Ethanol oxidation on Pt/CNF-GNPs/GDL electrode for fuel cell application

Among the direct alcohol fuel cells, ethanol fuel cell is considered the most pleasant in terms of safety and power density. In this research, Pt/CNF-GNPs /GDL electrode was developed by using GNPs and CNFs as a supporting medium on carbon paper and electrodeposition method to deposit Pt catalyst. The morphology and structure features of the prepared film samples are characterized by FESEM and XRD. Pt particles of about ۶.۵۳nm were uniformly deposited on porous support. Catalytic activities of the prepared electrode for the ethanol oxidation reaction was evaluated through cyclic voltammetry measurements. Based on the electrochemical properties it was found that the as prepared Pt/CNF-GNPs/GDL electrocatalyst exhibited a comparable activity for ethanol oxidation reaction with respect to the Pt/C, which may be attributed to high specific surface area of graphene nanoplates support as well as high conductivity of CNFs. A rather significant reduction in the peak potential of methanol electro-oxidation from ۰.۷۹V for Pt/C/GDL to ۰.۵۹V for Pt/CNFs-GNPs/GDL electrode indicates that an increase in the activity for EOR is achieved by replacing the C by CNF-GDL.In recent years, direct alcohol fuel cells (DAFCs) have attracted more and more attentions as an alternative to conventional internal combustion engines due to their potential applications in transportation and portable electronic devices. Due to the strong dependence of the DAFCs efficiency to catalyst layer, catalysts-supporting approaches strategies have been developed. Carbon black is usually used as catalyst support because of its large surface area, which elevates metal dispersion and due to its pore structure, which facilitate the transport of reactant gases, and high electrical conductivity [۱]. However, there are some disadvantages related to the use of carbon black such as corrosion of carbon surface in the fuel cell environment that can be caused fuel cell performance losses. On this basis, various alternative catalysts supports such as nanostructured carbon materials and composite of these materials to improve the stability and catalytic activity of the catalyst have been studied[۱]. Nanostructured carbon materials such as CNF[۲] and graphene nanoplates(GNPs) [۳] have been investigated as catalyst support in comparison with carbon black in many studies due to their excellent properties such as good electronic conductivity, high surface area and chemical stability. This study focuses on the electrodeposition of Pt on composite support of GNPs and CNFs on gas diffusion layer. Also ethanol electro oxidation investigated on the prepared Pt/CNF-GNP/GDL electrode.In the first step the suspension of the mixture of GNPs and CNF in ethanol/DI water was prepared with the aid of bath ultrasonic cleaner for ۱۵min. Then, ۱۰۰μL of prepared mixture was pipetted on a carbon paper and dried at room temperature. This electrode from at the dried suspension contained sides was exposed to the electrolyte and the other sides were used to take electrical contact through a cu wire. Electrodeposition was performed in a plating bath which contains a solution of ۴mM H۲Pt Cl۶.۶H۲O in ۰.۵ M NaCl. The peak current density was ۳۰۰mAcm-۲ an on/off time of ۱۰/۱۰۰ms. Following the deposition, the electrode was removed immediately from the electrolyte, rinsed thoroughly with deionized water and dried in air[۴].The microstructures of the electrode have been investigated by FESEM. The image (Fig۱a) shows that the large CNFs entangle to form a backbone where a fine meshwork of much smaller GNPs creates the surface covering layer. Well-dispersed Pt nanoparticles were observed on support.Fig.۱b shows the X-ray diffraction patterns of the Pt /CNF-GNPs/GDL electrode which reveal the diffraction peaks of both carbon and platinum. The sharper and narrow diffraction peaks at ۲θ=۲۶.۴۹ ͦ (۰۰۲) and ۵۴.۴۷ ͦ (۰۰۴) are the characteristics of the graphene layers and CNFs which indicate a highly graphitic and crystallinity ordered structure of these material. Based on the Pt(۱۱۱) peak on the spectrum, the mean sizes of Pt particles are estimated by Deby-Scherer formula and was ۶.۵۳nm. The typical cyclic voltammogram curves for ethanol electro-oxidation on Pt/CNF-GNP/GDL electrocatalyst recorded in (.....)at a scan rate of ۵۰ mv s -۱ were shown in Fig. ۱c. It can be seen that ethanol oxidation began at approximately ۰.۵۹ V for Pt/CNF-GNP/GDL and reached its current peak at about ۰.۷۹ V. On the reverse sweep, re-oxidation of ethanol began at approximately ۰.۶۵ V and reached a peak current density at around ۰.۴۵ V, after which strongly bonded surface inter-mediates began to block the catalyst surface. The electrochemical behaviors of Pt/C were similar to that of Pt/CNF-GNP/GDL. However, the peak current density of Pt/CNF GNP/GDL is significantly higher than Pt/C. The peak current density for Pt/CNF-GNP/GDL was about ۱.۵۷ ma cm -۱ while the peak current density for Pt/C was about۰.۹۷ ma cm -۱These facts indicate that the Pt/CNFGNPs/GDL have higher catalytic activity and better stability for ethanol oxidation than Pt/C because of the highelectrochemical activity due to the high specific surface area of GNPs support and high conductivity of CNF Fig۱:(a) FESEM images of the Pt/CNFs-GNPs/GDL electrocatalyst (b) X-ray diffractograms of the Pt/CNFs-GNPs/GDL electrocatalyst (c) CV of ethanol oxidation of Pt/CNFs-GNPs/GDL and Pt/C electrode۴. ConclusionIn this article a novel GNP-CNF hybrid support material was prepared on GDL and effective strategy used to depositcatalyst particles on GDL by electrochemical method. Special mixed support was developed by layeredmicrostructures with a large porous structures of CNFs networks at the surface, as well as dense and high-conductingGNPs networks as back supports. This unique microstructure led to improve Pt catalyst accessibility and massexchange properties. Pt/CNF-GNP/GDL demonstrated promise for anode electrode in DEAFCs application

کلیدواژه ها:

Ethanol oxidation ، CNF ، GDL ، fuel cell