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ZnCo2O4 has been studied as an electrode material for supercapacitor applications because of its excellent redox activity. It is known that morphology plays an important role in deciding the electrochemical behavior of material through factors such as specific surface area and active surface states. Surfactant plays a significant role in determining the morphology and hence surface area of the material. Here, we present an extensive comparative study on the effect of two surfactants, urea and hexamethylenetetramine (HMTA), on the morphology of ZnCo2O4 and its impact on both supercapacitor and oxygen evolution reaction (OER) performance. Synthesis of ZnCo2O4 using urea yields urchin-like morphology, which exhibits a specific capacity of 94 mAh g−1 at 2 A g−1 , which is much higher than the 34 mAh g−1 achieved through hexagonal sheet-type morphology obtained from HMTA as a surfactant. We fabricated a coin cell with the urea-derived material, which shows an energy density of 19 W h kg−1, a power density of 4125 W kg−1 , and a Coulombic efficiency of 97%. Further, a comparative study of OER for both types of morphology yields a lower overpotential of 336 mV for urea-derived urchin morphology compared to 362 mV for the HMTA-based sample. Other electrochemical parameters, such as Tafel slope, double-layer capacitance, and turn-over frequency, are also evaluated for both types of morphology. The better overall performance of urea-based urchin-like morphology is attributed to higher specific surface area and oxygen vacancies, as confirmed through Brunauer–Emmett–Teller (BET) and x-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

Abstract The structural, dielectric and ferroelectric properties of lead-free (Na 0.5- x K x Bi 0.5- x La x)TiO 3 (0 ≤ x ≤ 0.12) powders synthesized by modified sol-gel method was investigated. Rietveld refinement of synchrotron x-ray diffraction data confirms single phase rhombohedral crystal structure with R 3 c space group for all the compositions and anti-phase (a - a - a - ) octahedral tilting angle decreased with increase in composition. Homogeneity and elemental proportions were confirmed by Energy dispersive x-ray spectrometry. The temperature-dependent dielectric study has shown two diffuse type of dielectric anomaly for all the samples, due to A-site disorder in the lattice, which has been assigned to two-phase transitions: ferroelectric to anti-ferroelectric and anti-ferroelectric to the paraelectric phase transition. Thermal stability range of dielectric constant increases from ~100 to 220 °C as a function of composition. Stable dielectric constant first increases from 1557 ± 10% for x = 0 compositions and highest for x = 0.06 sample with ε mid ~ 2508 ± 10% of the temperature range ~180–340 °C, and after that decreases to 1608 ± 10% for x = 0.12, but remain higher than the x = 0 composition. Ferroelectric measurements have shown monotonously decreasing coercive field as a function of the composition due to decrease in the average grain size, confirmed by microstructural studies using field emission scanning electron microscope. An exponential increase in the energy storage efficiency from ~ 17% to 87% as a function of composition have also observed. These types of materials, with the high stable dielectric constant (ε r) and low loss (tanδ), have a vast scope in the field of the thermally stable dielectric constant materials and energy storage applications. [ABSTRACT FROM AUTHOR]