scholarly journals Investigation of the Repassivation Process of CoCrMo in Simulated Biological Fluids

CORROSION ◽  
10.5006/3423 ◽  
2020 ◽  
Vol 76 (6) ◽  
pp. 539-552
Author(s):  
Blake Thornley ◽  
Robert Beadling ◽  
Michael Bryant ◽  
Anne Neville
Keyword(s):  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Biological Fluids ◽  
Electrochemical Techniques ◽  
Reduction Reaction ◽  
Bulk Solution ◽  
Molybdenum Oxides ◽  
Inductively Coupled ◽  
The Reformation ◽  
Phosphate Buffered Saline

A thorough investigation into the repassivation process of CoCrMo in multiple simulated biological environments has been undertaken, looking in detail at both the kinetics and composition of the reformed oxide film. Specific focus of this research was aimed at determining the effect of bovine serum albumin (BSA) on these features. The kinetics of repassivation were obtained by using a variety of electrochemical techniques. The current transients formed were fitted to a second-order decay curve, which accouts for two separate phases: coverage and growth. The reformation of the passive film was fastest in a phosphate buffered saline environment, with the presence of BSA delaying this process because it inhibits the oxygen-reduction reaction as it obstructs the active sites of the alloy when adsorbed onto the surface. The composition of the newly formed film was analyzed with x-ray photoelectron spectroscopy. As expected, the film was primarily composed of chromium (III) oxide with small contributions from cobalt and molybdenum oxides. In the presence of BSA, the quantity of molybdenum within the film was drastically reduced; it was shown to be extracted into the bulk solution via inductively coupled mass spectroscopy. This is observed because BSA is able to complex preferentially to the molybdenum ions when the alloy is exposed, extracting them into solution and altering the composition and integrity of the film.

scholarly journals Bimetallic AgFe Systems on Mordenite: Effect of Cation Deposition Order in the NO Reduction with C3H6/CO

Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 58 ◽  
Author(s):  
Perla Sánchez-López ◽  
Yulia Kotolevich ◽  
Serguei Miridonov ◽  
Fernando Chávez-Rivas ◽  
Sergio Fuentes ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Inductively Coupled Plasma ◽  
Active Sites ◽  
No Reduction ◽  
Optical Emission ◽  
Reduction Reaction ◽  
Exchange Method ◽  
Inductively Coupled ◽  
Preparation Conditions ◽  
Bimetallic Systems

Mono- and bimetallic systems of Ag, Fe, and Ag–Fe exchanged in sodium mordenite zeolite were studied in the reaction of NO reduction. The transition metal cations Ag and Fe were introduced by ion exchange method both at room temperature and 60 °C; modifying the order of component deposition in bimetallic systems. These materials were characterized by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), ultraviolet-visible spectroscopy (UV-Vis), X-Ray photoelectron Spectroscopy (XPS) and High-resolution transmission electron microscopy (HR-TEM). The XPS and UV–Vis spectra of bimetallic samples revealed that under certain preparation conditions Ag+ is reduced with the participation of the Fe2+/Fe3+ ions transition and is present in the form of a Ag reduced state in different proportions of Agm clusters and Ag0 NPs, influenced by the cation deposition order. The catalytic results in the NO reduction reaction using C3H6/CO under an oxidizing atmosphere show also that the order of exchange of Ag and Fe cations in mordenite has a strong effect on catalytic active sites for the reduction of NO.

scholarly journals Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide

2019 ◽  
Author(s):  
Hyo Won Kim ◽  
Vanessa Jane Bukas ◽  
Hun Park ◽  
Sojung Park ◽  
Kyle M. Diederichsen ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Isotope Effects ◽  
Underlying Mechanism ◽  
Reduction Reaction ◽  
Graphene Oxides ◽  
Nitrogen Doped ◽  
General Chemical ◽  
Reduced Graphene

Doped carbon-based systems have been extensively studied over the past decade as active electrocatalysts for both the two-electron (2e-) and four-electron (4e-) oxygen reduction reaction (ORR). However, the mechanisms for ORR are generally poorly understood. Here we report an extensive experimental and first-principles theoretical study of the ORR at nitrogen-doped reduced graphene oxides (NrGO). We synthesize three distinct NrGO catalysts and investigate their chemical and structural properties in detail via X-ray photoelectron spectroscopy, infrared and Raman spectroscopy, high-resolution transmission electron microscopy and thin-film electrical conductivity. ORR experiments include the pH dependences of 2e- versus 4e- ORR selectivity, ORR onset potentials, Tafel slopes and H/D kinetic isotope effects. These experiments show very different ORR behavior for the three catalysts, both in terms of selectivity and the underlying mechanism which proceeds either via coupled proton-electron transfers (CPETs) or non-CPETs. Reasonable structural models developed from DFT rationalize this behavior. The key determinant between CPET vs. non-CPET mechanisms is the electron density at the Fermi level under operating ORR conditions. Regardless of the reaction mechanism or electrolyte pH, however, we identify the ORR active sites as sp2 carbons that are located next to oxide regions. This assignment highlights the importance of oxygen functional groups, while details of (modest) N-doping may still affect the overall catalytic activity, and likely also the selectivity, by modifying the general chemical environment around the active site.

HIGHLY ACTIVE AND REUSABLE RHODIUM CATALYST FOR SELECTIVE HYDROGENATION OF NITRILE–BUTADIENE RUBBER

2015 ◽  
Vol 88 (4) ◽  
pp. 547-559 ◽  
Author(s):  
Peng Cao ◽  
Lin Su ◽  
Cui Li ◽  
Liqun Zhang ◽  
Dongmei Yue
Keyword(s):  
Photoelectron Spectroscopy ◽  
Inductively Coupled Plasma ◽  
Active Sites ◽  
Rhodium Catalyst ◽  
Infrared Spectrometry ◽  
Butadiene Rubber ◽  
X Ray ◽  
Inductively Coupled ◽  
Nitrile Butadiene Rubber ◽  
Highly Active

ABSTRACT A recyclable heterogeneous rhodium catalyst (MTS-T-Rh) was prepared by loading Rh species onto an amino-silica support grafted by tannin, an intermediate linker and stabilizer, and fully characterized by X-ray diffraction, infrared spectrometry, scanning electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma. The importance of tannin in improving the activity and stability of the heterogeneous catalyst is discussed. Tannin is a stabilizer for chelating with the Rh-active sites through a chemical bond, which enhances interactions between the Rh nanoparticles and silica. The catalytic hydrogenation of nitrile–butadiene rubber was evaluated in solution. Above 96% conversion and 100% selectivity, the carbon–carbon double bond was obtained at 120 °C and 3.0 MPa H2 after 8 h over MTS-T-Rh. Compared with Rh/SiO2, the as-prepared MTS-T-Rh catalyst exhibited considerably improved reusability, which suffered about 11% deactivation for hydrogenation of nitrile–butadiene rubber, whereas Rh/SiO2 was 53%.

scholarly journals Multi-Walled Carbon Nanotubes Supported Pd(II) Complexes: A Supramolecular Approach towards Single-Ion Oxygen Reduction Reaction Catalysts

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5539
Author(s):  
Matteo Savastano ◽  
Maurizio Passaponti ◽  
Walter Giurlani ◽  
Leonardo Lari ◽  
Antonio Bianchi ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Platinum Group Metal ◽  
Reduction Reaction ◽  
Rotating Disk Electrode ◽  
Disk Electrode ◽  
Supported Pd

Lowering the platinum group metal content of oxygen reduction reaction catalysts is among the most prevalent research focuses in the field. This target is herein approached through supported Pd(II) complexes. Starting from a commercial macrocycle, a new ligand is synthesized, its solution behavior and binding properties briefly explored (potentiometry, UV-Vis) and then used to prepare a new catalyst. A supramolecular approach is used in order to obtain homogeneous decoration of carbon nanotubes surfaces, fostering novel possibilities to access single-ion active sites. The novel catalyst is characterized through X-ray photoelectron spectroscopy and scanning transmission electron microscopy and its promising oxygen reduction reaction performance is evaluated via rotating ring-disk electrode and rotating disk electrode in half-cell studies.

scholarly journals Gram-Scale Synthesis of Pt-Cu Nanowires with Enhanced Electrocatalytic Activity towards Methanol Oxidation Reaction

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Ning Sui ◽  
Hongxu Gao ◽  
Yukai Wang ◽  
Jiali Li ◽  
Shiyu Qu ◽  
...  
Keyword(s):  
Methanol Oxidation ◽  
Photoelectron Spectroscopy ◽  
Electrocatalytic Activity ◽  
Inductively Coupled Plasma ◽  
Active Sites ◽  
Structural Defects ◽  
Methanol Oxidation Reaction ◽  
X Ray ◽  
Cu Nanowires ◽  
Inductively Coupled

A facile method to prepare Pt-Cu nanowires (NWs) was introduced. Structural characterization such as high-resolution transmission electron microscope (HR-TEM), selected-area electron diffraction (SAED), EDS element mapping, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and inductively coupled plasma mass spectrometry (ICP-MS) showed the formation of Pt-Cu alloy, with a width of 4.5 nm on average. The formation process of Pt-Cu NWs was studied; it was found that bromine ion, who has preferential adsorption on Pt (100) face, served as a growth-directing agent; Brij58 not only served as a protector but also played an important role in forming Pt-Cu NWs; the mechanism was proposed. Their electrocatalytic activity towards methanol oxidation was investigated; we found that the current density of Pt-Cu NWs was 295 mA·mg-1 when the ratio of Pt/Cu is 1 : 1, which is 11.5 and 2.35 times higher than that of pure Pt (26 mA·mg-1) and commercial Pt/C (126 mA·mg-1). The high electrocatalytic activity is attributed to the presence of abundant structural defects and surface active sites on the synthesized Pt-Cu NWs.

scholarly journals Highly effective Fe-N-C electrocatalysts toward oxygen reduction reaction originated from 2,6-diaminopyridine

2021 ◽  
Author(s):  
Weixiang Yang ◽  
Shuihua Tang ◽  
Qiankuan Huang ◽  
Qian Zhang ◽  
Zhen Tang ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Cost Effective ◽  
Reduction Reaction ◽  
Limiting Current ◽  
X Ray ◽  
Onset Potential

Abstract Fe-N-C electrocatalysts have been intensively studied due to their extraordinary catalytic activity toward oxygen reduction reaction (ORR). Here we prepare a Fe-N-C electrocatalyst through cost-effective and nontoxic precursors of 2,6-diaminopyridine (DAP) and FeCl3, where iron ions react with DAP to formed Fe-Nx species first, followed by polymerization and pyrolysis. X-ray diffraction patterns display no obvious Fe2O3 peaks observed in the catalyst as the nominal content of iron addition is less than 10 wt%. X-ray photoelectron spectroscopy spectra indicate that the catalyst has rich pyridinic nitrogen, graphitic nitrogen and Fe-Nx species, which are considered as active sites for ORR. Therefore the catalyst demonstrates an excellent catalytic activity with an onset potential of about 0.96 V, half-wave potential of about 0.84 V, and a limiting current density of 5.8 mA cm-2, better than commercial Pt/C catalyst in an alkaline medium. Furthermore its stability is also much more excellent than that of Pt/C. This work provides a strategy to synthesize universal M-N-C catalysts.

A stacked structure comprising 3-dimensional nitrogen-doped graphene, silicon microchannel plate, and TiO2 for high-performance anode in lithium-ion battery

2019 ◽  
Vol 9 (6) ◽  
pp. 629-634 ◽  
Author(s):  
Fengjuan Miao ◽  
Rui Miao ◽  
Zang Yu ◽  
Cuiping Shi ◽  
Lei Zhu ◽  
...  
Keyword(s):  
Lithium Ion Battery ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
High Performance ◽  
Large Scale ◽  
Electrochemical Techniques ◽  
Lithium Ion ◽  
Nitrogen Doped ◽  
Nitrogen Doped Graphene ◽  
Doped Graphene

A hybrid electrode composed of silicon microchannel plates (Si MCPs) coated with nitrogen-doped graphene and TiO2 is prepared and used as the anode in a lithium-ion battery. The materials are characterized systematically by scanning electron microscopy, Raman scattering spectroscopy, X-ray photoelectron spectroscopy, and electrochemical techniques. The unique porous and ordered nanostructure of the TiO2/N-graphene/Si-MCP nanocomposite provides short paths for diffusion of Li ions and immobilized active sites, whereas N-doped graphene facilitates fast charge transportation. The synergetic effects result in high reversible specific capacities and stability. Owing to the compatibility with semiconductor processing and devices, the concept and technique have large potential in large-scale fabrication of high-performance anodes of lithium-ion batteries, especially those integrated into microelectronic chips.

scholarly journals Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide

2019 ◽  
Author(s):  
Hyo Won Kim ◽  
Vanessa Jane Bukas ◽  
Hun Park ◽  
So Jeong Park ◽  
Kyle M. Diederichsen ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Isotope Effects ◽  
Underlying Mechanism ◽  
Reduction Reaction ◽  
Graphene Oxides ◽  
Nitrogen Doped ◽  
General Chemical ◽  
Reduced Graphene

Doped carbon-based systems have been extensively studied over the past decade as active electrocatalysts for both the two-electron (2e-) and four-electron (4e-) oxygen reduction reaction (ORR). However, the mechanisms for ORR are generally poorly understood. Here we report an extensive experimental and first-principles theoretical study of the ORR at nitrogen-doped reduced graphene oxides (NrGO). We synthesize three distinct NrGO catalysts and investigate their chemical and structural properties in detail via X-ray photoelectron spectroscopy, infrared and Raman spectroscopy, high-resolution transmission electron microscopy and thin-film electrical conductivity. ORR experiments include the pH dependences of 2e- versus 4e- ORR selectivity, ORR onset potentials, Tafel slopes and H/D kinetic isotope effects. These experiments show very different ORR behavior for the three catalysts, both in terms of selectivity and the underlying mechanism which proceeds either via coupled proton-electron transfers (CPETs) or non-CPETs. Reasonable structural models developed from DFT rationalize this behavior. The key determinant between CPET vs. non-CPET mechanisms is the electron density at the Fermi level under operating ORR conditions. Regardless of the reaction mechanism or electrolyte pH, however, we identify the ORR active sites as sp2 carbons that are located next to oxide regions. This assignment highlights the importance of oxygen functional groups, while details of (modest) N-doping may still affect the overall catalytic activity, and likely also the selectivity, by modifying the general chemical environment around the active site.

scholarly journals Synergistic Effects of Active Sites’ Nature and Hydrophilicity on the Oxygen Reduction Reaction Activity of Pt-Free Catalysts

Nanomaterials ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 643 ◽  
Author(s):  
Mariangela Longhi ◽  
Camilla Cova ◽  
Eleonora Pargoletti ◽  
Mauro Coduri ◽  
Saveria Santangelo ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Carbon Nanotubes ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Photoelectron Spectroscopy ◽  
Carbon Nanostructures ◽  
Active Sites ◽  
Active Material ◽  
Reduction Reaction ◽  
X Ray

This work highlights the importance of the hydrophilicity of a catalyst’s active sites on an oxygen reduction reaction (ORR) through an electrochemical and physico-chemical study on catalysts based on nitrogen-modified carbon doped with different metals (Fe, Cu, and a mixture of them). BET, X-ray Powder Diffraction (XRPD), micro-Raman, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and hydrophilicity measurements were performed. All synthesized catalysts are characterized not only by a porous structure, with the porosity distribution centered in the mesoporosity range, but also by the presence of carbon nanostructures. In iron-doped materials, these nanostructures are bamboo-like structures typical of nitrogen carbon nanotubes, which are better organized, in a larger amount, and longer than those in the copper-doped material. Electrochemical ORR results highlight that the presence of iron and nitrogen carbon nanotubes is beneficial to the electroactivity of these materials, but also that the hydrophilicity of the active site is an important parameter affecting electrocatalytic properties. The most active material contains a mixture of Fe and Cu.

scholarly journals Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide

2019 ◽  
Author(s):  
Hyo Won Kim ◽  
Vanessa Jane Bukas ◽  
Hun Park ◽  
Sojung Park ◽  
Kyle M. Diederichsen ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Isotope Effects ◽  
Underlying Mechanism ◽  
Reduction Reaction ◽  
Graphene Oxides ◽  
Nitrogen Doped ◽  
General Chemical ◽  
Reduced Graphene

Doped carbon-based systems have been extensively studied over the past decade as active electrocatalysts for both the two-electron (2e-) and four-electron (4e-) oxygen reduction reaction (ORR). However, the mechanisms for ORR are generally poorly understood. Here we report an extensive experimental and first-principles theoretical study of the ORR at nitrogen-doped reduced graphene oxides (NrGO). We synthesize three distinct NrGO catalysts and investigate their chemical and structural properties in detail via X-ray photoelectron spectroscopy, infrared and Raman spectroscopy, high-resolution transmission electron microscopy and thin-film electrical conductivity. ORR experiments include the pH dependences of 2e- versus 4e- ORR selectivity, ORR onset potentials, Tafel slopes and H/D kinetic isotope effects. These experiments show very different ORR behavior for the three catalysts, both in terms of selectivity and the underlying mechanism which proceeds either via coupled proton-electron transfers (CPETs) or non-CPETs. Reasonable structural models developed from DFT rationalize this behavior. The key determinant between CPET vs. non-CPET mechanisms is the electron density at the Fermi level under operating ORR conditions. Regardless of the reaction mechanism or electrolyte pH, however, we identify the ORR active sites as sp2 carbons that are located next to oxide regions. This assignment highlights the importance of oxygen functional groups, while details of (modest) N-doping may still affect the overall catalytic activity, and likely also the selectivity, by modifying the general chemical environment around the active site.

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