Deactivation of hydroprocessing catalysts

In this paper, we wish to present an overview of the research carried out in our laboratories with low-cost transition metal oxides (manganese dioxide, iron oxide and vanadium oxide) as active electrode materials for aqueous electrochemical supercapacitors. More specifically, the paper focuses on the approaches that have been used to increase the capacitance of the metal oxides and the cell voltage of the supercapacitor. It is shown that the cell voltage of an electrochemical supercapacitor can be increased significantly with the use of hybrid systems. The most relevant associations are Fe3O4 or activated carbon as the negative electrode and MnO2 as the positive. The cell voltage of the Fe3O4/MnO2 device is 1.8 V and this value was increased to 2.2 V by using activated carbon instead of Fe3O4. These two systems have shown superior behavior compared to a symmetric MnO2/MnO2 device which only works within a 1 V potential window in aqueous K2SO4. Furthermore, the activated carbon/MnO2 hybrid device exhibits a real power density of 605 W/kg (maximum power density =19.0 kW/kg) with an energy density of 17.3 Wh/kg. These values compete well with those of standard electrochemical double layer capacitors working in organic electrolytes.

http://ma.ecsdl.org/content/MA2005-01/35/1348.full.pdf

Nanostructured Transition Metal Oxides for Aqueous Hybrid Electrochemical Supercapacitors

The oxides of copper (CuxO) are fascinating materials due to their remarkable optical, electrical, thermal and magnetic properties. Nanostructuring of CuxO can further enhance the performance of this important functional material and provide it with unique properties that do not exist in its bulk form. Three distinctly different phases of CuxO, mainly CuO, Cu2O and Cu4O3, can be prepared by numerous synthesis techniques including, vapour deposition and liquid phase chemical methods. In this article, we present a review of nanostructured CuxO focusing on their material properties, methods of synthesis and an overview of various applications that have been associated with nanostructured CuxO.

Nanostructured copper oxide semiconductors : a perspective on materials, synthesis methods and applications

The alarming rise of indoor pollution and the need to combat the associated negative effects have promoted increasing attention in modernizing the chemical sensing technologies by newly designed materials with rich and tunable functionalities at atomic or molecular levels. With the appealing physical, chemical, optical, and electronic properties for various potential applications, the state-of-art gas-sensing nanomaterials and their future perspectives are well-documented and summarized in this paper. Specifically, the key performance attributes are addressed in detail such as the sensitivity, selectivity, reversibility, operating temperature, response time, and detection limit. As such, this review provides both critical insights in exploring and understanding various gas sensing nanomaterials and points out limitations and opportunities for further developments, such as morphology control, doping and surface alteration, atomic-scale characterization, and applications in different fields. Finally, the challenges and outlooks are discussed on the basis of the current developments.

Functional gas sensing nanomaterials: A panoramic view

"Metal oxide -based heterostructures for gas sensors"- A review.

Two-dimensional (2D) materials have attracted significant attention for device applications due to their unique structural, electronic and catalytic properties. Here, we have deposited a vertically aligned, highly ordered Pd decorated MnO2 nanowalls directly on a porous anodic alumina (AAO) by reactive sputtering and then it used as a gas sensor without additional processing. The nanowalls sensor shows remarkably high and selective responses to hydrogen gas with low detection range 10–10000 ppm. Our results demonstrate the potential application of Pd decorated MnO2 nanowalls for fabricating highly sensitive and selective gas sensors.

Highly sensitive and selective hydrogen gas sensor using sputtered grown Pd decorated MnO2 nanowalls

An efficient α-MnO2 nanorods forests electrode for electrochemical capacitors with neutral aqueous electrolytes

Here, we have deposited bare SnO2 and SnO2/CuO bilayer thin films directly on porous anodic alumina (AAO) by pulsed laser deposition and then used them as a gas sensor without additional processing. The bilayer sensor shows remarkably high and selective responses to CO gas compared with bare SnO2 in a low detection range 5–500 ppm. Sensor response, selectivity, and stability studies reveal excellent sensing of the thin films. The working principle and role of hydrophobicity behind their good performance was discussed.

Highly sensitive and selective CO gas sensor based on a hydrophobic SnO2/CuO bilayer

We have developed a fast and highly sensitive gas sensor based on the Pd/V2O5 thin films for the low temperature detection of hydrogen in the range 2–500 ppm in air. Sensor response, selectivity, and stability studies reveal excellent sensing of the thin films. The formation of vanadium bronze was studied by spectroscopic ellipsometry. The low temperature operation under ambient conditions and the wide range sensing indicates that these hydrophobic nanocrystalline thin films can be explored for optical as well as chemiresistive gas sensing applications.

A fast response/recovery of hydrophobic Pd/V2O5 thin films for hydrogen gas sensing

The efficiency of silicon carbide (SiC) nanocauliflowers (NCs) as electrode material for supercapacitor application has been investigated in detail in the present work. The SiC NCs were deposited on Ag coated porous alumina (AAO) substrates via a DC magnetron cosputtering technique at room temperature. The Ag coated porous AAO substrate acts as an excellent current collector and also enhances the high specific capacitance of SiC NCs up to ∼300 F/g at 5 mV/s. The fabricated symmetric supercapacitor device delivered a high specific capacitance (188 F/g at 5 mV/s), good cycling ability (97.05% capacitance retention after 30,000 cycles), high energy density (31.43 Wh/kg), and also a high power density (∼18.8 kW/kg at 17.76 Wh/kg) in a voltage range of 1.8 V. These observed excellent electrochemical performances of the present SiC NCs based device suggest it has tremendous potential as supercapacitor electrodes in energy storage applications.

Ashwani Kumar

Papers

Highly sensitive and selective hydrogen gas sensor using sputtered grown Pd decorated MnO2 nanowalls

An efficient α-MnO2 nanorods forests electrode for electrochemical capacitors with neutral aqueous electrolytes

Highly sensitive and selective CO gas sensor based on a hydrophobic SnO2/CuO bilayer

A fast response/recovery of hydrophobic Pd/V2O5 thin films for hydrogen gas sensing

Silicon Carbide Nanocauliflowers for Symmetric Supercapacitor Devices