In the current research project, we have prepared a novel Sb@C nanosphere anode with biomimetic yolk-shell structure for Li/Na-ion batteries via a nanoconfined galvanic replacement route. The yolk-shell microstructure consists of Sb hollow yolk completely protected by a well-conductive carbon thin shell. The substantial void space in the these hollow Sb@C yolk-shell particles allows for the full volume expansion of inner Sb while maintaining the framework of the Sb@C anode and developing a stable SEI film on the outside carbon shell. As for Li-ion battery anode, they displayed a large specific capacity (634 mAh g), high rate capability (specific capabilities of 622, 557, 496, 439, and 384 mAh g at 100, 200, 500, 1000, and 2000 mA g, respectively) and stable cycling performance (a specific capacity of 405 mAh g after long 300 cycles at 1000 mA g). As for Na-ion storage, these yolk-shell Sb@C particles also maintained a reversible capacity of approximate 280 mAh g at 1000 mA g after 200 cycles.
Vertically aligned carbon nitride nanotubes with a uniform diameter of about 250 nm have been synthesized on a porous alumina membrane template (50–80 μm thick) in a microwave excited plasma of C2H2 and N2 using an electron cyclotron resonance chemical vapor deposition system. A negative dc bias voltage was applied to the substrate holder of graphite to promote the flow of ionic fluxes through the nanochannels of the alumina template. This allowed the physical, and subsequent chemical, absorption of species on the walls of the nanochannels that resulted in the formation of the carbon nitride nanotubes. The hollow structure and vertically aligned properties of the nanotubes have been clearly verified by field-emission scanning electron microscope images. The absorption band between 1250 and 1750 cm−1 in the Fourier transform infrared spectroscopy spectrum proves that nitrogen atoms have been incorporated into an amorphous network of carbon.
Resistive switching effect in conductor/insulator/conductor thin-film stacks is promising for resistance random access memory with high-density, fast speed, low power dissipation and high endurance, as well as novel computer logic architectures. NiO is a model system for the resistive switching effect and the formation/rupture of Ni nanofilaments is considered to be essential. However, it is not clear how the nanofilaments evolve in the switching process. Moreover, since Ni nanofilaments should be ferromagnetic, it provides an opportunity to explore the electromagnetic coupling in this system. Here, we report a direct observation of Ni nanofilaments and their specific evolution process for the first time by a combination of various measurements and theoretical calculations. We found that multi-nanofilaments are involved in the low resistance state and the nanofilaments become thin and rupture separately in the RESET process with subsequent increase of the rupture gaps. Theoretical calculations reveal the role of oxygen vacancy amount in the evolution of Ni nanofilaments. We also demonstrate electromagnetic coupling in this system, which opens a new avenue for multifunctional devices.
In
this work, the stability behaviors of the state-of-the-art Fe/N/C
and Pt/C catalysts (as well as the activation time of the latter)
were first systematically investigated, under different cathode catalyst
loadings, in the membrane electrode assemblies (MEA) in PEM fuel cells.
Based on that, two types of cathode electrodes with the combination
of Fe/N/C and Pt/C catalysts were developed (type I: layered hybrid
catalysts with Pt/C next to the membrane and type II: uniformly mixed
catalysts). In this way, the shortcomings of the Fe/N/C catalyst (the
fast decay) and the Pt/C catalyst (the long activation time) can be
compensated at the same time. The hybrid catalysts also showed a very
short activation time (a few hours vs over 10 h for Pt/C with the
same Pt loading). Comparing the two types of hybrid catalysts, type
I shows a much higher current density. The loadings of the Fe/N/C
and Pt/C catalysts in the hybrid electrode were systematically studied,
with optimal values of 1.0 mg cm–2 for Fe/N/C and
0.035 mgPt cm–2 for Pt/C. The Pt loading
of this hybrid catalyst (type I) at the cathode only takes ca. 30%
of the U.S. Department of Energy (DOE) target of Pt usage (0.100 mgPt cm–2), while its mass activity of Pt (in
H2/O2 PEMFC) is 0.22 A mgPt
–1 at 0.9
iR‑free V, reaching half
of the DOE activity target (0.44 A mgPt
–1), which is among the best performances reported so far. Via both
half-cell and single-cell electrochemical evaluations together with
other characterizations, the origin of the improved activity and stability
is believed to be the synergistic effect between Pt/C and Fe/N/C catalysts
to ORR. This work provides an effective strategy for engineering highly
performing MEA for the industrialization of PEM fuel cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.