Facile synthesis of continuous Pt island networks and their electrochemical properties for methanol electrooxidationw

Over the past few years, synthesis of nanostructured materials has received great interest in the technology due to its wide range of applications in biosensors, energy system, catalysis, and in self-assembly of supramolecular structures. Nanostructured platinum metals materials are very attractive because of their superior electrocatalytic performance than the blanket Pt electrode. Recently several methods have been reported for the preparation on nanostructure but it is difficult and time-consuming to prepare the nanostructures. Besides, platinum is very expensive, resource limited and irreversibly inactivated by CO-like poisoning species. Therefore, it is essential that the utilization of platinum should be kept as low as possible without sacrificing the catalytic performance. The one best way to accomplish this is to create continuous Pt island networks. The interconnected structure could have additional advantages in enhancing catalytic activities for reactions that involve two or more reactants, because such networks supply enough absorption sites for reactant molecules over a close range. Here, we report a new and simple method for fabricating continuous Pt island networks by pulse-potentiostatic electrodeposition using Si substrates of low resistivity, which act as the current collector. And thus, the silicon support was very appropriate for use as the Pt electrocatalytic electrode in respect of electrical conductivity. As shown in Scheme 1, the presence of the surface oxide layer on the silicon substrate can greatly enhanced the oxidation of CO adsorbed on the active Pt sites according to the bifunctional mechanism. Moreover, the electrocatalytical study of the continuous Pt island network on the silicon substrate indicates the potential application for electrodes in direct methanol fuel cells. The fabrication steps for the continuous island Pt network electrode are described in the following: a flat Si substrate was washed with acetone followed by DI water (18 MO), then etched in 10 wt% HF at room temperature for 5 min to remove the thin native oxide layer on the silicon surface. Then, the Pt particles were electrodeposited on the etched Si in the aqueous solution of 1 M K2PtCl6/1 M H2SO4 (100 mL/100 mL) at room temperature by potentiostatic pulse plating in a three electrode cell system with a saturated calomel reference electrode (SCE). The time durations for the high potential pulse (+0.08 V) and the low potential pulse ( 0.01 V) were 3 ms and 1 ms, respectively. The blanket Pt catalyst were prepared by potentiostatic pulse plating (1 M K2PtCl6/1 M H2SO4) on the silicon substrate. The time durations for the high potential pulse (+0.06 V) and the low potential pulse (–0.04 V) were 5 ms and 2 ms, respectively. The Ru decorated blanket Pt electrode was obtained by deposition of Ru on the blanket Pt by potentiostatic pulse plating at 0.07 V and +0.02 V in a 1 M RuCl3 (200 mL) solution for 5 ms and 1 ms, respectively. The catalyst mass loading (mg cm ) was calculated by measuring the difference in the mass of the electrodes before and after the Pt deposition, using amicro-balance (Sartorious, PBSAH) with a resolution of 0.001 mg. The mass loading of Pt on the continuous island Pt network/Si, the Ru decorated Pt film/Si, and the blanket Pt on silicon electrodes are B0.37 mg cm , B0.89 mg cm , and B0.94 mg cm , respectively. Fig. 1(A) and (B) illustrates a representative scanning electron microscopy (SEM) image of the blanket Pt on silicon substrate and Ru decorated on blanket Pt, respectively. From the SEM images, the blanket Pt and the Ru decorated on the blanket Pt were completely covered on the silicon substrate after the electrochemical deposition. Fig. 1(C) show the surface morphology of the pulse electrodeposited Pt on the Si substarte. The Pt islands are mutually connected over the Si substrate. The Pt islands forming the continuous Pt island film have size distribution fromB200 nm toB800 nm. X-Ray photoelectron spectroscopy (XPS) shown in Fig. 1(D) indicated that Pt and Ru were successfully deposited on the silicon substrate by the pulse electrodeposition. The electroactive surface area (ESA) of the electrodes was determined by the CO-stripping cyclic voltammetry, which was Scheme 1 Schematic illustration of the continuous Pt island network on the flat silicon substrate. The right hand side exhibits the bifunctional mechanism of CO electrooxidation. The adsorbed oxygen containing species on the surface of SiO2 can facilitate the oxidation of CO-like poisoning species adsorbed on the active Pt sites.