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Nickel-organic framework (NiOF) compound with layered structure was prepared by solvothermal synthesis using nickel chloride and bezenedicarboxylic acid precursors. NiOF could be converted into nickel with a face-centered cubic structure and nickel oxide with a cubic rock-salt crystal structure after heating above 425 °C in air atmosphere. The organic units played a key role in the formation of well-dispersed nickel/nickel oxide nanoparticles. Primary particle size could be decreased by lowering the calcination temperature. Electrophoresis allowed for depositing a thin layer of nickel/nickel oxide nanoparticles on the skeleton of macroporous nickel foam (NF) as a catalyst electrode for electrooxidation of urea. Nickel/nickel oxide nanoparticles derived from NiOF at 425 °C possessed large amounts of redox active sites (Ni2+/Ni3+), and thus was capable of enhancing the current density and efficiency in urea electrolysis. NF substrate with unique macroporous conductive structure exhibited electrocatalytic behavior towards urea electrolysis and allowed for rapid transport of electron, electrolyte, and gaseous products. Therefore, coating of nickel/nickel oxide nanoparticles on NF provided a possible way for further enhancing the electrocatalytic ability of electrode in urea electrolysis, making it favorable for large-scale applications.

The eMCMBs (expanded mesocarbon microbeads) composed of fluffy graphene oxide nanosheets were obtained by chemical oxidation of MCMB graphite powder. The eMCMBs were attached to the skeleton of nickel foam through electrophoretic deposition. After heat treatment in reducing atmosphere, the eMCMBs were converted into reduced eMCMBs (reMCMBs) composed of sponge-like graphene nanosheets. Nickel foam with attached reMCMBs was used as a highly conductive scaffold to support nickel cobaltite nanoflakes. The sponge-like reMCMBs accommodated electrolyte solution, afforded current collector, and functioned as a stress buffer to alleviate electrode damage. Macroporous nickel cobaltite film with mesoporous thin nanoflakes could provide large amounts of pores for easy penetration of electrolyte solution, huge interfacial area for facile redox reactions, and short transport distance for ions and electrons. Nickel cobaltite grown around nickel foam with attached reMCMBs could deliver a high specific capacitance of 1025 F g −1 at 5 A g −1 , greater than that grown around nickel foam (688 F g −1 ). Nickel cobaltite nanoflakes grown on reMCMBs turned out to decrease the kinetic resistance, diffusive impedance, and volumetric strain, resulting in better capacitance, rate capability, and electrochemical stability.

A cyanide-bridged bimetallic coordination polymer, nickel hexacyanoferrate, could be pyrolyzed to form carbon-encapsulated nickel-iron (CE-NiFe) nanoparticles. The formation of nitrogen-doped spherical carbon shell with ordered mesoporous structure prevented the structural damage of catalyst cores and allowed the migration and diffusion of electrolyte into the hollow carbon spheres. An ultra-thin layer of CE-NiFe nanoparticles could be tightly attached to the three-dimensional macroporous nickel foam (NF) by electrophoretic deposition. The CE-NiFe nanoparticles could lower the onset potential and increase the current density in anodic urea electrolysis and cathodic hydrogen production as compared with bare NF. Macroporous NF substrate was very useful for the urea electrolysis and hydrogen production, which allowed for fast transport of electron, electrolyte, and gas products. The superior electrocatalytic ability of CE-NiFe/NF electrode in urea oxidation and water reduction made it favorable for versatile applications such as water treatment, hydrogen generation, and fuel cells.

In this report, a simple and facile solvothermal method is developed for fabrication of platinum–ruthenium (PtRu) nanodendrites supported on reduced graphene oxide (PtRu-RGO) in the ethylene glycol (EG) system, using hexadecylpyridinium chloride (HDPC) as a shape-directing agent. The as-prepared nanocomposites show the superior catalytic activity and better stability towards EG oxidation, compared with RGO-supported Pt nanoparticles and commercial PtRu/C (Pt 30 wt. %, Ru 15 wt. %) catalysts. This strategy may open a new route to design and prepare advanced electrocatalysts in direct EG fuel cells.

Well-defined core shell gold palladium@palladium nanocrystals (AuPd@Pd) are facilely prepared by a simple and green wet-chemical method at 25 degrees C. A Good's buffer, 2-[4-(2-hydroxyethyl)-1-piperazinyl] ethanesulfonic acid (HEPES), is used as a reducing agent and a shape-directing agent, while there is no template, seed, organic solvent, or surfactant involved. The AuPd@Pd nanocrystals are uniformly dispersed on graphene nanosheets by ultrasonication, resulting in the formation of graphene supported AuPd@Pd (G-AuPd@Pd). The as-prepared nanocomposites exhibit the improved catalytic activity, good tolerance, and better stability for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline media, compared with the G-Pd and commercial Pd black catalysts. The as-developed method may provide a promising pathway for large-scale fabrication of AuPd-based catalysts. (C) 2014 Elsevier B.V. All rights reserved.

In this work, bimetallic alloyed platinum-palladium (PtPd) nanoflowers are fabricated by one-pot solvothermal co-reduction of Pt (II) acetylacetonate and Pd (II) acetylacetonate in oleylamine system. The as-prepared nanostructures show the enhanced electrocatalytic activity for oxygen reduction reaction (ORR), dominated by a four-electron pathway based on the Koutecky-Levich plots, mainly owing to the inhibition of the formation of Pt–OH ad via the downshift of d-band center for Pt. Meanwhile, PtPd nanoflowers display good methanol tolerance and improved stability for ORR. The chronoamperometry test reveals that the current of PtPd nanoflowers remains 45.9% of its original value within 6000 s, much higher than those of commercial Pt (36.7%) and Pd (32.2%) black catalysts. Therefore, PtPd nanoflowers with unique interconnected structures can be used as a promising cathode catalyst in direct methanol fuel cells.

In this work, a facile general strategy is developed for preparation of palladium-based bimetallic alloyed nanodendrites (PdM NDs, M = Pt, Co, and Ni) via coreduction of Pd(II) acetylacetonate and M(II/III) acetylacetonate salts with oleylamine. Hexadecylpyridinium chloride monohydrate (HDPC) is used as a co-surfactant for preventing the aggregation of nanodendrites. Control experiments varying the precursors and reaction time demonstrate that the dendritic nanocrystals are formed via aggregation-based crystal growth. The as-prepared hybrid nanocrystals display improved electrocatalytic activity and better stability for methanol and ethylene glycol (EG) oxidation, compared with home-made Pd NDs and commercial Pd black catalysts. The developed method provides a novel platform for synthesis of novel electrocatalysts in fuel cells.