Seven-nanometer FePt nanoparticles (NPs) were synthesized and assembled on graphene (G) by a solution-phase self-assembly method. These G/FePt NPs were a more active and durable catalyst for oxygen ...reduction reaction (ORR) in 0.1 M HClO4 than the same NPs or commercial Pt NPs deposited on conventional carbon support. The G/FePt NPs annealed at 100 °C for 1 h under Ar + 5% H2 exhibited specific ORR activities of 1.6 mA/cm2 at 0.512 V and 0.616 mA/cm2 at 0.557 V (vs Ag/AgCl). As a comparison, the commercial Pt NPs (2–3 nm) had specific activities of 0.271 and 0.07 mA/cm2 at the same potentials. The G/FePt NPs were also much more stable in the ORR condition and showed nearly no activity change after 10 000 potential sweeps. The work demonstrates that G is indeed a promising support to improve NP activity and durability for practical catalytic applications.
Advances in chemical syntheses have led to the formation of various kinds of nanoparticles (NPs) with more rational control of size, shape, composition, structure and catalysis. This review ...highlights recent efforts in the development of Pt and non‐Pt based NPs into advanced nanocatalysts for efficient oxygen reduction reaction (ORR) under fuel‐cell reaction conditions. It first outlines the shape controlled synthesis of Pt NPs and their shape‐dependent ORR. Then it summarizes the studies of alloy and core–shell NPs with controlled electronic (alloying) and strain (geometric) effects for tuning ORR catalysis. It further provides a brief overview of ORR catalytic enhancement with Pt‐based NPs supported on graphene and coated with an ionic liquid. The review finally introduces some non‐Pt NPs as a new generation of catalysts for ORR. The reported new syntheses with NP parameter‐tuning capability should pave the way for future development of highly efficient catalysts for applications in fuel cells, metal‐air batteries, and even in other important chemical reactions.
Efforts in searching for efficient nanoparticle catalysts for the oxygen reduction reaction (ORR) in fuel cells have led to various nanoparticle (NP) systems with precise control of size, shape, composition, and structure. Whereas the traditional Pt‐based catalysts are still under heavy investigation, recent studies have led to the emergence of non‐Pt systems. This Review highlights the recent efforts in developing Pt‐ and non‐Pt‐based NPs into advanced nanocatalysts for the ORR.
Today's urban transportation systems face increasing challenges such as greenhouse gas (GHG) emissions, urban air quality, and traffic congestion. In this context, various initiatives of mutualized ...mobility have emerged. However, notably lacking is assessing the environmental impacts of mutualized transportation modes from a life cycle perspective. Using the actual urban transportation big data and related product life cycle data, this study combined with the life cycle assessment methodology and a “bottom-up” approach, explores the effect of mutualized mobility on greenhouse gas emissions of urban transportation systems for both Beijing and Toronto. The results showed that mutualized mobility might positively affect the sustainability of urban transport systems, albeit in very different ways. In Toronto, the annual per capita greenhouse gas emissions in 2016 decreased by 2.8 kg of carbon dioxide equivalent (CO2-eq) compared to 2011. Both carpooling and car-sharing displayed a higher curbing potential than ride-hailing. In a city characterized by higher population density like Beijing, ride-hailing created negative impacts. Deadheading (i.e., pulling an empty trailer) was the critical factor affecting ride-hailing's environmental performance, which accounted for about 30% of the total vehicle life cycle emissions. Counter-intuitively, greenhouse gas emissions of station-based bike-sharing (SBBS) were almost six times that of privately-owned bicycles and even higher than public transportation. This study's results can be used as a starting base for decision-makers to devise more appropriate strategies and programs to promote the sustainability of mutualized mobility and urban transportation systems. Meanwhile, it can also help the public at large to better understand the characteristics and environmental impacts of mutualized mobility to adopt more sustainable mutualized mobility alternatives.
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•The actual environmental impact of mutualized mobility was examined by using LCA.•Mutualized mobility has reduced Toronto's per capita greenhouse gas emissions.•Carpooling and car-sharing display a higher curbing potential than ride-hailing.•The rising use of ride-hailing services is increasing GHG emissions.•Station-based bike sharing is not as environmentally friendly as expected.
We report a facile synthesis of monodisperse Pd nanoparticles by the reduction of Pd(acac)2 with oleylamine and borane tributylamine complex. The oleylamine-coated Pd nanoparticles are readily ...“cleaned” with a 99% acetic acid wash, and the Pd particles supported on Ketjen carbon are catalytically active for formic acid oxidation in HClO4 solution. The catalyst shows no obvious activity degradation after 1500 cyclic voltammetry cycles under ambient conditions. These Pd particles hold promise as a highly active non-Pt catalyst for fuel cell applications.
Monodisperse dumbbell-like Pt−Fe3O4 nanoparticles are synthesized by epitaxial growth of Fe onto Pt nanoparticles followed by Fe oxidation. The nanoparticle size in the structure is tunable from 2 to ...8 nm for Pt and 6 to 20 nm for Fe3O4. Pt nanoparticles in the Pt−Fe3O4 structure show a 20-fold increase in mass activity toward oxygen reduction reaction compared with the single component Pt nanoparticles and the commercial 3 nm Pt particles. The work proves that it is possible to maximize catalytic activity of the Pt nanoparticle catalyst through the control not only of Pt size and shape but also of its interaction with Fe3O4 nanoparticles.
Permanent magnets are a class of critical materials for information storage, energy storage, and other magneto‐electronic applications. Compared with conventional bulk magnets, magnetic nanoparticles ...(MNPs) show unique size‐dependent magnetic properties, which make it possible to control and optimize their magnetic performance for specific applications. The synthesis of MNPs has been intensively explored in recent years. Among different methods developed thus far, chemical synthesis based on solution‐phase reactions has attracted much attention owing to its potential to achieve the desired size, morphology, structure, and magnetic controls. This Minireview focuses on the recent chemical syntheses of strongly ferromagnetic MNPs (Hc>10 kOe) of rare‐earth metals and FePt intermetallic alloys. It further discusses the potential of enhancing the magnetic performance of MNP composites by assembly of hard and soft MNPs into exchange‐coupled nanocomposites. High‐performance nanocomposites are key to fabricating super‐strong permanent magnets for magnetic, electronic, and energy applications.
Hard magnetic nanomaterials: Chemical synthesis of magnetic nanoparticles has received great attention owing to its advantages, which lead to the desired control of the magnetic properties. This Minireview highlights recent developments in the chemical synthesis of hard magnetic nanoparticles and exchange‐coupled nanocomposites for permanent magnet applications.
Good support: A solution‐phase self‐assembly approach leads to Co/CoO core/shell nanoparticles deposited on graphene (G–Co/CoO NPs). Their catalytic activity for the oxygen reduction reaction in ...O2‐saturated KOH solution depends on the thickness of the CoO shell (green in picture). The optimized G–Co/CoO NPs have a comparative activity and better stability than the commercial Pt NP catalyst supported on carbon (C–Pt).
Multicomponent hybrid nanostructures that contain two or more nanometer‐scale components have attracted much attention recently owing to the synergistic properties induced by interactions between ...these different nanometer‐scale objects. Herein, we give an overview of the efforts to synthesize multicomponent nanoparticles with at least one component being magnetic, and focus on our recent developments. The syntheses are based on heterogeneous nucleation and growth of a second and third component onto seed nanoparticles. These multicomponent nanoparticles show interesting magnetic, magneto‐optical, plasmonic, and semiconducting properties that can be modulated by interfacial interactions between different nanocomponents. This opens up a new avenue to advanced multifunctional nanomaterials for device concepts and applications.
Multicomponent nanoparticles can be synthesized in high‐temperature organic phases. A variety of morphologies such as core/shell, binary heterodimer, nano‐dumbbell, and ternary nanostructures have been obtained. The nanostructures synergistically combine magnetic, plasmonic, and semiconducting properties, and may have unique applications.
Sea urchin-like (CoxFe1-x)2P shows Co/Fe-composition dependent catalysis for oxygen evolution reaction (OER) in 0.1 M KOH. The (Co0.54Fe0.46)2P is the most efficient OER catalyst, reaching 10 mA ...cm(-2) at an overpotential of 0.37 V (vs. RHE). The report offers a new synergistic approach to tune and optimize the electrocatalysis of OER.
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