Enhanced electrocatalytic activity and stability of monodisperse Pt nanocomposites for direct methanol fuel cells

Abstract

Direct methanol fuel cells (DMFCs) are one of the most important fuel cells operating at low temperature using methanol as fuel and they need very efficient catalysts to activate the methanol. Generally, the most efficient fuel cell catalysts are platinum-based nanoparticles that can be used by different supporting materials such as different as prepared and functionalized carbon derivatives. For this purpose, herein, the carbon black has been mainly functionalized with an acidification process in order to increase the electrical conductivity and heterogeneous electron transfer rate of supporting materials. After functionalization of carbon black (f-CB), platinum salt (PtCl₄) was stabilized with propylamine (PA) in the presence of ethylene glycol (EG) and f-CB by microwave synthesis method. XPS, XRD, TEM and Raman Spectroscopy techniques were used to determine the morphology of the prepared catalyst. The results showed that the prepared nanocatalyst has face-centered cubic (fcc) structure and uniformly distribution on supporting material. Besides, chronoamperometry (CA) and cyclic voltammetry (CV) techniques were used to determine the electrochemical activity of functionalized carbon black supported Pt NPs (Pt/f-CB) towards methanol. From the results obtained from the CV and CA, it was found that the activity of the Pt/f-CB NPs (50 mA/cm²) was almost 4–5 times higher than that of the Pt/CB NPs and commercial available Pt/C catalyst (ETEK).

Introduction

The petroleum and conventional fuels are very problematic in terms of the environment and sustainability. However, the use of fuel cells instead of the conventional fuels has been one of the most important energy policies [1], [2], [3], [4]. Generally, fuel cells have various advantageous such as low pollution and high conversion efficiencies compared to conventional power sources. During the recent years, direct methanol fuel cells (DMFCs) are one of the most important fuel cells because of their potential applications in the portable power source and electric vehicles [5], [6], [7], [8], [9] but they need very efficient catalysts in order to activate methanol as a fuel. Generally, catalytic activity depends on the size of the metal particles and their distribution on the supporting material. Therefore, in order to obtain highly efficient metal nanoparticles, the particles must be small size and well dispersed on the support material. Although different catalysts were used in these types of fuel cells in order to activate the methanol up to now [10], [11], [12], Pt-based nanocatalysts were mostly preferred anode catalysts due to their high durability and catalytic efficiency. However, the high cost of Pt metal used as electrode catalyst is one of the major obstacles to the commercialization of DMFCs [13], [14], [15], [16], [17], [18], [19]. For this reason, various support materials are used to maximize the surface area of the metal nanoparticles and to reduce the total amount of metal used [20], [21], [22], [23], [24], [25], [26], [27], [28]. Mostly, carbon derived materials were used as catalyst supports because of their good electrical conductivity, stability, higher surface area, lower cost and higher corrosion resistance in both acidic and basic media. Therefore, the use of carbon derived supports play an important role for DMFC technology. Besides, chemical reactions can be applied to maintain or modify the surface properties of those support materials in order to increase the catalytic activity of prepared materials. Through some modification of these supporting materials, the activities and the catalytic properties of the materials can be enhanced. For this reason, addressed herein, the functionalization of carbon black was performed to increase the active surface area, electrical conductivity, heterogeneous electron transfer rate and the uniform distribution for the prepared catalysts. Then, the microwave assisted polyol process has been used for the synthesis of Pt nanoparticles supported with functionalized carbon black (f-CB) as a promising method [29], [30], [31], [32], [33], [34], [35]. Besides, transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) techniques were used to determine the morphology of the Pt/f-CB nanocatalyst. Cyclic voltammetry technique was used to measure the activity of the catalyst for methanol oxidation reaction and chronoamperometry (CA) technique was used to determine the long-term stability of the prepared materials.