Ammonia Electro-oxidation Research Articles

Directly growing hierarchical nickel-copper hydroxide nanowires on carbon fibre cloth for efficient electrooxidation of ammonia

Ammonia is an attractive carbon-free chemical for electrochemical energy conversion and storage. However, the sluggish kinetic rates of the ammonia electrooxidation reaction, and high cost and poisoning of Pt-based catalysts still remain challenges. This also limits the development of direct ammonia fuel cells. In this work, we directly grew hierarchical mixed NiCu layered hydroxides (LHs) nanowires on carbon fibre cloth electrodes by a facile one-step hydrothermal synthesis method for efficient electro-oxidation of ammonia. This catalyst achieves a current density of 35mAcm−2 at 0.55V vs. Ag/AgCl, which is much higher than that of bare Ni(OH)2 catalyst (5mAcm−2). This is due to abundant active sites and a synergistic effect between Ni and Cu, possibly due to the formation of Ni1−xCuxOOH on the surface of the catalysts through the electrochemical activation of the mixture of Cu(OH)2 and α-Ni(OH)2. In the investigated first row transition elements, it is found that Cu is the sole first-row transition metal to effectively improve activity of Ni(OH)2 for ammonia electrooxidation. This mixed NiCu LHs nano-wire catalyst outperforms commercial Pt/C catalyst in the aspects of ammonia oxidation current and stability, demonstrating it to be a promising low-cost and stable catalyst for efficient ammonia electrooxidation in alkaline condition, which is a potential electrode for ammonia fuel cells for power generation or electrolysis of ammonia for ammonia-containing wastewater treatment.

High performance PtxEu alloys as effective electrocatalysts for ammonia electro-oxidation

Pt-rare-earth alloys are rarely studied as electrocatalysts for direct ammonia fuel cells. Thus, their electrocatalytic performance of ammonia electro-oxidation is worth studying, especially for PtxEu alloys. Herein, a series of PtxEu/C (x = 1, 3 and 5) electrocatalysts has been prepared using polyol reduction method. Among them, PtEu/C is found to be a promising candidate for ammonia electro-oxidation. Physical characterizations show that PtEu/C has a small lattice parameter and narrow size distribution. X-ray photoelectron spectroscopy peak shifts of PtEu/C indicate the electron transfer from Eu to Pt. Electrochemical measurement results indicate that PtEu/C is highly active. Particularly, it has a higher current density, lower activity loss and apparent activation energy toward ammonia electro-oxidation compared to Pt/C catalyst.

Synthesis, characterization, and application of CuO-modified TiO 2 electrode exemplified for ammonia electro-oxidation

Abstract In this study, a copper nanoparticle-modified titanium dioxide (CuO–TiO 2 ) catalyst was synthesized using the coprecipitation method with Cu(NO 3 ) 2 as the active component for the electrochemical oxidation (ECO) of ammonia (NH 3 ). The voltammetric behavior and characterization of the electrocatalyst, including oxidation behavior, were investigated using linear sweep voltammetry (LSV), polarization, and chronoamperometric measurements, combined with SEM, FTIR, XRD, EEFM and XPS. SEM and XRD spectroscopy revealed that CuO particles were highly dispersed on the anatase phase of the TiO 2 -supported surface. The XPS and FTIR analysis indicated that CuO was firmly deposited through the linkage of Cu O Ti bonding to the TiO 2 base and the sample exhibiting the stretching vibration mode associated with the Cu O bonds of the CuO nanoparticle. Results of EEFM analysis indicate that significant excitation/emission plots located at 218/280 nm is associated with the CuO nanoparticle. The LSV oxidation ability could explain the catalytic activities of the CuO–TiO 2 electrocatalysts, and NH 3 oxidation peak current on the CuO–TiO 2 electrocatalyst increased as scan rates increased, indicating that the adsorption-controlled process occurred at the electrocatalyst.

Synthesis of Cubic-Shaped Pt Particles with (100) Preferential Orientation by a Quick, One-Step and Clean Electrochemical Method.

A new approach has been developed for in situ preparing cubic-shaped Pt particles with (100) preferential orientation on the surface of the conductive support by using a quick, one-step, and clean electrochemical method with periodic square-wave potential. The whole electrochemical deposition process is very quick (only 6 min is required to produce cubic Pt particles), without the use of particular capping agents. The shape and the surface structure of deposited Pt particles can be controlled by the lower and upper potential limits of the square-wave potential. For a frequency of 5 Hz and an upper potential limit of 1.0 V (vs saturated calomel electrode), as the lower potential limit decreases to the H adsorption potential region, the Pt deposits are changed from nearly spherical particles to cubic-shaped (100)-oriented Pt particles. High-resolution transmission electron microscopy and selected-area electron diffraction reveal that the formed cubic Pt particles are single-crystalline and enclosed by (100) facets. Cubic Pt particles exhibit characteristic H adsorption/desorption peaks corresponding to the (100) preferential orientation. Ge irreversible adsorption indicates that the fraction of wide Pt(100) surface domains is 47.8%. The electrocatalytic activities of different Pt particles are investigated by ammonia electro-oxidation, which is particularly sensitive to the amount of Pt(100) sites, especially larger (100) domains. The specific activity of cubic Pt particles is 3.6 times as high as that of polycrystalline spherical Pt particles, again confirming the (100) preferential orientation of Pt cubes. The formation of cubic-shaped Pt particles is related with the preferential electrochemical deposition and dissolution processes of Pt, which are coupled with the periodic desorption and adsorption processes of O-containing species and H adatoms.

Removal of Nitrate from Drinking Water by Ion-Exchange Followed by nZVI-Based Reduction and Electrooxidation of the Ammonia Product to N2(g)

Ion-exchange (IX) is common for separating NO3− from drinking water. From both cost and environmental perspectives, the IX regeneration brine must be recycled, via nitrate reduction to N2(g). Nano zero-valent iron (nZVI) reduces nitrate efficiently to ammonia, under brine conditions. However, to be sustainable, the formed ammonia should be oxidized. Accordingly, a new process was developed, comprising IX separation, nZVI-based nitrate removal from the IX regeneration brine, followed by indirect ammonia electro-oxidation. The aim was to convert nitrate to N2(g) while allowing repeated usage of the NaCl brine for multiple IX cycles. All process steps were experimentally examined and shown to be feasible: nitrate was efficiently separated using IX, which was subsequently regenerated with the treated/recovered NaCl brine. The nitrate released to the brine reacted with nZVI, generating ammonia and Fe(II). Fresh nZVI particles were reproduced from the resulting brine, which contained Fe(II), Na+, Cl− and ammonia. The ammonia in the nZVI production procedure filtrate was indirectly electro-oxidized to N2(g) at the inherent high Cl− concentration, which prepared the brine for the next IX regeneration cycle. The dominant reaction between nZVI and NO3− was described best (Wilcoxon test) by 4Fe(s) + 10H+ + NO3− → 4Fe2+ + NH4+ + 3H2O, and proceeded at >5 mmol·L−1·min−1 at room temperature and 3 < pH < 5.

Iridium−Rhodium Nanoparticles for Ammonia Oxidation: Electrochemical and Fuel Cell Studies

AbstractThis study reports the use of carbon‐supported IrRh/C electrocatalysts with different iridium‐to‐rhodium atomic ratios (0 : 100, 50 : 50, 70 : 30, 90 : 10, and 100 : 0) for ammonia electro‐oxidation (AmER) in alkaline media. The materials prepared by using the sodium borohydride method showed a mean diameter of 4.5, 4.8, 4.2, and 4.5 nm for Ir/C, Ir90Rh10/C, Ir70Rh30/C, and Ir50Rh50/C, respectively. According to electrochemical and fuel cell experiments, the Ir50Rh50/C catalyst was the most promising towards AmER. This catalyst, which consisted predominantly of the metallic Ir/Rh phases, showed a 500 % higher current density and 55 % higher maximum power than that obtained for Ir/C. After 8 h galvanostatic electrolysis, 93 % of initial ammonia was degraded when using Ir50Rh50/C, whereas it was only 70 % with Ir/C. The high activity of the Ir50Rh50/C is attributed to a synergic effect of two metals at this iridium‐to‐rhodium ratio, which enhances the kinetics of AmER contributing towards ammonia dehydrogenation at lower potentials.

Revisiting the electrochemical oxidation of ammonia on carbon-supported metal nanoparticle catalysts

The ammonia electro-oxidation reaction (AOR) has been studied due to its promising applications in ammonia electrolysis, wastewater remediation, direct ammonia fuel cells, and sensors. However, it is difficult to compare and analyze the reported electrocatalytic activity of AOR reliably, likely due to the variation in catalyst synthesis, electrode composition, electrode morphology, and testing protocol. In this paper, the electro-oxidation of ammonia on different carbon-supported precious metal nanoparticle catalysts was revisited. The effect of experimental conditions, electrochemical test parameters, electrocatalytic activity, thermodynamics, and possible deactivation mechanism of the catalysts were investigated. Pt/C catalyst possesses the highest electrocatalytic activity, while Ir/C and Rh/C show lower overpotential. The onset potential of the AOR is related to the hydrogen binding energy of the catalyst. Nads is one major cause of deactivation accompanied with the formation of surface O/OHads at high potentials. The coulombic efficiency of Nads formation on Pt is about 1% initially and gradually decreases with reaction time. Increase in ammonia concentration leads to increase in current density, while increase in hydroxyl ions concentration can enhance the current density and reduce the overpotential simultaneously. The slopes of AOR onset potential and hydrogen adsorption/desorption potential of Pt/C as a function of pH follow Nernst equation. In contrast, potentials measured at different current densities exhibit non-Nernstian behavior, suggesting a critical role of the local pH change.

Promotion of PtIr and Pt catalytic activity towards ammonia electrooxidation through the modification of Zn

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.

Evaluation of carbon supported platinum–ruthenium nanoparticles for ammonia electro-oxidation: Combined fuel cell and electrochemical approach

Ammonia electro-oxidation reaction (AmER) was investigated by using conventional electrochemical experiments, direct ammonia fuel cell (DAFC) and galvanostatic electrolysis experiments. The working electrode/anodes were composed of carbon supported PtRu/C nanoparticles (NPs) with atomic Pt:Ru ratios of 100:0, 90:10, 70:30 and 50:50. The resulting nanoparticles ranged between 5.1 and 7.3 nm in size depending on the Ru content and were analyzed by XRD, TEM and synchrotron radiation photoelectron Spectroscopy (SRPES). Alloying Pt with Ru shifted AmER to the lower onset potentials compared to Pt/C. Among nanostructured PtRu/C electrocatalysts, the Pt90Ru10 composition showed the best activity and stability in the conventional electrochemical (cyclic voltammetry and chronoamperometry) experiments, DAFC and 8 h galvanostatic electrolysis. The concentration of nitrite and nitrate was doubled using PtRu/C 90:10 compared to Pt/C, because of excess of OHads species formed on Ru. The results show that the addition of small amount of Ru to Pt NPs improves the AmER due to additional formation of OHads that promote the reaction on alloyed PtRu nanoparticles.

Promotion of Ammonia Electrooxidation on Pt nanoparticles by Nickel Oxide Support

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.

Electrodeposited NiCu bimetal on carbon paper as stable non-noble anode for efficient electrooxidation of ammonia

Electrochemical remediation of ammonia-containing wastewater at low cell voltage is an energy-effective technology which can simultaneously recover energy via hydrogen evolution reaction. One of the main challenges is to identify a robust, highly active and inexpensive anode for ammonia electrooxidation. Here we present an alternative anode, prepared by electrochemical co-deposition of Ni and Cu onto carbon paper. This NiCu bimetallic catalyst is characterised by scanning electron microscope, scanning transmission electron microscope, X-ray diffraction, x-ray photoelelectron spectroscopy, cyclic voltammetry, linear sweep voltammetry and chronoamperometry techniques. The stability and activity of NiCu bimetallic catalyst are largely improved in comparison with Ni or Cu catalyst. Moreover this noble-metal-free NiCu catalyst even performs better than Pt/C catalyst, as NiCu is not poisoned by ammonia. An ammonia electrolysis cell is fabricated with NiCu/carbon paper as anode for ammonia electrolysis. The influences of pH value, applied cell voltages and initial ammonia concentration on cell current density, ammonia removal and energy efficiency are tested. An ammonia removal efficiency of ∼80% and coulombic efficiency up to ∼92% have been achieved. Ni-Cu bimetal on carbon paper is a stable non-noble anode for efficient electrooxidation of ammonia.

Bimetallic Nanocomposites of Palladium (100) and Ruthenium for Electrooxidation of Ammonia

Symmmetrically oriented Pd (100) and its bimetallic Pd (100)Ru electrocatalysts were chemically synthesized and their conductive properties employed in the electrochemical oxidation of ammonia. Electrochemical data based on EIS, SWV and CV revealed that the Pt/Pd (100)Ru electrode showed a better conductivity and higher catalytic response towards the electrooxidation of ammonia compared to Pt/Pd (100) electrode. This was demonstrated by the EIS results where Pt/Pd (100)Ru gave a charge transfer resistance (Rct) of 48.64 Ω, high exchange current and lower time constant (5.2738 x 10-1A and 3.2802 x 10-7 s /rad) values while the Pt/Pd (100) had values of 173.2 Ω, 1.4811 x 10-1A and 4.8321 10-7 s /rad. The drastic drop in Rct highlights the superiority of the Pt/Pd (100)Ru over the Pt/Pd (100) and confirms that facile interfacial electron transfer processes occur on the Pt/Pd (100)Ru electrode during the electrocatalytic ammonia oxidation. Investigations through voltammetry revealed that the Pt/Pd (100)Ru had a higher peak current density and a shift in potential to more negative values at ≈ -0.2 V and ≈ -0.4 V. The EASA value of Pt/Pd (100)Ru was found to be 119.24 cm2 whereas Pt/Pd (100) had value of 75.07 cm2. The high electrochemically active surface area of Pd (100)Ru at 119.24 cm2 compared to the 75.07 cm2 for Pd (100) strengthened this observation in performance between the two catalysts for ammonia electrooxidation.

Epitaxially Grown Pt and Pt-Ir Thin Films: Effect of the Deposition Conditions on the Electro-Oxidation of Ammonia

Ammonia (NH3) is a highly toxic gas, a major environmental pollutant, and a potential fuel for fuel cells. Thus, the electrooxidation of NH3 has important applications in NH3 safety sensors, NH3 decontamination in wastewater and power production. However, on most electrode materials, NH3 oxidation reaction proceeds with a high overpotential, low current density, and rapid poisoning rate. Better electrocatalysts for this reaction would lower the NH3 detection threshold in sensors, increase the rate of NH3 removal for decontamination, and boost power of NH3 fuel cells. Platinum is the electrocatalyst that shows the highest current density at the lowest overpotential for catalyzing the oxidation of NH3 to N2. The electrooxidation of NH3 on Pt is further complicated by the fact that the reaction rate strongly depends on the metal surface structure. In alkaline medium, the electrooxidation of ammonia on Pt occurs almost exclusively on surface sites with (100) symmetry, especially on wide terraces. Accordingly, the preferred way to study the effect of alloying Pt with other elements would be to rely on a series of mixed Pt-M alloy single crystals with the appropriate (100) surface termination. However, the preparation of single-crystals is difficult. In the case of Pt-Ir, the situation is even more complicated since the Pt-Ir binary phase diagram shows that Pt and Ir are barely miscible at temperature below 1000°C, which could translate into insurmountable technical difficulty in the preparation of Pt-M alloy single crystals. In recent years, Pulsed Laser Deposition (PLD) has emerged as an effective method for preparing thin films with preferential orientation and kinetically stable alloys. In this work, we will study the influence of different deposition parameters (composition, temperature and thickness) on the electro-oxidation of ammonia. To achieve this, a combination of X-ray diffraction (ϴ - 2ϴ scans, rocking curves and pole figures) and atomic force microscopy will be used to get information about the surface organisation and the length of the terraces. Then, electrochemical measurements will be performed to confirm the preferential (100) surface orientation and evaluate the electrochemical performances of the various films for the oxidation of NH3. It will be shown that the current for the electro-oxidation of NH3 varies with the Pt content and the thickness of the film (see Fig. 1). For the thinnest films, the role of Ir atoms in helping the formation of large (100) terraces will be emphasized. Figure 1 Variation of the current density for the electro-oxidation of NH3 with respect to the Pt content. The data were collected from the current at 0.71 V vs RHE during cyclic voltammetry (20 mV.s-1) in 0.1M NaOH + 0.1M NH3. Figure 1

Mechanism of the Electrochemical Oxidation of Ammonia over Platinum: An in Situ attenuated Total Reflection Infrared Study

The recent development of anion exchange membranes (AEMs) has increased the potential and the importance of ammonia as a fuel for anion exchange membrane fuel cells (AEMFCs). Although the reaction mechanism for the electrochemical ammonia oxidation over Pt electrode has been extensively studied, there is no report on the detection of the prospected intermediates and/or the poisoning species on Pt electrode. In this study, the electro-oxidation of ammonia over Pt electrode in alkaline aqueous solutions was studied by in situ attenuated total reflection infrared (ATR-IR) spectroscopy. In the presence of NH3, the band ascribable to the HNH bending mode of adsorbed NH3 was confirmed at 1662−1674 cm−1 in the potential range of 0.1−1.1 V. The intensity of this band decreased continuously with a rise in potential, indicating the oxidative consumption of adsorbed ammonia. In response to this behavior, the band at 1269 cm−1 appeared alternatively above 0.2 V, and its intensity reached the local maximal value at ca. 0.4 V. Note that this potential of ca. 0.4 V agreed well with the onset potential of ammonia oxidation, ca. 0.45 V, in the linear sweep voltammogram. This 1269 cm−1 band was assigned to the NH2 wagging mode of N2H4, which was one of the active intermediates, N2H x + y ,ad (x = 1 or 2, y = 1 or 2), according to the mechanism proposed by Gerischer and Mauerer. To the best of our knowledge, this is the first report for the detection of N2H4 as a reaction intermediate over Pt electrode. Furthermore, the formation of bridged NO was also observed above the onset potential of ammonia oxidation, ca. 0.5 V. Such adsorbed NO species probably inhibit the electrochemical reaction due to the occupation of reaction sites at higher potential. Figure 1

The effect of antimony-tin and indium-tin oxide supports on the catalytic activity of Pt nanoparticles for ammonia electro-oxidation

Platinum nanoparticles supported on carbon (Pt/C) and carbon with addition of ITO (Pt/C-ITO (In2O3)9·(SnO2)1) and ATO (Pt/C-ATO (SnO2)9·(Sb2O5)1) oxides were prepared by sodium borohydride reduction method and used for ammonia electro-oxidation reaction (AmER) in alkaline media. The effect of the supports on the catalytic activity of Pt for AmER was investigated using electrochemical (cyclic voltammetry and chronoamperometry) and direct ammonia fuel cell (DAFC) experiments. X-ray diffraction (XRD) showed Pt peaks attributed to the face-centered cubic (fcc) structure, as well as peaks characteristic of In2O3 in ITO support and cassiterite SnO2 phase of ATO support. According to transmission electron micrographs the mean particles sizes of Pt over carbon were 5.4, 4.9 and 4.7 nm for Pt/C, Pt/C-ATO and Pt/C-ITO, respectively. Pt/C-ITO catalysts showed the highest catalytic activity for ammonia electrooxidation in both electrochemical and fuel cell experiments. We attributed this to the presence of In2O3 phase in ITO, which provides oxygenated or hydroxide species at lower potentials resulting in the removal of poisonous intermediate, i.e., atomic nitrogen (Nads) and promotion of ammonia electro-oxidation.

Electrooxidation for simultaneous ammonia control and disinfection in seawater recirculating aquaculture systems

A new operational approach for seawater recirculating aquaculture systems (RAS), which is based solely on physicochemical water treatment techniques, is described. Within this concept the fish are grown at very high TAN concentration and slightly acidic pH, the latter calculated to maintain the NH3 concentration lower than a predetermined threshold (typically <0.1mgN/l). The inherently high Cl− concentration in seawater enables efficient electro-generation of Cl2(aq) species and consequent electrooxidation of ammonia directly to N2(g). Fish pond water is constantly recycled between electrolysis tanks and the pond, supplying both disinfected water and most of the acidity required to maintain the necessary low pH in the fish pond. For establishing proof-of-concept gilthead seabream (Sparus aurata) was grown at the pilot scale for 133 consecutive days. Throughout this period the fish showed excellent growth rate and survival, along with excellent general health condition. 88% of the NH3 mass excreted by the fish was electro-oxidized in the pilot system, while at the same time the pond water was efficiently disinfected. The high TAN concentrations in the rearing water resulted in high current efficiency in the electrooxidation step, reduced water treatment units volume and generation of very low trihalomethane (THM) concentrations, attributed to the low pH allowed to develop during the electrolysis stage. The pilot system was operated in two stages differing in TAN concentration (30 and 65mgN/l) and pH (6.7 and 6.4, leading to NH3(aq) concentrations of 0.047 and 0.052, respectively). Average current efficiency in the TAN electrolysis step was 68%. Cost analysis showed that both capital and operational costs were highly competitive, as compared with conventional RAS operation. Specifically, the cost of the water treatment component within the pilot operation (TAN removal to N2(g) and water disinfection) was estimated at ∼$0.205per kg feed, out of which $0.079 was attributed to electricity costs.

Theoretical Calculations of Ammonia Oxidation Kinetics on Platinum, Iridium and Their Bimetallic Clusters

Introduction Population increase and technology growth are the main reasons for increasing demand of energy sources and fossil fuels consumption as the main energy source consequently increases. However, these fuels emit large amounts of greenhouse gases to the atmosphere. Moreover, they are not renewable resources. Hydrogen as an energy carrier is attractive because the only product of its combustion is water. However, production and storage of hydrogen raises concerns about costs and safety. Ammonia (NH3) can be used as a hydrogen source and it requires about 5% of the thermodynamic cell voltage (0.06 V) needed to produce hydrogen from water [1-4]. 2NH3(aq)+6OH- → N2(g)+6H2O+6e- E°=-0.77V vs. SHE (1) 6H2O+6e- → 3H2(g)+6OH- E°=-0.83V vs. SHE (2) 2NH3(aq) → N2(g)+3H2(g) E°=0.06V (3) Objectives In order to decrease the cost of hydrogen production through ammonia electrolysis, the kinetics of the process should be known. While experimental techniques are the primary procedure for elucidating the kinetics especially on monometallic surfaces, theoretical calculation can be fascinating in terms of investigation of intermediates produced during the surface reaction. These intermediates can not be recognized with traditional experimental methods on monometallic, bimetallic or polymetallic surfaces. In this work, density functional theory calculations are performed on four platinum-iridium clusters, Pt3-xIrx (x=0-3) to examine ammonia oxidation in alkaline media. The adsorption of NH3-x(x=0-3) on these clusters and the effect of cluster composition on the adsorption are investigated. The hybrid B3LYP level of theory is used in Gaussian 09 along with the LANL2DZ and 6-311++g basis sets. Results Our Preliminary results for the HOMO-LUMO gap of adsorbed species on clusters, combined with activation and dissociation energy calculations of sequential dehydrogenation reactions of NH3→NH2→NH→N showed that Ir3 is more active than Pt3for ammonia oxidation. Additionally, the combination of iridium and platinum makes a more favorable pathway for the ammonia oxidation reaction. However, experimental analyses indicate improved reactivity on platinum in comparison to iridium in ammonia oxidation. This suggests the possibility of two different mechanisms for ammonia oxidation on platinum and iridium.

Improving the Electrocatalytic Activity of Pt Monolayer Catalysts for Electrooxidation of Methanol, Ethanol and Ammonia by Tailoring the Surface Morphology of the Supporting Core

AbstractThe front cover artwork is provided by the group of Dr. Cheng Zhong, Tianjin University (Tianjin, China). The image shows the presence of a high density of catalytically active defect sites such as surface atomic steps on the flower‐like Pt‐based particles, as revealed by atomic‐resolution spherical‐aberration‐corrected transmission electron microscopy. Read the full text of the Article at 10.1002/celc.201500451.

Cover Picture: Improving the Electrocatalytic Activity of Pt Monolayer Catalysts for Electrooxidation of Methanol, Ethanol and Ammonia by Tailoring the Surface Morphology of the Supporting Core (ChemElectroChem 4/2016)

The Front Cover picture shows how atomic-resolution spherical-aberration-corrected transmission electron microscopy reveals the presence of a high density of defect sites such as surface atomic steps on the flower-like Pt-based particles. These defect sites play an important role in the improved electrocatalytic performance. More information can be found in the Full Paper by C. Zhong and co-workers on page 537 in Issue 4, 2016 (DOI: 10.1002/celc.201500451).

Improving the Electrocatalytic Activity of Pt Monolayer Catalysts for Electrooxidation of Methanol, Ethanol and Ammonia by Tailoring the Surface Morphology of the Supporting Core

AbstractPt‐monolayer‐decorated Au particles with different surface morphologies were prepared by Au electrodeposition, followed by Cu under‐potential deposition and a Pt replacement reaction. Spherical Au particles with relatively smooth surfaces and flower‐like Au particles consisting of interconnecting thin nanosheets were obtained by controlling the deposition potential and electrolyte concentration. Pt‐monolayer‐decorated flower‐like Au particles exhibit much higher specific activity and stability in the electrooxidation of methanol, ethanol and ammonia compared to Pt‐monolayer‐decorated spherical Au particles. Pt‐monolayer‐decorated flower‐like Au particles also showed better poisoning‐tolerance, especially in the electrooxidation of methanol. The improved electrocatalytic performance is attributed to the high density of catalytically active sites such as surface atomic steps, the edges at sharp tips and edges on the surface of the flower‐like particles, which is revealed by spherical‐aberration‐corrected transmission electron microscopy with atomic resolution.