Direct current (DC) and pulse current (PC) electrodeposition of Pt-Co alloy onto pretreated electrodes has been conducted to fabricate catalyst electrodes for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). The effect of plating mode and pulse plating parameters on the Pt-Co alloy catalyst structure, composition and electroactivity for the ORR in PEMFC has been investigated. The electrodeposited Pt-Co alloy catalyst indicates higher electrocatalytic activity towards the ORR than the electrodeposited Pt catalyst. The activity of the electrodeposited Pt-Co catalysts is further improved by applying the current in a pulse waveform pattern. The electrodeposition mode and the pulse plating parameters do not have the significant effect on the Pt:Co composition of deposited catalysts, but show the substantial effect on the deposit structures produced. The Pt-Co catalysts prepared by PC electrodeposition have finer structures and contain smaller Pt-Co catalyst particles compared to that produced by DC electrodeposition. By varying the Pt concentration in deposition solution, the Pt:Co composition of the electrodeposited catalyst that exhibits the highest activity is found. The Pt-Co alloy catalyst with the Pt:Co composition of 82:18 obtained at the charge density of 2 C cm -2 , the pulse current density of 200 mA cm -2 , 5% duty cycle and 1 Hz was found to yield the best electrocatalytic activity towards the ORR in PEMFC.
Ultra-fine fiber mats of dextran (powder; M w = 64,000-76,000 Da) were fabricated by electrospinning, using water as the solvent. The effects of solution concentration (i.e., 0.7-1.3 g mL -1 ) and applied electric field (9-21 kV/15 cm) on morphological appearance and size of the obtained fibers were investigated. Under a fixed electric field of 15 kV/15 cm and a fixed solution flow rate of 0.25 mL h -1 , beaded fibers were observed up to a critical concentration of about 0.9 g mL -1 , beyond which only smooth fibers were obtained. The average diameter of these fibers increased monotonically with increasing the solution concentration (i.e., from *290 to *1950 nm). For the dextran solutions investigated, increasing the electric field generally caused the diameters of the obtained fibers to increase, with the average diameter of the obtained fibers ranging between 520 and 1760 nm. To improve the usefulness of the electrospun dextran fiber mats in an aqueous medium, cross-linking with glutaraldehyde was necessary. The effects of curing temperature (i.e., 70-90°C), curing time (i.e., 3-48 h), and added MgCl 2 catalyst (i.e., 0.01-0.03 g) on physical integrity of the cross-linked dextran membranes in water were investigated. Both the swelling and the weight loss in water of the crosslinked membranes were generally found to decrease with increasing curing temperature, curing time, and MgCl 2 loading and the cross-linking did not affect the morphology of the obtained membranes.
The preparation of catalyst electrodes by electrodeposition for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) has been studied. This work looks at the potential to apply the electrodeposition technique, in the forms of direct current (DC) and pulse plating electrodepositions, to prepare Pt and Pt-Co alloy catalysts for membrane electrode assemblies (MEAs). The preparation of the non-catalyst layer was found to be important for the electrodeposition of Pt catalysts. The activities of the electrodeposited catalysts, both pure Pt and Pt-Co alloy, produced by pulse plating are substantially higher than that of the Pt catalyst produced by DC electrodeposition. The improvement in electroactivity towards the ORR of the electrodeposited catalysts produced by pulse plating is likely due to the finer structures of electrodeposited catalysts which contain smaller catalyst particles compared to those produced by DC electrodeposition. A maximum performance towards the ORR in PEMFCs was achieved from the catalysts prepared by pulse plating using a charge density of 2 C cm -2 , a pulse current density of 200 mA cm -2 , a 5% duty cycle and a pulse frequency of 1 Hz.
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