt electrodes, prepared by pulse potentiostatic electrodeposition on glassy carbon, was investigated by cyclic voltammetry and chronoamperometry. The morphology of the platinum deposits was observed by scanning electron microscopy. It was demonstrated that the crystallographic structure of the Pt electrodes probed by electrochemistry, instead of their morphology, has an important impact on the activity of platinum for the oxidation of ammonia in alkaline media. A deposition sequence, where a very negative reducing potential in the hydrogen evolution region and an oxidative potential in the H-desorption region are applied, leads to the formation of preferentially oriented Pt (1 0 0) electrodes. The presence of large (1 0 0) terraces enhances the Pt electrode activity for the oxidation of ammonia but has no impact on its poisoning by reaction intermediates. The stability of these electrodes was investigated by applying a repeated oxidation/reduction cycling procedure. It was found that when the upper potential is less positive than 0.6 V (beginning of the formation of Pt oxides) the preferential orientation of platinum is not affected by the oxidation/reduction cycling whereas for more positive upper potential limit, long range order of Pt is perturbed. As a consequence, the electrochemical activity of the resulting electrodes for the oxidation of ammonia significantly decreased in the latter case.

Synthesis of Pt–Ir catalysts by coelectrodeposition: Application to ammonia electrooxidation in alkaline media

The electrochemical activity for ammonia oxidation of Pt(x)-Ir(1-x) electrodes prepared by coelectrodeposition on carbon substrate was investigated by cyclic voltammetry and potentiostatic methods. Morphologies of deposits were observed by field emission scanning electron microscopy and their chemical composition and crystallographic structure were analyzed by X-ray photoelectron spectroscopy and X-ray diffraction. It is demonstrated that the atomic composition of the catalysts is strongly influenced by the deposition conditions (e.g. relative concentration of the metallic complexes and deposition potential). Ammonia oxidation was investigated in alkaline media for concentrations varying from 0.005 to 0.1 M. Cyclic voltammetry experiments revealed an increase of activity for the Pt(90)–Ir(10) electrode in comparison with Pt at low NH3 concentration (<0.02 M). Moreover all the Pt(x)–Ir(1−x) electrodes showed improved catalytic properties at low oxidation potentials (−0.55 to −0.4 V vs. Ag/AgCl) with respect to pure Pt. Finally, potentiostatic experiments indicated that an increase of the Ir content led to weaker poisoning effect of the resulting electrode despite that Ir does not seem to display a significant activity for the electrochemical oxidation of ammonia.

A novel approach for ammonia removal from fresh-water recirculated aquaculture systems, comprising ion exchange and electrochemical regeneration

A new physico-chemical process for ammonia removal from fresh-water recirculated aquaculture systems (RASs) is introduced. The method is based on separating NH4+ from RAS water through an ion-exchange resin, which is subsequently regenerated by simultaneous chemical desorption and indirect electrochemical ammonia oxidation. Approach advantages include (1) only slight temperature dependence and no dependence on bacterial predators and chemical toxins; (2) no startup period is required and the system can be switched on and off at will; and (3) the fish are grown in much lower bacterial concentration, making the potential for both disease and off-flavor, lower. A small pilot scale RAS was operated for 51d for proving the concept. The system was stocked by 105 tilapia fish (initial weight 35.8g). The fish, which were maintained at high TAN (total ammonia nitrogen) concentrations (10–23mgNL−1) and fish density of up to 20kgm−3, grew at a rate identical to their established growth potential. NH3(aq) concentrations in the fish tank were maintained lower than the assumed toxicity threshold (0.1mgNL−1) by operating the pond water at low pH (6.5–6.7). The low pH resulted in efficient CO2 air stripping, and low resultant CO2(aq) concentrations (<7mgL−1). Due to efficient solids removal, no nitrification was observed in the fish tank and measured nitrite and nitrate concentrations were very low. The system was operated successfully, first at 10% and then at 5% daily makeup water exchange rate. The normalized operational costs, calculated based on data derived from the pilot operation, amounted to 28.7 $ cent per kg fish feed. The volume of the proposed process was calculated to be ∼13 times smaller than that of a typical RAS biofilter. The results show the process to be highly feasible from both the operational and economical standpoints.

Electrochemical Oxidation of Ammonia by Multi-Walled Carbon Nanotubes-Supported Pt-Core/Ir-Shell and Pt-Core/Pd-Shell Nanoparticles

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Electrochemistry by First-Principles Calculations: Electrochemical Oxidation of Ammonia at Pt(hkl)/Alkaline Solution Interfaces

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Microgravity effects on the electrochemical oxidation of ammonia: A parabolic flight experiment

The diffusion of molecular species through nanoporous systems in microgravity conditions is of interest due to the implications of nanotechnology in aerospace technologies. Herein we present the electrochemical oxidation of ammonia at Pt nanoparticles/nano-supporting electrode systems. The decomposition of ammonia has become of critical importance since it is a common component in aqueous streams. The experiments were carried out in a parabolic flight by using different materials to test the electrooxidation of ammonia. Linear polarization curves were attained in microgravity for all materials. In general, a reduction in catalytic performance of 20–65% was observed.

Oxygen reduction reaction on a Pt/carbon fuel cell catalyst in the presence of trace quantities of ammonium ions: An RRDE study

The effect of trace quantities of ammonia on oxygen reduction reaction (ORR) on carbon-supported platinum catalysts in perchloric acid solutions is assessed using rotating ring disk electrode (RRDE) technique. The study demonstrates that ammonia has detrimental effects on ORR. The most significant effect takes place in the potential region above 0.7 V vs RHE. The effect is explained by the electrochemical oxidation of ammonia, which blocks Pt active sites and increases the formation of H2O2. This leads to losses in the disk currents and increments in the ring currents. The apparent losses in ORR currents may occur in two ways, namely, through the blocking of the active sites for ORR as well as by generating a small anodic current, which is believed to have a lower contribution. In addition, a detrimental effect of sodium cations in the potential range below 0.75 V vs RHE was demonstrated. This effect is most likely due to the co-adsorption of sodium cations and perchlorate anions on the Pt surface.

Efficient Electrochemical Removal of Ammonia with Various Cathodes and Ti/RuO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;-Pt Anode

Electrochemical oxidation of ammonia was studied with an objective to enhance the selectivity of ammonia to nitrogen gas and to remove the by-products in an undivided electrochemical cell, in which various cathodes and Ti/RuO 2-Pt anode were assembled. In the present study, anodic oxidation of ammonia and cathodic reduction of by-products were achieved, especially with Cu/Zn as cathode. In the presence of 1.0 g/L NaCl the ammonia-N decreased from 100.0 to 0 after 120 min electrolysis at current density of 30 mA/cm2, and no nitrite was detected in the treated solution. The lowest amount of nitrate was formed with Cu/Zn as cathode during electrolysis due to its high reduction ability. Initial pH range from 7 and 9 and uncontrolled temperature were favorable for electrochemical ammonia oxidation and the ammonia oxidation rates with Cu/Zn cathode was higher than that with Ti and Fe cathode. The reduction rate increased with increasing current density in the range of 5 - 50 mA/cm2. As ammonia could be completely removed by the simultaneous oxidation and reduction in this study, it is suitable for deep treatment of ammonia polluted water.

DEMS-monitoring liquid | gas interfacial ammonia oxidation at carbon nanofibre membranes

Electrochemical ammonia oxidation is of interest in waste treatment as well as in electrochemical sensing applications and demonstrated here at a carbon nanofibre (“bucky-paper”) electrode. The electrode is placed at the aqueous electrolyte | gas interface, and current (cyclic voltammetry) as well as ambient differential electrochemical mass spectrometry (DEMS, cyclic voltbarometry) data are recorded as a function of solution composition and pH. The oxidation of oxalate to CO2 is employed as a test and calibration system. Anodic polarization of the carbon nanofibre membrane in inert aqueous electrolyte is shown to result in direct sustained anodic CO2 evolution. In alkaline aqueous media (starting at pH 9) significant levels of nitrogen from ammonia are produced in competition to CO2 formation from carbon nanofibres without the need for additional catalysts. However, for applications with low level ammonia, catalysts will be required to minimize current losses, carbon nanofibre corrosion, and side product formation.

Revealing the mechanism of indirect ammonia electrooxidation

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 oxidation of ammonia on carbon-supported bi-metallic PtM (M = Ir, Pd, SnO x) nanoparticles

Ammonia electro-oxidation was studied in alkaline solution on carbon-supported Pt and bimetallic Pt y M 1− y (M = Pd, Ir, SnO x and y = 70, 50 at.%) nanoparticles. Catalysts were synthesized using the modified polyol method and deposited on carbon, resulting in 20 wt.% of metal loading. Particle size, structure and surface composition of the particles were investigated using TEM, XRD and XPS. Mean size of PtM bi-metallic nanoparticles varied between 2.0 and 4.7 nm, depending on the second metal (M). XRD revealed the structure of all bi-metallic particles to be face-centered cubic and confirmed alloy formation for Pt y Pd 1− y ( y = 70, 50 at.%) and Pt 7Ir 3nanoparticles, as well as partial alloying between Pt and SnO x . Electrochemical behaviour of ammonia on Pt and PtM nanoparticles is comparable to that expected for bulk Pt and PtM alloys. Addition of Pd to Pt at the nanoscale decreased the onset potential of ammonia oxidation if compared to pure platinum nanoparticles; however stability of the catalyst was poor. For Pt 7(SnO x ) 3, current densities were similar to Pt, whereas catalyst stability against deactivation was improved. It is found that carbon supported Pt 7Ir 3 nanoparticles combine good catalytic activity with enhanced stability for ammonia electro-oxidation. Electronic effect generated between two metals in the bimetallic nanoparticles might be responsible for increase in the catalytic activity of Pd- and Ir-containing catalysts, causing weakening of the adsorption strength of poisonous N ads intermediate.

Optimization of electrochemical ammonia removal using Box–Behnken design

Electrochemical oxidation of ammonia in an undivided cell was studied in the present experiments. The optimization of the influencing factors on electrochemical removal of ammonia by response surface methodology (RSM) was also studied. Ammonia could be effectively removed by electrochemical method, and which was mainly oxidized into harmless nitrogen gas. The Box–Behnken design can be employed to develop mathematical models for predicting electrochemical ammonia removal geometry. The desired electrochemical ammonia removal can be achieved by choosing the predicted conditions using the developed models. In the present experiments, the optimal NaCl dosage, current density and electrolysis time are 0.31 g/L, 42.75 mA/cm 2, and 100.64 min, respectively, at which the ammonia-N and nitrate-N concentration in the treated solution are 0 and 1.1 mg/L, respectively, which will meet the standards for drinking water.

Electrochemical Oxidation of Ammonia on Pt-Ir Thin Films Prepared by Pulsed Laser Deposition

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Amperometric electrode for determination of urea using electrodeposited rhodium and immobilized urease

► Rhodium electrodeposition provides high active surface for enzyme immobilization. ► Rhodium ensures the electrochemical oxidation of ammonia avoiding the use of a second enzyme. ► The membrane carrier is a separate element and can be replaced after deactivation. ► Membrane pore asymmetry protects the trapped urease from any electrochemical interference. ► Low-cost and efficient biosensor is developed for the detection of urea. An amperometric biosensor was developed for determination of urea using electrodeposited rhodium on a polymer membrane and immobilized urease. The urease catalyzes the hydrolysis of urea to NH 4 + and HCO 3 − ions and the liberated ammonia is catalytically and electrochemically oxidized by rhodium present in the rhodinized membrane on the Pt working electrode. Three types of rhodinized polymer membranes were prepared by varying the number of electrodeposition cycles: membrane 1 with 10 deposition cycles, membrane 2 with 40 cycles and membrane 3 with 60 cycles. The morphologies of the rhodinized membranes were investigated by scanning electron microscopy and the results showed that the deposition of rhodium was like flowers with cornices-like centers. The influence of the amount of electrodeposited rhodium over the electrode sensitivity to different concentrations of ammonia was examined initially based on the cyclic voltammetric curves using the three rhodium modified electrodes. The obtained results convincingly show that electrode with rhodinized membrane 1, which contain the lowest amount of electrodeposited rhodium is the most active and sensitive regarding ammonia. It was found that the anodic oxidation peak of ammonia to nitrogen occurs at 0.60 V. In order to study the performance of urease amperometric sensor for the determination of urea, experiments at constant potential (0.60 V) were performed. The current–time experiments were carried out with urease rhodinized membrane 1 (10 cycles). The amperometric response increased linearly up to 1.75 mM urea. The detection limit was 0.05 mM. The urea biosensor exhibited a high sensitivity of 1.85 μA mM −1 cm −2 with a response time 15 s. The Michaelis–Menten constant K m for the urea biosensor was calculated to be 6.5 mM, indicating that the immobilized enzyme featured a high affinity to urea. The urea sensor showed a good reproducibility and stability. Both components rhodium and urease contribute to the decreasing of the production cost of biosensor by avoiding the use of a second enzyme.