Rapid Heating Rate Reveal Particular Catalytic Properties of the Pt/rGO Synthesised By Microwave Assisted EG Reduction
Authors: Zhang Xuelin , Wang Xilian , Cao Jiamu , Zhou Jing , Liu Xiaowei , Zhang Yufeng 
Published: February 2020

The severe exhaustion of fossil fuels causes serious environmental pollution and the substantial research on the sustainable, environmental, abundant, and highly efficient energy systems [1]. Currently, fuel cells, such as Proton Exchange Membrane Fuel Cell (PEMFC) and Direct Methanol Fuel Cell (DMFC) are considered to be a next-generation power source for a wide range of applications in portable, stationary and transportation markets due to their high power density and relatively low temperature of operation [2]. However, the low current efficiency and poor stability of fuel cell catalyst remains one of the biggest problems for the commercialization of PEMFC and DMFC [3]. As is well-known, Pt-based catalysts play a dominant role among all the examined catalysts for fuel cell applications due to its highest activity. However, the soaring price, limited resources and low stability of Pt hinder wider use of fuel cells. Therefore, improvement of the efficiency of the catalyst by the development of Pt nanoparticles on high-surface-area carbonaceous supporting materials has been proposed as one of the most effective approaches to reduce the Pt use and continues to be an important R&D activity. To solve the aforementioned problems, it has been determined to be feasible to prepare catalysts by combining Pt with supporting material. Particularly, graphene is an attractive candidate as the supporting material, thanks to its greater abundance, relatively low cost, similar lattice constant, comparable catalytic activity with respective to Pt and they can enhance the dispersion of Pt, thereby maximizing the surface area available for the reaction and minimizing particle growth. However, because graphene basal planes are chemically inert, especially in the case of high-loading (metal content ≥40 wt.%) catalyst materials, it is necessary to apply an adequate preparation technique to ensure good dispersion of the catalyst nanoparticles on its surface with good control over the particle size and distribution. To date, several methods have been developed for the synthesis of Pt/rGO such as, impregnation, colloidal, electrodeposition impregnation reduction route, etc. As described above, the aforementioned fabrication procedures usually involve time-consuming and complicated procedures and harsh reaction conditions, which seriously limit their largescale preparation and applications in practice. Hence, it is desirable to develop a simple method for the synthesis of Pt/rGO catalyst. Microwave-assisted techniques have been widely used for the preparation of many nano materials because these offer a quick, simple, homogeneous and efficient method. The use of microwaves for material synthesis can have several advantages compared to conventional heating methods due to the uniform and volumetric nature of microwave irradiation. One of the main advantages of the high-power microwave irradiation is uniform heat transfer to the substrate, which leads to a more homogeneous nucleation and shorter crystallization time compared to the conventional heating during which unavoidable temperature gradients occur and can adversely affect the particle size distribution and yield. In addition, because microwave heating generates heat within graphene supporting materials, the graphene can act as preferred nucleation sites, consequently leading to satisfactory utilization and a uniform dispersion of the catalyst nanoparticles. Furthermore, microwave heating has a remarkable energy efficiency and can save time with respect to conventional treatments. However, although microwave irradiation provides many practical advantages over conventional heating for synthesis, it should be mentioned that it can have few potential disadvantages associated with the limitations such as batch process and the effect of temperature and heating rate on particle size of Pt and thickness of graphene sheet in synthesis process, by which the catalytic efficiency of the catalyst is affected. To the best of our knowledge, there has been no report on the use of high-power microwave as an improved synthesis technique. In the present study, we report the effect of the heating rate and the temperature for the catalytic performance by high-power microwave assisted which provides the guidance for the mass production of the high activity Pt/rGO catalyst. The nanosized materials were characterized by TEM and XRD and their electrocatalytic behavior was evaluated using cyclic voltammetry and in situ infrared studies. Physical and chemical measurements were conducted to elucidate the better performance that the rapid heating rate (heating to 120℃ in 17s) of the prepared Pt/rGO have the electrochemically active surface area which superior to the commercial Pt/C.

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Figure 1