Raihan Othman

Ionic conductivity studies of poly(vinyl alcohol) alkaline solid polymer electrolyte and its use in nickel–zinc cells

Abstract X-ray diffraction (XRD) pattern reveals that potassium hydroxide (KOH) disrupts the crystalline nature of poly(vinyl alcohol) (PVA)-based polymer electrolytes and converts them into an amorphous phase. The PVA–KOH alkaline solid polymer electrolyte (ASPE) system with PVA/KOH wt.% ratio of 60:40 exhibits the highest room temperature ionic conductivity of 8.5×10−4 S cm−1. This electrolyte was used in the fabrication of a nickel–zinc (Ni–Zn) cell. The cell was charged at a constant current of 10 mA for 1 h providing it with 1.6 V. The cell was cycled 100 times. At the end of the last cycle, the cell still contained a capacity of 5.5 mA h.

A zinc-air cell employing a porous zinc electrode fabricated from zinc-graphite-natural biodegradable polymer paste

Porous zinc anodes have been fabricated from a mixture of zinc and graphite powder using gelatinized agar solution as the binding agent. Agar is a biodegradable polysaccharide polymer extracted from marine algae. The graphite content and the agar solution concentration were varied to find the best electrode composition. Zinc–air cells were fabricated using the porous zinc anode, a commercially available air cathode sheet and KOH electrolyte in the form of elastic jelly granules. The electrode performance was evaluated from the zinc–air cell galvanostatic discharge capability. In the cell design, a thin agar layer was introduced between the electrode-gelled electrolyte interfaces, resulting in substantially improved cell discharge performance. The inclusion of particulate graphite into the electrode did not enhance the electrode performance due to the formation of a graphite-rich layer, which obscured the electrode porosity. A zinc–air cell employing the optimized porous zinc electrode demonstrated a capacity of 2066 mA h and specific energy density of 443 Wh kg−1.

Comparative Electrochemical Performance Characteristics of Aluminium-Air Cell Employing Seawater and NaCl Electrolytes

The electrochemical performance of Al-air cell employing seawater and NaCl electrolyte of various concentrations has been investigated. The open circuit voltage and discharge capacity of the cell correlate well with the electrolyte conductivity data. Using 4 M NaCl electrolyte which possesses the highest conductivity, the Al-air cell registers an open circuit potential (OCV) of 1.1 V and demonstrates discharge capacity of 250 mAh, rated at 1 mA. Upon employing seawater, the OCV reduced to 0.68 V and discharge capacity decreased to 150 mAh. However, utilizing an exposed cell configuration which mitigates the hydroxide gel water binding effect, the Al-air seawater cell performance is greatly enhanced until almost compatible to Al-air cell employing 4 M NaCl.

Fabrication of Flexible Au/ZnO/ITO/PET Memristor Using Dilute Electrodeposition Method

DRAM has been approaching its maximum physical limit due to the demand of smaller size and higher capacity memory resistor. The researchers have discovered the abilities of a memristor, a Non Volatile Memory (NVM) that could overcome the size and capacity obstacles. This paper discussed about the deposition of zinc oxide (ZnO) on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrate by electrodeposition. Metallic Zn film was deposited on substrates with varying deposition time from 15 to 120 seconds in very dilute zinc chloride (ZnCl2) aqueous and subsequently oxidized at 150 °C to form ZnO/ITO coated PET junction. The deposited thin film was characterized via x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The results from I-V measurement show the deposited ZnO exhibits pinched hysteresis loop. The hysteresis loop becomes smaller with increasing deposition time. The 15 seconds electrodeposition gave the largest hysteresis loop and largest value of resistive switching ratio of 1.067. The result of the synthesized ZnO on the flexible substrate can be one of the alternatives to replace the current memory system as the flexible memory system.

Dependence of preferred c-axis orientation on RF magnetron sputtering power for AZO/Si acoustic wave devices

We report the deposition of high quality c-axis oriented Aluminium doped Zinc Oxide (AZO) on silicon substrate for surface acoustic wave (SAW) applications. AZO thin film is prepared by Radio frequency magnetron sputtering method. Sputtering is a preferred method because it is able to perform deposition at low temperature, produce uniform thin film and possesses high deposition rates. In preserving the functionality of the device during post CMOS process, low deposition temperature is crucial. In order to obtain the preferred AZO structural properties with strong acoustoelectric interaction, we investigate the influence of RF power on c-axis preferred orientation of AZO/Si multilayer. The deposited thin films are characterized by X-Ray diffractometer and scanning electron microscopy (SEM). The crystal structures are evaluated in terms of c-axis lattice constant, d-spacing and crystallite size. It is observed that as RF power increases, the AZO film is predominantly oriented at c-axis (002) and achieved high crystalline quality. However, if the applied RF power is too high, the energized ions would impede the growth of high quality film. The optimum RF power was found to be at 250 W, at which the material exhibits hexagonal wurtzite-type lattice of ZnO structure, high crystallinity (lowest FWHM value) and crystallite size, and high deposition rate.

Dynamic batch rekeying scheme using Multiple Logical key trees for secure multicast communication

A group key management has an important role in multicast security in order to achieve data integrity and confidentiality. The session key is a common secret key for a group of users in key trees that is shared securely and efficiently among them. It is used to encrypt other session keys and transmitted data in order to protect group communication. This paper proposed a new key management protocol using Multiple Logical key trees for dynamic groups. To minimize the communication overhead of rekeying process, a one-way key derivation are integrated with multiple logical key trees. New keys created by the server of the key tree are not sent to the members who are able to derive their own keys. As a result each rekeying process requires less number of encrypted keys sent within the group tree. The performance analysis of the proposed scheme shows that it has less communication cost than the other compared protocols.

Optimization of Zinc Oxide Thin Films for Silicon Surface Acoustic Wave Resonator Applications

High quality ZnO thin films are required to produce CMOS SAW resonators operating with low losses and high Q. This work intends to develop high performance CMOS SAW resonators through optimization of both the quality of the ZnO and the design of the SAW resonator. Zinc oxide was chosen for this work as the piezoelectric material due to its superior acoustic propagation properties and compatibility with integrated circuit fabrication techniques. ZnO has demonstrated good performance characteristics for a variety of piezoelectric devices. For optimization of the quality of the deposited ZnO thin film, different RF-sputtering conditions will be used to investigate which condition produces the best piezoelectric quality of the ZnO thin film. The experiments were carried using Taguchi optimization method, which studies a large number of variables with a small number of experiments.

Bioenergy from Gloeophyllum -Rhizopus Fungal Biofuel Cell

Fungal biofuel cell comprising of liquid culture suspension of Gloeophyllum and Rhizopus fungal strains is studied. Gloeophyllum liquid culture forms the anolyte of the microbial fuel cell (MFC) while Rhizopus liquid culture which forms the catholyte. Bioenergy is harvested from biocatalytic redox reactions of glucose/oxygen as a result of metabolic activities of respective fungi. Pyranose-2-oxidase of Gloeophyllum catalyzes oxidation of glucose, whereas laccase produced by Rhizopus catalyzes oxygen reduction. Upon incubation period of 8 days, the Gloeophyllum-Rhizopus MFC is capable to deliver 5 mW of power output continuously for 21 days under uncontrolled, open ambient surroundings. MFC with such performance characteristics is sufficed to power remote sensing devices.

Discharge, microstructural and mechanical properties of ZrO2 addition on MgO for plasma display panel materials

Abstract One of the major parts in the plasma display panel is its protecting layer. MgO thin film has been widely used as a protective layer for dielectric materials. Adding another material to the MgO base material is an alternative method for improving its property as protective layer. A study on reducing the surface discharge potential of a single pure MgO protecting layer by the addition of ZrO2 with several compositions is presented in this paper. The microstructural and mechanical properties are also described. The discharge properties were measured utilising the flashover treeing for material characterisation, produced by a scanning electron microscope. The mechanical properties were measured using the pure bending moment. The MgO and ZrO2 powders with 99·95 and 99% purity were used for powder mixtures of various desired compositions. In this work, investigation was carried out for sintered samples at 1250°C for 24 h. From observation, ZrO2 addition into high purity MgO has influenced the properties of MgO. Since secondary electron emission coefficient contributes in increasing the electrical field of the surface, it could be found that 5 wt-%ZrO2 added MgO has the highest secondary electron emission coefficient because the charging and discharging process happened within a shorter time.

Characterization of ZnxCd1-xO Nanorods for PV Applications

This paper describes the growth of ZnxCd1-xO nanorods (NRs) by a single step electrodeposition process. Thin films of polycrystalline nature with cadmium and zinc concentration changing from 10% - 90% were electrodeposited onto ITO conductive glass substrates. XRD analysis confirms a hexagonal wurtzite structure having grain size 57.2 nm. From the FESEM analysis, the synthesized ZnxCd1-xO nanorods have uniform hexagonal crystallographic planes, and their diameters are about 100 nm. Remarkably, the ultra-violet (UV) near-band-edge (NBE) emission was red-shifted from 2.75 eV to 3.02 eV due to the direct modulation of band gap caused by Zn/Cd substitution, revealed by UV visible spectroscopy. Finally, ZnCdO thin film deposited on ITO glass substrate is used as one electrode in photovoltaic cells to produce energy by absorbing the energy from the sun, this single junction cells have been put forward as a potential low-cost alternative to the widely used solar cells.