Vanadium pentaoxide, V 2 O 5 is an attractive cathode material for Li-ion batteries, which can store up to three Li-ion per formula unit. At deep discharge an irreversible reconstructive phase transition occurs with formation the disordered ω-Li x V 2 O 5 bronze, which despite the lack of long range order exhibits a high reversible capacity (~310 mAh/g) without regaining the crystallinity upon recharge. Here, we utilize operando powder X-ray diffraction and total scattering (i.e. pair distribution function analysis) to investigate the atomic-scale structures of the deep-discharge phase ω-Li x V 2 O 5 (x ~ 3) and, for the first time, the highly disordered phase β-Li x V 2 O 5 (x ~0.3) formed during subsequent Li-extraction. Our studies reveal, that the deep discharge ω-Li 3 V 2 O 5 phase consists of ~60 Å domains rock salt structure with a local cation ordering on ~15 Å length scale. The charged β-Li x V 2 O 5 phase only exhibits very short range ordering (~10 Å). The phase transition between these phases is structurally reversible and appears unexpectedly to occur via a two-phase transition mechanism.
Gold nanoparticles
(Au NPs) and gold-based nanomaterials
combine
unique properties relevant for medicine, imaging, optics, sensing,
catalysis, and energy conversion. While the Turkevich–Frens
and Brust–Schiffrin methods remain the state-of-the-art colloidal
syntheses of Au NPs, there is a need for more sustainable and tractable
synthetic strategies leading to new model systems. In particular,
stabilizers are almost systematically used in colloidal syntheses,
but they can be detrimental for fundamental and applied studies. Here,
a surfactant-free synthesis of size-controlled colloidal Au NPs stable
for months is achieved by the simple reduction of HAuCl4 at room temperature in alkaline solutions of low-viscosity mono-alcohols
such as ethanol or methanol and water, without the need for any other
additives. Palladium (Pd) and bimetallic Au
x
Pd
y
NPs, nanocomposites and multimetallic
samples, are also obtained and are readily active (electro)catalysts.
The multiple benefits over the state-of-the-art syntheses that this
simple synthesis bears for fundamental and applied research are highlighted.
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