With
the increased interest in the development of hydrogen fuel
cells as a plausible alternative to internal combustion engines, recent
work has focused on creating alkaline fuel cells (AFC), which employ
an alkaline environment. Working in alkaline as opposed to acidic
media yields a number of tangible benefits, including (i) the ability
to use cheaper and plentiful precious-metal-free catalysts, due to
their increased stability, (ii) a reduction in the amount of degradation
and corrosion of Pt-based catalysts, and (iii) a longer operational
lifetime for the overall fuel cell configuration. However, in the
absence of Pt, no catalyst has achieved activities similar to those
of Pt. Herein, we have synthesized a number of crystalline ultrathin
PtM alloy nanowires (NWs) (M = Fe, Co, Ru, Cu, Au) in order to replace
a portion of the costly Pt metal without compromising on activity
while simultaneously adding in metals known to exhibit favorable synergistic
ligand and strain effects with respect to the host lattice. In fact,
our experiments confirm theoretical insights about a clear and correlative
dependence between measured activity and chemical composition. We
have conclusively demonstrated that our as-synthesized alloy NW catalysts
yield improved hydrogen oxidation reaction (HOR) activities as compared
with a commercial Pt standard as well as with our as-synthesized Pt
NWs. The Pt7Ru3 NW system, in particular, quantitatively
achieved an exchange current density of 0.493 mA/cm2, which
is higher than the corresponding data for Pt NWs alone. Additionally,
the HOR activities follow the same expected trend as their calculated
hydrogen binding energy (HBE) values, thereby confirming the critical
importance and correlation of HBE with the observed activities.
Silver nanoparticles with narrow size distribution were prepared in the presence of a water-soluble pillar[5]arene. They could be used for visual detection of spermine analogues in water through host-guest interactions.
Metal oxides represent a set of promising
materials for use as electrodes within lithium ion batteries, but
unfortunately, these tend to suffer from limitations associated with
poor ionic and electron conductivity as well as low cycling performance.
Hence, to achieve the goal of creating economical, relatively less
toxic, thermally stable, and simultaneously high-energy-density electrode
materials, we have put forth a number of targeted strategies, aimed
at rationally improving upon electrochemical performance. Specifically,
in this Perspective, we discuss the precise roles and effects of controllably
varying not only (i) morphology but also (ii) chemistry as a means
of advancing, ameliorating, and fundamentally tuning the development
and evolution of Fe3O4, Li4Ti5O12, TiO2, and LiV3O8 as viable and ubiquitous energy storage materials.
"Flower-like" motifs of Li4Ti5O12 were synthesized by using a facile and large-scale hydrothermal process involving unique Ti foil precursors followed by a short, relatively low-temperature calcination in air. Moreover, a detailed time-dependent growth mechanism and a reasonable reaction scheme were proposed to clearly illustrate and highlight the structural evolution and subsequent formation of this material. Specifically, the resulting "flower-like" Li4Ti5O12 microspheres consisting of thin nanosheets provide for an enhanced surface area and a reduced lithium-ion diffusion distance. The high surface areas of the exposed roughened, thin petal-like component nanosheets are beneficial for the interaction of the electrolyte with Li4Ti5O12 , which thereby ultimately provides for improved high-rate performance and favorable charge/discharge dynamics. Electrochemical studies of the as-prepared nanostructured Li4Ti5O12 clearly revealed their promising potential as an enhanced anode material for lithium-ion batteries, as they present both excellent rate capabilities (delivering 148, 141, 137, 123, and 60 mAh g(-1) under discharge rates of 0.2, 10, 20, 50, and 100 C, at cycles of 50, 55, 60, 65, and 70, respectively) and stable cycling performance (exhibiting a capacity retention of ≈97 % from cycles 10-100, under a discharge rate of 0.2 C, and an impressive capacity retention of ≈87 % by using a more rigorous discharge rate of 20 C from cycles 101-300).
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