Browsing by Author "Shahrul Razi bin Meskon"

Although MCM-41 inorganic membrane could act as separator in primary cells such as zinc-air and zinc-manganese dioxide, its efficacy in a rechargeable cell such as nickel-zinc (Ni-Zn) has never been determined. The impracticality of MCM-41 incorporation in Ni-Zn battery system is fortified by the fact that silica is etched away by potassium hydroxide (KOH); besides, MCM-41 transforms into MCM-50 in a concentrated KOH. In order to ascertain the hypothesis, MCM-41 inorganic membrane was employed as a separator in the Ni-Zn cells and microbatteries. Its hexagonally arranged pore channels are expected to act as an electrolyte reservoir and ionic diffusion pathways for the electrochemical reactions. It is due to the hydrophilic nature of its pore walls and the high surface area it possesses. A multilayer MCM-41 thin film was synthesized onto the nickel hydroxide electrode by drop coating of the parent solution consisting of cethyltrimethylammonium bromide (CTAB), hydrochloric acid (HCl), distilled water (H2O), ethanol (C2H5OH) and tetraethyl orthosilicate (TEOS) with a molar ratio formulation of 0.05 CTAB, 1.0 TEOS, 0.5 HCl, 25 C2H5OH and 75 H2O. Zinc and nickel hydroxide thin films were electrodeposited onto copper current collectors to form the anode and the cathode, respectively and a zinc oxide slurry was drop coated onto the electrodeposited zinc, forming a complete anode. The structural formation of MCM-41, zinc and nickel hydroxide was confirmed by X-ray diffraction (XRD) measurements. The surface morphologies of the zinc and nickel hydroxide essentially consisted of nanoflakes and hierarchically structured aggregated nanoparticles, respectively. The structural integrity study of MCM-41 separator in the Ni-Zn cells showed that the MCM-41 partially transformed into MCM-50 phase at the early stage of charge-discharge process i.e. the 5th cycle, almost completely at the 25th cycle, while completely at the 80th cycle. The viability of MCM-41 as separator for alkaline secondary cells was confirmed through the structural properties of the resulting separator materials and the discharge capacity profiles. The reversibility of zinc electrodes in various KOH-MCM-41 surrounds was demonstrated in the cyclic voltammetry measurements which lead to a conclusion that 70:30 KOH-to-MCM-41 weight ratio should result in a lower solubility of zinc discharge products in the electrolyte. Very thin, circular shaped rechargeable Ni-Zn microbatteries were fabricated employing a side-by-side-electrode design with an electrode separation distance of ca. 800 µm. The microbatteries sustained > 130 cycles of cycling with a high depth of discharge. The microbatteries were 200 µm thick, measured 6.41 cm2 in area and weighed 1.14 g (excluding the cap and the substrate). The microbattery discharged at a rate of 0.1 mA possessed an energy density of 3.82 Wh l-1 and power levels of 0.014–0.023 mW cm-2 (i.e. a current density of 15.6 µA cm-2). Whereas the microbattery discharged at a rate of 0.2 mA possessed an energy density of 2.65 Wh l-1 and power levels of 0.023–0.040 mW cm-2 (i.e. a current density of 31.2 µA cm-2). Nevertheless, the present microbattery performance was not optimized since it was noted that cuprous oxide and cupric oxide layers were really forming during the charge-discharge process, i.e. based on the XRD results.

In order to obtain high ionic conductivity of a solid electrolyte at intermediate temperatures for intermediate-temperature solid oxide fuel cells (IT-SOFC), a very thin dense film is crucial due to its reduced ohmic losses. This work describes the fabrication of yttria-stabilized zirconia (8YSZ) thin films using radio frequency (RF) magnetron sputtering method. The thin films are deposited onto carbon paint coated stainless steel sheets with varying substrate temperature (Ts) of 150, 200, 250 and 300°C. Other sputtering parameters, i.e., argon gas flow rate, RF power and deposition time are fixed. The sputtering targets used are sintered YSZ pellets. Ultrathin YSZ films were successfully deposited with a thickness range of 300 to 600 nm as determined from the scanning electron microscopy (SEM). Phase composition analysis using X-ray diffraction (XRD) revealed cubic matrix with tetragonal and monoclinic crystalline phases of zirconia. Impedance spectroscopy (IS) is conducted at room temperature (RT) to measure the alternating-current (AC) total conductivity of the thin films. The conductivity increases with increasing substrate temperature Ts from 150°C to 250°C but drops slightly at Ts of 300°C. The highest room temperature AC total conductivity obtained is 1.81 x 10-6 Ω-1.cm-1 and the value is comparable with the reported direct-current (DC) bulk conductivity measured at a significantly higher temperature around 283°C.