Akbar I. Inamdar

Effects of Ultrathin Al Layer Insertion on Resistive Switching Performance in an Amorphous Aluminum Oxide Resistive Memory

We prepared resistive switching Al–AlOx multilayered junctions and observed considerably improved endurance properties. The mechanism of the observed resistance switching basically reflects the filament model. The temperature dependence of the transport in each resistance state revealed additional features, that is a well-defined thermal activation behavior in the high-resistance state is not observed in the layered device and the metallic conduction in the low-resistance state is not affected. The improved endurance properties are discussed in terms of the increased effective number of active regions, where the Reset and Set processes probably occur before a permanent dielectric breakdown.

Multicoloured electrochromic thin films of NiO/PANI

NiO/polyaniline (PANI) thin films have been prepared by a two-step process. NiO thin films were electrodeposited from an aqueous solution of NiCl2 6H2O at pH 7.5 on fluorine-doped tin oxide coated glass substrates and a layer of PANI was formed on NiO thin films by chemical bath deposition. The films were characterized for their structural, optical, morphological and electrochromic properties. X-ray diffraction and Fourier-transform infrared spectroscopy indicated the formation of NiO and PANI, in which NiO is of cubic structure. Scanning electron micrographs represent porous granular NiO, which get uniformly carpeted with PANI, leading to a matty morphology of NiO/PANI samples. The electrochromic performance of NiO/PANI films has been studied using cyclic voltammetry and chronoamperometry over the −1.2 to +2.2 V (versus saturated calomel electrode (SCE)) potential window in 1M LiClO4 + propylene carbonate. The NiO/PANI films exhibit electrochromism with colour that changes from pale yellow (leucoemeraldine base at −0.7 V versus SCE) to dark green (emeraldine salt at 0.4 V versus SCE) to purple (pernigraniline at 0.8 V versus SCE) in the reduced states and dark blue (nigraniline at 0.5 V versus SCE) to dark green (emeraldine salt at 0.1 V versus SCE) to light green (photoemeraldine at −0.3 V versus SCE) in its oxidized states. These colours, though akin to pure PANI, have higher contrast, high speed of operation and high stability, owing to the properties of NiO. The colouration efficiency of the NiO/PANI film was estimated to be 85 cm2 C−1.

Multi-functional reactively-sputtered copper oxide electrodes for supercapacitor and electro-catalyst in direct methanol fuel cell applications.

This work reports on the concurrent electrochemical energy storage and conversion characteristics of granular copper oxide electrode films prepared using reactive radio-frequency magnetron sputtering at room temperature under different oxygen environments. The obtained films are characterized in terms of their structural, morphological, and compositional properties. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscope studies reveal that granular, single-phase Cu2O and CuO can be obtained by controlling the oxygen flow rate. The electrochemical energy storage properties of the films are investigated by carrying out cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy tests. The electrochemical analysis reveals that the Cu2O and CuO electrodes have high specific capacitances of 215 and 272 F/g in 6 M KOH solution with a capacity retention of about 80% and 85% after 3000 cycles, respectively. Cyclic voltammetry and chronoamperometry are used to study the electrochemical energy conversion properties of the films via methanol electro-oxidation. The results show that the Cu2O and CuO electrodes are electro-catalytically active and highly stable.

Facile Route to NiO Nanostructured Electrode Grown by Oblique Angle Deposition Technique for Supercapacitors

We report an efficient method for growing NiO nanostructures by oblique angle deposition (OAD) technique in an e-beam evaporator for supercapacitor applications. This facile physical vapor deposition technique combined with OAD presents a unique, direct, and economical route for obtaining high width-to-height ratio nanorods for supercapacitor electrodes. The NiO nanostructure essentially consists of nanorods with varying dimensions. The sample deposited at OAD 75° showed highest supercapacitance value of 344 F/g. NiO nanorod electrodes exhibits excellent electrochemical stability with no degradation in capacitance after 5000 charge-discharge cycles. The nanostructured film adhered well to the substrate and had 131% capacity retention. Peak energy density and power density of the NiO nanorods were 8.78 Wh/kg and 2.5 kW/kg, respectively. This technique has potential to be expanded for growing nanostructured films of other interesting metal/metal oxide candidates for supercapacitor applications.

Self-assembled two-dimensional copper oxide nanosheet bundles as an efficient oxygen evolution reaction (OER) electrocatalyst for water splitting applications

A high activity of a two-dimensional (2D) copper oxide (CuO) electrocatalyst for the oxygen evolution reaction (OER) is presented. The CuO electrode self-assembles on a stainless steel substrate via chemical bath deposition at 80 °C in a mixed solution of CuSO4 and NH4OH, followed by air annealing treatment, and shows a 2D nanosheet bundle-type morphology. The OER performance is studied in a 1 M KOH solution. The OER starts to occur at about 1.48 V versus the RHE (η = 250 mV) with a Tafel slope of 59 mV dec−1 in a 1 M KOH solution. The overpotential (η) of 350 mV at 10 mA cm−2 is among the lowest compared with other copper-based materials. The catalyst can deliver a stable current density of >10 mA cm−2 for more than 10 hours. This superior OER activity is due to its adequately exposed OER-favorable 2D morphology and the optimized electronic properties resulting from the thermal treatment.

Nickel-titanium oxide as a novel anode material for rechargeable sodium-ion batteries

Nickel-titanium oxide (NiTiO3; NTO) of an ilmenite structure that comprises a layered transition-metal octahedral structure, wherein the zigzag open tunnels are possible routes for Na intercalation, can be a potential anode material for sodium (Na) ion batteries (SIBs). In this study, nanocrystalline NTO particles that are of sizes 3 to 5 nm were prepared using a simple hydrothermal process followed by annealing, and the particles were then tested for SIB applications. The pure-NTO electrode that comprises a hexagonal crystal structure and mesoporous morphology demonstrated a reversible capacity of approximately 521 mA h g−1 that corresponds to a coulombic efficiency of 67% in the first cycle, which further improved to ∼98% in the following cycles, at an applied specific current of 50 mA g−1, and stable cycling performance for 200 cycles. Further, due to the synergetic effect of the porous network structure and high surface area, the NTO electrode exhibited an exceptional rate capability, delivering a capacity of 192 mA h g−1 at a high specific current of 4000 mA g−1. The excellent cyclability and rate capability of the NTO electrode are attributed to the improved electronic conductivity and highly porous microstructure of the NTO material, whereby fast charge transfer and facile diffusion of the Na-ions to the active sites are enabled.

Nickel titanate lithium-ion battery anodes with high reversible capacity and high-rate long-cycle life performance

We demonstrate the impressive performance of sparsely studied nickel titanate anode materials for Li-ion batteries (LIBs). The nickel titanate anode delivers a high reversible discharge capacity of 435 mA h g−1 at a current density of 35 mA g−1, high-rate performance and excellent cycling retention of 96% with a long-term cycling stability at 1500 mA g−1 over 300 cycles. The coulombic efficiency is obtained as high as 98%. This superior nickel titanate electrode material could be used as a safe, low-cost, long cycle life anode material for next-generation LIBs with a high power capability.

Ultrathin graphene nanosheets derived from rice husks for sustainable supercapacitor electrodes

Graphene nanosheets are synthesized via the carbonization of brown-rice husks followed by a one-stage KOH-activation process for the design of a sustainable electrochemical energy-storage electrode. The graphene nanosheets exhibit an ultra-thin crumpled-silk-veil-wave, sheet-like structure with a high surface area of ∼1225 m2 g−1 and a high porosity. The graphene-nanosheet electrode shows a specific capacitance of 115 F g−1 at 0.5 mA cm−2 and a high energy density of 36.8 W h kg−1 at a power density of 323 W kg−1, with an excellent cyclic stability of 88% over 2000 cycles. The observed good electrochemical energy-storage performance of the biomaterial-derived graphene-nanosheet electrode is due to the synergistic effect of the intrinsically large electrochemically active surface area, an enhanced ion diffusion, and an improved electrical conductivity.

Effect of Electronegativity on Bipolar Resistive Switching in a WO3-Based Asymmetric Capacitor Structure

This study investigates the transport and switching time of nonvolatile tungsten oxide based resistive-switching (RS) memory devices. These devices consist of a highly resistive tungsten oxide film sandwiched between metal electrodes, and their RS characteristics are bipolar in the counterclockwise direction. The switching voltage, retention, endurance, and switching time are strongly dependent on the type of electrodes used, and we also find quantitative and qualitative evidence that the electronegativity (χ) of the electrodes plays a key role in determining the RS properties and switching time. We also propose an RS model based on the role of the electronegativity at the interface.

Switching Power Universality in Unipolar Resistive Switching Memories.

We investigate the resistive switching power from unipolar resistive switching current-voltage characteristics in various binary metal oxide films sandwiched by different metal electrodes, and find a universal feature (the so-called universality) in the switching power among these devices. To experimentally derive the switching power universality, systematic measurements of the switching voltage and current are performed, and neither of these correlate with one another. As the switching resistance (R) increases, the switching power (P) decreases following a power law P ∝ R−β, regardless of the device configurations. The observed switching power universality is indicative of the existence of a commonly applicable switching mechanism. The origin of the power universality is discussed based on a metallic filament model and thermo-chemical reaction.