Composite Hypo-Hyper-d-Intermetallic and Interionic Phases as Supported Interactive Electrocatalysts

Spark Ablation for the Fabrication of PEM Water Electrolysis Catalyst-Coated Membranes

Proton-exchange-membrane (PEM) electrolyzers represent a promising technology for sustainable hydrogen production, owing to their efficiency and load flexibility. However, the acidic nature of PEM demands the use of platinum-group metal-electrocatalysts. Apart from the associated high capital costs, the scarcity of Ir hinders the large-scale implementation of the technology. Since low-cost replacements for Ir are not available at present, there is an urgent need to engineer catalyst-coated membranes (CCMs) with homogeneous catalyst layers at low Ir loadings. Efforts to realize this mainly rely on the development of advanced Ir nanostructures with maximized dispersion via wet chemistry routes. This study demonstrates the potential of an alternative vapor-based process, based on spark ablation and impaction, to fabricate efficient and durable Ir- and Pt-coated membranes. Our results indicate that spark-ablation CCMs can reduce the Ir demand by up to five times compared to commercial CCMs, without a compromise in activity. The durability of spark-ablation CCMs has been investigated by applying constant and dynamic load profiles for 150 h, indicating different degradation mechanisms for each case without major pitfalls. At constant load, an initial degradation in performance was observed during the first 30 h, but a stable degradation rate of 0.05 mV h−1 was sustained during the rest of the test. The present results, together with manufacturing aspects related to simplicity, costs and environmental footprint, suggest the high potential of spark ablation having practical applications in CCM manufacturing.

Long-term, stable, and improved oxygen-reduction performance of titania-supported PtPb nanoparticles

Anatase-type titania-supported intermetallic PtPb nanoparticles synthesized through a wet-chemical route showed a long-term, stable, and improved oxygen reduction reaction performance.

Spillover Phenomena and Its Striking Impacts in Electrocatalysis for Hydrogen and Oxygen Electrode Reactions

The core subject of the present paper represents the interrelated spillover (effusion) phenomena both of the primary oxide and the H-adatoms, their theory and practice, causes, appearances and consequences, and evidences of existence, their specific properties, and their alterpolar equilibria and kinetic behavior, structural, and resulting catalytic, and double layer charging features. The aim is to introduce electron conductive and d-d interactive individual and composite (mixed valence) hypo-d-oxide compounds, of increased altervalent capacity, or their suboxides (Magnéli phases), as the interactive catalytic supports and therefrom provide (i) the strong metal-support interaction (SMSI) catalytic effect and (ii) dynamic spillover interactive transfer of primary oxides (M-OH) and free effusional H-adatoms for further electrode reactions and thereby advance the overall electrocatalytic activity. Since hypo-d-oxides feature the exchange membrane properties, the higher the altervalent capacity, the higher the spillover effect. In fact, altervalent hypo-d-oxides impose spontaneous dissociative adsorption of water molecules and then spontaneously pronounced membrane spillover transferring properties instantaneously resulting with corresponding bronze type (Pt/HxWO3) under cathodic and/or its hydrated state (Pt/W(OH)6), responsible for Pt-OH effusion, under anodic polarization, this way establishing instantaneous reversibly revertible alterpolar bronze features (Pt/H0.35WO3 Pt/W(OH)6) and substantially advanced electrocatalytic properties of these composite interactive electrocatalysts. Such nanostructured-type electrocatalysts, even of mixed-valence hypo-d-oxide structures (Pt/H0.35WO3/TiO2/C, Pt/HxNbO3/TiO2/C), have for the first time been synthesized by the sol-gel methods and shown rather high stability, electron conductivity, and nonexchanged initial pure monobronze spillover and catalytic properties. Such a unique electrocatalytic system, as the striking target issue of the present paper, has been shown to be the superior for substantiation of the revertible cell assembly for spontaneous reversible alterpolar interchanges between PEMFC and WE. The main target of the present thorough review study has been to throw some specific insight light on the overall spillover phenomena and their effects in electrocatalysis of oxygen and hydrogen electrode reactions from diverse angles of view and broad contemporary experimental methods and approaches (XPS, FTIR, DRIFT, XRD, potentiodynamic spectra, UHRTEM).

Synthesis and applications of ionic liquids derived from natural sugars

Aiming to develop environmentally compatible chemical syntheses, the replacement of traditional organic solvents with ionic liquids (ILs) has attracted considerable attention. ILs are special molten salts with melting points below 100 degrees C that are typically constituted of organic cations (imidazolium, pyridinium, sulfonium, phosphonium, etc.) and inorganic anions. Due to their ionic nature, they are endowed with high chemical and thermal stability, good solvent properties, and non-measurable vapor pressure. Although the recovery of unaltered ILs and recycling partly compensate their rather high cost, it is important to develop new synthetic approaches to less expensive and environmentally sustainable ILs based on renewable raw materials. In fact, most of these alternative solvents are still prepared starting from fossil feedstocks. Until now, only a limited number of ILs have been prepared from renewable sources. Surprisingly, the most available and inexpensive raw material, i.e., carbohydrates, has been hardly exploited in the synthesis of ILs. In 2003 imidazolium-based ILs were prepared from o-fructose and used as solvents in Mizoroki-Heck and Diels-Alder reactions. Later on, the first chiral ILs derived from sugars were prepared from methyl D-glucopyranoside. In the same year, a family of new chiral ILs, obtained from commercial isosorbide (dianhydro-D-glucitol), was described. A closely related approach was followed by other researchers to synthesize mono- and bis-ammonium ILs from isomannide (dianhydro-D-mannitol). Finally, a few ILs bearing a pentofuranose unit as the chiral moiety were prepared using sugar phosphates as glycosyl donors and 1-methylimidazole as the acceptor.

Porous manganese oxide octahedral molecular sieves and octahedral layered materials

This Account first gives a historical overview of the development of octahedral molecular sieve (OMS) and octahedral layer (OL) materials based on porous mixed-valent manganese oxides. Unique properties of such systems include excellent semiconductivity and porosity. Materials that are conducting and porous are rare and can offer novel properties not normally available with most molecular sieve materials. The good semiconductivity of OMS and OL systems not only permits potential applications of the conductivity of these materials but also allows characterization of these systems where charging effects are often a problem. Porous manganese oxide natural materials are found as manganese nodules, and these materials when dredged from the ocean floors have been used as excellent adsorbents of metals such as from electroplating wastes and have been shown to be excellent catalysts. Rational for synthesis of novel OMS and OL materials is related to the superb conductivity, microporosity, and catalytic activity of these natural materials. The natural systems are often found as mixtures, are poorly crystalline, and have incredibly diverse compositions due to exposure to various aqueous environments in nature. Such exposure allows ion exchange to occur. Preparation of pure crystalline OL and OMS systems is one of the very significant goals of this work. The status of this research area is one of moderate development. Opportunities exist for preparation of a multitude of novel materials. Some applications of these materials have recently been achieved primarily in the area of catalysis and membranes, and others such as sensors and adsorptive systems are likely. Characterization studies are becoming more sophisticated as new materials and proper preparation of materials for such characterization studies are being done. The research area involved in this work is solid state chemistry. The fields of materials synthesis, characterization, and applications of materials are all important in developments of this field. Researchers in chemistry, chemical engineering, materials science, physics, and biological sciences are actively pursuing research in this area. The most significant results found in this work are related to the novel structural and physical properties of porous manganese oxide materials. Variable pore size materials have been synthesized using structure directors and with a variety of synthetic methodologies. Transformations of tunnel materials with temperature and in specific atmosphere have recently been studied with in situ synchrotron methods. Conductivities of these materials appear to be related to the structural properties of these systems with more open structures being less conductive. Catalytic properties of these OMS and OL materials have been shown to be related to the redox cycling of various oxidations states of manganese such as Mn2+, Mn3+, and Mn4+. Chemists interested in synthesis of new materials, the chemistry of solids, enhancing the rates of catalytic reactions, and finding new applications of materials would be interested in these novel materials. Fundamental properties of electron transfer are critical to this research. Concepts of nonstoichiometry, defects, oxygen vacancies, and intermediates are fundamental to many of the syntheses, characterization, and applications such as fuel cells, catalysis, adsorption, sensors, batteries, and related applications.