Enhanced Electrochemical Performance of Li4Ti5O12 by Niobium Doping for Pseudocapacitive Applications

Niobium-doped nanocrystalline Li4Ti5O12 (LTO) is synthesized by the solid-state reaction method, and the influence of dopant concentration (x = 2–10 mol%) on microstructural and electrochemical properties is studied. The X-ray diffraction and Raman patterns assessed the cubic spinel structure of Li4Ti5−xNbxO12 phase in all samples. Marginal changes in the lattice parameters, unit cell volume and dislocation density of LTO are observed with Nb substitution. The higher ionic radius of Nb induces a lattice expansion, which may be favorable for more ion intercalation/deintercalation. The SEM and TEM images display uniformly distributed nano-sized cubical particles. The represented (hkl) orientations of the SAED pattern and d-spacing (0.46 nm) between bright fringes confirm the well-crystallized LTO phase. The EDS and elemental mapping results demonstrate that Nb elements are uniformly doped in LTO with a proper stoichiometric ratio. The optimized 8%Nb-doped LTO electrode exhibits pseudocapacitive behavior and delivers a high specific capacitance of 497 F g−1 at a current density of 1 A g−1 with 92.3% of specific capacitance retention even after 5000 cycles.

EFFECTS OF NIOBIUM-DOPING ON THE DIELECTRIC AND SWITCHING PROPERTIES OF BARIUM TITANATE CRYSTALS

В работе представлены результаты исследований диэлектрических свойств, процессов переключения и доменной структуры ниобийсодержащих кристаллов титаната бария. Показано, что существенную роль в поведении доменной структуры кристаллов BaTiO:Nb : Nb играет примесь ниобия Nb, ионы которого замещают Ti и изменяют ионный состав решетки. При изменении температуры со скоростью порядка 0,3 К⋅с механически свободных кристаллов BaTiO : Nb в отсутствие внешних электрических полей, процессы перестройки доменной структуры происходят под воздействием внутренних термоупругих напряжений ~ 0,7 МПа и деполяризующих полей ~ 20 кВ-м. This paper reports the results of investigations of dielectric properties, switching processes and the domain structure of niobium-containing barium titanate crystals. It was shown that an impurity of niobium Nb, whose ions replace Ti and change the ionic composition of the lattice, is important for behavior of the domain structure of BaTiO: Nb crystals. At a change in temperature (0,3 К⋅с ) a transformation of the domain structure occurs in the BaTiO: Nb crystals under the influence of the internal thermoelastic stresses ~ 0,7 MPa and the depolarizing fields ~ 20 kV/m.

Soot Combustion over Niobium-Doped Cryptomelane (K-OMS-2) Nanorods—Redox State of Manganese and the Lattice Strain Control the Catalysts Performance

A series of Nb-doped (0–23 wt%) cryptomelane catalyst (Nb-K-OMS-2) was synthesized and thoroughly characterized by XRD, TEM/EDX, XRF, XPS, XAS, UV-Vis, and Raman techniques corroborated by the work function measurements. The obtained catalysts were tested for soot oxidation (Printex U) in model tight and loose contact modes. It was shown that the catalytic properties of the Nb-K-OMS-2 are controlled by the amount of Nb dopant in a strongly non-monotonous way. The introduction of niobium gives rise to the strain in the cryptomelane lattice, accompanied by significant Mn+3/Mn+4 ratio variations and concomitant work function changes. The isotopic exchange experiments revealed that the catalytic activity of the Nb-OMS-2 catalysts in soot combustion proceeds via the pathways, where both the activated suprafacial 18O and the surface 16O2− species participate together in the reaction. The niobium doping level controls the non-monotonous changes of the catalyst work function and the lattice strain, and variations of these parameters correlate well with the observed deSoot activity. To our best knowledge, the role of the lattice strain of the cryptomelane catalysts was documented for the first time in this study.