CeO2–TiO2 nanocomposites with different Ce weight percentages (2, 4, 6 and 8%) were synthesized by sol-gel method. The influence of cerium inclusion on the structural, morphological, optical properties and elemental composition has been analyzed via XRD, BET surface area analysis, UV-DRS, HR-SEM, EDAX, TEM, Raman and photoluminescence spectra. The structural study showed that all the CeO2–TiO2 nanocomposites crystallized in tetragonal structure with anatase phase. Morphological study revealed that the nanocomposites are in spherical shape with size between 13–15 nm. Raman and PL spectra confirmed the presence and influence of oxygen vacancy defects. The adsorption ability of the CeO2–TiO2 nanocomposites was investigated for congo red dye under dark condition. CeO2–TiO2 nanocomposites have enhanced adsorptive performance in comparison with bare TiO2 nanoparticles. The enhanced adsorptive activity of CeO2–TiO2 nanocomposites is due to the higher surface area of the nanocomposites and oxygen vacancies present in the surface of the nanocomposites. The pseudo second order kinetic equation fits well with higher correlation coefficient compared to the pseudo first order in explaining the reaction kinetics.
Careful
development and optimization of negative electrode (anode)
materials for Na-ion batteries (SIBs) are essential, for their widespread
applications requiring a long-term cycling stability. BiFeO3 (BFO) with a LiNbO3-type structure (space group R3c) is an ideal negative electrode model
system as it delivers a high specific capacity (770 mAh g–1), which is proposed through a conversion and alloying mechanism.
In this work, BFO is synthesized via a sol–gel method and investigated
as a conversion-type anode model-system for sodium-ion half-cells.
As there is a difference in the first and second cycle profiles in
the cyclic voltammogram, the operating mechanism of charge–discharge
is elucidated using in operando X-ray absorption spectroscopy. In
the first discharge, Bi is found to contribute toward the electrochemical
activity through a conversion mechanism (Bi3+ →
Bi0), followed by the formation of Na–Bi intermetallic
compounds. Evidence for involvement of Fe in the charge storage mechanism
through conversion of the oxide (Fe3+) form to metallic
Fe and back during discharging/charging is also obtained, which is
absent in previous literature reports. Reversible dealloying and subsequent
oxidation of Bi and oxidation of Fe are observed in the following
charge cycle. In the second discharge cycle, a reduction of Bi and
Fe oxides is observed. Changes in the oxidation states of Bi and Fe,
and the local coordination changes during electrochemical cycling
are discussed in detail. Furthermore, the optimization of cycling
stability of BFO is carried out by varying binders and electrolyte
compositions. Based on that, electrodes prepared with the Na-carboxymethyl
cellulose (CMC) binder are chosen for optimization of the electrolyte
composition. BFO–CMC electrodes exhibit the best electrochemical
performance in electrolytes containing fluoroethylene carbonate (FEC)
as the additive. BFO–CMC electrodes deliver initial capacity
values of 635 and 453 mAh g–1 in the Na-insertion
(discharge) and deinsertion (charge) processes, respectively, in the
electrolyte composition of 1 M NaPF6 in EC/DEC (1:1, v/v)
with a 2% FEC additive. The capacity values stabilize around 10th
cycle and capacity retention of 73% is observed after 60 cycles with
respect to the 10th cycle charge capacity.
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