Nanostructured Platinum and Carbon Supported Pt-Ni Catalyst for Polymer Electrolyte Fuel Cell

Among various types of fuel cells, the polymer electrolyte exchange membrane fuel cell (PEFC) using hydrogen and alcolhol are promising to be commercialized for vehicles due to hydrogen and alcohol usage. Till now, platium (Pt) is the most effective catalyst for electrode reactions in fuel cells. However, challenges for this catalyst are its scarcity and high cost, as well as the poisoning by the intermediates of the fuel oxidation, such as CO. Using nanoscale metallic or bimetallic electrocatalytic materials is supposed to facilitate the cost reducing and to increase the catalytic activity. In this work, nanoscale bimetallic PtNi catalysts with different atom ratios of Pt to Ni on carbon support (PtNi/C) have been synthesized by the polyol reduction method under ultrasonic irradiation. The reducing reagent was ethylene glycol (EG) and NaBH₄ and support materials were carbon Vulcan XC-72R and carbon nanotube (CNT). The morphology, structure and specific area of synthesized materials were analyzed by transmission electron microscopy (TEM), nitrogen adsorption (BET) and X-Ray diffraction (XRD). The electrocatalytic activity of Pt/C, PtRu/C, PtNi/C and commercial Pt/C electrodes (Aldrich Sigma, 10%wt Pt/activated carbon) for alcohol oxidation was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The electrocatalyst for oxygene reduction reaction (ORR) was evaluated using Rotating Disk Electrode (RDE) techniques in acidic solution contanning 20mg/L dissolved oxygene at 25^oC.

The TEM images clearly showed that the PtNi nanoparticles were precipitated on the surface of carbon aggregates. The size of the PtNi particles synthesized by in both methods were distributed from 1 to 3 nm. XRD pattern indicated the face-centered cubic structure of the metal and alloy. The electrochemical surface area (ECA) of the PtNi catalytic electrode was estimated from the charge in the hydrogen adsorption/desorption region on the CVs measured in 0.5 M HClO₄. The calculated ECA of 20PtNi(1:1)/C were highest at 55.0 m²/g. In addition, the CV data in 1.0M KOH solution containing alcohol show the best electrocatalytic performance of PtNi(1:1)/C for the alcohol oxidation. 

The results showed the high catalytic of PtNi/C for ORR at room temperature. The number of electron transfer and mechanism of ORR will be discussed too.

 Acknowledgement:

The authors gratefully acknowledge Vietnam Ministry of Science and Technology for supporting NCCB – ĐHƯD.2011/G11 project. We thank ONRG and VNU-HCM for financial support throught grants N62909-13-1-N235 and HS2013-76-01.

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