Mir Wasim Raja

Filter paper templated interconnected nanocrystalline LiMn2O4 with high coulombic efficiency and rate capability

A novel filter paper templating method has been developed to prepare nanocrystalline LiMn2O4. Whatman 42 filter paper impregnated with the precursor gel produces ultrafine powder (80–100 nm) when calcined at 800 °C. The structure and morphology of the powder and the template have been studied in detail by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). A single phase cubic spinel with interconnected powder morphology is found. The electrochemical properties have been studied using 2032 coin type cells in the potential window of 3.4 to 4.5 V versusLi/Li+. Sharp oxidation–reduction peaks at 4.09/3.90V and 4.22/4.04V in the cyclic voltagram indicate high crystallinity and good reversibility of the cathode. A typical cell shows an initial discharge capacity of 97 mAh/g with ∼98% columbic efficiency. Rate capability study of the synthesized cathode has been performed by cycling the cell for 130 cycles at different current densities (0.1–1.5 mA/cm2) and it is observed that 80–100% retention of initial capacity is possible when cycled at 0.1–0.6 mA/cm2. A capacity fading of only 0.03 mAh/g per cycle is observed even at 1.5 mA/cm2 (8C). Thus, we have shown that simple filter paper templating technique can produce nanocrystalline LiMn2O4 with high coulombic efficiency (100–95%) and rate capability.

Alanine Assisted Low-Temperature Synthesis and Characterization of Nanocrystalline SOFC Cathodes

Nanocrystalline SOFC cathode materials of perovskite family, La(1-x)Sr(x)M(1-y)Co(y)O(3), where 0<x <= 0.5, 0<y <= 0.8 (M is transitional metal=Mn or Fe) have been synthesized at a relatively low temperature by combustion technique using alanine as novel fuel. The thermal analyses of the precursor gels show sharp single step combustion with low decomposition temperature (170-200 degrees C). Detailed X-ray powder diffraction analyses show 47-96% phase purity in the assynthesized powder and upon calcination at temperature similar to 825 degrees C, single phase material is obtained wherein the nanocrystallinity (crystallite size similar to 19-24 nm) is retained. Densification studies of the materials are carried out within 900-1100 degrees C. The coefficient of thermal expansion (CTE) of the sintered cathodes is also measured. Detailed electrical characterizations of the sintered cathodes are evaluated and correlated with the microstructures. The electrochemical performances of SOFC single cells (Ni-YSZ anode-support /YSZ similar to 20 mu m/LaFeO(3)-based cathodes) with ceria interlayer show high current density of similar to 1.2 A/cm(2) at 0.7 V at 800 degrees C.

Filter paper derived cross-linked interconnected BaBi0.2Co0.35Fe0.45O3−δ morphology with an enhanced oxygen permeation property

This study aims to investigate the effect of an engineered microstructure on the oxygen permeation property of a BaBi0.2Co0.35Fe0.45O3−δ (BBCF) type perovskite membrane. The interconnected multi-level cross-linked structure of the BBCF membrane has been synthesized by mimicking a common laboratory grade filter paper. The controlled calcination of the cellulose matrix results in a single phase BBCF structure when calcined at 950 °C in air. The average diameter of the interconnected BBCF fiber is about 1 μm as confirmed by FESEM. The electrical conductivity is measured to be ∼20 S cm−1 at 800 °C, higher than that of other conventionally prepared BBCF based membranes. The perovskite membrane derived by exo-templating of the filter papers cellulose fiber reveals an enhanced oxygen permeation flux of 0.98 ml min−1 cm−2 at 900 °C.

Low temperature synthesis of nanocrystalline scandia-stabilized zirconia by aqueous combustion method and its characterizations

Zirconia stabilized with 11 mol% scandia (11ScSZ) has been successfully synthesized by novel alanine-assisted soft chemical aqueous combustion method. The reaction kinetics during combustion synthesis has been studied in detail by analysing thermal behaviour of different metal–alanine complexes. A single phase 11ScSZ powder is achieved at significantly low calcination temperature of 500∘C. Field emission scanning electron micrograph reveals an agglomerated morphology with particle size ranging from 80 to 100 nm. The thermal expansion coefficient is found to be 11.03 × 10−6∘C−1 in the temperature range between room temperature and 1000∘C. Optical bandgap of 5.19 eV has been determined using UV–Vis spectroscopy and results are compared with the help of theoretical density of states. The total electrical conductivity of sintered pellet is found to be 7.3 × 10−3 S cm−1 at 700∘C as measured by impedance spectroscopy.