Durable ultra-low-platinum ionomer-free anode catalyst for hydrogen proton exchange membrane fuel cell

An ultra-low-platinum catalyst based on finely dispersed platinum (Pt) deposited on a highly porous complex microporous layer was investigated as a candidate of durable anode catalyst for hydrogen oxidation reaction (HOR) in proton exchange membrane fuel cells. Etching of teflonated and nitridized base carbon substrate in oxygen plasma and simultaneous deposition of cerium oxide were applied to increase active surface area and electrochemical activity of the platinum nanocatalyst. Ultra-low loadings of Pt (between 0.85 and 8.5 μg cm⁻²) deposited by magnetron sputtering on this substrate were assembled with Nafion 212 membrane and commercially available Pt/C cathodes (300-400 μg cm⁻² Pt). Such membrane electrode assembly (MEA) with extremely low Pt content at anode can deliver high output power densities, reaching 0.95 W cm⁻² or 0.65 W cm⁻² with only 1.7 μg cm⁻² of Pt, using H₂ as fuel and pure O₂ or air as an oxidant, respectively. Although electrocatalysts with highly dispersed active metals are known to often suffer from irreversible degradation, the above MEAs proved to be very stable when the cell was subjected to a durability test under heavy duty conditions of on/off cycling. The system with lower Pt content is more prone to water flooding which can, however, be eliminated by maintaining better control over the fuel humidity. Average decay of the cell voltage less than 50 μV h⁻¹ was obtained in the cycling regime, while excellent stability <10 μV h⁻¹ is achievable under the static load of 0.4 A cm⁻².     

Polyoxometalates in the Design of Effective and Tunable Water Oxidation Catalysts

Water oxidation catalysts (WOCs) are of core importance in several green energy production technologies, including water splitting and water reduction of CO₂ driven by electrochemical potential and/or photons (radiant energy). General challenges in solar fuel generating structures, WOC design concepts, and some success-limiting considerations in WOC development are described. The first class of WOCs are presented that combine the stability benefits of heterogeneous WOCs with the reactivity and other benefits of homogeneous WOCs.     

Structure and properties of micro-arc calcium phosphate coatings on pure titanium and Ti–40Nb alloy

The microstructure, physical and mechanical, and chemical properties of micro-arc calcium phosphate (CaP) coatings deposited under different process voltages in the range of 150–400 V on the commercially pure titanium (Ti) and Ti–40%Nb (Ti–40Nb) (mass fraction) alloy were investigated by the SEM, TEM, XRD and EDX methods. The coating thickness, roughness, and sizes of structural elements were measured and showed similar linear character depending on the process voltage for the coatings on both substrates. SEM results showed the porous morphology with spherical shape structural elements and rough surface relief of the coatings. XRD and TEM studies exhibited the amorphous structure of the CaP coating. With increasing the process voltage to 300–400 V, the crystalline phases, such as CaHPO₄ and β-Ca₂P₂O₇, were formed onto the coatings. The annealing leads to the formation of complex poly-phase structure with crystalline phases: CaTi₄(PO₄)₆, β-Ca₂P₂O₇, TiP₂O₇, TiNb(PO₄)₃, TiO₂, NbO₂, and Nb₂O₅. The applied voltage and process duration in the ranges of 200–250 V and 5–10 min, respectively, revealed the coating formed on Ti and Ti–40Nb with optimal properties: thickness of 40–70 μm, porosity of 20%–25%, roughness (R_a) of 2.5–5.0 μm, adhesion strength of 15–30 MPa, and Ca/P mole ratio of 0.5–0.7.     

Mie resonances and Bragg-like multiple scattering in opacity of two-dimensional photonic crystals

The lowest (main) and high-order Mie resonances and the Bragg-like multiple scattering of electromagnetic (EM) waves are determined as three mechanisms of formation and frequency position of two opaque bands, with narrow peaks in one of the bands in the transmission spectra of 2D photonic crystals composed of dielectric cylinders arranged parallel to the EM wave's electric vector in the square lattice. The main Mie resonance in a single cylinder defines the frequency position of the main gap whose formation results from the Bragg-like scattering. An additional gap with narrow transmission peaks opens in the spectrum of a cylinder layer and becomes pronounced with the number of layers. It is argued that higher-order Mie resonances are responsible for the transmission peaks within the additional band of a perfect crystal. It is shown that 2D photonic crystals with a filling factor ranging from 3% to 20% at a fixed crystal period may be a good zero approximation to study wave transmission through a localizing 2D dense random medium slab.     

Design of composite porous cermets synthesized by hydrothermal treatment of CrAl powder followed by calcination

The microstructure of the porous Cr–Al metal–oxide cermet was studied by means of XRD, SEM, EDX as well as IR and Raman spectroscopy. This cermet was synthesized by mechanical alloying of Cr–Al powders in an AGO-2 planetary ball mill followed by hydrothermal treatment in a special stainless steel die and calcination in air. As a result, a highly porous monolith comprised of metal-like particles randomly distributed in the oxide matrix (Cr₂O₃ and Al₂O₃) was formed. Two types of the composite cores were found in cermets. The first one consisted of chromium phase containing nanoparticles sized from 50 to 140 nm and Al-enriched phase at the interfaces. The second one consisted of new chromium oxide phases with hexagonal Cr₂N-like and fcc CrN-like structures probably with Cr₂O and CrO stoichiometry. These new phases were stabilized within aggregates of the nanocomposite particles containing inclusions of alumina. The relations between different preparation stages and the cermet microstructure are discussed.     

Recent Advances in Research on Carbon Nanotube–Polymer Composites

Carbon nanotubes (CNTs) demonstrate remarkable electrical, thermal, and mechanical properties, which allow a number of exciting potential applications. In this article, we review the most recent progress in research on the development of CNT–polymer composites, with particular attention to their mechanical and electrical (conductive) properties. Various functionalization and fabrication approaches and their role in the preparation of CNT–polymer composites with improved mechanical and electrical properties are discussed. We tabulate the most recent values of Young's modulus and electrical conductivities for various CNT–polymer composites and compare the effectiveness of different processing techniques. Finally, we give a future outlook for the development of CNT–polymer composites as potential alternative materials for various applications, including flexible electrodes in displays, electronic paper, antistatic coatings, bullet‐proof vests, protective clothing, and high‐performance composites for aircraft and automotive industries.     

Ultra-stable nanoparticles of CdSe revealed from mass spectrometry

Nanoparticles under a few nanometres in size have structures and material functions that differ from the bulk because of their distinct geometrical shapes and strong quantum confinement. These qualities could lead to unique device applications. Our mass spectral analysis of CdSe nanoparticles reveals that (CdSe)(33) and (CdSe)(34) are extremely stable: with a simple solution method, they grow in preference to any other chemical compositions to produce macroscopic quantities. First-principles calculations predict that these are puckered (CdSe)(28)-cages, with four- and six-membered rings based on the highly symmetric octahedral analogues of fullerenes, accommodating either (CdSe)(5) or (CdSe)(6) inside to form a three-dimensional network with essentially heteropolar sp(3)-bonding. This is in accordance with our X-ray and optical analyses. We have found similar mass spectra and atomic structures in CdS, CdTe, ZnS and ZnSe, demonstrating that mass-specified and macroscopically produced nanoparticles, which have been practically limited so far to elemental carbon, can now be extended to a vast variety of compound systems.     

Studying the Properties of Supercooled Strongly-Coupled Plasma Created by Artificial Injection into Space

Attention is drawn to the possibility of creation of the supercooled strongly-coupled (nonideal) plasma by an explosive ejection from spacecraft into vacuum. The values of the Coulomb's coupling parameter *_e=(e²N^1/3)/(k_BT_e) attained in such process can be as large as 3, i.e., considerably greater than in laboratory devices. By using the virial relations and the assumption of ergodicity, we developed an efficient method for reduction of the many-particle distribution function for the system of strongly-coupled electrons to the effective one-particle function, which enabled us to calculate a concentration of free charge carriers. This quantity turns out to be substantially suppressed by the quasi-localization of electrons in the vicinity of nearby ions; and, as a result, an anomalous electrical resistance should be expected.     

On the number of nodes in universal networks of evolutionary processors

We consider the networks of evolutionary processors (NEP) introduced by J. Castellanos, C. Martí n-Vide, V. Mitrana and J. Sempere recently. We show that every recursively enumerable (RE) language can be generated by an NEP with three nodes modulo a terminal alphabet and moreover, NEPs with four nodes can generate any RE language. Thus, we improve existing universality result from five nodes down to four nodes. For mNEPs (a variant of NEPs where operations of different kinds are allowed in the same node) we obtain optimal results: each RE language can be generated by an mNEP with one node modulo a terminal alphabet, and mNEPs with two nodes can generate any RE language; this is not possible for mNEPs with one node. Some open problems are formulated.