Transition Metal Carbides and Nitrides as Electrode Materials for Low Temperature Fuel Cells

Stabilizing polysulfide-shuttle in a Li–S battery using transition metal carbide nanostructures

Metal carbides nanostrcutures to stabilize polysulfide shuttle which is a key bottleneck for practical applications of Li–S battery.

Things go better with coke: the beneficial role of carbonaceous deposits in heterogeneous catalysis

Carbonaceous deposits on heterogeneous catalysts are traditionally associated with catalyst deactivation. However, they can play a beneficial role in many catalytic processes, e.g. dehydrogenation, hydrogenation, alkylation, isomerisation, Fischer–Tropsch, MTO etc. This review highlights the role and mechanism by which coke deposits can enhance catalytic performance.

Structural effects of a carbon matrix in non-precious metal O2-reduction electrocatalysts

The unique geometric and electronic structural effects of a carbon matrix in several typical non-precious metal O₂-reduction electrocatalysts are discussed.

The role of carbon in structural evolution during single step synthesis of nano tantalum carbide

Carbon-coated nano TaC has been synthesized at 800 °C in single step from TaO₂. Structural features of synthesized cubic TaC depend on the initial carbon concentration. The reaction analysis depicts the role of Mg in lowering the reaction temperature.

Assembly of ultrasmall Cu3N nanoparticles into three-dimensional porous monolithic aerogels

We present the assembly of ultrasmall Cu₃N nanoparticles into aerogels with a high surface area and porosity by thermally destabilizing colloidal nanoparticles.

A high-performance catalyst support for methanol oxidation with graphene and vanadium carbonitride

In this study, a graphene-vanadium carbonitride (G-V(C, N)) hybrid is reported as a novel support for the Pt catalyst in methanol oxidation. The catalytic activity of the Pt/G-V(C, N) hybrid for methanol oxidation is greatly enhanced compared with that of a commercial Pt/C catalyst with carbon black as the catalyst support. The outstanding catalytic activity of the Pt/G-V(C, N) catalyst suggests the potential of using graphene-metal carbonitride as the catalyst support in fuel cells.

Recent advancements in Pt and Pt-free catalysts for oxygen reduction reaction

Based on the understanding of the ORR catalytic mechanism, advanced Pt-based and Pt-free catalysts have been explored.

Evolution of structural and thermal properties of carbon-coated TaC nanopowder synthesized by single step reduction of Ta-ethoxide

Carbon-coated nano-TaC has been synthesized at 800 °C using tantalum-ethoxide by single step chemical reaction route and no external carbon source

Noble metal-free hydrogen evolution catalysts for water splitting

This review summarizes the recent research efforts toward noble metal-free hydrogen evolution electrocatalysts.

Enhanced H2 dissociative phenomena of Pt–Ir electrocatalysts for PEMFCs: an integrated experimental and theoretical study

Bimetallic Pt–Ir electrocatalysts enhance the H₂ dissociation for PEMFCs.

The importance of nanometric passivating films on cathodes for Li-air batteries

Recently, there has been a transition from fully carbonaceous positive electrodes for the aprotic lithium oxygen battery to alternative materials and the use of redox mediator additives, in an attempt to lower the large electrochemical overpotentials associated with the charge reaction. However, the stabilizing or catalytic effect of these materials can become complicated due to the presence of major side-reactions observed during dis(charge). Here, we isolate the charge reaction from the discharge by utilizing electrodes prefilled with commercial lithium peroxide with a crystallite size of about 200-800 nm. Using a combination of S/TEM, online mass spectrometry, XPS, and electrochemical methods to probe the nature of surface films on carbon and conductive Ti-based nanoparticles, we show that oxygen evolution from lithium peroxide is strongly dependent on their surface properties. Insulating TiO2 surface layers on TiC and TiN - even as thin as 3 nm-can completely inhibit the charge reaction under these conditions. On the other hand, TiC, which lacks this oxide film, readily facilitates oxidation of the bulk Li2O2 crystallites, at a much lower overpotential relative to carbon. Since oxidation of lithium oxygen battery cathodes is inevitable in these systems, precise control of the surface chemistry at the nanoscale becomes of upmost importance.

Highly active and stable hydrogen evolution electrocatalysts based on molybdenum compounds on carbon nanotube-graphene hybrid support

Highly active and stable electrocatalysts for hydrogen evolution have been developed on the basis of molybdenum compounds (Mo2C, Mo2N, and MoS2) on carbon nanotube (CNT)-graphene hybrid support via a modified urea-glass route. By a simple modification of synthetic variables, the final phases are easily controlled from carbide, nitride to sulfide with homogeneous dispersion of nanocrystals on the CNT-graphene support. Among the prepared catalysts, Mo2C/CNT-graphene shows the highest activity for hydrogen evolution reaction with a small onset overpotential of 62 mV and Tafel slope of 58 mV/dec as well as an excellent stability in acid media. Such enhanced catalytic activity may originate from its low hydrogen binding energy and high conductivity. Moreover, the CNT-graphene hybrid support plays crucial roles to enhance the activity of molybdenum compounds by alleviating aggregation of the nanocrystals, providing a large area to contact with electrolyte, and facilitating the electron transfer.

The effects of annealing on mechanical, chemical, and physical properties and structural stability of Parylene C

Parylene C is one of the established encapsulation polymers for chronic implants. We investigated the influence of annealing Parylene C on its mechanical properties, chemical structure, and on the stability of Parylene C - platinum - Parylene C sandwich structures as a model of flexible neural interfaces in 0.9 % saline solution. Films of Parylene C were annealed at 200 °C, 300 °C, 350 °C, and 400 °C in nitrogen atmosphere. Temperatures of 350 °C and higher as well as annealing in air destroyed the Parylene C layers; films annealed at lower temperatures showed identical infrared spectra. Higher anneal temperatures produced increased values of elongation at break, tensile and yield strength, and yield strain while at the same time Young's modulus was shown to decrease. Crystallinity increased with annealing temperature. The structural stability of sandwich structures benefitted remarkably from annealing. Sandwich structures annealed at 300 °C maintained their structural integrity during 320 days in saline solution at 37 °C and the insulation capability stayed consistently high.

Enhanced electrocatalytic activity of nano-TiN composited Ti/Sb–SnO2 electrode fabricated by pulse electrodeposition for methylene blue decolorization

The Sb-doped SnO₂ electrode is modified by TiN nanoparticles and has higher stability and significantly enhanced electrochemical decolorization activity.

Stability of Pt near surface alloys under electrochemical conditions: a model study

The stability is one of the key requirements for commercializing the fuel cell electrocatalysts in automotive applications.

Mixed close-packed cobalt molybdenum nitrides as non-noble metal electrocatalysts for the hydrogen evolution reaction

A two-step solid-state reaction for preparing cobalt molybdenum nitride with a nanoscale morphology has been used to produce a highly active and stable electrocatalyst for the hydrogen evolution reaction (HER) under acidic conditions that achieves an iR-corrected current density of 10 mA cm(-2) at -0.20 V vs RHE at low catalyst loadings of 0.24 mg/cm(2) in rotating disk experiments under a H2 atmosphere. Neutron powder diffraction and pair distribution function (PDF) studies have been used to overcome the insensitivity of X-ray diffraction data to different transition-metal nitride structural polytypes and show that this cobalt molybdenum nitride crystallizes in space group P63/mmc with lattice parameters of a = 2.85176(2) Å and c = 10.9862(3) Å and a formula of Co0.6Mo1.4N2. This space group results from the four-layered stacking sequence of a mixed close-packed structure with alternating layers of transition metals in octahedral and trigonal prismatic coordination and is a structure type for which HER activity has not previously been reported. Based on the accurate bond distances obtained from time-of-flight neutron diffraction data, it is determined that the octahedral sites contain a mixture of divalent Co and trivalent Mo, while the trigonal prismatic sites contain Mo in a higher oxidation state. X-ray photoelectron spectroscopy (XPS) studies confirm that at the sample surface nitrogen is present and N-H moieties are abundant.

Catalytic Aminohalogenation of Alkenes and Alkynes

Catalytic aminohalogenation methods enable the regio- and stereoselective vicinal difunctionalization of alkynes, allenes and alkenes with amine and halogen moieties. A range of protocols and reaction mechanisms including organometallic, Lewis base, Lewis acid and Brønsted acid catalysis have been disclosed, enabling the regio- and stereoselective synthesis of halogen-functionalized acyclic amines and nitrogen heterocycles. Recent advances including aminofluorination and catalytic enantioselective aminohalogenation reactions are summarized in this review.

TiN nanoparticles on CNT-graphene hybrid support as noble-metal-free counter electrode for quantum-dot-sensitized solar cells

The development of an efficient noble-metal-free counter electrode is crucial for possible applications of quantum-dot-sensitized solar cells (QDSSCs). Herein, we present TiN nanoparticles on a carbon nanotube (CNT)-graphene hybrid support as a noble-metal-free counter electrode for QDSSCs employing a polysulfide electrolyte. The resulting TiN/CNT-graphene possesses an extremely high surface roughness, a good metal-support interaction, and less aggregation relative to unsupported TiN; it also has superior solar power conversion efficiency (4.13 %) when applying a metal mask, which is much higher than that of the state-of-the-art Au electrode (3.35 %). Based on electrochemical impedance spectroscopy measurements, the enhancement is ascribed to a synergistic effect between TiN nanoparticles and the CNT-graphene hybrid, the roles of which are to provide active sites for the reduction of polysulfide ions and electron pathways to TiN nanoparticles, respectively. The combination of graphene and CNTs leads to a favorable morphology that prevents stacking of graphene or bundling of CNTs, which maximizes the contact of the support with TiN nanoparticles and improves electron-transfer capability relative to either carbon material alone.

Controlled synthesis of tantalum oxynitride and nitride nanoparticles

Synthesis of monodisperse metal nitride and oxynitride nanoparticles with a controllable chemical composition, size, and a well-defined morphology are useful for applications in fields of catalysis, optoelectronics, and electrochemistry. In this paper a novel method for the controllable synthesis of highly crystalline tantalum oxynitride and nitride nanoparticles with a relatively low polydispersity is presented using urea as the nitrogen source. In the presence of calcium ions as assisting agents, by simply varying the initial urea/Ta molar ratio, both the composition and size of the final product can be tailored to switch from TaON to Ta3 N5. The mechanism proposed is that Ca2+ slows down the release of NH3 from the decomposition of urea, which is indispensable for the controllable synthesis of oxynitride and nitride based nanoparticles.