4 research outputs found
Reversible Surface Engineering via Nitrone-Mediated Radical Coupling
Efficient
and simple polymer conjugation reactions are critical
for introducing functionalities on surfaces. For polymer surface grafting,
postpolymerization modifications are often required, which can impose
a significant synthetic hurdle. Here, we report two strategies that
allow for reversible surface engineering via nitrone-mediated radical
coupling (NMRC). Macroradicals stemming from the activation of polymers
generated by copper-mediated radical polymerization are grafted via
radical trapping with a surface-immobilized nitrone or a solution-borne
nitrone. Since the product of NMRC coupling features an alkoxyamine
linker, the grafting reactions can be reversed or chain insertions
can be performed via nitroxide-mediated polymerization (NMP). PolyÂ(<i>n</i>-butyl acrylate) (<i>M</i><sub>n</sub> = 1570
g·mol<sup>–1</sup>, <i>D̵</i> = 1.12)
with a bromine terminus was reversibly grafted to planar silicon substrates
or silica nanoparticles as successfully evidenced via X-ray photoelectron
spectroscopy (XPS), time-of-flight secondary ion mass spectrometry,
and grazing angle attenuated total reflection Fourier-transform infrared
spectroscopy (GAATR-FTIR). NMP chain insertions of styrene are evidenced
via GAATR-FTIR. On silica nanoparticles, an NMRC grafting density
of close to 0.21 chains per nm<sup>2</sup> was determined by dynamic
light scattering and thermogravimetric analysis. Concomitantly, a
simple way to decorate particles with nitroxide radicals with precise
control over the radical concentration is introduced. Silica microparticles
and zinc oxide, barium titanate, and silicon nanoparticles were successfully
functionalized
Chemical Composition of an Aqueous Oxalato-/Citrato-VO<sup>2+</sup> Solution as Determinant for Vanadium Oxide Phase Formation
Aqueous solutions of oxalato- and
citrato-VO<sup>2+</sup> complexes
are prepared, and their ligand exchange reaction is investigated as
a function of the amount of citrate present in the aqueous solution
via continuous-wave electron paramagnetic resonance (CW EPR) and hyperfine
sublevel correlation (HYSCORE) spectroscopy. With a low amount of
citrate, monomeric <i>cis</i>-oxalato-VO<sup>2+</sup> complexes
occur with a distorted square-pyramidal geometry. As the amount of
citrate increases, oxalate is gradually exchanged for citrate. This
leads to (i) an intermediate situation of monomeric VO<sup>2+</sup> complexes with a mix of oxalate/citrate ligands and (ii) a final
situation of both monomeric and dimeric complexes with exclusively
citrato ligands. The monomeric citrato-VO<sup>2+</sup> complexes dominate
(abundance > 80%) and are characterized by a 6-fold chelation of
the
vanadiumÂ(IV) ion by 4 RCO<sub>2</sub><sup>–</sup> ligands at
the equatorial positions and a H<sub>2</sub>O/R–OH ligand at
the axial position. The different redox stabilities of these complexes,
relative to that of dissolved O<sub>2</sub> in the aqueous solution,
is analyzed via <sup>51</sup>V NMR. It is shown that the oxidation
rate is the highest for the oxalato-VO<sup>2+</sup> complexes. In
addition, the stability of the VO<sup>2+</sup> complexes can be drastically
improved by evacuation of the dissolved O<sub>2</sub> from the solution
and subsequent storage in a N<sub>2</sub> ambient atmosphere. The
vanadium oxide phase formation process, starting with the chemical
solution deposition of the aqueous solutions and continuing with subsequent
processing in an ambient 0.1% O<sub>2</sub> atmosphere, differs for
the two complexes. The oxalato-VO<sup>2+</sup> complexes turn into
the oxygen-deficient crystalline VO<sub>2</sub> B at 400 °C,
which then turns into crystalline V<sub>6</sub>O<sub>13</sub> at 500
°C. In contrast, the citrato-VO<sup>2+</sup> complexes form an
amorphous film at 400 °C that crystallizes into VO<sub>2</sub> M1 and V<sub>6</sub>O<sub>13</sub> at 500 °C
Polymeric Backbone Eutectogel Electrolytes for High-Energy Lithium-Ion Batteries
This work introduces a polymeric backbone eutectogel
(P-ETG) hybrid
solid-state electrolyte with an N-isopropylacrylamide
(NIPAM) backbone for high-energy lithium-ion batteries (LIBs). The
NIPAM-based P-ETG is (electro)chemically compatible with commercially
relevant positive electrode materials such as the nickel-rich layered
oxide LiNi0.6Mn0.2Co0.2O2 (NMC622). The chemical compatibility was demonstrated through (physico)chemical
characterization methods. The nonexistence (within detection limits)
of interfacial reactions between the electrolyte and the positive
electrode, the unchanged bulk crystallographic composition, and the
absence of transition metal ions leaching from the positive electrode
in contact with the electrolyte were demonstrated by Fourier transform
infrared spectroscopy, powder X-ray diffraction, and elemental analysis,
respectively. Moreover, the NIPAM-based P-ETG demonstrates a wide
electrochemical stability window (1.5–5.0 V vs Li+/Li) and a reasonably high ionic conductivity at room temperature
(0.82 mS cm–1). The electrochemical compatibility
of a high-potential NMC622-containing positive electrode and the P-ETG
is further demonstrated in Li|P-ETG|NMC622 cells, which deliver a
discharge capacity of 134, 110, and 97 mAh g–1 at
C/5, C/2, and 1C, respectively, after 90 cycles. The Coulombic efficiency
is >95% at C/5, C/2, and 1C. Hence, gaining scientific insights
into
the compatibility of the electrolytes with positive electrode materials
that are relevant to the commercial market, like NMC622, is important
because this requires going beyond the electrolyte design itself,
which is essential to their practical applications
Factors Influencing the Conductivity of Aqueous Sol(ution)–Gel-Processed Al-Doped ZnO Films
Solution
processing of Al-doped ZnO (AZO) is interesting from an
economical point of view for reducing synthesis and deposition costs
in comparison to that for vacuum methods. Several (aqueous) chemical
solution deposition routes have been explored for AZO, but the question
that has never been answered is how state-of-the-art conductivity
is achieved. Here, we fine tune an aqueous solution precursor for
AZO, resulting in resistivities within the 10<sup>–3</sup> Ohm
cm range after a reductive treatment. Profound insights are gained
through the study of the density of the film, the crystal phase, the
optimum Al doping, and the effect of Al positioning in the ZnO lattice,
as determined by <sup>27</sup>Al magic-angle-spinning nuclear magnetic
resonance (MAS NMR) spectroscopy in combination with <sup>1</sup>H
NMR, in order to understand the conductivity mechanism. As the conductivity
of the AZO films drops as a function of time, the position of Al is
studied with respect to the observance of charge carriers using Fourier
transform infrared spectroscopy. The influences of all of these different
factors on conductivity are summarized in a general overview