Electrochemical charge storage performance of mesoporous MoO3@Co3O4nanocomposites as electrode materials.

Constructing a novel nanocomposite structure based on Co3O4is of the current interest to design and develop efficient electrochemical capacitors. The capacitive performance of MoO3@Co3O4nanocomposite is compared with pristine Co3O4nanoparticles, both of them being synthesized by hydrothermal technique. A BET surface area of ∼41 m2g-1(almost twice that of Co3O4) and average pore size of 3.6 nm is found to be suitable for promoting Faradaic reactions in the nanocomposite. Electrochemical measurements conducted on both samples predict capacitive behavior with quasi-reversible redox reactions. MoO3@Co3O4nanocomposite is capable of delivering a superior specific capacitance of 1248 F g-1at 0.5 A g-1along with notable stability of 92% even after 2000 cycles of charge-discharge and Coulombic efficiency approaching 100% at 10 A g-1. The outstanding results obtained in this work assure functional adequacy of MoO3@Co3O4nanocomposite in fabricating high-performance electrochemical capacitors.

Influence of size polydispersity on magnetic field tunable structures in magnetic nanofluids containing superparamagnetic nanoparticles.

We probe the influence of particle size polydispersity on field-induced structures and structural transitions in magnetic fluids (ferrofluids) using phase contrast optical microscopy, light scattering and Brownian dynamics simulations. Three different ferrofluids containing superparamagnetic nanoparticles of different polydispersity indices (PDIs) are used. In a ferrofluid with a high PDI (∼0.79), thin chains, thick chains, and sheets are formed on increasing the in-plane magnetic field, whereas isotropic bubbles, and hexagonal and lamellar/stripe structures are formed on increasing the out-of-plane magnetic field over the same range. In contrast, no field-induced aggregates are seen in the sample with low polydispersity under the above conditions. In a polydisperse sample, bubbles are formed at a very low magnetic field strength of 30 G. Insights into the structural evolution with increasing magnetic field strength are obtained by carrying out Brownian dynamics simulations. The crossovers from isotropic, through hexagonal columnar, to lamellar/stripe structures observed with increasing field strength in the high-polydispersity sample indicate the prominent roles of large, more strongly interacting particles in structural transitions in ferrofluids. Based on the observed microstructures, a phase diagram is constructed. Our work opens up new opportunities to develop optical devices and access diverse structures by tuning size polydispersity.