Harsharaj S. Jadhav

Hierarchical Mesoporous 3D Flower-like CuCo2O4/NF for High-Performance Electrochemical Energy Storage.

Ternary spinel CuCo2O4 nanostructure clenches great potential as high-performance electrode material for next-generation energy storage systems because of its higher electrical conductivity and electrochemical activity. Carbon free and binder free 3D flower-like CuCo2O4 structure are grown on nickel foam (NF) via a facile hydrothermal synthesis method followed by annealing. The obtained CuCo2O4/NF is directly used as electrode for lithium ion batteries (LIBs) and supercapacitors (SCs) application. The electrochemical study of 3D flower-like CuCo2O4 as an electrode for LIB and SC shows highly mesoporous unique architecture plays important role in achieving high capacity/capacitance with superior cycle life. The high surface area and mesoporous nature not only offer sufficient reaction sites, but also can accelerate the liquid electrolyte to penetrate electrode and the ions to reach the reacting sites. In outcome, it exhibits highest capacity of 1160 mA h g−1 after 200 cycles when used as an anode for LIB and specific capacitance of 1002 F g−1 after 3000 cycles. The superior electrochemical of synthesized material is attributed to direct contact of electrode active material with good intrinsic electrical conductivity to the underneath conductive NF substrate builds up an express path for fast ion and electron transfer.

One-step approach for preparing ozone gas sensors based on hierarchical NiCo2O4 structures

Nanostructured semiconducting oxides have been used as resistive gas sensors of toxic and non-toxic gases, but little emphasis has been placed on ozone sensing. Here we present a new ozone gas sensor based on hierarchical NiCo2O4 cubic structures synthesized via a facile urea-assisted co-precipitation method and annealed at 450 °C, which showed a low detection level. Ozone detection was carried out through electrical measurements with an optimized performance at 200 °C, with fast response (∼32 s) and recovery (∼60 s) time with suitable concentration range (from 28 to 165 ppb) for technological applications. Furthermore, NiCO2O4 platelets are selective to ozone compared to other oxidizing and reducing gases. The low detection level can be attributed to the coexistence of 3D structures based on hexagonal platelet-like and porous flower-like shape, which were revealed by field emission scanning electron microscopy (FE-SEM). In summary, NiCo2O4 is promising for detection of sub-ppb levels of ozone gas.

Green solvent ionic liquids: structural directing pioneers for microwave-assisted synthesis of controlled MgO nanostructures

Magnesium oxide (MgO) is one of the auspicious metal oxides which attracts much attention because of its superior performance in scientific applications. Controlled facial arrangement of MgO nanostructures with tailored properties is highly important in nanotechnology and nanoscience. Here, various MgO nanostructures were obtained via one-pot microwave (MW)-assisted synthesis in various structural directing ionic liquids (ILs). These selected ILs are based on monocationic and dicationic moieties which consist of N-methyl imidazolium and 3-methyl pyridinium cations with various halide anions. Different designer solvents with respect to their counter anions produced various nanostructures, varying from nanoflakes, interconnected nanoparticles, hexagonal nanoparticles, irregular nanoparticles and nanocapsules. In this method, green solvent ILs not only act as solvent but also act as structural directing agents. In addition, a plausible mechanism of nanomaterial formation under MW irradiation in the presence of ILs was also determined. Formation of hydrogen bonding with favorable π–π interactions by simply tailoring the IL structures by means of MW conditions is the key factor for the development of different morphology. To define the catalytic activity of the prepared nanostructures, a Claisen condensation reaction was performed. The results showed that all the nanostructures have efficient catalytic activity due to their tailored structure, basicity, and surface area. Particularly, a catalytic amount of hexagonal morphology MgO obtained from dicationic [C4(mIm)2Cl2] IL showed 100% conversion and a remarkable 95% selective yield of the respective product. The proposed approach for nanomaterial preparation does not require an additional template and harsh reaction conditions which establishes this as a simple method to reduce the cost of production using environmentally benign solvents.

Free standing growth of MnCo2O4 nanoflakes as an electrocatalyst for methanol electro-oxidation

Binary metal oxides are emerging as a new class of electro-catalyst for the direct methanol fuel cell (DMFC). In this report, porous MnCo2O4 nanoflakes were directly grown on a nickel foam (NF) substrate using a simple and template-free electrodeposition method followed by annealing treatment. The MnCo2O4/NF electrode showed an initial current density of 96 A g−1 (at a scan rate of 10 mV s−1) with a retention of 90% after 1000 cyclic voltammetry cycles. The binder and carbon-free MnCo2O4/NF electrode showed high electrocatalytic activity, lower overpotential and long-term stability in methanol electro-oxidation compared to a Co3O4/NF electrode. The superior electrochemical performance is mainly attributed to the unique porous structure directly grown on the NF substrate, offering faster ion/electron transfer. According to our investigation, it can be concluded that the present simple and low cost electrodeposition technique can be used for the synthesis of other metal oxides for different energy storage and conversion applications.

Electrochemical growth of Co(OH)2 nanoflakes on Ni foam for methanol electro-oxidation

Recently, direct methanol fuel cells (DMFCs) have been considered as one of the most promising energy sources for portable devices and transportation applications. Herein, cobalt hydroxide (Co(OH)2) nanoflakes were directly grown on a conducting Ni foam substrate via an electrodeposition route. Electrodeposition technique is an excellent method in which active materials can be directly grown on a substrate without the addition of any binder and conducting agent. The hydroxide was deposited from 0.05 M aqueous cobalt nitrate electrolyte at −0.75 V vs. SCE without the addition of any surfactant. Co(OH)2 showed excellent electrocatalytic activity with a superior long-standing stability towards electro-oxidation of methanol. The observed current density of Co(OH)2 in 1 M KOH with 0.5 M methanol was 150 A g−1 at the scan rate of 10 mV s−1. The onset potential of methanol oxidation for the Co(OH)2 catalyst was found to be 0.27 V. The excellent electrocatalytic properties of the electrocatalyst are mainly attributed to the direct growth of an electroactive nanostructure that enhances mechanical adhesion and facilitates a fast electron transfer between the current collector and the electrocatalyst.

Facile and cost-effective growth of a highly efficient MgCo2O4 electrocatalyst for methanol oxidation

A MgCo2O4 based electrode is employed as a novel electrocatalyst material for the electrochemical oxidation of methanol. The binder-free and carbon-free spinel MgCo2O4 nanorod-like structures were grown directly on nickel foam (NF) using a facile and cost-effective co-precipitation method followed by calcination. Cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests were used to study the electrocatalytic performance of the MgCo2O4/NF electrode. The MgCo2O4/NF electrode exhibits higher electrocatalytic activity, a lower onset potential and superior stability when tested as an electrocatalyst for methanol electrooxidation. The high surface area and large pore volume of MgCo2O4 with a mesoporous structure offer higher numbers of active sites for methanol electrooxidation. The higher catalytic activity and stability, along with the facile and scalable synthesis route are promising features for the use of cheap non-Pt based catalyst materials for methanol electrooxidation.