Metal Nitrogen Research Articles

Rare‐Earth Complexes with the 5,5′‐Bitetrazolate Ligand – Synthesis, Structure, Luminescence Properties, and Combustion Catalysis

A complete series of complexes of the lanthanides and yttrium (except radioactive Pm) with the 5,5′‐bitetrazolate (BT2–) ligand were synthesized from sodium 5,5′‐bitetrazolate and available rare‐earth (RE) salts. Eight new complexes were structurally characterized by single‐crystal XRD. The [M(BT)(H2O)7]2[BT]·6H2O [M = Pr (1), Gd (2)] complexes are isomorphous and consist of [M(BT)(H2O)7]+ ions in which only one BT2– ligand acts as a chelate for each metal center. The complexes [M(H2O)8]2[BT]3·4H2O [M = Y (3), Dy (4), Ho (5), Tm (6), Yb (7), Lu (8)] are saltlike compounds that do not exhibit any significant metal–nitrogen contacts. Luminescence was very informative for the determination of the number of inner‐sphere coordinated water molecules in the solid samples. Despite its low luminescence intensity owing to its high hydrate composition, the deuterated europium complex exhibited an internal quantum yield of 44 %. The catalytic activities of the 5,5′‐bitetrazolate salts for the decomposition and combustion reactions of energetic materials were tested. Although no effect was found for nitramine (HMX) explosive, the impact of the salts on the thermolysis of ammonium perchlorate (AP) was established. The addition of 5 % [Dy(H2O)8]2[BT]3·4H2O decreases the temperature at the maximum reaction rate by 100 °C. The catalytic effect during combustion is apparently masked by the inhibitory influence of water; however, for [Pr(BT)(H2O)7]2[BT]·6H2O, a 20 % increase in the AP burning rate was observed.

Ultrathin and Porous Carbon Nanosheets Supporting Bimetallic Nanoparticles for High‐Performance Electrocatalysis

AbstractDeveloping hybrid carbon materials with unique micro/nanostructured and multicomponent features is of great importance in catalysis, energy storage, and energy conversion. Herein, we demonstrate the formation of a novel kind of hybrid carbon material, that is, bimetallic nanoparticles supported by ultrathin (≈5.5 nm) and porous carbon nanosheets, by the pyrolysis of preformed bimetallic metal–organic framework nanosheets. This hybrid carbon nanostructure combines the advantages of highly exposed nanoparticles that are readily accessible to the reactant, multiple active sites such as metal–metal and metal–nitrogen sites and ultrathin carbon layers, and highly efficient electron transport. Owing to these unique features, the bimetallic carbon nanosheets exhibit excellent electrocatalytic performance for the oxygen reduction reaction.

Deconvolution of Utilization, Site Density, and Turnover Frequency of Fe–Nitrogen–Carbon Oxygen Reduction Reaction Catalysts Prepared with Secondary N-Precursors

Metal–nitrogen–carbon (MNC) catalysts represent a potential means of reducing cathode catalyst costs in low temperature fuel cell cathodes. Knowledge-based improvements have been hampered by the difficulty to deconvolute active site density and intrinsic turnover frequency. In the present work, MNC catalysts with a variety of secondary nitrogen precursors are addressed. CO chemisorption in combination with Mossbauer spectroscopy are utilized in order to unravel previously inaccessible relations between active site density, turnover frequency, and active site utilization. This analysis provides a more fundamental description and understanding of the origin of the catalytic reactivity; it also provides guidelines for further improvements. Secondary nitrogen precursors impact quantity, quality, dispersion, and utilization of active sites in distinct ways. Secondary nitrogen precursors with high nitrogen content and micropore etching capabilities are most effective in improving catalysts performance.

Bimetallic zeolite imidazolate framework for enhanced lithium storage boosted by the redox participation of nitrogen atoms

In this work, a bimetallic zeolitic imidazolate framework (ZIF) CoZn-ZIF was synthesized via a facile solvothermal approach and applied in lithium-ion batteries. The as-prepared CoZn-ZIF shows a high reversible capacity of 605.8 mA h g−1 at a current density of 100 mA g−1, far beyond the performance of the corresponding monometallic Co-ZIF-67 and Zn-ZIF-8. Ex-situ synchrotron soft X-ray absorption spectroscopy, X-ray diffraction, and electron paramagnetic resonance techniques were employed to explore the Li-storage mechanism. The superior performance of CoZn-ZIF over Co-ZIF-67 and Zn-ZIF-8 could be mainly attributed to lithiation and delithiation of nitrogen atoms, accompanied by the breakage and recoordination of metal nitrogen bond. Morever, a few metal nitrogen bonds without recoordination will lead to the amorphization of CoZn-ZIF and the formation of few nitrogen radicals.

Some Interfacial Interactions between Isocyanates and Metals that Affect Release in Composite Wood-Panel Production*

Abstract Isocyanate- and polyurethane-based adhesives for composite wood-panel production are well known. They are useful for the manufacture of high-performance assemblies, particularly for moisture resistance, durability, and strength. However, isocyanate-based adhesives have several opportunities for improvements related to composite panel manufacture. Of particular note is the ability of isocyanates to bond, not only to wood, but to metal press platens used to produce the composite panels. Although several methodologies exist to overcome this, there is a lack of understanding of the nature of the interactions between isocyanates and metal. The purpose of the current study was to provide insights into these interactions and to help to develop strategies for releasable isocyanate-based resins. Variable-thickness isocyanate–metal and metal–wood assemblies were prepared and the interface exposed by various methods, e.g., surface analysis combined with cluster beam etching and simple peel tests. The interfaces were then analyzed by X-ray photoelectron spectroscopy or time-of-flight–secondary ion mass spectrometry (or both). These surface analytical methods have revealed several chemical interactions between the isocyanates and the metal surfaces, including carbamate-type links and metal–nitrogen linkages. Further, the surface analysis has revealed the compositional character of the locus of failure in wood–metal joints. The locus of failure depends on the presence of wood extractives. With nonextracted wood, the locus of failure is within the wood, which is characterized by a certain concentration of the penetrated resin. With solvent-extracted wood, the locus of failure is within the glue line.

Electrocatalysis of oxygen reduction on heteroatom-doped nanocarbons and transition metal–nitrogen–carbon catalysts for alkaline membrane fuel cells

Electrochemical oxygen reduction behaviour and AEMFC performance using non-precious metal cathode catalysts are reviewed.

EDTA-derived Co N C and Fe N C electro-catalysts for the oxygen reduction reaction in acid environment

Abstract Here, in-house Co N C and Fe N C have been prepared by, first, chelating the metals (Co or Fe) with ethylene diamine tetra acetic acid, known as EDTA (nitrogen precursor). UV–Visible (UV–Vis) spectrometry has been used to ensure the chelated metal formation. In the next step, the chelated metals have been deposited on a high surface area oxidized carbon support to increase the electrical conductivity. The latter composite material has been thermally treated at 800 °C (CoNC8 and FeNC8) or 1000 °C (CoNC10 and FeNC10) in nitrogen atmosphere in order to create the catalytic sites that will be able to perform the oxygen reduction reaction (ORR) in the acid medium. Electrochemical tests have been carried out to investigate the activity and durability of the electro-catalysts for the ORR. Methanol tolerance properties have been also evaluated for a possible application in direct methanol fuel cells. It appears that FeNC8 is the most active electrocatalyst in the presence of methanol in the base electrolyte, thus showing promising characteristics for direct methanol fuel cells. Instead, stability tests of these metal nitrogen catalysts indicate the best resistance to corrosion for the catalysts treated at 1000 °C.

Prediction of interstitial diffusion activation energies of nitrogen, oxygen, boron and carbon in bcc, fcc, and hcp metals using machine learning

Study of diffusion in solids is of fundamental importance in understanding the materials properties such as phase transformations, segregation, and corrosion in processing and operations. Reliable diffusion data is crucial in the successful design of materials and manufacturing processes. In this work, we use gradient boosting with decision tree regression, a robust machine learning method, to develop the model for predicting interstitial diffusion activation energies of the light element X (B, C, O, and N) in 54 metals with bcc, fcc and hcp lattices. With the introduction of elastic strain energy, a dominant concept of interstitial diffusion theory, we are able to train the machine learning model achieving high accuracy of R-squared 0.9 without being over-fitted by using 94 impurity – host binary systems reported in the literature. Furthermore, our study reveals that apart from elastic strain energy, the electronic interaction between the impurity and the host (represented by two fundamental parameters in the well-known Miedema model) also plays an important role. By accurately predicting the diffusion activation energies, we report their trends across 4th, 5th and 6th period and Lanthanides series of the host atoms. More importantly, our predicted data can be used to approximate the transport rates in materials for which little or no diffusion data are available, thus accelerating the design of a wide range of new application-specific materials.

Facile Metal Coordination of Active Site Imprinted Nitrogen Doped Carbons for the Conservative Preparation of Non‐Noble Metal Oxygen Reduction Electrocatalysts

AbstractIron‐ or cobalt‐coordinated heteroatom doped carbons are promising alternatives for Pt‐based cathode catalysts in polymer‐electrolyte fuel cells. Currently, these catalysts are obtained at high temperatures. The reaction conditions complicate the selective and concentrated formation of metal–nitrogen active sites. Herein a mild procedure is introduced, which is conservative toward the carbon support and leads to active‐site formation at low temperatures in a wet‐chemical metal‐coordination step. Active‐site imprinted nitrogen doped carbons are synthesized via ionothermal carbonization employing Lewis‐acidic Mg2+ salt. The obtained carbons with large tubular porosity and imprinted N4 sites lead to very active catalysts with a half‐wave potential (E1/2) of up to 0.76 V versus RHE in acidic electrolyte after coordination with iron. The catalyst shows 4e− selectivity and exceptional stability with a half‐wave potential shift of only 5 mV after 1000 cycles. The X‐ray absorption fine structure as well as the X‐ray absorption near edge structure profiles of the most active catalyst closely match that of iron(II)phthalocyanine, proving the formation of active and stable FeN4 sites at 80 °C. Metal‐coordination with other transition metals reveals that Zn–Nx sites are inactive, while cobalt gives rise to a strong performance increase even at very low concentrations.

Role of Surface Chemistry on Catalyst/Ionomer Interactions for Transition Metal–Nitrogen–Carbon Electrocatalysts

The role of the interaction between doped carbon-based materials and ionic conductors is essential in multiple technologies, from fuel cells and energy storage devices to conductive polymer composites. In this paper, we report how the surface chemistry of transition metal–nitrogen–carbon (MNC) electrocatalysts affects catalyst–ionomer interaction and the resulting structure of cathodes. The cathode structure resulting from these interactions is directly related to the performance in membrane electrode assembly (MEA) fuel cells. To advance the development of platinum group metal (PGM)-free electrodes for the oxygen reduction reaction it is necessary to understand the structure of the catalyst layers with focus on chemistry and distribution of active sites and ionomer morphology. To assess catalyst interaction with an ionomer, X-ray photoelectron spectroscopy is applied to study the chemistry of catalyst layers while density functional theory (DFT) is used to calculate adsorption energies of the ionomer sid...

Ammonia Defective Etching and Nitrogen-Doping of Porous Carbon toward High Exposure of Heme-Derived Fe–Nx Site for Efficient Oxygen Reduction

The utilization of metal and nitrogen doped carbon as a Pt-free oxygen reduction electrocatalyst depends largely on the homogeneous composition of the metal–nitrogen sites with limited content. Herein a simple and feasible ammonia defective activation strategy is explored on ordered mesoporous carbon (APC) to confine hematin precursor and suppress the formation of inorganic Fe-based derivatives during pyrolysis. Thus, a hierarchically nanoporous Fe/N/APC catalyst with high numbers of exposed iron–nitrogen sites exhibits an impressive performance for oxygen reduction reaction in alkaline media, with large diffusion-limited current density and positive half-wave potential with respect to commercial Pt/C catalyst. The enhanced ORR properties can be majorly ascribed to synergistic contributions of high numbers of exposed catalytic sites completion from high contents of Fe–N and pyridinic N along with the fast mass-transport properties arising from the etched high permeable porous structure. When applied as ca...

Cu–MOF-Derived Cu/Cu2O Nanoparticles and CuNxCy Species to Boost Oxygen Reduction Activity of Ketjenblack Carbon in Al–Air Battery

Developing a highly efficient and low-cost catalyst on a large scale is still a big challenge for fuel cells and metal–air batteries. Decorating carbon supports with some active sites (e.g., nitrogen doping, metal–nitrogen doping) seems to be a promising strategy. In this work, we first reported a Cu-centered metal organic framework (Cu–MOF) as a self-sacrificing precursor to modify the Ketjenblack (KB) carbon, where crystalline Cu/Cu2O nanoparticles and noncrystalline CuNxCy species were derived after calcination. The catalytic activity toward the oxygen reduction reaction (ORR) of this modified KB carbon was significantly boosted probably because of the synergistic effect between crystalline Cu/Cu2O nanoparticles and noncrystalline CuNxCy species. This hybrid catalyst exhibited a comparable half-wave potential (0.82 V versus reversible hydrogen electrode, RHE) and superior limiting-current density and durability to the commercial 20 wt % Pt/C. The excellent activity was also further confirmed by the app...

Use of electron microprobe analysis to explain metallurgical phenomena and their effect on properties when welding stainless steel

A modified electron probe microanalysis (EPMA) instrument containing six wavelength dispersive spectrometers has been used for mapping cross-sections of stainless steel base material and welds. It made it possible to measure the composition in specific small areas and to illustrate element partitioning; ranging from centerline segregation to concealed sub-microstructure. Examples from industrial research are given to demonstrate the versatile application field for this established technology. EPMA was used to study the chemical composition of gas tungsten arc welds in the lean duplex grade UNS S32101 performed with and without nitrogen additions to the argon-based shielding gas. The level of nitrogen in the shielding gas not only determined the weld metal nitrogen content, but also affected evaporation of other elements from the weld metal. Mapping could also be used to reveal detailed information about the dendritic substructure in welds and the fusion line that could not be seen with conventional microscopy as the weld metal microstructure is controlled by nitrogen. With the measured local composition, it was possible to calculate the pitting resistance equivalent number, PRE = Cr + 3.3 × Mo + 16 × N (wt%) and thereby visualize the local variation in the microstructure. Nitrogen is strongly concentrated in the austenite and has the largest impact on the PRE. Pitting corrosion testing confirmed that the ferrite phase was most susceptible to pitting attack and that a higher average PRE does not significantly increase the critical pitting temperature. The EPMA instrument was also applied to study all-weld metal of E347T0 type flux-cored wire with and without bismuth additions. Bismuth can have a negative effect on weld metal ductility after post-weld heat treatment and/or applications at high temperature. It has been suggested that this is due to grain boundary bismuth segregation, and it has been debated whether it occurs as bismuth or bismuth oxide Bi2O3. Hot tensile testing confirmed that the bismuth content affects the weld metal ductility at 700 °C and EPMA proved that bismuth segregates as round particles after post-weld heat treatment and not as bismuth oxide.

On the role of the energetic species in TiN thin film growth by reactive deep oscillation magnetron sputtering in Ar/N2

The properties of TiN films deposited by direct current magnetron sputtering strongly depends on the composition of the discharge since the N2 fraction is the main deposition parameter controlling the poisoning of the target and, thus, the flux and energy of the species bombarding the growing films. Accordingly, the properties of the films are also intimately linked to the N2 fraction. In this work TiN films were deposited by deep oscillation magnetron sputtering, a variant of high power impulse magnetron sputtering, with increasing N2 content in the discharge gas.The TiN films deposited under relatively low intensity bombardment conditions have surface chemistry processes that favour the formation of [111] preferential orientation. On the contrary, the TiN films deposited at N2 fraction of 11% and above are grown under heavy bombardment by the plasma species and are less crystalline than at lower N2 fraction, have high compressive stresses and their grain size decreases. The increased bombardment of the films with increasing N2 fraction was attributed to changes of N species energy flux as corroborated by the ion energy distributions. The evolution of the films properties was accounted for by assuming that the energetic metallic and monoatomic nitrogen species interact with the growing film through different mechanisms and thus they have differentiated effects on the films properties. The structural properties of the films are mainly influenced by the bombardment by energetic N species while the microstructure of the films and their hardness mainly depends on the bombardment by energetic Ti species. The different roles of the energetic metallic and monoatomic nitrogen species in the growth process of TiN films implies that proper control and balance of the two types of bombardment are mandatory in order to optimize the properties of the TiN for the targeted application.

Co Nanoparticles Encapsulated in N-Doped Carbon Nanosheets: Enhancing Oxygen Reduction Catalysis without Metal-Nitrogen Bonding.

It is known that introducing metal nanoparticles (e.g., Fe and Co) into N-doped carbons can enhance the activity of N-doped carbons toward the oxygen reduction reaction (ORR). However, introducing metals into N-doped carbons inevitably causes the formation of multiple active sites. Thus, it is challenging to identify the active sites and unravel mechanisms responsible for enhanced ORR activity. Herein, by developing a new N-heterocyclic carbene (NHC)-Co complex as the nitrogen- and metal-containing precursor, we report the synthesis of N-doped carbon nanosheets embedded with Co nanoparticles as highly active ORR catalysts without direct metal-nitrogen bonding. Electrochemical measurements and X-ray absorption spectroscopy indicate that the carbon-nitrogen sites surrounding Co nanoparticles are responsible for the observed ORR activity and stability. Density functional theory calculations further reveal that Co nanoparticles could facilitate the protonation of O2 and thus promote the ORR activity. These results provide new prospects in the rational design and synthesis of heteroatom-doped carbon materials as non-precious-metal catalysts for various electrochemical reactions.

Enhancing Selective Photooxidation through Co–Nx-doped Carbon Materials as Singlet Oxygen Photosensitizers

Singlet oxygen (1O2) is considered one of the most effective and selective oxygen agents. However, it is always obtained with the help of heavy atoms in the photosensitizers to sensitize 3O2. Herein, metal–nitrogen (M–Nx) doped 1O2 photosensitizers were readily prepared from metal–nitrogen complex. Their relative metal centers (e.g., Co) chelated with the N/C moiety (Co–Nx/C) provide the primary active sites for 1O2 generation and selective oxidation. The structures of Co–Nx active sites are investigated by scanning and transmission electron microscopy and X-ray photoelectron, Fourier transform infrared, and X-ray absorption fine structure spectroscopy. Their functions for 1O2 generation are confirmed by electrons spin resonance, 1O2 emission, KSCN poisoning test, and H2SO4 etching test. These Co–Nx photosensitizers show excellent selective photooxidation abilities for 1,5-dihydroxynaphthalene after irradiation by a light-emitting diode lamp. After simple concentration and filtration, it is easy to obtain...

(Invited) Platinum Group Metal-Free Oxygen Reduction Reaction Electrocatalysts from Fe-N-C Family: Activity, Durability and Manufacturability

PEM fuel cells have been recognized as one of the most promising candidates for motive and stationary power source. Among the PGM-free catalysts known today, Fe-N-C catalysts (especially made by high temperature pyrolysis) are considered the most viable candidates for platinum substitution from cathode side of fuel cell. There are several ways for synthesis of highly active M-N-C electrocatalysts which involved dispersion of organic N-C precursor and metal salts on support (carbon, MOF or silica), followed by high temperature pyrolysis and post pyrolysis treatments. Among them imidazole-based materials have been the most promising. In this talk we will describe GPGM-free catalysts materials derived from imidazoles using 3 different synthesis methods. The INRS team has developed a MOF-based Fe/N/C catalyst (synthesized using FeAc+Phen+ZIF-8 precursors) with catalyst initial mass activity of 10.6 mA/mg at 0.9 V and maximum initial performance (0.91 W/cm2) [1]. The long term stability of the catalyst was also evaluated and compared with the best literature value (LANL catalyst, which was measured at 0.4 V and 80 oC) [2]. As shown earlier by the Mukerjee group at NEU, encapsulation of Fe chelates within the confines of a MOF as a part of wet chemical synthesis results in formation of highly active and durable M-N-C electrocatalysts [3]. This presentation will provide synthetic, mechanistic and steady state polarization results measured both at a PEM and PAFC single cell. Some aspects of durability and immunity towards anions will also be presented. The UNM team used Sacrificial Support Method (SSM) for preparation of highly active electrocatalysts derived from different imidazole precursors. The influence of imidazole precursors, SSM synthetic parameters (number of post treatments, duration of treatment, heat treatment temperature etc) on the final activity of ORR electrocatalysts was studied in Rotating Ring Disc Electrode as well as in Membrane Electrode Assembly set ups [4-5]. Pajarito Powder performed an extensive R&D on scaling up of the Fe-N-C catalysts made from imidazole MOFs. Such parameters, which will influence the catalyst activity and durability as heat treatment temperature, post treatment conditions, catalyst layer fabrication in MEA were optimized for the materials on the level of 25-50g per batch. It was shown that VariPore™ allows to reproducibly synthesize commercial amount of ORR PGM-free catalysts with improved activity matching smaller lab scale batches and improve the durability of imidazole-derived catalysts [6]. [1] E. Proietti, F. Jaouen, M. lefèvre, N. Larouche, J. Tian, J. Herranz, J. P. Dodelet “Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells”, Nature Communications 2 (2011) 416. [2] G. Wu, K.L. More,C.M. Johnston, P. Zelenay "High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt" Science 332 (2011) 443-447. [3] K. Strickland, E. Miner, Q. Jia, U. Tylus, N. Ramaswamy, W. Liang, M.-T. Sougrati, F. Jaouen. S. Mukerjee "Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal–nitrogen coordination" Nature Comm. 6, Article number: 7343 (2015) [4] D. Sebastian, A. Serov, K. Artyushkova, J. Gordon, P. Atanassov, A. S. Arico, V. Baglio "High Performance and Cost‐Effective Direct Methanol Fuel Cells: Fe‐N‐C Methanol‐Tolerant Oxygen Reduction Reaction Catalysts" ChemSusChem 9 (15) (2016) 1986-1995. [5] D. Sebastian, A. Serov, K. Artyushkova, P. Atanassov, A. S. Arico, V. Baglio "Performance, methanol tolerance and stability of Fe-aminobenzimidazole derived catalyst for direct methanol fuel cells", J. Power Sources 319 (2016), 235–246. [6] A. Serov, M. J. Workman, K. Artyushkova, P. Atanassov, G. McCool, S. McKinney, H. Romero, B. Halevi, T. Stephenson "Highly stable precious metal-free cathode catalyst for fuel cell application", J. Power Sources 327 (2016) 557-564.

Observation of Oxygen Binding on PGM-Free Electrocatalysts By Ambient Pressure XPS and XAS

The most promising class of PGM-free materials for oxygen reduction reaction (ORR) is based on graphene-like carbon containing nitrogen and transition metal (MNC). They show promise as replacement of Pt in two different technological platforms - alkaline exchange membrane fuel cells (AEMFCs) and proton exchange membrane fuel cells (PEMFC). [1-3] It is well established that nitrogen coordination with metal in the carbon network of MNC materials is directly related to ORR activity; however, the exact nature of the active sites is still debated even after over 50 years of research. Understanding the specific roles of nitrogen and metal in the properties/activity/stability/durability of MNC-based catalytic materials is a prerequisite for the rational design of ORR electrocatalysts with improved performance. The key component in elucidating the relationship between the chemistry of active sites and activity is a better understanding of the formation of adsorbates, intermediates, and products during reactions occurring within the fuel cell. In situ monitoring reaction steps under realistic conditions in metal-free and metal-containing building blocks will shed light onto the reaction mechanism that is essential for developing active and durable PGM-free catalyst for ORR. [4] We will report on AP-XPS analysis for series of electrocatalysts belonging to Fe-N-carbon families based on sacrificial support method (SSM) [1, 2] and Metal-organic frameworks (MOF) [5]. The effect the nitrogen chemistry and the type of iron have on the oxygen binding was investigated by ambient pressure X-ray Photoelectron Spectroscopy (XPS) and X-ray Adsorption Spectroscopy (XAS) under an O2 environment at operating temperature of the fuel cell. The effect of the relative abundance of different types of nitrogens, such as pyridinic, coordinated to iron and hydrogenated nitrogens (pyrrolic and hydrogenated pyridine) on the preference of oxygen binding is studied by high-resolution nitrogen photoelectron spectra. The role of metallic and atomically dispersed iron is investigated by a combination of XAS and XPS. Pyridinic N and N-coordinated to metal have been reported as active sites promoting the reduction of oxygen to water while hydrogenated N was hypothesized to reduce oxygen only partially, forming hydrogen peroxide. Figure 1a and 1c shows a difference between N 1s spectra acquired at 200 mTorr total pressure of oxygen/water mixture and that at UHV conditions for two different types of Fe-N-C electrocatalysts. For the catalyst Fe-N-C SSM, the largest change happens in the area of hydrogenated nitrogen while for the catalysts Fe-N-C MOF the largest change is occurring in the region of pyridinic nitrogen. This is also confirmed by different degree of change observed in Fe L-edge upon oxygen binding shown in Figure 1 b and 1d). Rearrangement of Fe(II) and Fe(III) intensity upon oxygen binding is observed only one of the catalysts. Linking differences in oxygen binding to the differences in the chemistry of the electrocatalysts are of ultimate importance for elucidating the oxygen reduction reaction mechanism. 1. Workman, M.J., et al., Platinum group metal-free electrocatalysts: Effects of synthesis on structure and performance in proton-exchange membrane fuel cell cathodes. Journal of Power Sources, 2017. 348: p. 30-39. 2. Gokhale, R., et al., Direct synthesis of platinum group metal-free Fe-N-C catalyst for oxygen reduction reaction in alkaline media. Electrochemistry Communications, 2016. 72: p. 140-143. 3. Strickland, K., et al., Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal–nitrogen coordination. Nature Communications, 2015. 6: p. 7343. 4. Artyushkova, K., et al., Oxygen Binding to Active Sites of Fe–N–C ORR Electrocatalysts Observed by Ambient-Pressure XPS. The Journal of Physical Chemistry C, 2017. 121(5): p. 2836-2843. 5. Li, J., et al., Structural and mechanistic basis for the high activity of Fe-N-C catalysts toward oxygen reduction. Energy & Environmental Science, 2016. 9(7): p. 2418-2432. Figure 1

Effect of Infiltrated Transition Metals in Ni/Sm-Doped CeO2 Cermets Anode in Direct NH3-Fueled SOFCs

Ammonia (NH3) has attracted much attention as a fuel for SOFCs. In the case of well-established Ni-based cermets anode, however, the cell performance is poor due to the low catalytic activity for NH3 reforming. In this respect, it is necessary to develop the highly active anode for realizing direct NH3-fueld SOFCs. Previously, we prepared Ni-M (M : Mo, Ta, W and Nb)/ Sm-doped CeO2(SDC) anodes by infiltration of metal solutions into pre-sintered Ni/SDC cermets and revealed the activity of them as an anode for direct NH3-fueled SOFCs at temperature of 700 to 900 °C [1-2]. From these studies, we have proposed that the synergetic effect of Ni and added metals, which weakly and strongly bind to N atom, enhances the activity of the anodes for NH3 oxidation(NH3 reforming, followed by hydrogen oxidation). In addition, it was found that the enhancement of the activity for NH3 oxidation strongly depended on the added metal. Among them, Mo was the most effective element as an additive. On the other hand, the obvious enhancement of the activity for NH3 oxidation was not observed when Nb, Ta and W were added, which have the larger metal-nitrogen (M-N) binding energy than Mo. The activity of the Ni-M binary anode seemed to be determined by the interaction potential between catalytic surface and N atom, produced by Ni and added metals. Here, we focus chromium(Cr) and vanadium(V) as an additive, because Cr and V have the moderate M-N binding energy (ranked in the order of Mo < Cr < V < W < Nb < Ta) among the metals used in our previous studies. The addition of Cr and V into the Ni/SDC cermets enhanced the activity of the anode for NH3 oxidation at temperature of 700 to 900 °C. The formation of Ni metal and nitrides (CrN and VN) was confirmed in each anode at 700 °C. This suggests that the synergetic effect of Ni and Cr(V), which has weekly and strongly bind to N atom enhances the activity of the anode for NH3 oxidation. Cr was more effective than Mo as an additive, but V was not. The relationship between the activity of the anode and the M-N binding energy of the added metal are discussed. Acknowledge This work was supported by “Kyoto Environmental Nanotechnology Cluster” and “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan. Reference [1] M. Hashinokuchi et al., Solid State Ionics, 285, (2016) 222 [2] R. Yokochi et al., ECS Trans. 68(2015) 2745.

Effect of nitrogen in shielding gas of keyhole GTAW on properties of duplex and superduplex welds

Keyhole gas tungsten arc welding (GTAW) is a relatively new variant used for fabrication of pressure equipment where up to 10-mm-thick material can be autogenously welded in one pass. As the shielding gas used for keyhole mode is typically Ar + 5% H2, the suitability of this method for welding of duplex stainless steels has been investigated. Duplex UNS S31803 and superduplex UNS S32750 schedule 40 seamless pipe was welded using a closed square butt joint configuration. Shielding gas compositions were applied with increasing nitrogen content in argon or argon-hydrogen mixtures. An investigation of the completed welds included examinations of the microstructure, corrosion and mechanical properties of the weld metal. All shielding gases resulted in high-quality welds free from defects, showed high strength and excellent corrosion resistance. Hydrogen additions increased the weld metal nitrogen loss and resulted in lower austenite formation. Ar + 5% H2 showed up to 20 vol.% less austenite than the gas types containing nitrogen and also showed the lowest impact toughness. At least 2% nitrogen would be recommended for optimizing the phase balance and impact toughness. Taking all aspects into account, Ar + 2% N2 is the preferred shielding gas for welding duplex and superduplex with the keyhole GTAW process.